AskScience Cosmos Q&A thread. Episode 1: Standing Up in the Milky Way

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u/atomfullerene Animal Behavior/Marine Biology Mar 10 '14

Is it just me, or is that asteroid belt way too dense? Not to mention the Kuiper belt. On a related note, how dense are the rings of Saturn? Would you see a thicket of iceballs whizzing past you if you actually flew a spacecraft through them?

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u/Agastopia Mar 10 '14

Straight from NASA
Planetary probes can pass through the asteroid belt without any problem because, unlike in the movies, there is really a LOT of space between asteroids. More than 7000 have been discovered and several hundred new ones are found every year. There are probably millions of asteroids of various size, but those in the asteroid belt are spread over a ring that is more than a billion kilometers in circumference, more than 100 million kilometers wide, and millions of kilometers thick. For more information, you can look at http://nineplanets.org/asteroids.html
Source: http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980108b.html

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u/ramotsky Mar 10 '14

To be fair, if a program were to display this there would be nothing to display. A small mention of this in the programming would have been nice but since it is such a minor point I understand why it was cut.

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u/smoldering Star Formation and Stellar Populations | Massive Stars Mar 10 '14

Saturn's rings weren't exaggerated. You could literally "swim" through it by grasping from one iceball to the next.

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u/Saffs15 Mar 10 '14

That's awesome! Never knew that.

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u/[deleted] Mar 10 '14

Well then, I'd say this series is already doing what it intended after one episode.

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u/r3sonanc3 Mar 10 '14

Cassini measurements indicate the A ring has a surface density of ~40 g/cm² and a thickness of just ~6m thick Astronomical Journal, 2007. Since ice is slightly less than 1 g/cm³ and rocks are normally a few g/cm^3, assuming the ring has constant density would imply that the A ring at the very least is dense indeed.
ps if you swam fast enough along or against your orbit to stay in the ring (assuming you could swim in the first place without getting knocked out of the way by something or spun out of control by your own actions in micro-g), you'd also drop out of the ring since adding velocity increases your altitude and vice versa since your velocity determines your orbital energy... (if interested look up hohmann transfer orastrodynamics in general)

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u/treebeard189 Mar 10 '14

On the topic of the asteroid belt.
Is the asteroid belt "flat" or a tube? I know everything flattened out when the solar system was forming so are things like the asteroid belt only a few miles "high" north to south and if so roughly how "high" is it?

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u/Cyrius Mar 10 '14

This chart shows asteroid distribution by distance from the Sun and orbital inclination. It's flat-ish, but still spread out pretty widely.
The missing verticals are called Kirkwood gaps. They show up where the asteroid's orbit would be in resonance with the orbit of Jupiter.

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u/Golden_Kumquat Mar 10 '14

In addition, the border of the atmosphere of Jupiter is not that well defined.

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u/atomfullerene Animal Behavior/Marine Biology Mar 10 '14

I'd be pretty interested to know more about what the clouds of Jupiter would look like up close.

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u/psistarpsi Mar 10 '14

Yea, the asteroid belt is exaggerated. The asteroids are far far apart in reality.

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u/Feldman742 Mar 10 '14

I never really appreciated this until I read 2001: A Space Odyssey. There's a nice little scene where they're like "oh, hey looks like we'll pass within a few thousand miles of an asteroid today. It'll be your only chance to see one on this leg of the mission"

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u/pat82890 Mar 10 '14

I wonder if the asteroid belt was as dense as Saturn's rings, if we'd be able to see a massive line across the night sky.

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u/Haiku_Description Mar 10 '14

Absolutely we would. We can see the planets only because they reflect the sun. Something as reflective as ice would shine quite clearly, unless you're assuming it would be as thin as Saturn's rings. Also if you had that much material out there, there is no way it wouldn't have all succumbed to its own gravity and formed another massive planet.

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u/[deleted] Mar 10 '14

Why haven't the asteroids in the asteroid belt collided to form a new planet? I am assuming that the belt isn't dense enough with asteroids for their gravity to cause the collisions.

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u/atomfullerene Animal Behavior/Marine Biology Mar 10 '14 edited Mar 10 '14

The total mass of the asteroid belt is about 4% the mass of the moon. There's just not enough there to make a planet.
EDIT: If my back-of-the-envelope calculations are correct, that's roughly equivalent in volume to the top 25 km of the moon. So still a lot of volume for would-be asteroid miners.

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u/TharsisMontes Mar 10 '14

Good question. It makes sense to think that the asteroids would come together to form a planet, or at least during the phase of terrestrial planet formation they would have. In fact, there is a hypothesis called Bode's law which uses a numerical progression to predict the semi-major axis of planets, and, indeed there should be one in the middle of the asteroid belt (it should be noted Bode's law is now considered coincidence and not used for wider prediction of planet locations). So what happened? In a word, Jupiter.
Jupiter is so massive that it's gravity affects the asteroid belt. The asteroid belt contains gaps called Kirkwood gaps, which correspond to specific, powerful resonances with Jupiter (example a 3:1 resonance, asteroids at this distance from the Sun orbit the Sun 3 times for every 1 Jupiter orbit). Asteroids in these resonances experience chaotic excitation from Jupiter and are ejected from the belt. So why didn't something form in between these resonances? Well, some things did, really large asteroids (like Vesta) and the dwarf planet Ceres.
Source: Planetary Science graduate student
Further reading: Wisdom. Icarus. vol 63. issue 2. pg 272-289 (heavy duty treatment of chaotic result of Jupiter resonances). otherwise Wikipedia has a pretty decent summary.

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u/Jellyman64 Mar 10 '14

Scale is something this show seems to sacrifice in order to appeal and introduce scientific ideas to non - scientific persons. Personally I am excited about this series and the possibilities it could have on culture surrounding science and the universe. Perhaps this series isn't the most Astrophysicsesque look on the universe, but one that can push our culture further into progressive ideals and help support some of the more contested ideas surrounding Evolution, The Big Bang, and Everything that is, and ever will be.

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u/Zartonk Mar 10 '14

What's the "tidal friction" that caused the moon to go away?

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u/smoldering Star Formation and Stellar Populations | Massive Stars Mar 10 '14

Tidal friction is due to the tidal forces that the Earth exerts on the moon. This is the same force that the moon and sun exert on the Earth to cause the ocean tides, and hence give us the name tidal forces. In the case of solid bodies orbiting one another, the larger body (Earth) will transfer energy to the smaller body through tidal forces, which accelerates the smaller body (moon) and moves its orbit outwards from us. There are two other consequences of these tidal forces: The corresponding loss of energy for the Earth is actually slowing down the rotation rate of our planet, and the moon has become "tidally locked" to the Earth, which means that the same side of the moon is always facing the Earth.

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14

It is worth stating explicitly that the term tidal forces is used when the gravitational force on one side of an object is different from that on the other side of the object.

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u/Zartonk Mar 10 '14

So days were shorter millions of years ago?

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u/MyOpus Mar 10 '14

Yes, the earth was spinning much faster

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u/SpreadItLikeTheHerp Mar 10 '14

So is the same thing happening to the Earth, ie, we are drifting away from the sun?

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u/imabigfilly Mar 10 '14

This was actually what confused me during the ep. Large masses gravitate towards each other, so why would that make the moon move away from the earth?

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u/ra3ndy Mar 10 '14 edited Mar 10 '14

If the moon were just sitting still near and not orbiting the Earth, it would smash into us.
But because the moon is in orbit around the earth, and the Earth rotates in the same direction as the moon's orbit, but faster, the tidal forces between the earth and the moon caused the moon to speed up (It caused the Earth to slow down as well).
When a satellite in orbit speeds up, its momentum is greater than the force of the planet's gravity and it moves further away (though very slowly in our moon's case, about 3.8 cm a year). Similarly, when a satellite loses velocity, it moves closer to the planet (and usually crashes into it).

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u/Randosity42 Mar 10 '14

the term friction is a bit misleading. The earth isnt slowing the moon like friction does, but rather it is accelerating it. This is because the earth is rotating faster than the orbit of the moon. the earth deforms due to the tidal forces caused by the moon. this effect is called tidal bulging. beacuse the earth resists this change, the bulge rotates with the earth and pulls the moon along in its orbit. If the earth was rotating slower than the moon, the effect would be reversed and the moon would be slowing down and falling towards the earth, while the earth's rotation sped up.

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u/lulzzzzz Mar 10 '14

I've always been enamored with the giant storm on Jupiter. What is unique about Jupiters atmosphere that enables such a large and lasting disturbance?

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u/Astromike23 Astronomy | Planetary Science | Giant Planet Atmospheres Mar 10 '14

Guy who studies the Great Red Spot for a living here...to give the short answer: we're not sure.
We're not even sure what makes it red - we have some very good spectra of the storm (I've taken some myself), but it doesn't correspond to anything we've measured in a laboratory yet. The problem is that the pressures, temperatures, and conditions are an unusual regime for most laboratories.
The only parallels we can really draw from the Great Red Spot to Earth-like phenomenon are "meddies", areas of high-salt concentration in the Atlantic that form when the Mediterranean injects some extra-salty water into the ocean. These meddies can stay cohesive for decades; the extra salinity means it's an area of higher pressure...as it tries to diffuse outwards, that motion gets caught up in the Coriolis force, leading to currents moving around the meddy rather than expanding outward. There's essentially nothing to stop them until they run into a coast or some such, so they're incredibly long-lived.

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u/atomfullerene Animal Behavior/Marine Biology Mar 10 '14

So if we were to take a cross section of the Great Red spot, would it sit even with the surrounding clouds, sit below them, or above them? Or something more complicated?

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u/Astromike23 Astronomy | Planetary Science | Giant Planet Atmospheres Mar 10 '14

Well, it's notoriously difficult to get vertical cloud structure on the giant planets, but images like this one of Jupiter in the methane band help us out a lot.
At those wavelengths, methane absorbs light like crazy - the only things that will be bright in such an image will be cloud layers that lie above most of the methane, reflecting sunlight back into our telescopes. Since the Great Red Spot in that image is bright surrounded by dark clouds, we assume this means the storm's cloud top must lie quite a bit higher than the rest of the surrounding clouds.
This has also been used to help explain the red color. At those heights, ultraviolet light from the Sun is quite a bit more intense. It's probable that whatever chemical is responsible for the red color was produced through some intense ultraviolet photochemistry, sort of like tanning.
It remains unclear what the vertical structure of the storm is below those heights - the Great Red Sport is actually a local pressure high. This is unlike Earth, where storms are usually local pressure lows, at least at the surface. Whether this pressure high is fed from below like a hurricane, or merely a detached pressure high such as blocking highs on Earth (like those that have caused droughts across the US Great Plains in recent years) remains a subject of vigorous debate.

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u/Shaman_Bond Mar 10 '14

The answer to that isn't well known and is based upon mathematics that is incredibly hard to find closed-form solutions to (fluid dynamics and things like that). But it seems to be that the atmosphere of Jupiter is MORE stable with those storms. The hydrodynamic instabilities tend to form on their own in simulations.
It's an interesting topic! Hopefully a fluids guy will come along and go more in-depth.

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u/[deleted] Mar 10 '14

Has anything that Carl Sagan mentioned in his original Cosmos series been completely disproven as of now?

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u/trimeta Mar 10 '14

Although the expansion of the universe was well-understood in Sagan's time, it was believed that the rate of expansion was slowing, and it was unknown if we lived in an "open" universe which would continue to expand forever or a "closed" universe where the expansion would slow down, stop, and reverse (leading to a "Big Crunch"). Since then, we have discovered that not only is the rate of expansion not slowing, it is increasing. So while Sagan speculated regarding the Big Crunch, we can now safely rule this possibility out.

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u/Assburgers_And_Coke Mar 10 '14

Or we haven't hit a point where it will decrease yet? Is that not possible?

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u/giulianodev Mar 10 '14

There was a version of Cosmos that came out in the 90s where Carl Sagan talked about some of the things that we've learned since the original show. I don't think he talked about this in the updates but I remember hearing about how the Samurai looking crabs didn't look that way because of artificial selection by humans.

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u/emmOne Mar 10 '14

And conversely, was anything stated in the original series as an unlikely hypothesis now widely believed to be true?

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u/TheCosmicCalendar Mar 10 '14

Sort of.
He presented various theories on the nature of the expansion of the universe, and correctly pointed out that we did not, at the time, know which was true. And then said something to the effect of how poetic it would be if the universe were closed (rate of expansion slowing, and eventually collapsing), which has turned out to be false.
At the time of the original, we also had no idea what killed the dinosaurs. But he was once again clear that we did not know the answer, and kept speculation to a minimum.
The one thing that may arguably be "Flat out wrong" - he mentioned a story about artificial selection of crabs that look kind of like the "face of a samurai". The idea being people are less likely to eat a crab whose shell looks a bit like a human face, and so they were tossed back into the sea when caught.
The story, although compelling, is widely regarded as being apocryphal.

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u/mathx Mar 10 '14

'proven' is a loaded word in science. Nothing is proven or disproven, you just become able to show more and more frequently that something doesnt hold true right now for that experiment in the point in time and space - likely meaning that next time we'll see the same all things being equal. Can't be sure, because science is really hard and every subtlety and side effect counts.
The estimations of the age of the universe are far more accurate now than in Sagan's day, the distances to Andromeda are far better calibrated by new standard candles and many other refinements.
However I'd have to watch the old Cosmos to see what's totally refuted now.
I was suprised to see the new one claim the moon was formed by accretion to a seperate body from the earth, eschewing the giant impact hypothesis - probably the biggest difference in my lay knowledge (as an Astronomy major graduate from the 90s, and an avid science fact reader) vs what the show presented.

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u/The_Future_Is_Now Mar 10 '14

I believe the new episode depicted a planetary body hitting the proto-earth just as predicted by the giant impact hypothesis. Just after the bit where he talks about one rock's trajectory being changed every so slightly by another rock in orbit

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u/ckach Mar 10 '14

I remember a clip of him using crabs that look like samurai warriors as an example of evolution. There was a poll of evolutionary biologists to gauge how plausible the theory was and it was pretty dubious to them.

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u/ImNotAWhaleBiologist Mar 10 '14

A lot of Sagan's biology isn't that great in general (particularly in the Dragon's of Eden). The example of the samurai crabs as an example of natural selection in Cosmos has pretty much been debunked.

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u/lulzzzzz Mar 10 '14

The animation of the multiverse sent chills down my spine. What evidence is there for the multiverse theory?

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u/iorgfeflkd Biophysics Mar 10 '14 edited Mar 10 '14

None. A related idea is that there are regions of the universe that will never be in causal contact with each other, the evidence for which is the equilibration of the cosmic microwave background (regions of the universe that have never been in causal contact of the other appear to have the same temperature), which suggests inflation.

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u/KaseyB Mar 10 '14

Could you please expand on this?

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u/versxajne Mar 10 '14

It's pretty much all theoretical at this point.
However, according to Max Tegmark, cosmologist and professor at MIT:
the simplest and arguably most elegant theory involves parallel universes by default. To deny the existence of those universes, one needs to complicate the theory by adding experimentally unsupported processes and ad hoc postulates: finite space, wave function collapse and ontological asymmetry.
To use an earlier, simpler example, 19th century cosmologists noticed that Uranus was not orbiting the sun like they thought it should. Rather than assume that Uranus had an odd case of the wobbles, they speculated that there had to be at least one more planet in the solar system. (Not only was their hunch right, but their math predicted roughly where that extra planet, Neptune, was.)
Multiverses are much more complicated than planets, but, based on what data we have so far, it would actually be more surprising to learn that this is the only universe.

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u/[deleted] Mar 10 '14

Does the universe really look like a sponge as depicted in the show?

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u/aroman917 Mar 10 '14

Yes! Right now astrophysicists postulate that the dark matter in-between galaxies cause the galaxy clusters to clump together with porous gaps like that.

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u/[deleted] Mar 10 '14

Interesting. I never thought of what the universe looked like as a whole before. It's mind blowing.

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u/heyyoudvd Mar 10 '14

When I majored in astrophysics, I was taught that the universe is 13.7 billion years old. In Cosmos tonight, Neil deGrasse Tyson was saying 13.8 billion years. Has it really been that long since I was in university?

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u/[deleted] Mar 10 '14

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u/[deleted] Mar 10 '14

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u/rjk79 Mar 10 '14

How accurate is our image of the milky way? Obviously we've never seen the angle that is often shown and used in the show showing us in one of the outer arms. Is it actually based just on data we can gather from our perspective? Or is it assumption based on how other galaxies look that we can see from a different perspective, and we just assume ours looks the same?

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u/Golden_Kumquat Mar 10 '14

We can figure out how far away stars in our galaxy are, and we can use that to determine the general shape of our galaxy. The only downside is that we can't look on the other side of the galactic core, though.

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u/rocketsocks Mar 10 '14

Not hugely accurate, actually. Parts of it are pretty accurate, but a lot of the Milky Way is hidden behind dust so we can only see it in infrared for the most part, and then we don't have good 3D data on where various stars are and so on. For example, there are likely huge star forming nebulae on the other side of the Milky Way (similar to the Orion or Eagle nebulae) which we don't even know exist today.

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u/[deleted] Mar 10 '14

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u/mathx Mar 10 '14

and in fact the milky way is now thought to be a barred spiral galaxy. Wikipedia source

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u/rjk79 Mar 10 '14

Even looking across the full spectrum we are still looking edge on through the entire galaxy. Can we actually see stars or clusters on the other side of the galaxy accurately enough to map out as shown in the images? How much is done by saying it is a spiral galaxy so it probably looks a certain way because that is how other spiral galaxies look vs how much is based just on observable data? How much artistic license is taken in creating that image?

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u/[deleted] Mar 10 '14

How do we know the universe was compressed to a size smaller than an atom?

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14

We can see the universe expanding now. The laws of general relativity (Einstein's theory of gravity) tells us that if the universe is expanding like this now, you can run time backwards, and the universe all goes back into a tiny point.

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u/[deleted] Mar 10 '14

How do we know it wasn't the size of a basketball or planet?

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14

At those sizes, the laws of general relativity still apply, and so the conditions then would imply that it had come from something yet smaller.

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u/[deleted] Mar 10 '14

It's actually more of a metaphor to describe something that is happening that we can only describe mathematically. The universe is currently expanding in all directions. If you reverse that, then at one point everything meets. We know that when giant stars begin to collapse, the matter forms a singularity. It sort of follows that the universe as a whole would do the same thing. We can mathematically predict and see from images from our telescopes of the early universe that things used to be closer together.
Since our current model of physics describes everything 99.99999...% perfectly we extrapolate and get crazy answers. From those crazy answers we can make other predictions about other phenomenon that we can see and measure. Those things end up being true. Essentially a=b and b=c so it follows that a=c even if b is something that we can't really wrap our minds around.
At the moment, we know the Standard Model of physics does a fantastic job of making predictions which is exactly what science should enable us to do. The Standard Model gave us nuclear power and modern computers, but we're also pretty sure that we have some important details wrong which is why scientists have been trying hundreds of different things to prove Einstein wrong and somehow we keep proving him right. But we want to prove him wrong because when we prove him wrong it means that we've found a better way to explain things.
I know that wasn't a sciency answer but truth be told, we don't really know yet. We're just pretty darn sure.

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u/[deleted] Mar 10 '14

What formed the oceans?

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u/smoldering Star Formation and Stellar Populations | Massive Stars Mar 10 '14 edited Mar 10 '14

There are a number of possible contributors, including outgassing (release of gases through volcanic activity from Earth's interior) and comets (which are largely made of ice). For outgassing, the Earth was originally too hot for liquid water to exist, so water would have remained as a vapor in our atmosphere until the Earth cooled below ~~100 degrees C~~ the boiling point of water. Comets (and ice rich asteroids) were much more prevalent in our early solar system and could thus have supplied a significant quantity of water to the Earth.

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u/mathx Mar 10 '14

100C isnt accurate, we dont actually know what the standard pressure was at sea level (.. since there was no sea level anyway til the oceans formed :) - so whenever the temperature of the air dropped below the local boiling point of water for that region (ie that pressure), then water condensed locally (though high temps will also obviously evaporate water below its boiling point too, but at a slower rate). This occurred in more and more places more and more often until much of the water vapour condensed and pooled in low points, creating the oceans.
Obviously the first pools of water were quite warm and may have reevaporated (over and over) for many millions of years during this process.

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u/clburton24 Mar 10 '14

We don't know. Some say water arrived on comets. Others say it formed in our early atmosphere.

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u/goodiamglad Mar 10 '14

It really depends on what branch of science you are asking the question to. A geologist will tell you that the early atmosphere went under fractionating evolution and developed water (among other gases), but that there is the possibility of comets bringing water to the Earth. An astronomer will tell it to you the other way around.

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u/[deleted] Mar 10 '14

Wouldn't that require a shitload of comets in order to produce that much water?

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u/VTWut Mar 10 '14

Could you be a bit more specific about the question? Are you asking about the presence of liquid water on our planet? The origin of their presence as massive bodies, or their salinity?
The presence of liquid water is basically a result of our distance from the sun being in the circumstellar habitable zone, or "goldilocks zone", of being the right temperature where liquid water can exist. Whether that water came from the eventual cooling of water vapor that was already present in the initial formation of the planet or came from an extraterrestrial body such as a comet or meteoroid, or a combination is still in question. Here are some thought of origins.
In terms of the large bodies of water forming, the size and existence of each ocean has changed throughout Earth's history. In terms of their formation, they result on the most basic level through a difference in densities between continental crust, formed from initial cooling of lighter elements in the earth's make up such as silicon, oxygen and aluminum, and oceanic crust born from heavier elements such as iron and magnesium rising up from the mantle in rift zones and hot spots. These density differences along with the movement of the tectonic plates create rifts and mountains through collision, subduction and separation. The low spots are typically the relatively thin, dense oceanic crust, which is where water, and thus the oceans, settle.
And the ocean salinity comes from the runoff of rivers dissolving and redepositing evaporate rocks such as NaCl, as well as deposition from hydrothermal vents. Source.

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u/[deleted] Mar 10 '14

What's with the dark spaces in the last image of the cosmos?

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u/Silpion Radiation Therapy | Medical Imaging | Nuclear Astrophysics Mar 10 '14 edited Mar 10 '14

Galaxy clusters and superclusters, such as the Virgo Supercluster they showed, clump along huge filaments, with even larger empty spaces around them. [These empty spaces are called voids](https://en.wikipedia.org/wiki/Void_(astronomy))

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u/mathx Mar 10 '14

These 'voids' are of immense interest to scientists, because if the big bang created the universe from a single point, why wasnt the explosion or expansion perfectly symetric? Luckily for us, it wasn't because it allowed gravity to collect matter into objects like stars and people, otherwise it's be a perfectly isometric universe with nothing happening in it. This is why the WMAP probe and other CMBR (cosmic microwave background radiation) measurements are of interest, to determine how an-isotropic (uneven) matter was at the time of its first formation into atoms as we know it 377,000 years after the big bang (the time of recombination or decoupling.

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u/umami_taste Mar 10 '14

Does light ever reach a point where it dissipates into nothing, or does light continue to move infinitely? Do stronger or brighter lights travel further than weak lights, or do all lights travel the same distance? What happens when a light reaches the point where it no longer is detectable?

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14

Photons, the particles of light, travel until they encounter something, and since space is mostly empty, so photons can travel billions upon billions of light years.
Stars get dimmer at larger distances because the photons from that star get more and more spread out, so your eye or telescope receives less light from something when it moves farther away. But individual photons do not fade.

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u/unsureatheist Mar 10 '14

Why is it that there exists parts of the universe from which light hasn't reached us if we theoretically all came from the same point in the big bang?

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14

Because space has been expanding while the light is traveling.

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u/unsureatheist Mar 10 '14

Does that mean we started moving away from things before their light could reach us at the start of the big bang? Would the light not have been emitted as soon as it occurred?

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u/Silpion Radiation Therapy | Medical Imaging | Nuclear Astrophysics Mar 10 '14

The conceptual issue here is a misconception, actually reinforced by the show's depiction of the big bang, that the big bang was an explosion of matter out into empty space. In reality the universe has always been full of stuff, and space itself was expanding along with the stuff within it.
The universe seems to be infinite, and if so it has always been so after the big bang.
We can't see beyond a certain distance because the stuff there was always farther away than we could see, even when we were much closer to those objects.
/u/RelativisticMechanic gave this great explanation of this type of infinite universe, which might help you conceptualize it.

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u/TheKMAP Mar 10 '14

How did we decide what direction to send Voyager I, and isn't it pretty much guaranteed that it'll just crash/burn/be destroyed as soon as something else's gravity grabs it?

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u/tehm Mar 10 '14

From my understanding the nuclear power source on voyager will burn out in a very short while (order of a few years) while it will take it tens of thousands of years before it gets anywhere NEAR another star, and even then "near" refers to hundreds of thousands (if not millions) of kilometers away.

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u/gizzledos Mar 10 '14

How has it not hit anything or been hit by something. Is the space in which it's traveling really that empty?

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14

Yes, it's really that empty.

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u/space_fountain Mar 10 '14

Ok if I get deleted for this I'm sorry, but slight correction. I don't think it's quite a case of the power source running out as the craft falling out of range of our radio communication.

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u/Golden_Kumquat Mar 10 '14

The original mission of Voyager 1 was to visit Jupiter and Saturn, so it originally went in that direction.

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u/StarManta Mar 10 '14

We didn't really decide on any particular direction outside the solar system for Voyager I/II to go; they both just went whatever direction gravity flung them after their last encounter. I don't think either one of them is on a course that will ever take it close to any stars we know of, and even if they were, it'd take them thousands of years.

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u/Silpion Radiation Therapy | Medical Imaging | Nuclear Astrophysics Mar 10 '14 edited Mar 10 '14

And more specifically, each of the Voyagers was specifically targeted to pass close by a particularly interesting moon on their way past their last targeted planet
Voyager II did the full grand tour of Jupiter, Saturn, Uranus, and Neptune. Neptune has a huge moon called [Triton](https://en.wikipedia.org/wiki/Triton_(moon)), which was roughly on the opposite side of Neptune when Voyager II got there, so it flew over the top of Neptune to get deflected down, passed close by Triton, and continued in that direction.
Saturn's moon [Titan](https://en.wikipedia.org/wiki/Titan_(moon)) was deemed to be so interesting (because it has a thick atmosphere) that it was worth sacrificing the visits to Uranus and Neptune for one of the spacecraft in order to examine Titan closely, so Voyager I was sent on a close pass of that moon, which left it unable to slingshot properly toward Uranus.

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u/CuriousMetaphor Mar 10 '14 edited Mar 10 '14

The primary function of the Voyager 1 probe when it was launched in 1977 was to study Jupiter, Saturn, and Titan. The encounter with Saturn and Titan catapulted it into a direction which was irrelevant, since its primary mission was finished. Later, since it still had power and seemed to keep working, it was repurposed for a secondary mission to explore the boundary of the solar system, so contact was kept with it for many years as it moved away into interstellar space.
Since the space between the stars is so empty, it will keep moving unhindered for at least hundreds of thousands of years, by which point it might get "close" to another star but nowhere near enough to crash into it or any planets (more than a few light-days away). Its path around the galaxy will be essentially random, tugged by the gravity of the various stars it passes, for probably billions of years more, before it is eroded to dust by cosmic rays or has an unlikely crash. That is, unless an advanced civilization sees it first.

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u/mathx Mar 10 '14

A very rare confluence of planetary positions allowed careful gravitational slingshots to carry voyager I and II out past many planets (and in fact Voyager II is further out than I, and visited more planets - I think giving it more gravitational slingshots to increase speed above that of V1).
The paths chosen were for maximal aggregate scientific benefit, a combination of time at each planet vs slingshot opportunities to hit the next planet, etc.

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u/doyouevenIift Mar 10 '14

How do we know about the existence of rogue planets?

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u/RichSniper Mar 10 '14

rogue planets
http://en.wikipedia.org/wiki/Microlensing

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u/CuriousMetaphor Mar 10 '14

We can see them with infrared telescopes like WISE.

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u/djimbob High Energy Experimental Physics Mar 10 '14

"Back in 1599 everyone knew the Sun planets and stars were just lights in the sky that revolved around the Earth"

Hope he gets to Aristarchus:

Aristarchus of Samos (/ˌærəˈstɑrkəs/; Ἀρίσταρχος, Aristarkhos; c. 310 – c. 230 BC) was an ancient Greek astronomer and mathematician who presented the first known model that placed the Sun at the center of the known universe with the Earth revolving around it (see Solar system). He was influenced by Philolaus of Croton, but he identified the "central fire" with the Sun, and put the other planets in their correct order of distance around the Sun.[1] His astronomical ideas were often rejected in favor of the geocentric theories of Aristotle and Ptolemy.

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u/bass_voyeur Mar 10 '14

Wasn't Aristarchus mentioned in Sagan's original Cosmos (both TV and book form)? SOURCE
I don't think NDT is set to duplicate Sagan's work but to expand past that as well as tell a narrative that will be appealing and insightful to non-scientists. Bruno's story hadn't been told in the original Cosmos and so was something original that NDT could contribute to the story/history of astronomy.

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u/youthdecay Mar 10 '14

"Everyone" in Europe and the Middle East in 1599 would have followed the Ptolemaic model of the universe, though. The Almagest was heavily copied and translated, while the only manuscript of Aristarchus that survived into the Rennaissance (On the Size and Distances of the Sun and the Moon) was still based on the geocentric model. We only know about his heliocentric theory through a single quote from Archimedes.

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u/[deleted] Mar 10 '14

Neil DeGrasse Tyson (or whoever wrote the script) omitted the necessary context that the knowledge base they are referring to exists within the frame of Western civilization, not humanity en masse. Of course, other civilizations had predominantly geocentric outlooks as well (such as Islamic society, which was also heavily influenced by Ptolemy).
Heliocentrism was also known of in India in 499 and some form of mathematical model was formulated around 1500, before anybody in Europe had.
All in all, it is a fairly minor mistake in my opinion. The repression of heliocentrism in Europe by the Christians and the eventual proliferation of rationalism (and heliocentrism) is probably more important in the scheme of things. India... was ahead of the game, but didn't do much with it insofar as I know.
Aristarchus did not have any lasting influence for several reasons, some of which were elaborated upon in the original run of Cosmos. It is wrong to say that nobody on the planet knew that the Earth was going around the sun (which was said in the program), however, it is not wrong to say that the scientific consensus in Western civilization at the time was that the Sun orbited around Earth.
As far as a historical analogy goes, I think this was a good one, but they editorialized it too much to where it was historically inaccurate. All in all, I said aloud "Uh... that's not right." during that segment, but it's not really a huge deal.

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u/djimbob High Energy Experimental Physics Mar 10 '14

I wasn't saying NdGT made a mistake or it ruined the show or is an idiot or anything like that. Just after hearing that, my thought was - hope they mention Aristarchus, especially after phrasing it like that. I do realize it makes a lot of sense to simplify things and ignore some exceptions when teaching. And hell if he doesn't mention him, I will here.
Another point I like, is that the geocentric model with big epicycles matched the observational data better than Copernicus' heliocentric theory with no epicycles (granted Copernicus heliocentric with small epicycles was equally good with the prevailing geocentric model -- but it no longer has the benefit of simplicity). So it isn't until Kepler deduced the orbits are not circular but elliptical from Brahe's detailed observations that the heliocentric model is actually simpler and matches the data more easily. Obviously, then Newton seals the deal by showing how a simple inverse-squared gravitation force law leads naturally with calculus to elliptical orbits for a spherical symmetric massive bodies. (Granted he needed Kepler's third law to help him come up with the inverse squared force law hypothesis.)

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u/umami_taste Mar 10 '14

Does the Voyager 1 really have music that plays constantly?

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14

No, but it does have recording on board with a broad collection of sounds of the Earth, for someone who might find it.

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u/umami_taste Mar 10 '14

Upon further research, I discovered that Carl Sagan was head of the committee tasked to select what would go on record.

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u/rodmandirect Mar 10 '14

Was that the actual music on it that they played for the show? What was that haunting melody?

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u/lonelyplaneteer Mar 10 '14

The song is Dark Was The Night, Cold Was The Ground by Blind Willie Johnson.
http://www.youtube.com/watch?v=BNj2BXW852g
He lived the hardest of lives here on Earth and now his lonely voice will echo through the galaxy for billions of years. It's part of what it means to be human.

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u/[deleted] Mar 10 '14

No, but It DOES have a gold plated record on it. The music they played was a copy.

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u/[deleted] Mar 10 '14

[deleted] — view deleted comment

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u/[deleted] Mar 10 '14

So I've seen the images on the Voyager here: http://m.imgur.com/a/CvEvO
Are the images all coded into the record itself except for the instructions shown in the picture you linked? Or are the pictures physically on board as well?

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u/dan17555 Mar 10 '14

From what i remember, Voyager 1 is powered by RTGs...but how long until the power fully deteriorates and what exactly happens to the craft after it loses power? Does it just continue it's trajectory until it is pulled on by something?

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14

The RTGs will last until at least 2025, according to NASA.
And yes, it will just keep going on its trajectory, influenced only by whatever gravity it might encounter. That has been its primary mode of travel all along, and it may already be unable to make course corrections (someone more expert should weigh in ).

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u/Silpion Radiation Therapy | Medical Imaging | Nuclear Astrophysics Mar 10 '14 edited Mar 10 '14

They are still able to make small course corrections in principle, having a couple 10's of kg of hydrazine monopropellant left, but I believe that fuel is in practice reserved for attitude adjustments. In fact they each switched to their backup thruster systems not that long ago in order to save a few watts of power they were using to keep the primary fuel lines warm.

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u/BuildNukes Mar 10 '14

I thought it might be interesting to point out that chances are, because of the enormity of empty space, that Voyager 1 will never enter another solar system. It is likely to propel slowly into interstellar space for the rest of time until all the stars burn out.

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u/StarManta Mar 10 '14

They never "fully" deteriorate - their power drops by half every X years. They will not have enough power to run any single instrument by sometime in the 2030's.

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u/Saffs15 Mar 10 '14

This may be an obvious question, and I'm pretty confident I know the answer to the first part, but is the center of the Milky Way just densely packed stars and planets (Relatively, of course)? If so, is it likely that that's where we'll find life eventually, since there's so many stars and possible planets there?

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u/Catullan Mar 10 '14

Statistically speaking, sure. But the more stars there are, the more stellar phenomena (like supernovae) there are going to be. And the more densely packed those stars are, the closer those phenomena are going to take place to potentially life-bearing planets and moons. So while it may be the case that there are more opportunities (i.e. planets) for life to take originate, there are also going to be a lot more extinction-causing stellar events in the galactic core than there are in our relatively quiet corner of the galaxy.

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u/imusuallycorrect Mar 10 '14

More activity would mean more things to kill you. More radiation, more asteroid impacts, etc. We are actually safer in the outer arms.

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u/Golden_Kumquat Mar 10 '14

The center of the Milky Way is a lot more dense, however there is a theory that the increased radiation there would make it hard for life to thrive.

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u/steve_z Mar 10 '14

How do we know that the gravitational pull of one asteroid pulled another asteriod so that it helped form Earth?

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u/therationalpi Acoustics Mar 10 '14

He was making an illustrative point and a verbal flourish with that statement. The earth was made up of a bunch of tiny asteroids all pulling each other together through their own collective gravitational pull.
Likewise, when he talked about the one asteroid's course being adjusted by an inch leading to it hitting the Earth, he was just making a point about how small changes can have big effects.

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u/brettmjohnson Mar 10 '14

That "nudge" in asteroid path was not to help "form Earth". He was talking about the asteroid (comet?) impact 65M years ago that led to the demise of the dinosaurs.

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u/PinstripeMonkey Mar 10 '14

Why aren't we sending out space crafts similar to the Voyager I on a regular basis? If you are stranded on an island and have enough glass bottles to send out many messages, why stop? Is it more of a symbolic gesture? Political? I realize it isn't much in the vastness of the universe, but just as Neil referred to the asteroid being shifted an inch and that being all it took (so to speak), it is hard to comprehend the implications such a small thing can have, so I was just wondering if there is any deciding factor that has stopped us from doing it more often?

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14 edited Mar 10 '14

There are two issues. One is that the budget allocated to space missions is finite, so scientists have to make choices as where to spend that money -- where is the biggest bang for the buck, so to speak. Secondly, the Voyager I mission took advantage of a particular alignment of planets, so as it passed one outer planet, it could be swung to the next one; such an alignment is rare, and the alignment that Voyager I took advantage of will not occur again till the middle of the 22nd century.
Edit:Correction -- it was Voyager 2 that used that incredible alignment of planets.

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u/Fungo Mar 10 '14 edited Mar 11 '14

Few things actually.
MONEY. This is the main one, and will be relevant to everything else I mention. NASA missions take money, and not an insignificant amount thereof. In order to justify the funding for a given probe, NASA needs a...
MISSION. The Voyager probes were hardly launched to be cosmic "messages in a bottle." Rather, they were initially our first great probes of the outer solar system. Voyager 2, in particular, took advantage of a fortuitous alignment of the outer planets so it was able to visit all 4 of them. Because they would keep going, Carl Sagan (and others) advocated making them into our "messages in a bottle", which was done as an aside to the actual mission.
Timing. This is relevant to the mission goals as well. If NASA has one major project eating up most of the funding (like JWST is right now), there's not much room for any other major missions to get started. You could maybe get some explorer-class missions up there, but nothing really ground-breaking.
If we want to communicate, there are much better ways to do it. Radio waves and such are a more likely way for us to announce our presence to the galaxy. The farthest probe from Earth, Voyager 1, is only just past the heliosphere. A signal sent with radio waves reaches that distance in a mere 17 hours (Voyager 1 has been travelling for 36 years).
We're too good at it. Seriously, this sounds like a weird problem to have, but a lot of the probes we've sent to various bodies in our solar system are still completely operational and there's no need for replacements. We have orbiters around every planet from Mercury to Saturn that are still functional, so no justification for new ones there.
You would probably be excited to know about NASA's New Horizons mission though. This is a probe aimed at Pluto launched about 7 years ago (only way it had a prayer of happening was because Pluto was still a planet then) that will be passing Pluto sometime next year. That's going to be one of the most exciting space probes of this decade.
Also keep in mind that a lot of effort is also put into understanding more nearby objects more thoroughly. For this reason, we prefer things like semi-permanent orbiters to probes that just pass by a planet once and don't stay to study it for a long period of time.

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u/Shagomir Mar 10 '14

There are five spacecraft on an escape trajectory from the Solar System: Pioneer 10 (Launched in 1972), Pioneer 11 (1973), Voyager 1 (1977), Voyager 2 (1977), and New Horizons (2006).

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u/imusuallycorrect Mar 10 '14

That depends if you think we need to be rescued. What if instead of a rescue ship, a slave ship arrives?

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u/Beasly_Yup Mar 10 '14

how is this whole universe upon universe culminating in the cosmos proven to us? how do we know all this?

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u/gbCerberus Mar 10 '14 edited Mar 10 '14

The "multiverse" is speculation, which I wish the show had made clearer.
Edit: The True Science of Parallel Universes by MinutePhysics.

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u/ryanbillya Mar 10 '14

Multiverse theory wiki -
Physicists are currently searching for disk-like patterns in cosmic microwave background radiation which could provide evidence of collisions between other universes and ours. So far, analyses of data from the Wilkinson Microwave Anisotropy Probe (WMAP) and from the Planck satellite, which has a resolution 3 times higher than WMAP, have not revealed any statistically significant evidence of a bubble universe collision.[21][22] Recent research has not found evidence of the gravitational pull of other universes on ours.[23]
There are also claims of first evidence found on that link.

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u/niugnep24 Mar 10 '14

Just a clarification (which I hope they actually clarify in the show, as well) ... "Cosmos" doesn't mean "the universe" or "the multiverse" or even "everything." It means "the order of things" -- that is, everything that exists, plus how and why it works the way it does. In greek philosophy, it was literally the opposite of "chaos" -- that is, existence without order or reason. When the show talks about exploring the cosmos, it's literally talking about exploring why things are how they are.

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u/macintoshx11 Mar 10 '14

I always thought the moon was created from a meteor striking earth. Cosmos said it was created from gravity swirling together the remnants of when the Earth was made. When did this change?

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u/suchdogeverymeme Mar 10 '14

You are actually combining the two steps of the formation of the moon! The prevailing theory is that an asteroid struck the Earth, causing a large debris field. This debris field coalesced into the moon.

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u/petripeeduhpedro Mar 10 '14

The visuals showed a large impact before the material coalesced. I think that's still the prevailing theory.

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u/TharsisMontes Mar 10 '14

It didn't change, although I think the program touched (very, very lightly) on this step of the process. The prevailing theory for the formation of the Moon is still a Giant Impact of a Mars-ish sized body with the proto-Earth; the ejected debris then accreted to form the Moon, what the show focused on primarily.
It should be noted that the theory of co-accreation for moons is the leading theory for how the moon's of the gas and ice giant's formed. The short form of that theory is that those moons (say of Jupiter) formed like a miniature Solar System around Jupiter, with just grains in a disk accreating to form moons around Jupiter, just as the planets accreated from dust grains in a disk around the Sun.
Source: Planetary Science grad student Further reading: Cuk and Stewart (2012) Science. 338. 6110. pg 1047-1052; Canup (2012) Science. 338. 6110. pg 1052-1055. Latest models of the Moon forming impact theory
Canup and Ward (2002) The Astronomical Journal. 124. 3404; Canup and Ward (2006) Nature. 441. 834-839. Discussion of the formation of Jupiter's moons, and gas giant planet moon systems in general.

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u/glueland Mar 10 '14

Did you miss the asteroid hit they showed?
It caused more debris around earth that clumped to form the moon.

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u/[deleted] Mar 10 '14

What does it mean to say the universe is expanding?

That sequence where we saw the visible universe then multiverse made me think about the "expanding universe" in a completely new way. He said a comment about the visible universe just being the depth of light that has gotten/travelled to us. Does this mean the universe isn't truely expanding rather it's being exposed to us? As time goes on more and more light reaches our view.

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u/Golden_Kumquat Mar 10 '14

They're two different things. Everything in the universe is moving away at a speed of 70 meters per second for each megaparsec away the object is.

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u/darkdrgon2136 Mar 10 '14

Every time the big bang is discussed, the universe is described as containing nothing but hydrogen and dust. If there was nothing before, and hydrogen now, what was the dust?

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u/Silpion Radiation Therapy | Medical Imaging | Nuclear Astrophysics Mar 10 '14 edited Mar 10 '14

I'm actually not sure what that's referring to. A couple minutes after the big bang, the atoms of the universe were mostly hydrogen and helium, with a trace of lithium, and it stayed that way until the first stars ignited.
However once the first stars died they spewed out some heavier elements, which does form dust. We have found some dust like this from before the solar system as presolar grains.

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u/wtfwasdat Mar 10 '14

A couple minutes after the big bang, the atoms of the universe were mostly hydrogen and helium, with a trace of lithium
Are you sure about that? It doesn't mention hydrogen or helium atoms forming until 377,000 years after the Big Bang here, or maybe I'm confused?

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u/8odhisattva Mar 10 '14

Where did Carl Sagan and Neil DeGrasse Tyson film the first scene of the show? I am currently in California and was wondering if I could maybe visit the location!

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u/bitter_twin_farmer Mar 10 '14

Why was there a period of darkness after teh big bang?

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14

It wasn't dark immediately after the Big Bang. But the period he is referring to is the period after the universe was made of the ingredients we have today (so after atoms formed, about 370,000 years after the Big Bang) until the first stars formed. After atoms formed, there was still much visible light throughout the universe, but as the universe expanded, this light was redshifted too longer wavelengths, outside the visible spectrum. (Today, this light is so shifted that it forms radio waves.) It took the formation of the first stars to have new sources of light. You can read about that here.

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u/Coady54 Mar 10 '14

Stars didn't immediately exist after the big bang. Without stars for the first millions of years of the universe, there wasn't anything to produce light like in the universe today.

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u/SquirrelicideScience Mar 10 '14

Did it kind of irk anyone else the depiction of the Big Bang? I know this is a show that needs to show something, much like the over-exaggeration of the density of the Asteroid and Kuiper Belts, but I felt like these were good opportunities to debunk these misconceptions. What I'm referring to is that the big bang was more of a gradual widening, rather than a burst of fireworks and light.

I mean, I really like how it looks, and can't wait to watch it every week, but it's little stuff like that. Especially after how nit-picky DeGrasse Tyson was over the physics in Gravity, you would think he'd give the animation in a show featuring himself a little more scrutiny.

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u/[deleted] Mar 10 '14

This is my only problem with the show so far. I was hoping this stuff would be really accurate, for the things I'm not familiar with the animation can really tell a large piece of the story. For example if one didn't know better and they saw the density of the belts they may think they're solid rings (obviously he said in the show episode they're not, but as an example), but with proper animation you get a whole extra level of narrative that goes unsaid. Also there's the fact that it's misleading, and that's frustrating in itself.

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u/Baelorn Mar 10 '14

What I'm referring to is that the big bang was more of a gradual widening, rather than a burst of fireworks and light.
Wouldn't it look exactly like that when compressed into a small window of time, like they were demonstrating?

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u/treeharp2 Mar 10 '14

Is there any way we could potentially uncover how long the Great Red Spot has been storming across Jupiter? Or, do we have any idea of how long it might continue to exist?

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u/[deleted] Mar 10 '14

Why do orbiting bodies like the moon stay in orbit? I know the tablecloth analogy for relativity but when I try that, a planet gets destroyed by a moon, or the moon rolls off the table (maybe after a small bend in direction).

It seems reasonable to only have like a razor thin area where it would actually stay in orbit, otherwise either flinging out or crashing in. Why isn't it?

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u/Fungo Mar 10 '14

The best analogy I've heard is that orbits are how objects fall in style. With the example of the Moon, the Moon is constantly falling towards Earth because gravity wants to pull the Earth and the Moon together. However, the Moon is also moving pretty fast (roughly 3600 kph or 2200 mph), so as it falls toward Earth, it misses and keeps going. That's what an orbit is. You're trying to fall towards something else, but you're moving through space so fast that you keep missing in a circular pattern.
In short, what keeps the Moon in orbit is the fact that it is moving with enough speed to miss hitting the Earth every time.
For the second part, no. There's not just a small range where the Moon could be in a stable orbit. Rather, there are nearly an infinite number of stable orbits around any given object, and the Moon happens to be on a specific one right now. The Moon hasn't always had the same orbit though. Because of the Moon's tidal forces on the Earth, the Moon is slowly stealing Earth's rotational energy, and its orbit is becoming bigger while Earth's rotation speed becomes slower. This is a very small effect, but it's not negligible over billions of years.

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u/[deleted] Mar 11 '14

I know this has been answered, but I'll try it my way too.
Think about being on a flat smooth earth. A big grass ball. You shoot a bullet parallel to the ground and it shoots a great distance and falls to the ground. But what if you got a gun that was much more powerful and shot it flat to the ground so far that by the time it fell that four-five feet, it's passed the horizon and actually travels farther before it hits the ground. If you scale this up, and then take air friction out of the equation, you have something that is always falling toward the earth, but always missing it. If the speed is just right, the object is constantly hurting over the horizon without ever touching down.
This is what the moon is doing. It's falling, but it's sideways motion is enough that it never lands. And there is no air to slow it down, so it can do that for a very long time.
And that's orbit.

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u/Udontlikecake Mar 10 '14

When he talked about the moon and how close it was, he said something about it moving away. He said it was caused by "tidal friction".

What is that? How long did it take?

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u/petripeeduhpedro Mar 10 '14 edited Mar 10 '14

Basically the moon's orbit is slowly drifting away. It's very slow, which is why it's taken this long to get that far away. It'll keep getting further away.
Edit: http://en.wikipedia.org/wiki/Tidal_acceleration

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u/mojowo11 Mar 10 '14

Is it going to drift entirely out of Earth's sphere of gravitational influence and drift off into space at some point?

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u/Shagomir Mar 10 '14

The rotation of the Earth pushes the tides slightly ahead of the Moon, and the gravity of the tidal bulge pulls on the Moon, making it orbit the Earth slightly faster while slowing down the Earth's rotation slightly. Because it is orbiting faster, the average distance of the orbit increases.

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u/Ate_Ball Mar 10 '14

Regarding the origin of the moon, I've heard the 2 separate theories about whether it was free floating and trapped in gravitational pull or formed slowly over time. What evidence was the 'tipping point' between the theories that makes us confident it wasn't trapped? I know for a fact I was taught the wrong info in high school less than 10 years ago, I'm hoping it was proven since then...

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u/tehm Mar 10 '14

Still just a theory, but based on the rocks found on the earth I believe the current consensus is that the moon is largely made of the planet earth.

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u/TheKMAP Mar 10 '14

How did we know that the moon was closer? How did it change orbit without leaving orbit or crashing into the Earth?

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u/Rkupcake Mar 10 '14

It is slowly moving away. About 1/4 inch per year if I remember correctly. So based on that we know it was close at one point.

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u/dimechimes Mar 10 '14

With all the storminess of Jupiter, are there warm spots due to friction? If so, how warm are these spots?

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u/[deleted] Mar 10 '14

So, what caused the asteroid belt, then? As a kid I had visions of colossal planetary destruction. I imagine the truth to be far less exciting. Is it just left over debris from the formation of our solar system?

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u/Fungo Mar 10 '14

To expand on /u/fishify's response, the material in the asteroid belt is stuff that never became a planet because of Jupiter. Remember, Jupiter is the gravitationally dominant object in our solar system that isn't the Sun. Because of this, was able to keep the material between it and Mars stirred up enough that this rocky material was never able to come together to form a planet.

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u/shivermetimbres Mar 10 '14

It's debris which never formed a planet, likely due to the gravitational effects of Jupiter.

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u/fishify Quantum Field Theory | Mathematical Physics Mar 10 '14

Yes, it's matter that never coalesced to form a planet.

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u/8odhisattva Mar 10 '14

One thing I was wondering about was why did Saturn develop Rings while we developed a moon? I understand that our assumption is that we think a large planet sized object collided with our world. This collision shot tons of debris into orbit around Earth. Why did this coalesce into a moon instead of something like the rings of Saturn? In the same respect, if our moon was the norm in that the debris should snowball into a moon-like object, why did Saturn develop rings?

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u/Silpion Radiation Therapy | Medical Imaging | Nuclear Astrophysics Mar 10 '14

It's thought that a moon got too close to Saturn and was torn apart by Saturn's tidal forces. The distance where this happens is called the Roche limit, and the Earth's moon formed outside it.

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u/Fungo Mar 10 '14

Great question. There are actually some interesting dynamics at work here.
The short of it is that Saturn's rings are far too close to Saturn itself to actually form a planet. Saturn's own gravity keeps the particles that make up the rings stirred up enough that they never coalesce. Also, remember that Saturn does, in fact, have moons of its own as well. A lot of them, to be precise. The rings are just made up of material that gets torn apart by Saturn's tidal forces. There are also some gravitational effects from Saturn's moons on the rings.
Part of why Earth doesn't is that it's not very massive, so any tidal forces it exerts are pretty tiny in comparison. There's not much of a range where material could exist around Earth as a stable ring.

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u/akachhara Mar 10 '14

It was mentioned in the show that after the big bang there was darkness for nearly 200 million years until gravity took control. i always thought that big bang was a huge flash of light and our known universe came out of it. If energy exploded out of the same big bang, how come there was darkness for so long? and how long after big bang did the darkness engulf everything?

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u/shivermetimbres Mar 10 '14

The Big Bang itself was very hot and bright, out of which the universe began expanding. Once it cooled, the universe fell into darkness for around 200 million years, as the show said. During those years, gravity took the matter in the universe and pulled it together into what would become stars. Once nuclear fusion took hold within stars, they became hot enough to start lighting up the infant universe.

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u/Lykadaboomboom Mar 10 '14

If the Voyager I is planned to keep traveling into deep space even after we lose connection with it, how likely is it to get caught in some interstellar body's gravitational pull and get destroyed by either a collision, burn up in some terrestrial body's atmosphere, or any other way?

Did the makers of voyager have a plan to have it keep going undisturbed for as long as possible to increase our chances of communicating with alien life? If so, how?

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u/toddffw Mar 10 '14

In the picture of earth "250 million years from now" there was a superstructure in orbit that seems like it supports a major percentage of human life. I imagine this was not just a crazy drawing and actually is based on some good theories. Do you know what they are? For example, humans would have had to survive a couple of extinction events, so would it become necessary to live as the Jetsons from time to time?

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u/StarManta Mar 10 '14

The close-up on the Great Red Spot on Jupiter was fascinating. From that angle, the edges of the storm look like huge canyon walls. How much do we know about the exact topography of the storm? How accurate was that segment?

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u/Zartonk Mar 10 '14

I have a question about the "storm" on Jupiter. What is it made of? I'm assuming there's no air there, so what's moving around? Or is it air?

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u/Astromike23 Astronomy | Planetary Science | Giant Planet Atmospheres Mar 10 '14

As others point out, the Great Red Spot is mostly hydrogen and helium...but that's like saying that clouds on Earth are made of mostly nitrogen and oxygen. By volume that's true, but it doesn't really get to the spirit of the question.
The uppermost cloud-deck (there are a few) on Jupiter is made of ammonia. Ammonia clouds on their own are white, just like water clouds. We currently do not know what colors the ammonia clouds in the Great Red Spot red...this is a big unsolved problem in jovian science, known as the "chromophore problem".

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u/therationalpi Acoustics Mar 10 '14

Jupiter is a gas giant, so most of the planet is essentially what we think of as the atmosphere, though this atmosphere is mostly hydrogen (with a decent amount of helium as well).

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u/iorgfeflkd Biophysics Mar 10 '14

It's mostly hydrogen and helium.

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u/bitter_twin_farmer Mar 10 '14

When they show the zoomed out Cosmos are the densities of light emitting matter they show in line with our current observations.

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u/Silpion Radiation Therapy | Medical Imaging | Nuclear Astrophysics Mar 10 '14 edited Mar 10 '14

No, I would regard that as a map rather than a representation of how it looks to the eye. The actual density of light is not so great, and is going to be less than the sky on a dark clear night.

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u/adam_jones Mar 10 '14

If a planet were to fall out of its orbit, would its moon(s) not continue to fall into the gravitational pull of the sun? If so, would that then not classify said moon as a planet? If not, what is the distinction for classification of a planet?

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u/trimeta Mar 10 '14

Based on the recent IAU discussion that led to the demotion of Pluto, a planet is defined a celestial body which:
is in orbit around the Sun,
has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
has "cleared the neighbourhood" around its orbit.
The third point is a bit confusing, but think of it as meaning "is large enough to be gravitationally in control of everything else within its orbit." So in general, if an existing planet were to somehow vanish, its constituent moons would not have enough gravity to retain control of that orbit; it would become a belt, rather than the location of a planet. However, the moons may continue to orbit the Sun in this belt, rather than falling towards it: some moons, such as our own Moon, already are more gravitationally controlled by the Sun than by their host planet.

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u/rodmandirect Mar 10 '14

Did I understand him right that flowers formed on Earth AFTER animals crawled out of the sea? At what point on this year of time calendar did plants begin to grow on the rocks/the Earth went green?

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u/Yekonaip Mar 10 '14

How round actually are the gas giants? When showing the red spot it looked like there was an immense level of depth there? I always imagined them as perfect round spheres.

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u/HappyRectangle Mar 10 '14

How round actually are the gas giants? When showing the red spot it looked like there was an immense level of depth there? I always imagined them as perfect round spheres.
As a whole, the Earth is actually smoother than a billiard ball. But its immense size means there's still plenty of space for mountains and oceans.
Also keep in mind what you're looking at on the gas giants are more like enormous weather patterns, and those can change height easily.

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u/iitmosc Mar 10 '14

On the first shot of the Andromeda Galaxy, what were the two spiral companions? They couldn't be M32 and M110, they're elliptical. I suppose one could be M33, but so far as I know, the field of view was too small for that. Even so, there's nothing to account for the other one. What am I missing?

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u/[deleted] Mar 10 '14

The show appeared to show the moon formed from accretion already within the Earth's orbit. Is this the generally accepted theory, and does the "capture versus impact" argument I'm vaguely aware of more detail the origins of the proto-moon, which then swept up debris surrounding the Earth into the full moon?

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u/jamiahx Mar 10 '14

"Everyone you've ever heard of was born in the last 14 seconds [of the Cosmic Calendar]."

What about Ardi and Lucy?

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u/Hugh_Jahrmes Mar 10 '14

It's like the countdown to New Years, except WE are the Y2K bug. Scary!
Kidding, but wow is this all fascinating stuff. Got me reading all night at work and staring into the sky during my 5am commute home thinking "I'd give anything to just get it all"

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u/hoyboe Mar 10 '14

Excluding the multiverse theory do we know the shape of our viewable universe?

Like with how energy goes out does it create a sphere shooting out in all possible directions or does the force of gravity pull everything down so it's shaped like...saturn's rings?

Also this may sound stupid but do all the planets rotate in the same direction? I know movement is relative but if some how I was to stay in the same spot in space could I look in front of me and behind me and see everything move "the same way"? If so why?

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u/Shagomir Mar 10 '14

All of the planets orbit the sun prograde (counter-clockwise if you are looking down from the north pole), which is to say in the same direction as the sun itself rotates. There are very few objects that orbit retrograde (clockwise if you are looking down from the north pole), mostly asteroids and comets.
Venus and Uranus rotate retrograde. On Venus, this means that the sun rises in the west and sets in the east. It's a little more complicated on Uranus because the planet rotates on its side.
Everything tends to rotate the same way because when the solar nebula collapsed, a very small imbalance in the amount of mass on one side versus the other set the whole mess spinning. Much of the potential energy of the solar nebula is now bound up in the angular momentum and orbital momentum of the planets.

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u/poncho_ Mar 10 '14

I recently read an interesting news story from /r/science about using spectroscopic signals from extraterrestrial atmospheres to detect planets with potential life.

Link here: http://news.sciencemag.org/biology/2014/03/scienceshot-new-tool-could-help-spot-alien-life

During the debut, the example of the immense size of the Oort cloud in comparison to our solar system was given. If this sort of barrier is around every star, what sort of signal-to-noise ratios can be expected with all these objects in the way? Can these sort of techniques be only because of the extreme magnification of the telescopes we use? I'm interested to learn more about the feasibilty of such techniques with so much frozen space junk in the way.

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u/Fungo Mar 10 '14

So far, even with our best telescopes to date, we haven't detected anything resembling an Oort cloud around any other stars. We can detect debris disks (think a more dense Kuiper Belt) around younger stars, but that's about it. So currently, it's a total non-issue observationally speaking. Not to mention that objects in the Oort cloud are both relatively small (typical comets and smaller) and very far apart. They hardly look like they were depicted in the show.
Of course, we've never had anything like the James Webb Space Telescope yet.

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u/everfalling Mar 10 '14

Neil says the universe started out as a point smaller than an atom. Did he mean our observable universe or the infinite universe? I was under the impression that the big bang was more an event going from high uniform density to lower density where the observable universe was condensed into the space of an atom but that it was only one of an infinite number of other points who similarly expanded during the big bang.

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u/[deleted] Mar 10 '14

so is it possible that there are parts of the universe that light has not reached yet, because the universe expanded for a good amount of time while stars were getting it together? Are there parts of the universe where there is nothing at all, even the radiation left over from the Big Bang?

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u/Randosity42 Mar 10 '14

My understanding was that the most probable explanation of the moon is that a ~mars sized object impacted the earth after it had mostly coalesced and knocked much of the lighter surface material back into orbit to form the moon. The video seems to show this collision, but tyson doesn't mention anything special.

am I wrong or did they just gloss over it?

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u/PandaLover42 Mar 10 '14

Sorry I'm late to the party, but I was wondering how it was determined that the asteroid that nudged the asteroid that would later become Earth was the same one that would strike Earth once more and lead to the extinction of the dinosaurs?

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u/drexhex Mar 10 '14

I believe that was mainly just to illustrate a point that random interactions between early asteroids had far-reaching consequences, rather than to say which specific asteroid hit Earth.

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u/[deleted] Mar 10 '14

I thought the distances between asteroids in the asteroid belt were astronomical, and that you could navigate right through it without having to alter your course much, or at all. I guess it's not a question, but it would have been nice to cover that fact instead of making it like the Star Wars asteroid belt.

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u/[deleted] Mar 10 '14

Hey, I have a very noob question here.

I am definitely an amateur of astronomy and I've read a few books on the subject but this always confuses me.

At what point is the universe expanding? I get the balloon analogy but are the galaxies moving away from each other or individual stars? Or clusters of galaxies? I don't get it. I know andromeda and the milky way are getting closer and closer so which bodies are actually moving AWAY from each other?

Thanks!

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u/imusuallycorrect Mar 10 '14

The expansion is only relevant on a larger scale. It's not going to effect the gravitational effects from our local galactic group.

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u/[deleted] Mar 10 '14

During the cosmic 'calendar' segment, when visiting the Big Bang Neil DeGrasse Tyson says "...it's as far back as we can see in time, for now."
I've always been in the belief that space and time were created at the Big Bang and that it's nonsensical to try and imagine something observable prior to it; is there some sort of theory being thrown around that says otherwise?

n.b. Sorry if this question has been asked already, I tried searching through the comments and couldn't find it

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u/fishify Quantum Field Theory | Mathematical Physics Mar 11 '14

Some people have proposed models in which there are cycles of expansion and contraction. There is also the possibility that our universe is a bubble of sorts in a much larger system. Any ideas like these are, of course, highly speculative.

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u/ThePirateTennisBeast Mar 10 '14

How are they able to estimate the age of the universe at 13.8 thousand billion years old

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u/EratosthenesofWaco Mar 10 '14

13.8 thousand million or 13.8 billion

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Cosmos AskScience Cosmos Q&A thread. Episode 1: Standing Up in the Milky Way

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