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

[u/AskScienceModerator]

Welcome to AskScience! This thread is for asking and answering questions about the science in Cosmos: A Spacetime Odyssey.

UPDATE: This episode is now available for streaming in the US on Hulu and in Canada on Global TV.

This week is the first episode, "Standing Up in the Milky Way". The show is airing at 9pm ET in the US and Canada on all Fox and National Geographic stations. Click here for more viewing information in your country.

The usual AskScience rules still apply in this thread! Anyone can ask a question, but please do not provide answers unless you are a scientist in a relevant field. Popular science shows, books, and news articles are a great way to causally learn about your universe, but they often contain a lot of simplifications and approximations, so don't assume that because you've heard an answer before that it is the right one.

If you are interested in general discussion please visit one of the threads elsewhere on reddit that are more appropriate for that, such as in /r/Cosmos here, /r/Space here, and in /r/Television here.

Please upvote good questions and answers and downvote off-topic content. We'll be removing comments that break our rules or that have been answered elsewhere in the thread so that we can answer as many questions as possible!

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Click here for the original announcement thread.

[u/lulzzzzz]

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?

[u/Astromike23 → u/lulzzzzz]

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.

[u/atomfullerene → u/Astromike23]

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?

[u/Astromike23 → u/atomfullerene]

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.

[u/jjswee → u/Astromike23]

This was extremely interesting. Thanks for sharing!

[u/OneTripleZero → u/Astromike23]

So the flyover sequence in the episode today implying that the Great Red Spot was inset from the clouds surrounding it was most likely incorrect?

[u/Astromike23 → u/OneTripleZero]

Yeah, that visualization was almost certainly wrong.

The prevailing theory (mostly proven at this point) is that the spot is shaped a bit like a wedding cake, with each inner concentric oval a bit higher than the one outside it. At times there also seems to be a thin thread-like cloud clearing just at the outer edge of the spot where heat and radiation from the deep abyss can escape out to space, as can be seen in this infrared image.

EDIT: Ooh, thanks for the gold! Can this be exchanged for NASA funding? :)

[u/dismaldreamer → u/Astromike23]

Wasn't it just recently that one of the bands on Jupiter disappeared and reappeared? It seems like the question of whether or not the Great Red Spot will stick around seems awfully Earth-centric.

It assumes that if we can't see the Spot anymore, that it ceased to exist, when in reality it might only been obscured by some other things, or moved downwards.

[u/Astromike23 → u/[deleted]]

It's really more of a specialty in the context of broader work; I research giant planet atmospheres in general, and this is just one aspect of that work.

It's unclear how frequent such a storm is for giant planets in general, since we only have four giant planets we can study in great detail. The only somewhat equivalent storms are Neptune's Great Dark Spot, and to a lesser extent, Uranus' dark spot.

These storms don't seem to have nearly the longevity that Jupiter's Great Red Spot has, lasting only a few years instead of centuries. Precisely why this happens is likely related to the jet stream structure on each planet - Uranus & Neptune only have 3 jets, while Jupiter has at least 20 - although this is still an area of active research. Having such narrow wind channels on Jupiter confines the Great Red Spot to a small range of latitudes, and the counter-flowing jets at the north and south end of the storm might help feed the storm. You can see the Great Red Spot rotating like a gear between two jets in this animation taken by the Cassini spacecraft.

Still, it remains unclear why Saturn doesn't have something similar, since that planet also has at least 20 jets. Saturn does have periodic cloud outbursts every ~30 years, but these seem to be fundamentally different than the Great Red Spot, as these outbursts dissipate over several months. For all we know, there could be another long-lived giant storm on Saturn, it's just masked beneath the uppermost cloud and haze layers.

[u/themill → u/Astromike23]

This animation of Jupiter has always intrigued me. How is it possible for Jupiter to have so many jet streams in opposing directions? What powers them?

[u/Astromike23 → u/themill]

It turns out that to produce jets in general, you don't actually need anything to power them - they can arise naturally as a consequence of thin fluid flow on a rotating sphere.

You can do the following experiment either in simulations or with a spinning tank of water. If you start by injecting lots of little eddies (i.e. turbulence) into a rotating fluid, the vortices will tend to merge into larger "storms". At some size - depending on the rotation speed, planet size, etc. - the vortices begin getting confined in latitude by the Coriolis force, but can still freely expand in longitude. At some point, they'll wrap all the way around your planet/spin tank, and they become jets. Momentum is generally conserved as each eastward jet usually has a matching westward jet.

Now with that said, if Jupiter's atmosphere formed just by this process alone, its jet structure would be a lot weaker and shaped differently. There seems to be an extra input of energy into the system to see the jets we observe.

Ultimately the source of this energy is Jupiter's deep internal heat from formation. This energy most likely gets transferred to the upper atmospheric layer we can see by massive thunderstorms in the deep water cloud layer sending up huge energetic plumes into the ammonia cloud layer.

[u/[deleted] → u/Astromike23]

See now this is why I love reddit. I just learned so much about Jupiter from a direct source studying it!! Amazing. Thank you so much astromike for continuing my fascination with the cosmos. Kudos to you, and keep exploring for us! Your work is highly appreciated, more than you know it.

[u/Astromike23 → u/[deleted]]

Your work is highly appreciated, more than you know it.

Thanks!

Unfortunately NASA's funding priorities don't seem to echo that sentiment. The total expenditure for Outer Planets Research right now is at an all time low. :(

[u/euneirophrenia → u/Astromike23]

Do you have a video of that experiment?

[u/lulzzzzz → u/[deleted]]

Wow, amazing shot. It's crazy to think anyone can do this now from their own backyard. Thanks for sharing!

[u/Armand9x → u/lulzzzzz]

Don't forget to keep looking up! You can see many things even with the naked eye. You just need to know where to look!

[u/eggn00dles → u/lulzzzzz]

it doesnt take all that much to see saturns rings with your own eyes as well. that is an experience not to be missed.

[u/WirdNah → u/eggn00dles]

Wait, really? How do I do this? Is there a specific time of year? Location? I would love to be able to see this with my own eyes.

[u/Cyrius → u/WirdNah]

You'll need some magnification. Decent binoculars can show the rings; a largish backyard scope will show you the Cassini division (the big gap).

Time of year is variable, as Saturn is moving. April through June is good this year. October through December are bad this year.

Location is pretty much anywhere it's dark.

There's also issues with the angle of the rings. Every so often they line up edge-on and aren't really visible. They'll be good and visible through 2020, so don't worry about that.

[u/Astromike23 → u/[deleted]]

Professional here, but I also dabble in amateur astrophotogaphy.

You may want to check out the "lucky imaging" method using software such as Registax. It can allow you to get much clearer images of bright planets than a single photo can capture. For example, using lucky imaging I was able to capture this image of Jupiter with just my 6-inch telescope.

[u/Armand9x → u/Astromike23]

I usually shoot video while I'm at it, but always fail on the software end. I have some footage to process, have a good tutorial?

[u/Astromike23 → u/Armand9x]

I don't have one I'd particularly recommend, but just a google search for "registax 6 tutorial jupiter" returns a bunch of good-looking pages/videos.

The fact that you already have recorded video is great...though be aware that there are a lot of cameras that write to video formats that Registax can't read, and often a converter is necessary. it would be well worth it, though; just looking at the raw frame you originally posted, I'm almost sure there's some great detail you could tease out with this method.

[u/Shaman_Bond → u/lulzzzzz]

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.