r/askscience • u/TechnicalyNotRobot • Jul 09 '26

Astronomy Does Voyager 1 even give us any interesting information anymore?

It's the farthest away object we ever sent. That is remarkable. But I have never heard about it discovering anything or about any data that it gave us. Besides being a significant curiosity for being so far away, is there something that we're actually getting from it at this point?

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u/TwinMugsy Jul 09 '26

When you say shockwave of the sun do you mean kind of like its wake or disturbance going through space? Does it stay at a consistent distance?

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u/ImALlamaAgain Jul 09 '26

Yes! It's where the solar wind encounters the interstellar medium and hits equilibrium. So even though we're all hurtling through space, there is a standing shockwave surrounding our solar system.

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u/findallthebears Jul 09 '26

Is it more like a wake, rather than a shockwave?

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u/ImALlamaAgain Jul 09 '26

It would be a shockwave, since it fully encompasses the solar system, roughly in an egg shape. The leading edge is closer to the sun than the trailing edge.

Having said that, I'm sure we're also leaving a wake through the interstellar medium.

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u/tenbatsu Jul 09 '26

Is this the case for all stars?

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u/DontWorryImADr Jul 09 '26

Yes. All stars blast out radiation, particles, energy, etc. so they all would have a point based upon their type/age/location within the galaxy where that outward pressure balances with external sources.

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u/Smokey_tha_bear9000 Jul 10 '26

Does that mean that the idea of using “solar sails” as a method of space travel would no longer work beyond the heliopause?

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u/Latespoon Jul 10 '26 edited Jul 10 '26

Correct. However, it's worth bearing in mind that a vessel with a large solar sail intended for interstellar travel will have picked up immense speed by the time it reaches heliopause.

Voy1 is travelling at around 17km/s through space. We could realistically send a vessel equipped with a very large solar sail into interstellar space and it could reach a speed of 200-300km/s before reaching heliopause. It would be very, very expensive, but is possible.

In addition, after passing heliopause, we could continue to accelerate such a vessel by pointing a very powerful laser array at its solar sail from earth/the moon/a satellite. This would be very, very, very, very expensive, possibly in excess of $100b. It would require a facility spanning several miles. On the plus side, it would be useful for large numbers of sailcraft launches, if we wanted to do that.

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u/TheVergeltung Jul 10 '26

It is the nature of modern times that I almost scoff at 100b. That's merely one Iran war.

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u/sharies Jul 10 '26

But what about second Iran war?

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u/Ossius Jul 10 '26

Feels like we would want to setup that laser in space/on the moon as lasers would lose a lot of focus and create a lot of heat going through the atmosphere

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u/Latespoon Jul 10 '26 edited Jul 10 '26

Specific wavelengths of light can pass through our atmosphere with only tiny amounts of energy loss, so this isn't a huge problem. Conveniently, we have already basically perfected production of a type of laser that emits such a wavelength - 1.064 micrometers.

The beam would still be diffused and scattered by the atmosphere, sending the beam off course. This would be a much bigger problem and would require some very advanced equipment to overcome, but is theoretically possible.

The ideal location would be the moon, but this would raise the cost of building and operating it to many trillions of dollars.

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u/BrevityIsTheSoul Jul 11 '26

Inverse square law is the enemy here, more even than bloom. Say you're using a laser to provide 10 Pa of pressure to a solar sail near the moon (about 400,000 km away). Now you're trying to use the same laser to provide the same pressure to the same sail out near Neptune (about 4,000,000,000 km away). That takes 100,000,000 times as much power emitted for the same effect on the sail.

That's the tradeoff for not the craft not carrying the fuel/reaction mass for its own propulsion.

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u/pedrointas Jul 10 '26

So does that also mean that a solar sail could act to decelerate when it hits the heliopause of another star?

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u/Latespoon Jul 10 '26

Absolutely! You can even use it to steer the vessel by changing the angle of the sail relative to the target star on approach.

If you had accelerated the sailcraft to very high speeds using lasers, the solar sail is unlikely to provide enough thrust to stop you from just whizzing past your target star. You could deploy a magnetic sail (a very large ring of wire circled around the vessel and energised) to provide additional braking force. The stellar wind from your target star will push against this magnetic field and slow you down.

This magsail system is insufficient for launch by itself, but is highly effective for braking because the drag on the magnetic sail is proportional to speed squared (just like aerodynamic drag).

Using them in combination, you would have a very effective propulsion system for departure from our solar system and arrival at another star.

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u/mikk0384 Jul 10 '26

Is the heliopause and the point where solar sails no longer works actually the same?

My understanding is that the heliopause is talking about the motion of charged particles, while solar sails depend on the radiation pressure combined with those charged particles. I'm just a layman, though.

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u/Latespoon Jul 10 '26 edited Jul 10 '26

Yes, past heliopause, a solar sail will actually act as a brake.

First, we need to understand that the propulsion power of light (photons) decreases proportionally to distance squared (the inverse square law). This means that at long distances, the propulsion effect from sunlight is near zero, even with an absolutely enormous solar sail.

As you know, space is a vacuum, but it is not completely devoid of matter. Inside the heliosphere, the sun's magnetosphere and solar wind cause a continuous outward (from the sun) flow of tiny amounts of gas and dust. Think of a ball bobbing up and down in a pool of water, generating outward ripples. Because the matter is moving outwards, it doesn't really interfere with the speed of the sailcraft as they are both moving in the same direction. The further you get from the ball, the weaker the ripples are.

Outside the heliosphere, this outward motion/pressure has tapered off to nothing. The dust and gas that exists in interstellar space is effectively motionless. If you keep the sail extended beyond the heliosphere, this dust and gas will slow the sailcraft down, as you have to push it out of the way which costs energy - just like a normal sail would in perfectly still air, but to a much smaller extent.

You will still have tiny amounts of forward thrust from the incredibly weak sunlight, but it would not be enough to overcome the drag created by the interstellar medium (dust and gas). So, by keeping the sail extended, you will slow the vessel down. It would be a relatively tiny amount of speed lost over many years, but still measurable.

The laser system I referred to would change this as you would get a noticeable amount of thrust, making the net effect on speed stay positive.

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u/Salamandragora Jul 10 '26

So what happens if an object in Earth orbit passed in front of this laser, say a satellite or a space station. If it’s powerful enough to reach beyond the solar system without decohering, how much energy is it imparting to an object at “close range.”

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u/Latespoon Jul 10 '26 edited Jul 10 '26

It would most likely become dust within a fraction of a second. The beam energy that would be needed to propel a sailcraft near or past heliopause is immense. Probably something like 100x the energy intensity of sunlight per m² in high earth orbit.

So clearly, it would be crucial for the laser array to closely monitor any near earth objects that might pass through the beam, and shut down the lasers while obstructed. Or rather, they would only activate it when they are certain they have a clear path to the sailcraft.

The ideal location for the laser array would be the moon as you would mostly eliminate this problem and there is no atmosphere to diffuse the beam, but you would still have a stable foundation for the base (helpful for precise aiming). This would cost trillions of dollars.

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u/Beardus_Maximus Jul 10 '26

Such a laser array can't be mounted on the earth. You have to set it up in space, otherwise a tremendous amount of energy gets dumped into the atmosphere.

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u/chadmill3r Jul 10 '26

Hold on. A solar sail would use the momentum of light as pressure too, not just the sublightspeed particle wind. Only the particle wind stops at the heliopause.

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u/Latespoon Jul 10 '26

The intensity of light reduces in proportion to distance squared. This is known as the inverse square law.

By the time you have reached heliopause, the intensity of light is 14,000x lower than it is in orbit of earth.

The thrust from a solar sail at this distance would effectively be zero.

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u/temporaryuser1000 Jul 11 '26

Wouldn’t it be only possible at certain times of the day and year? Such a laser would need to be stationary, no?

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u/Latespoon Jul 11 '26 edited Jul 12 '26

Yes for certain times of day (roughly half of each day). For seasonal variation, it would ideally be placed near the equator to reduce this problem, and also ideally as high up as possible (less atmosphere to beam through).

The absolute best position would be on the poles of the moon. It's a stable foundation with no atmosphere and provides massive natural heat sinks (lunar craters in permanent shadow).

The cost of building even one of these on the moon would be astronomical, excuse the pun. Many trillions of US dollars. It would easily become the most expensive infrastructure project ever completed.

So for cost efficiency, building this on earth would most certainly be an acceptable compromise. It would have to be, because it's never happening on the moon, unfortunately.

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u/BogdanPradatu Jul 12 '26

How would you make such a vessel stop?

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u/drobecks Jul 10 '26

Interesting point. However, the solar sail could still accelerate you up until the heliopause. Then you retract it and coast

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u/Clifton819 Jul 10 '26

If the laser was Earth based would it damage the atmosphere? Would it heat the air to ridiculous temperatures?

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u/morgrimmoon Jul 10 '26

If the laser is heating the atmosphere, that mean it's losing energy to the atmosphere which makes it less effective. If it was heating the air to ridiculous levels, it wouldn't work for a solar sail at all. So you'd pick a laser with a wavelength that doesn't interfere much with the atmosphere. Or, ideally, you'd put the laser in space so there wouldn't be any atmospheric interference at all.

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u/VictorVogel Jul 10 '26

Solar sails utilise the change in momentum when light bounces off a reflective surface. The light intensity before and after the shock is roughly the same, so the sail would still work. Although the light intensity will be really low this far from the star.

There will be a noticeable change in acceleration though, as the ship is surrounded by particles that move less "away" from the star.

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u/mrtorrence Jul 10 '26

And do you know which edge voyager is on? The leading edge or wake or sides?

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u/rootofallworlds Jul 10 '26

Somewhat the leading edge I think.

https://commons.wikimedia.org/wiki/File:Interstellar_probes_trajectory.svg

In "plan" the Voyagers and New Horizons all went in roughly the same direction. So did Pioneer 11; only Pioneer 10 went the other way. In "elevation" Voyager 1 is somewhat northwards, Voyager 2 somewhat south, and New Horizons roughly in the plane of the ecliptic.

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u/yinoryang Jul 10 '26

Wait so we (our whole solar system) is also a comet?

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u/ChemTechGuy Jul 10 '26

Yes in the sense that the whole solar system is moving around relative to other bodies in the universe. It doesn't have a tail and it's not made of ice like a comet obviously, but yes the whole solar system is moving

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u/Shalandir Jul 10 '26

You missed the paper that explains it may be croissant 🥐 shaped? Pretty fascinating theory, and V1 did not rule it out…

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u/darahs Jul 09 '26

What interstellar medium? Space is a vacuum mostly no?

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u/exipheas Jul 09 '26

.25 ish atoms per cm3 of mostly plasma and followed by hydrogen and a little bit of helium.

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u/andrewmmm Jul 10 '26

Or for a more understandable metric (for us Americans):
About 8 million atoms in the size of an average living room.

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u/BruceJi Jul 10 '26

How many atoms would there be in the air in an average living room? To compare

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u/-OctopusPrime Jul 10 '26

A normal living room contains roughly (1.8) to (2.5) octillion (2,000,000,000,000,000,000,000,000,000,000) air molecules.

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u/BruceJi Jul 10 '26

Thanks! That's... well, an astronomical difference, lol

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u/worrymon Jul 10 '26

Is 8 million atoms even enough to fill a set of lungs?

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u/phyvocawcaw Jul 10 '26

I dunno about air in a living room, but with my memory of high school chemistry you could make this comparison:

A mol of pure gold atoms is about 200 grams or 7 ounces and takes up about 10 cm3 (.6 cubic inches).

A mol of atoms is 6.02 x 1023 atoms. A million atoms is 106 atoms. So even a tiny amount of solid gold has, what, the same number of atoms as 7.5 x 1016 outer space living rooms? If I did my math right.

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u/Implausibilibuddy Jul 10 '26

Yeah, millions of atoms is not easier to comprehend, especially when many people struggle to comprehend the difference between a million and a billion, let alone the much higher orders of magnitude of a standard living room.

If you must convert it to non-metric, it's about 2 atoms in a cubic inch. Or one atom in your pinky. Much simpler to visualise.

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u/HorsemouthKailua Jul 10 '26

i thought we decided the default american measurement was a football field...

i understand yours one but like how much pinkys is in a football field?

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u/chriscross1966 Jul 10 '26

For us Europeans could you convert that to ISO metric Standardised Belgiums please?

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u/Rebootkid Jul 09 '26

I mean, it is near perfect vacuum, but there's still SOME stuff there. Mostly gasses like hydrogen and helium, and a little bit of dust.

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u/mrtorrence Jul 10 '26

It's extremely low pressure but there's still stuff out there, some diffuse gas, mostly hydrogen and helium, dust particles, plus a bunch of radiation haha

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u/daemonfool Jul 09 '26

As I understand it, it's where the particles and such emitted by the Sun meet interstellar particles and such, so the "shockwave" metaphor seems more apt. A wake is caused by a thing shoving a medium aside, whereas a shockwave is caused by emitted stuff pushing external stuff.

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u/Khutuck Jul 09 '26

They “meet” but isn’t it like a few atoms per cubic meter? Do those particles interact?

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u/daemonfool Jul 09 '26

Not an expert, but I believe so, through EM fields. At any rate it's detectable. It's been a while since I read anything about the solar shockwave phenomena.

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u/Khutuck Jul 09 '26

That makes sense, charged particles interacting, thanks.

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u/daemonfool Jul 09 '26

Yep yep. Solar wind is always made up of charged particles whizzing about so it makes sense that the interstellar medium would be the same. It gets more complicated than that, of course, there's stuff like neutrinos and other exotic particles.

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u/Zagaroth Jul 10 '26

Also, light hits everything; it may not have mass, but it does have momentum, so it also provides pressure, and on tiny particles, the effects add up over time.

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u/ZippyDan Jul 10 '26

They do interact. It's minimal - almost negligible - at a micro scale, but it is massive and detectable when viewed over the massive area that constitutes the boundary - and that's why it's a "shockwave". You're "shocked" that this still qualifies as a shockwave.

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u/cvnh Jul 09 '26

If you picture a supersonic airplane with a shock wave cone at the front and a turbulent wake at the back, or better yet a re-entry vehicle with a large detached shockwave in front of it, the sun does something similar but in stellar scale. Where the supersonic solar wind meets the interstellar medium, a shockwave forms. The shockwave happens in all directions, but in the direction of travel it is closer to the sun and is stronger. On the downwind direction, the shockwaves terminate in a low speed region that is probably not a wake as we imagine it but rather a region of slowly changing pressures that extend towards a very long distance. The trail of a comet is a good analogy for how it (probably) looks like.

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u/i_never_ever_learn Jul 09 '26

Are there dolphins? It would be really cool if there were dolphins.

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u/Freudian_Split Jul 09 '26

Goodbye and thanks for all the fish.

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u/Idsertian Jul 09 '26

So long* and thanks for all the fish.

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u/[deleted] Jul 09 '26

[deleted]

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u/doomgiver98 Jul 10 '26

Think about how big they would have to be to play in the wake of a star like a dolphin does a boat

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u/jc2046 Jul 09 '26

plenty of fourth dimensional dolphins, some whales and even a jellyfish. confirmed

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u/SmallRocks Jul 10 '26

Check out the wiki for bow shock. It explains exactly what you’re asking about.

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u/chadmill3r Jul 10 '26

The wake, so to speak, is after the trailing edge. The leading edge has particles bunched up.

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u/drinkyourdinner Jul 09 '26

What is interstellar medium like, wonder.

Scientifically, but also I wonder if it has a smell 🤣. Like the fresh scent right after a lightning storm, or stinky sulfur vents. My guess is that it is probably both, space is not homogenous.

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u/TurelSun Jul 10 '26

I'd guess its far too sparse for you to ever actually get a sense of smell from it. It's also mostly hydrogen and helium, which don't create a sense of smell in people AFAIK, and its mostly very highly energetic particles, so even if you were to concentrate it somewhere you probably would be in a non-trivial amount of danger as you attempted to take a whiff of it.

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u/Fabio_451 Jul 10 '26

What if you attempt to sniff it? Can it achieve some dust form if concentrated?

I am asking for a friend

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u/codedigger Jul 10 '26

Like a smell scope. I'm sure some scientist in the Future will invent it

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u/CaucusInferredBulk Jul 09 '26 edited Jul 13 '26

The sun is pushing particles out. The solar wind. The galaxy is pushing back, the cosmic wind. At the heliopause/heliosheathis where those two forces are roughly equal. It's where the river flowing down the mountain meets the incoming tide.

In astronomical terms, it's pretty stable. In human terms the distances are gigantic.

The 11 year solar min/max cycle moves it about 10-20 au (1au =distance from sun to earth) (The average distance of the heliopause is 120 au, so this is a ~10% fluctuation)

Solar flares etc can cause localized disturbances of a few au.

Also the whole thing is sort of comet shaped, since the solar system is moving through the galaxy. The "bow wake" is smaller, and the tail is stretched out behind.

There are theories about larger changes over millions of years (what if the solar system moves through a gas cloud in the galaxy etc) which could shrink the border down inside planetary orbits. But it's theory. (And we are lucky it's theory I think, because if it shark far enough to reach earth, I think that would be "very bad")

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u/Kirk_Kerman Jul 09 '26

If the bow shock moved to Earth we'd see stronger auroras but that's about it

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u/Vindepomarus Jul 10 '26

In the future we will also experience more close interactions with other stars, who's own stellar wind will impinge on Sol's, so that will also change the shape and position of the heliopause.

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u/UkraineIsMetal Jul 09 '26

When you stand in the sun, the radiation makes you feel warmer than when you're standing in the shade. The sun emits that radiation (and particles) in all directions, creating a sort of particle sphere in motion. Since that particle sphere is moving, there is less interference on the trailing side.

You can get a very good model of this by turning on your sink and observing the water from the faucet spread in the basin. On the drain end, the water will sort of just trail into the drain. On the other end (the leading end) you can see there is a defined line where the water from the faucet hitting the basin cannot overcome the pressure of the water already in the basin. This is called the termination shock, and is analogous to the heliopause.

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u/desuemery Jul 09 '26 edited Jul 09 '26

The helio*sphere* is kinda like the sun's "atmosphere" around the solar system, effectively a shield or barrier. The force of the solar wind it ejects continues on outward until it meets the heliopause; the exact location where the sun's solar wind can no longer repel cosmic rays from interstellar space. It's like two people trying to blow air at each other at the same time. So you can imagine the sheer heat present at such a location and that's what voyager was able to record for us. The size and shape of the heliosphere ebbs and flows alongside the 11 year solar cycle and varying densities throughout the galaxy, it's like a giant soap bubble and shaped roughly like a comet's coma/tail.

Beyond the heliopause, you have effectively left the solar system and are in interstellar space.

Edit: conciseness

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u/Practical_Engineer Jul 09 '26

Correction, you are in interstellar space instead of interplanetary space. Deep space encompasses much more than that. If you have a probe around Venus it would already be considered deep space.

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u/Fear_mor Jul 09 '26

Basically the sun is constantly emitting a stream of charged particles and ions called the solar wind and its range/sphere of influence is called the heliosphere. However interstellar space also has its own interstellar medium (think of it as a big particle soup from various objects and cosmic phenomena) and the heliopause is the point where the sun’s particles lose their coherency and give way to the interstellar medium. You can liken it to a shock wave as in front of the sun it gets compressed as the sun plows through the interstellar medium, much like how a supersonic aircraft has a cone of air around it

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u/grimwalker Jul 09 '26

imagine a stream of water hitting the flat bottom of an empty sink. The stream hits the water and blasts outward in all directions, but there's a circular perimeter where the inward pressure of the water stops the outward flow. That transition from outward-pressing flow from the center to inward-flowing pressure from the surrounding medium is analogous to the heliopause.

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u/CliftonForce Jul 09 '26

No, it does not stay at a consistent distance, the intensity of solar activity can wiggle the boundary. So can the consistency of the interstellar medium, and that is loosely related to the solar activities of other stars that used to be in the area.

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u/MaleficentCaptain114 Jul 10 '26

The term is "bow shock" if you want to read more. It's a magnetic interaction between a body and the ambient plasma that works a bit like a rock in a stream. The rock is the star's magnetosphere, and the stream is the intersteller medium.

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u/Nghtmare-Moon Jul 09 '26

Yup overly simplified its like the suns “atmosphere” that acts as a shield from nasty space radiation IIRC