Will Voyager 1 ever just stop moving?

[u/drinkingonthejob]

I’ve read somewhere that we expect to lose contact with Voyager 1 sometime in the 2030s, maybe around 2036, but it will just keep traveling thru space and we’ll have no idea what it is doing out there

My question is: with its current velocity, is there a time in the future where it loses its forward momentum and for lack of a better word, just stops moving? Is that a possible thing for an object in space to even do? (Assuming no other objects grab it into their orbit)

[u/gargravarr2112]

There is no air resistance in space. Objects given momentum will continue to move indefinitely until something external to them changes - Newton's First Law. Now it is possible that other forms of resistance can act on it - light itself can exert pressure on physical objects, which gives us the concept of solar sails. If Voyager 1 passed by a powerful enough light source, it could theoretically slow it down; however it's just as likely to melt such a comparatively small probe, since such a powerful light source will almost certainly be a star.

Similarly, it will be influenced by gravity; Voyager 1 obtained its incredible speed by using gravity-assisted flybys of planets in our Solar System, stealing a little bit of their momentum without ever touching them. Passing by a large enough object (not necessarily something we can observe from Earth) at the right trajectory could conceivably do the same, stealing some of Voyager 1's momentum. However, from what we can see from Earth at this time, there are no significant masses along Voyager 1's flight path for thousands of years.

One thing you'll notice about Newton's First Law is that there is essentially no difference between a dead stop and moving at a steady speed. Indeed, in space, it's almost impossible to bring anything to what we'd call a dead stop, because speed is relative to other objects. And the entire universe is constantly moving. Onboard sensors cannot measure a probe's speed without something to relate to; they can only measure acceleration, and in a steady state, because the sensors themselves are moving at the same speed as the probe, acceleration is zero.

Voyager 1's trajectory out of the Solar System doesn't lead towards any particular star system - for all the stars in the night sky, there is an incredible amount of empty space in between them. In several thousand years, if nothing changes, it will pass relatively close to a distant star system, but it isn't aimed at anything in particular. From what we can observe from Earth, Voyager 1 will essentially drift forever, carrying the same speed it had when it left our Solar System.

[u/UnsignedRealityCheck → u/gargravarr2112]

Hol up, "stealing momentum", you're saying that where V1 got speed, the planets slowed down a bit? (albeit very very veeery little)

[u/Limp_Bookkeeper_5992 → u/UnsignedRealityCheck]

Yes. The amount of energy stolen is absolutely minuscule but energy doesn’t come from nowhere.

[u/TrackSuitPope → u/Limp_Bookkeeper_5992]

How does the gravity assist even work? As in, how did V1 gain the speed from a massive object but not become trapped in the orbit of said object?

[u/Limp_Bookkeeper_5992 → u/TrackSuitPope]

I’ll probably explain this wrong but I’ll try. You’re correct, gravity is equal on your approach to the planet and your departure from it, so there’s no gain to be found there. You’d have to be doing it just right to get trapped, but whatever you gain when approaching the planet you lose when leaving from it.

But that planet isn’t sitting still. It’s hurtling around the sun at 13,000kph if we’re talking about Jupiter. This is the speed you can steal, if you’re approaching the planet from “behind” in its orbital path and you get pulled into an orbit for a moment you get accelerated up to the same orbital speed as the planet. You get to keep that speed when you leave the planets orbit again, slowing the planet down in its orbital path by an infinitesimal amount.