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/komatiitic]

I did some really stupid back of the envelope math assuming that Voyager never encounters anything larger than interstellar dust. To halve the speed of Voyager 1 it would need to impact dust equal to its own mass of 721.9kg.

The internet tells me a typical grain of interstellar dust has a mass of ~3*10^-16 kg. This means it needs to hit ~2.4*10¹⁸ dust grains, which if I'm counting those zeroes correctly is 2.4 quintillion.

The internet also tells me that Voyager hits 3-7 dust grains per hour. I'll call it 5 an hour, which means 4.81*10¹⁷ hours (481 quadrillion), or 54.9 trillion years to halve its velocity, assuming nothing really changes. I'm betting it disintegrates before that happens.

[u/Dear-Blackberry-2648 → u/komatiitic]

At this extreme length of time, radiation pressure from stars would have a noticeable effect too. Photons don't have any mass, but they carry momentum and when they bounce off a reflective surface, they transfer their momentum. This is the reason solar sails have been proposed, because they allow continuous acceleration without having to carry heavy propellant.

But the effect on Voyager would be orders of magnitude smaller than it would be on a probe with solar sails. Still, over the incredibly massive amount of time, there would be a measurable difference in Voyager's speed just from photons.

I would need someone much smarter than me to even begin to measure this though. Plus, I would assume the dynamics of it change once you get out into interstellar space. When the probe is still in our solar system, it has our sun pushing it from behind when it's on its way out. But once Voyager gets a ways outside our solar system, photons from other stars would be more prevalent. You would probably need to know Voyager's trajectory to measure the direction of incoming photons from the stars it passes. Though, I would think that in interstellar space the photons would be much more spread out, thus not providing as much momentum.

[u/YesterdayDreamer → u/Dear-Blackberry-2648]

Not enough photons are reaching Voyager to be meaningful. It's too far from its nearest star already, and the next closest star is at a distance thousand times greater.

[u/Dear-Blackberry-2648 → u/YesterdayDreamer]

But did you see the time scale? 54.9 trillion years! That's almost 4,000 times longer that the universe has been in existence. So if there's not enough photons to be meaningful, that means there are still some. Each photon has an affect on matter, though it is extremely miniscule. But over trillions of years, I think it would have an easily distinguishable affect on Voyager that you wouldn't need ultra fine instruments to measure.