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Comment by dostick | Hacker News Reader

> 3I/ATLAS is thought to have been drifting through interstellar space for many billions of years before encountering our solar system.

It is hard to believe, but it means it’s been a fiery comet for billions of years, how is that possible that it havent burned up…

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Well nothing much in hard vacuum is "fiery" - comets in our solar system do get ablated by the solar wind as they orbit the sun more closely; I assume in this case the majority of those billions of years were in deep space where there wasn't much pushing/pulling mass off.

Yeah but then it wouldn’t be drifting would it?

Joke explanation: a drifting vehicle is burning tires and leaving a cloud of smoke behind, like a comet.

Whether it's drifting through space or hammering through at dozens of kilometres a second is rather a matter of perspective. Perhaps as far as it's concerned, its sedate drift has been interrupted by a very ill-mannered solar system making a reckless close pass.

Yes, the solar system is moving (rotating) relative to the galactic core at 230 KM/s, far faster than this object is moving relative to us.

Depending on its origin/history, it’s getting run over by a runaway train, or taking a sedate walk.

Tangentially, I enjoy reminding my kids how long it takes our star to complete a rotation around the Milky Way, and then also point out that we can go to a museum and see fossils of what life looked like one galactic rotation ago. It gives the right amount of backward and forward perspective about the rock we live on that I want them to keep tucked away in the corner of their mind.

This object is "moving" at roughly 58 km/s. It's doing a leisurely Sunday drive and getting overtaken by someone 3x their speed.

Hopefully our solar system isn't making a reckless pass into the path of the fragments from a historic explosion and we're just seeing the first few.

Wind in a vacuum, that's interesting.

Because what makes it glow is actually solar wind from our sun as it passes through the solar system.

For possibly billions of years, it has simply been an inert lump of ice passing through the universe.

It could be extra-galactic. It's going at a fair clip, and (if I haven't dropped a zero or ten) it would only take around 800 million years to get here from one of the Magellanic Clouds.

Just as an indicator of the speed and possible distances.

> “But based on the researchers’ analyses of the interstellar object’s vertical motion in the galaxy (its path is known to weave up and down in the galactic disk), they concluded that it likely originated from the Milky Way’s thin disk, not its thick disk as was mentioned some months ago. The thin disk contains somewhat younger objects than the thick disk.”

If it were traveling through interstellar space, it would have been highly irradiated but it would also have been far from any source of heat. From what we know of it so far, it has some strange chemistry going on, but that’s somewhat expected given its estimated age. We’d also need to assume that a few billion years of interstellar radiation would do strange things we haven’t really seen before hence pointing every instrument possible at it.

Comets don’t do anything much until they get close to a star.

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