
Second known interstellar visitor after Oumuamua - QueensGambit
https://science.sciencemag.org/content/366/6465/558.1
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fernly
Does this suggest a serious danger to any hypothetical interstellar ship? If
the density of such kilometer-scale objects is such that disk of our solar
system intercepts them by the dozen, there is one fuck of a lot more solid
matter drifting through interstellar space than I have ever seen suggested.
Sure, as Douglas Adams said, "Space is big. Really big," but still: if you
imagine traveling even a very modest fraction of C, this begins to make the
Millenium Falcon in the asteroid field[1] look like real science.

[1] [https://youtu.be/c8deRYotdng?t=133](https://youtu.be/c8deRYotdng?t=133)

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dandelany
Let's back-of-the-envelope this a bit... Let's say that there are 10 big
interstellar rocks with a volume of 1 km^3 each that are currently within 30
au of the sun (roughly Neptune's orbit). If we assume this is a good estimate
of nearby galactic space, then if you chose a random 1km^3 "voxel" in our
neighborhood of the galaxy, the odds that it would contain a 1km interstellar
asteroid would be roughly (10 * 1km^3) / ((4/3) * pi * 30^3 au^3) ~= 3 in
10^29.

Now imagine a spaceship that travels 100 light years. It's going to pass
through roughly 10^15 1km "voxels" on its journey, which means the chances of
it hitting one of those 1km rocks is ~(10^15/10^29) or 1 in 100 trillion.
Space is biiiig.

The real danger, though, is the smaller stuff. It's hard to know the
distribution of interstellar dust size, but there are a LOT more small things
than big things, and it only takes a grain of sand at relativistic speeds to
cause a really bad day. If sand-sized rocks turn out to be 100 trillion times
more common than these big ones, well, that's going to be a problem...

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Angostura
Wouldn’t a grain of sand, even at relativistic speeds, Bournemouth up
instantaneously with a small >tffffop<!

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simonh
It’s impact energy would be similar to that of a bullet. The penetration power
would be relatively high though due to its small size and extremely high
velocity. Of course as the size of the particle goes up the impact energy goes
up too. A pebble the size of a fingernail would be pretty bad news at about a
million times the energy and many of them will be mostly iron.

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QueensGambit
2I/Borisov, the second known interstellar visitor after Oumuamua, looks like a
normal comet from our own Solar System. The size of the two objects, along
with the rate of their discovery suggests this could be common occurrence - at
any given moment about a dozen interstellar visitors are passing through the
Solar System.

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anjel
They will be finding more of these, in large part because Oumuamua, "the news
story" got huge ratings.

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zaphirplane
Or oumuamua is the long range scout and now the aliens are setting up their
forward base ;)

All hail our new overlords

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vages
By alien (as in the article’s headline, do the authors limit their claim to
“from another star”, or do they actually mean that some other intelligence
constructed it?

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namarie
It'd be much bigger news if it was constructed, I'd think.

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aetherspawn
Hey if I were observing humans, all my ships would look and scan like comets.

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perl4ever
As we see from New Horizons, a flyby gives you very limited options for
scanning. But hanging around requires eliminating nearly all the velocity you
had to get there, which is infeasible.

