Second known interstellar visitor after Oumuamua | Hacker News Reader

Second known interstellar visitor after Oumuamua

science.sciencemag.org

88 pointsQueensGambit26 comments

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

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...

Never tell me the odds.

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

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.

Shields, duh...

Wouldn’t star trek’s polarized hull work better? Just electrostatically repel neutral objects.

I think the "polarized hull" is only in the Star Trek Enterprise prequel which takes place prior to the founding of the federation and takes place where humanity had just achieved Warp 5 and has pathetic weaponry. Every single other Star Trek show (Original Series, The Next Generation, Voyager, Deep Space 9, and the later movies) use shields as in "shields up" or "raise shields". I believe the new Star Trek Discovery should also have shields.

Yeah but shields are sci fi and were used as a storytelling device. Electrostatic repulsion is a real thing.

If these are pretty common and pass by within range, perhaps we can seed them with scanners and transmitters, and start building a weird observation/relay network.

We can, but why would we? If you have a set of scanners/transmitters here on earth and want to attach it to one of these interstellar traveling rocks you need a rocket capable of matching their speed. These rockets are by definition also capable of leaving the solar system, otherwise they couldn’t match speed. So if all you care is a spreading observation/relay network, and not say the objects themselves then you are better off by just sending the scanners/transmitters out without complicated space balett and all the issues associated with it.

Out of ignorance, I was guessing it takes a lot less fuel to put a payload in the path of an incoming interstellar traveling rock and let that get "crashed into" to embed on the surface.

Although that's still complicated space ballet.

We don't really have any "scanning and transmitting" technologies that can survive crashing at, say, 1km/s. You need at least 50 km/s of delta-v to catch the likes of 'Oumuamua, so if you could get within 1 km/s of its orbit you might as well spend the tiny extra bit to land gracefully.

My impression is that a way to look at it is that at 50 km/s, everything is liquid, if not plasma.

Things zip around at 50 km/s all the time and stay solid, that's not a problem.

We can even imagine technologies that survive a 50 km/s impact. Like self-replicating nanobots based on tardigrades, stashed in the interior of an asteroid - plenty of people already think life has been spread in asteroid-planet collisions. But we definitely don't have those now.

I do wonder if, after enough of these are discovered, we can start making estimates of how much interstellar mass they represent compared to what we see in stars and their gravitationally-bound objects.

Alternately I wonder if you could exploit these for propulsion or gravity assist somehow? A lot of the "interstellar travel is almost impossible" calculations rely on interstellar space modeled as an absolute void and thus requiring you to carry all fuel and all propellant.

Of course these calculations also tend not to consider staging, just like the "reaching the moon is impossible" calculations prior to Apollo.

My first though was risk to Earth. Those things move fast and give you much less time to plan/build/launch.

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.

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

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

All hail our new overlords

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?

Nothing to do with intelligence at all. It's a comet, and a pretty ordinary one, not a spacecraft. What makes it alien is that it's not in orbit around the sun, it's just passing through.

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

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

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.

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