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Interstellar Comet 3I/Atlas: What We Know Now

skyandtelescope.org

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Re: Interstellar Comet 3I/Atlas: What We Know Now

#31

Post by kristianp »

signa11 wrote: post #29
kqgnkqgn wrote: post #20

Earlier quoted context omitted.

Visiting one with a probe would surely be amazing in it's own right...but hitching a ride would mean matching velocities with them. And if you can do that...you're already in the same orbit, so the comet doesn't really help.

matching velocities till you can hitch the ride. from that point onwards, you can just do…nothing (at least in that department)

They're saying if you can match velocities in the first place, you don't need to hitch a ride, because you're already travelling fast enough.

Re: Interstellar Comet 3I/Atlas: What We Know Now

#32

Post by andrekandre »

themgt wrote: post #23
kqgnkqgn wrote: post #20

Earlier quoted context omitted.

Visiting one with a probe would surely be amazing in it's own right...but hitching a ride would mean matching velocities with them. And if you can do that...you're already in the same orbit, so the comet doesn't really help.

There's disposable FPV drones that launch with 50km spools of kevlar cable. Seems like smart people could work out a way to "hitch" a probe on a comet without fully matching velocities first.

that would probably be... extremely hard?

i mean aren't we talking like km/s of speed difference? idk of any kind of material even 50km long that could absorb that kind of stretch/sheering like that...

Re: Interstellar Comet 3I/Atlas: What We Know Now

#33

Post by motoboi »

signa11 wrote: post #29
kqgnkqgn wrote: post #20

Earlier quoted context omitted.

Visiting one with a probe would surely be amazing in it's own right...but hitching a ride would mean matching velocities with them. And if you can do that...you're already in the same orbit, so the comet doesn't really help.

matching velocities till you can hitch the ride. from that point onwards, you can just do…nothing (at least in that department)

When you achieve speed in space, after acceleration, the speed won’t change forever unless you encounter some other force, like a celestial body gravity to change it. So if you achieve interestelar comet’s speed, you can shutdown the rocket and just travel at that speed for eternity like the comet does.

Even better: you can forget the comet, accelerate, keep accelerating until there is no more power or even a working motor while also extending a big sail to let solar wind accelerate you a little more.

Re: Interstellar Comet 3I/Atlas: What We Know Now

#34

Post by mkw5053 »

drewg123 wrote: post #3

> The Rubin observations also show hints of a dusty tail, but oddly this elongation points directly toward the Sun. Typically, the push of the Sun’s radiation moves dust in comet’s tails so that it points away from the Sun. Deceleration burn?

Gas released from fresh ice on the illuminated hemisphere can push millimeter-scale grains out at a few m/s, and since these particles weigh thousands of times more than typical cometary dust, solar radiation pressure at 3 au is too weak to bend their trajectories, letting them overtake the nucleus and form a sunward anti-tail. Finson–Probstein dust dynamics predicts this plume should flip to the normal anti-solar direction or fade once 3I/ATLAS moves inside 1 au later this year. Watch the position angle around September to see the theory tested.

Re: Interstellar Comet 3I/Atlas: What We Know Now

#35

Post by TMEHpodcast »

Fripplebubby wrote: post #14

One interesting thing I learned from this was how they determined the probable size of this comet probabilistically, rather than using direct observation - basically, based on the observations, it could either be really big (10km) or really small (0.5km), and we can basically rule out really big because we've been looking for comets for years, and during that time, to see one that is that big implies that we _should…

What you’re describing is Bayesian inference in action. Given how rare big interstellar comets should be, and how common small ones should be, the lack of detections makes the big-comet hypothesis incredibly unlikely. So we update our beliefs: it’s probably small. Space statistics at work

Re: Interstellar Comet 3I/Atlas: What We Know Now

#36

Post by lazide »

kristianp wrote: post #31
signa11 wrote: post #29

Earlier quoted context omitted.

matching velocities till you can hitch the ride. from that point onwards, you can just do…nothing (at least in that department)

They're saying if you can match velocities in the first place, you don't need to hitch a ride, because you're already travelling fast enough.

And also, good luck hitting 70+km/s with chemical rockets, even without it going in the wrong direction relative to us for that to go well.

Re: Interstellar Comet 3I/Atlas: What We Know Now

#37

Post by lmm »

unsupp0rted wrote: post #6

Could an object like 3I theoretically tell when eyes are being pointed at it? Probably not ground-based eyes, but possibly Hubble. i.e. "the inhabitants are scanning us"

Extremely unlikely, given that there is no "active" scanning happening (no "give me a ping, Vasily"), we're just passively looking. I'd think the most likely way to find out would be listening in on our radio broadcasts (I assume someone's been talking about this object on the radio) rather than being able to directly detect the Hubble being pointed at it.

Re: Interstellar Comet 3I/Atlas: What We Know Now

#38

Post by ordu »

drewg123 wrote: post #3

> The Rubin observations also show hints of a dusty tail, but oddly this elongation points directly toward the Sun. Typically, the push of the Sun’s radiation moves dust in comet’s tails so that it points away from the Sun. Deceleration burn?

Pity it travels too fast to decelerate enough to be captured by the Sun.

Re: Interstellar Comet 3I/Atlas: What We Know Now

#39

Post by grues-dinner »

pandemic_region wrote: post #21
kqgnkqgn wrote: post #20

Earlier quoted context omitted.

Visiting one with a probe would surely be amazing in it's own right...but hitching a ride would mean matching velocities with them. And if you can do that...you're already in the same orbit, so the comet doesn't really help.

The comet having virtually unlimited fuel would be of great help.

The comet probably doesn't have a great amount of fuel. Even if it's all ice, how are you going to split the water? Only if you have a fusion reactor that can do H-H fusion, or you can scrape enough dueterium out of it, can you use that. You will find no tritium as it has a short half life, and He-3 (probably) won't have been implanted by solar wind in interstellar space, so if you need that, you have to bring it or breed it somehow.

It does have a great amount of mass, so you could rendezvous, construct a mass driver or ion drive and start taking it apart and using chunks of it as extra reaction mass. That would allow you to essentially get a free reaction mass "refill". You will still need a lot (a lot) of power, and solar will be near zero.

Re: Interstellar Comet 3I/Atlas: What We Know Now

#40

Post by TheOtherHobbes »

actionfromafar wrote: post #30
thegrim33 wrote: post #24

Earlier quoted context omitted.

Some quick prompting seems to say a G force of somewhere between 16-160 billion Gs, for a CPU-equivalent object getting hit by a solid object moving at 3I's escape velocity. Compared to a "typical" artillery shell of 10-15 thousand Gs. Not sure you're manufacturing anything that could survive 6-7 orders of magnitude more Gs than an artillery shell. Of course the G-load would lessen based on how much you sped up to ma…

Wow, I clearly didn't think this through. That's brutal. That leads to another idea - if something more substantial was placed in its path - the resulting debris and gas cloud from the impact could reveal something about the contents of the object. Or, if it's an alien probe, it would force their hand. :-D We could see some exotic manuevering.

Or an interstellar war.

But they're probably used to it. At 61,000 m/s, 0.5mv^2 must turn every collision with a small rock into quite a big bang.

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