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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

#41

Post by lazide »

lmm wrote: post #37
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.

We have a LOT of energy outbound in the form of space radars and interplanetary comms. We’re lit up like a christmas tree.

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

#42

Post by lmm »

lazide wrote: post #41
lmm wrote: post #37

Earlier quoted context omitted.

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.

We have a LOT of energy outbound in the form of space radars and interplanetary comms. We’re lit up like a christmas tree.

Sure, but none of that was pointed at this comet specifically.

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

#43

Post by pklausler »

bdamm wrote: post #26
pklausler wrote: post #7

Earlier quoted context omitted.

At a closest approach of 1.8AU, you really don't have to worry about a collision with Earth. But that film is relevant to this comet in another way -- several missions that made it into space before the administration's war on the scientific enlightenment may be able to image the comet when we can't see it (perihelion) or when they're much closer to it than we'll ever be.

Do you happen to know which missions those might be?

The linked article has a good summary.

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

#44

Post by lazide »

lmm wrote: post #42
lazide wrote: post #41

Earlier quoted context omitted.

We have a LOT of energy outbound in the form of space radars and interplanetary comms. We’re lit up like a christmas tree.

Sure, but none of that was pointed at this comet specifically.

Ah, fair point - I see what you mean.

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

#45

Post by nocoiner »

XorNot wrote: post #27
mathgeek wrote: post #15

Earlier quoted context omitted.

Theoretically, any sentient being with the necessary technology to get a craft to our solar system and spot the aiming of a telescope at that distance would have even better technologies for detecting what we are doing.

It's a logistics problem: if you can build one of something, you can definitely build two.

Why build one, when you can build two at twice the price?

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

#46

Post by mcswell »

XorNot wrote: post #27
mathgeek wrote: post #15

Earlier quoted context omitted.

Theoretically, any sentient being with the necessary technology to get a craft to our solar system and spot the aiming of a telescope at that distance would have even better technologies for detecting what we are doing.

It's a logistics problem: if you can build one of something, you can definitely build two.

If you can build two, then build three. In fact, always do things in threes.

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

#47

Post by mcswell »

lazide wrote: post #36
kristianp wrote: post #31

Earlier quoted context omitted.

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.

Question: I know that our planetary probes often use planetary gravity to boost their speeds. That only works for prograde speeds, right? Because you're subtracting a miniscule amount of orbital speed from the planet and adding it to your spacecraft's speed. You couldn't whip around a planet and somehow use that to give you retrograde speeds, could you? (Presumably an airless planet, like Mercury.) Or what about using a large moon during the retrograde (relative to the planet's motion around the sun) part of its orbit?

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

#48

Post by mcswell »

thegrim33 wrote: post #24
actionfromafar wrote: post #22

Earlier quoted context omitted.

At first I thought, "no silly, it has to gain matching speed first, what's the point". Then it occurred to me - if we can make something which can survive the impact, we "just" have to place it in the path of the comet and it will be swept with it. The whole thing would be like something like shooting a bullet at a moving target, but it's an idea. That hypothetical probe will not look anything like any other space pr…

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…

A "solid object". But it's not clear how solid a comet is (or more to the point, this or any interstellar comet). If it were a fuzzball of snow, maybe 20 km across, you could in theory decelerate through it more slowly, maybe using a very large parachute initially, then discarding that for successively smaller parachutes as you approach denser and denser parts of the comet. The EPOXI mission to the Hartley 2 comet was reportedly hit nine times by "snowflakes" coming off the comet, but not damaged (https://www.astronomy.com/space-exploration/spacecraft-sees-...).

Of course your point is probably still valid.

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

#49

Post by lazide »

mcswell wrote: post #47
lazide wrote: post #36

Earlier quoted context omitted.

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.

Question: I know that our planetary probes often use planetary gravity to boost their speeds. That only works for prograde speeds, right? Because you're subtracting a miniscule amount of orbital speed from the planet and adding it to your spacecraft's speed. You couldn't whip around a planet and somehow use that to give you retrograde speeds, could you? (Presumably an airless planet, like Mercury.) Or what about usin…

I’m not an expert on orbital mechanics, I just want to provide some data points.

The voyager craft, which not only had very good acceleration early on (the best we could do, really), combined with exceptional gravity slingshots and a lot of time - and are by all accounts some of the fastest man made objects ever - are going 15.4 km/s and 17 km/s relative to the sun.

3I/ATLAS is going so much faster than these objects they might as well be stationary.

Even ignoring the limited amount of time we have to intercept, catching up to 3I/ATLAS would be incredibly difficult to do. Perhaps impossible with our current technology*. Like catching up to a semi-truck going full speed on a highway with a bicycle. After it’s already passed us and is a couple miles down the road.

*barring theoretical (and kind of insane and dangerous) tech like Orion drives.

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

#50

Post by simne »

mcswell wrote: post #47
lazide wrote: post #36

Earlier quoted context omitted.

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.

Question: I know that our planetary probes often use planetary gravity to boost their speeds. That only works for prograde speeds, right? Because you're subtracting a miniscule amount of orbital speed from the planet and adding it to your spacecraft's speed. You couldn't whip around a planet and somehow use that to give you retrograde speeds, could you? (Presumably an airless planet, like Mercury.) Or what about usin…

Problem is another. To got additional speed from other body, you need to move very close to it and in perigee use some powerful acceleration to increase rotation speed fast, so could not use slow acceleration engines, like ion engines.

Idea of gravity-assist acceleration, mechanically is just rotation of pair tightly tied bodies (and cut tie in right moment, so one body got acceleration and other got deceleration), but as it is impractical to tie for example to Moon with rope, used gravity force.

What also interesting, gravity-assist could use not only orbital speed of large body, but also got some acceleration from rotation of large body, as for gravitation, large planet is not just one material point, but system of few smaller (sub)bodies, and closer (sub)bodies give more acceleration than others.

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