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Interstellar Comet 3I/Atlas: What We Know Now
- NitpickLawyer 1y ago> The Rubin team realized that their telescope had — unbeknownst to them — imaged the object starting 10 days before its discovery. This is so cool! Vera Rubin is designed to detect lots and lots of similar things, and having a test case where they can go back and "track" 3I through data is probably a great thing for tuning their models. Can't wait to see what Rubin finds over the years. Also, it's so cool that they found 3I pretty early, we'll now have lots and lots of data from multiple powerful observatories and probably from some remote ones as well. It's nuts that we'll probably get some images/data from probes out in the solar system (mars orbiters, maybe JUICE).
- drewg123 1y ago> 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?
- bee_rider 1y agoI guess at some point we should expect dust to launch toward the Sun as that side gets heated more, right? But I have no idea when that is supposed to happen…
- jandrewrogers 1y agoWhile uncommon, some ordinary comets also have an "anti-tail" that points toward the sun. As a recent famous example, the very bright comet in October 2024 [0] had a prominent anti-tail. The main photo on the wikipedia page shows it clearly. [0] https://en.wikipedia.org/wiki/C/2023_A3_(Tsuchinshan–ATLAS) https://en.wikipedia.org/wiki/C/2023_A3_(Tsuchinshan–ATLAS)
- ge96 1y agoWe might be the blue people
- mkw5053 1y agoGas 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.
- ordu 1y agoPity it travels too fast to decelerate enough to be captured by the Sun.
- supportengineer 1y agoI'm inspired to re-watch Don't Look Up this afternoon.
- pklausler 1y agoAt 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.
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- gnabgib 1y agoRelated: Astronomers discover 3I/ATLAS – Third interstellar object to visit Solar System (308 points, 26 days ago, 171 comments) https://news.ycombinator.com/item?id=44451329 https://news.ycombinator.com/item?id=44451329 Vera C. Rubin Observatory Observations of Interstellar Comet 3I/Atlas (3 points, 7 days ago) https://news.ycombinator.com/item?id=44638392 https://news.ycombinator.com/item?id=44638392 Feasibility of a Spacecraft Flyby with the Third Interstellar Object 3I/Atlas (3 points, 6 days ago) https://news.ycombinator.com/item?id=44649150 https://news.ycombinator.com/item?id=44649150 First Hubble telescope images of interstellar comet 3I/ATLAS (109 points, 6 days ago, 29 comments) https://news.ycombinator.com/item?id=44649653 https://news.ycombinator.com/item?id=44649653
- unsupp0rted 1y agoCould 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"
- dysfunction 1y agoI don't believe so, unless the object had such a powerful telescope it could image Hubble itself in high definition and literally see where it was pointing, which would require an absurdly large lens. A telescope like Hubble absorbing light is purely passive, it doesn't emit anything "back" that would tell the observed object it is being observed.
- Enginerrrd 1y agoObserving passive observation systems over those distances is pretty unlikely even with an optimistic view of future technology. But perhaps not impossible. We have all kinds of space radars though that are active.
- yetihehe 1y agoIf it had several kilometer wide imaging array, then yes. Hubble and other telescopes are totally passive optics. You need to see the distant dot and have enough resolution to identify it as a telescope and see that it is pointing at you. Seeing hubble from more than 1 au would require optics about 8km in size. This doesn't need to be one giant mirror, could be two cameras 8km apart, but synchronized optically (distance known to a small part of wavelength of light). Seeing Hubble as more than 1 pixel to tell that it's a telescope pointing at you needs something much larger.
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- mathgeek 1y agoTheoretically, 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.
- Fripplebubby 1y agoOne 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 have seen_ thousands that are quite small over that time period, because the size of space objects follows a power law since they're always whacking into each other and breaking up. Since we've only seen one small interstellar object during that time rather than thousands, a large comet is so impossibly unlikely that we can conclude that it is 0.5km in size. I'm sure at some point this will be confirmed in a more conventional way, as well.
- TMEHpodcast 1y agoWhat 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
- akk0 1y ago[dead]
- EspadaV9 1y agoWith the number of interstellar objects being detected only going up, it would be amazing if we could get some probes to hitch a ride on them. Imagine something lasting as long as Voyager 1 but travelling 3.5x the speed as it leaves the solar system.
- bmiekre 1y agoI would guess there all kinds of technical logistics reasons as to why this is improbable, but I agree that would be really cool.
- kqgnkqgn 1y agoVisiting 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.
- signa11 1y agomatching velocities till you can hitch the ride. from that point onwards, you can just do…nothing (at least in that department)
- kristianp 1y agoThey'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.
- lazide 1y agoAnd 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.
- mcswell 1y agoQuestion: 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?