6 ms·
On the topic: What the heck was Oumuamua anyway? Do we have a good hypothesis for the (apparent) low density / high velocity by now?
by hcarvalhoalves 7y ago
On the topic:
What the heck was Oumuamua anyway? Do we have a good hypothesis for the (apparent) low density / high velocity by now?
- bmurphy1976 7y agoIt's a rock. It's a kind of rock we've never seen before, so it's got some properties that... we've never seen before. But it's still just a rock. :)
- aaronharnly 7y agoMy utterly layperson understanding was that interstellar comet is the most likely case. https://www.space.com/42437-oumuamua-interstellar-object-small-shiny-comet.html https://www.space.com/42437-oumuamua-interstellar-object-sma...
- soulofmischief 7y agoWe have no reason to believe that is the most likely case. It's simply the least surprising hypothesis. This is an important distinction to make. Unfortunately we'll never really know until we have studied more extra-solar visitors, which may not happen in our lifetime.
- YayamiOmate 7y agoIsn't "the least surprising hypothesis" "the most likely case" by definition?
- deleted 7y ago[deleted]
- slg 7y agoThe former deals with our expectations and the latter deals with probability. They are similar, but when we don't have a good grasp of the probability it might be better to phrase it in terms of our expectations.
- nl 7y agoNo. See, for example the Birthday Paradox: https://www.scientificamerican.com/article/bring-science-home-probability-birthday-paradox/ https://www.scientificamerican.com/article/bring-science-hom...
- deleted 7y ago[deleted]
- carlosdp 7y agoI don't think so, I think it more means it would fall more in line with other observations, whereas other (currently just as plausible) theories would mean we saw something very new. The "comet" theory, for example, suffers from the fact that while we observed acceleration from the object, we haven't yet found evidence that there was any gas or matter being expelled from it that would cause the acceleration, which you'd usually see with a comet. It would be less surprising for someone to come out tomorrow and say they found evidence of matter being expelled from the object, suggesting it's a comet, than someone proving it was a solar sail, but that doesn't make it more likely based on the evidence itself (and not our preconceived notions of how common certain stellar objects are based on our very tiny observational window).
- salty_biscuits 7y agoI think of surprise as the effect of data on the update of your prior probabilities. If you previously considered an hypothesis unlikely, but the data changes that probability to be much higher it is a surprise (same with voting a prior high probability down).
- inflatableDodo 7y ago>What the heck was Oumuamua anyway? A lenticular cloud consisting of around 300 billion fine china teapots. edit, It is a lot less than I thought. Only 10204.08, apparently. Oumuamua, 1*(10^7)g - https://arxiv.org/abs/1903.06300 https://arxiv.org/abs/1903.06300 Selfridges Royal Albert Old Country Roses Teapot, 980g - https://www.selfridges.com/GB/en/cat/royal-albert-old-country-roses-large-teapot_5096-10010-IOLCOR00145/ https://www.selfridges.com/GB/en/cat/royal-albert-old-countr...
- Gibbon1 7y agoIt's a Cosmic Dust Bunny.
- taylorfinley 7y agoThat seemed to be the general consensus a few months ago at an informal event I attended with a bunch of astronomers from Mauna Kea. Edit: as discussed here https://news.ycombinator.com/item?id=19201582 https://news.ycombinator.com/item?id=19201582
- keyle 7y agoI think there is noone agreeing 100% on this. Theories range from solar sail of some kind of ship, to alien ship, to comet, to debris... I read so many theories on it, it's quite fascinating. Just search HN for Oumuamua.
- wallace_f 7y agoInteresting: to explain its acceleration, it needs to be a fraction of a millimeter thick: https://m.phys.org/news/2018-11-oumuamua-extraterrestrial-solar.html https://m.phys.org/news/2018-11-oumuamua-extraterrestrial-so...
- czbond 7y agoPBS Space time had a good series on it: "To repeat the space time maxim: it’s never aliens … until it is. So let’s talk about ‘oumuamua." https://www.pbs.org/video/oumuamua-is-not-aliens-zjpppc/ https://www.pbs.org/video/oumuamua-is-not-aliens-zjpppc/
- ajross 7y agoOr they just messed up a routine measurement in a routine way. This is not a "There Can Be No Other Explanation" kind of situation. But the numbers are anomalous enough to be notable, and the speculation is for sure a lot of fun to read.
- dandelany 7y agoNot quite - this is only true if you discount the outgassing hypothesis entirely & assume that all of the acceleration is from solar radiation pressure. There is at least one good recent paper strongly advocating for outgassing as a more realistic (if less exciting) explanation: https://www.darrylseligman.com/oumuamua https://www.darrylseligman.com/oumuamua https://arxiv.org/abs/1903.04723 https://arxiv.org/abs/1903.04723
- wallace_f 7y agoThanks for the link. The difference between the paper from the two physicists I linked to, and yours, is the assumption of outgassing vs an assumption of solar radiation pressure, as explanations for acceleration. I have no idea how plausible the assumption of outgassing is in which you linked, as it is qualified by additional necessary assumptions to explain why no outgassing was observed (from the paper: venting which migrated to a non-visible path). Is that assumption more likely than this object just being a thin slate of rock? I guess, anything is going to be more plausible "than aliens, until its aliens."
- russdill 7y agoNext? It's still well within the orbit of Neptune and traveling about 30km/s. We can still perform a flyby with existing technologies.
- walrus01 7y agowith a NERVA powered craft launched on top of something the size of a fully expendable Falcon heavy, maybe...
- mdorazio 7y agoHad to look up some numbers to see if that's actually feasible and you're right, but catching it would take a long time. If we used a New Horizons-type straight launch at maximum velocity on a Falcon Heavy and a really light probe, it might get there in something like 20 years, well beyond the orbit of Pluto. If BFR was able to launch in 2021 and carry a fat booster-enabled payload, it might be able to get to rendezvous faster. Some interesting charts and explanations available at [1]. [1] https://spectrum.ieee.org/tech-talk/aerospace/space-flight/how-we-could-explore-that-interstellar-asteroid https://spectrum.ieee.org/tech-talk/aerospace/space-flight/h...
- strebler 7y agoWhat, the elongated, shiny, rotating thing that was able to accelerate without any effect on its rate of rotation? Totally a comet, definitely, 100% guaranteed.
- 127 7y agoA huge snowflake.
- rjf72 7y agoThe big question is about what caused its non-gravitational acceleration? The only thing that makes sense there is a comet - comets are icy and when that ice heats up, such as by passing around the sun, it can result in an outgassing that can create an acceleration. But it showed absolutely no indicators of being a comet, such as the tail or coma that comets display. Another problem for the comet theory is that the object was very elongated like a submarine and spinning fairly quickly. Outgassing to the point of creating a net acceleration would have further increased this spin and likely torn it to to pieces. For those that'd like to go for the 'its aliens' theories, it accelerated at the exact time you'd accelerate to have the most substantial impact on your orbit. Of course that's also the most likely point for a natural source of acceleration as well. So ultimately? Nobody knows what it was and while you have more or less plausible hypotheses, all have various flaws. Except aliens, but you can use aliens to explain any and every unknown phenomena. For instance pulsars are rapidly rotating stars that emit a high energy beam. As it rotates this beam, when the pulsar is aligned with earth, can result in it regularly pinging Earth. The first pulsar signal was detected in 1967 and, unsurprisingly, was labeled LGM-1: Little Green Men-1. Regardless, this is one of the many reasons that evolving our space technology should be priority number 1 for humanity. There are a countless numbers of reason that lacking the ability to intercept, or even identity, relatively large objects flying right next to us in space is a very bad thing. The Fermi Paradox being somewhat meaningless in the interim is just one of those reasons.
- russdill 7y agoPlenty of comets outgas and accelerate without visible outgassing.
- rjf72 7y agoThe level of coma and other factors are related to how close the comet comes to the sun. Oumuamua came extremely close (about 25% the distance from Earth to the Sun), and displayed no such characteristics. This is why thought it was originally classified as a comet, it was quickly reclassified as an asteroid. But then it started accelerating which means it's also probably not an asteroid. And on top of this all a comet would also likely have torn itself to pieces accelerating given the shape and tumble of Oumuamua. It somewhat cleanly refutes every possible classification leaving only the ¯\_(ツ)_/¯ group of celestial bodies.