Going on fantasy here, but imagine if the Prime Directive were real and that the Litmus Test for making First Contact was to do random random fly-bys at high speeds... only qualifying civilizations would be able to detect the fly-by, send a probe, and catch up to it.
This is one of several projects planning to send equipment to L2. It's a good staging point for a variety of missions. Looks to me like an ideal location for a space station.
A permanent space station at the solar l2 point would need a massive amount of I lnfrastructure to survive. We do t have any way of safely getting people there, and we have to solve the radiation problem.
Then Earth-Moon L2. And we are, in fact, building a space station there. We have the rockets and capsules to get folks and equipment there. Or will within two to 5 years.
The NASA plans to build the station in Earth-Moon L1, which is between Earth and Moon, not in Earth-Moon L2, which is behind the Moon looking from the Earth.
Earth-Moon L1 though would be a pretty good spot to park probes ready to launch pursuing a comet though.
Technically, the orbit baselined for NASA's Gateway is Near-rectilinear Halo Orbit, which is a particular class of EML2 halo orbit that happens to loop around the Moon... ...and it is chosen partially so Earth is never eclipsed (unlike many other EML2 halo orbits). EML1 is no longer baselined.
The 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.
The 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.
Not 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/oumuamuahttps://arxiv.org/abs/1903.04723
Thanks 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."
I've been following the papers a bit, but I'm also not an expert in the field, so I likewise have a hard time assessing the plausibility of outgassing given the lack of an observed coma. I can't find a reference, but I seem to recall reading that there are still possible (though implausible) scenarios (depending on grain size & albedo & lots of other variables) where outgassing could be significant enough to produce the observed "thrust" but not enough to be visible in our scopes. Of course it could also be a combination of outgassing and solar radiation.
I will say though that physics people I've spoken to about it are much more skeptical of the solar radiation hypothesis, simply because radiation pressure is so weak. I'd be surprised if it were a thin slate of rock as the dimensions are so outlandish compared to anything we've ever observed, plus I would think be there might be "structural integrity" problems with an asteroidal body that thin and sheetlike. The "solar sail" calculations done by the folks linked to above may also assume/require that the sail "turns" itself somehow to constantly face the sun, since the observed acceleration vector was entirely pointed radially away from the sun.
I have heard one radiation pressure idea that I liked, though, which is the "dust bunny hypothesis". If 'Oumuamua were, instead of a solid body, more like a very loose, fluffy agglomeration of dust, it might just have enough surface area for us to see it (and to be hit by enough sunlight to get a push), while also having a low enough mass to produce the observed acceleration. IIRC this may have other problems, though, eg. requiring the dust to be super-high albedo for it to be visible. Seems like there aren't any "nice" answers left, so sifting through the "least improbables" is pretty difficult :)
> more like a very loose, fluffy agglomeration of dust, it might just have enough surface area for us to see it (and to be hit by enough sunlight to get a push), while also having a low enough mass to produce the observed acceleration
Wouldn't that be a great cloud to surround your spaceship with. If you have some way to generate artificial gravity, this would be a really advanced alien stealth technology.
You'd still have the mass of the spaceship to accelerate. The point of the dust cloud hypothesis is that it works if the whole thing is very light.
If you have a spaceship inside the dust cloud with its own means of propulsion, you don't need the dust cloud to get the same effect. Just use the propulsion and paint the spaceship white if you want to reflect a lot of light, or black if you don't.
But then the shape of this light-absorbent object would be resolvable. If you surround yourself with a cloud of absorbent material, you get "plausible deniability" to your expedition.
When you're asked, "hey were your forces in our solar system", you get to say "are you sure it wasn't just a cloud".
Had 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].
You don't want to just catch it though, you want to rendevous and spend time alongside/orbiting it.
That could be doable with a Jupiter flyby and close-solar-encounter, but you also want to do it close enough to earth to be able to get meaningful data back, and have enough instrumentation on it to be able to fully explore it (ideally a lander too)
Even if something else comes along, maybe this one was special. It acted very strangely. What if we detect 5 more in the coming century, but none does that interesting "accelerating without pluming" thing?!
I 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).
I 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).
It depends on what is meant by "the most likely case".
Considering that we have no knowledge or data on these objects we in fact cannot assign a statistical likelihood on what it is.
On the other hand, we know of objects flying around the solar system: comets and asteroids. We therefore assume that it should be something similar and that's what would surprise us the least.
What, the elongated, shiny, rotating thing that was able to accelerate without any effect on its rate of rotation? Totally a comet, definitely, 100% guaranteed.
