Is it possible for an object like Oumuamua, which is rotating around its intermediate axis, be accelerated by outgassing? I understand that outgassing can accelerate comets, but I didn’t think comets could tumble without falling apart. I think somebody knows we’re here…
Of course it’s possible. Why wouldn’t it be? Too much acceleration might break an object apart, but the sort of accelerations you’d get from outgassing would be very, very small.
Any* outgassing would imply acceleration; not necessarily, though, along a constant axis.
So my question is:
From what we know, can outgassing explain Oumuamua‘s observed acceleration? It seems that outgassing would change a tumbling object’s angular momentum, not its flightpath.
‘Oumuamua is only rotating once every 7 or 8 hours (estimates vary). At 230 metres long, this is not enough speed to pull it apart. Recent studies of its trajectory show that it does seem to have been a comet, with mild outgassing resulting in non-gravitational effects on its orbit.
https://www.nature.com/articles/d41586-018-05552-9
Quoting the Nature article:
After considering other possible explanations, the researchers concluded that the effect comes from comet-like outgassing. As ‘Oumuamua approached the Sun, it began to heat up, and its icy heart started to melt. This released gas that made its way to the comet’s surface and shot outward, giving the object a little push.
I’ve read the news articles - I was hoping for a more technical explanation
Well, here’s a nice technical overview of nongravitational effects.
https://www.lpi.usra.edu/books/CometsII/7009.pdf
So the science says Oumuamua isn’t a comet. So it’s probably a probe sent out by aliens, just like our Mars Rovers and our other observation machines. Depending on how far away the machine builders are, we might need to get our shit together pretty soon. Yeah some humor some truth
Outgassing could produce a torque that changes the objects’ angular momentum, or could cause a force that changes the orbit, or both. But the fact that outgassing occurs on the side of the object facing the sun reduces the change of a torque (I think). As the previous cites mention, a non-rotating object would have experience a force that was always outward (from the sun). Unless the object was asymmetrical, this would be a force that caused no torque and no change in rotation. For an object that’s rotating, the force could be pointed a little bit away from the sun - because the hottest spot is not the spot that is currently directly in the sun’s light, it’s the spot that had been in the sun’s light a little while ago, and is now pointed a bit away from the sun (for much the same reason as it’s not the hottest day of the year in the northern hemisphere on June 22). This force now can cause acceleration in a direction that’s not quite aligned with the direction of the sun, but it’s still mostly in the wrong direction to cause a change to the rotation rate of the object.
Where are you getting the “some truth” part from? All I see is humor.
If aliens are looking for food, then they’ve hit jackpot …
The science says that I’m not a comet, either. Does that mean that I’m an alien space probe?
That’s exactly the sort of disingenuous question an alien space probe would ask.
Looking at you suspiciously now…
I suppose we probably shouldn’t expect an alien probe to look like Sputnik…but Sputnik did look pretty cool
“Science” didn’t say it’s not a comet. Astronomers who looked at it initially said that it had a low albedo and no signs of a tail, so it was most likely an asteroid and not a comet. But if they detected outgassing, then that changes things. Asteroids don’t outgas, as they are solid. Scientists being good Bayesians, they are always ready to change their minds when the facts on the ground change.
So it’s more likely that this thing started life as a comet, and over billions of years has accrued enough dust and been bombarded with enough cosmic radiation that it’s icy core is under a fairly thick layer of old, reddish material. So it’s crunchy on the outside with a soft nugat center…
Not that this thing was an alien probe, but I remember saying to someone after we discovered it, “Wouldn’t it be a trip if this thing suddenly fired up a rocket to make a course correction as it used our sun as a gravitational slingshot?” My idea then if that happened would be to analyze the orbit before and after to see if whatever the ‘burn’ was took it someplace more interesting than where it was originally going. Like, if the corrected orbit took it smack dab to Alpha Centauri within the limits of our measuring capability, that would be very interesting.
Also, it would be interesting to see if the rotation rate did change. A natural outgassing event would very likely not occur directly at the center of rotation, so it should affect the rate. On the other hand, intentional propulsion would probably be done at the center of rotation and wouldn’t change it. So that would be a marginally interesting test if the change was enough to be measured. If we could measure the velocity of the outgassed material that would also help tell us if it was just natural release from heat and the solar wind, or if it was something more energetic.
That’s assuming we wanted to expend the money and effort to answer those questions, since this thing is almost certainly just a natural piece of the galaxy.
I guess I’m hoping an alien probe is a natural piece of the galaxy…
You can get objects that are somewhere in between.
I assume that the celestial body in the Solar System with the most outgassing is Uranus?
(Yes, I have the soul of a seven year old boy. 
)
Anything is an alien space probe, if you are brave enough.