'Oumuamua is a visitor from a distant solar system. Image Credit: ESO / M. Kornmesser
Originally classed as an asteroid, the object known as 'Oumuamua is now believed to be a comet.
The 400-meter-long object, which flew past our planet back in October, became the focus of much debate and intrigue after it was found to have come from a distant solar system.
When it was originally observed, 'Oumuamua did not seem to possess the characteristics consistent with a comet, leading scientists to conclude that it was most likely an asteroid.
Now though, a new study has revealed that it may be a comet after all, as evidenced by its acceleration which can be best explained by the Sun heating up its icy surface.
"Comets likely formed towards outer regions of other planetary systems, so perhaps they can escape the gravity of their parent star and go into interstellar space more easily than an asteroid," Professor Sara Russell of London's Natural History Museum told the BBC.
"Oumuamua and other interstellar travellers that may visit our solar system can potentially give us some brilliant clues about the nature and composition of other planetary systems."
"Ultimately these objects may show us whether our solar system is unique, or one of many habitable systems in our galaxy."
During the initial hype surrounding Oumuamua, I had wondered, at least once or twice, if it could have been part of a large, fast-moving debris field, maybe from an ancient supernova. That was an ominous thought. If it is accelerating now, I doubt that would be the case so this is nice to hear. So, an interstellar comet? That is interesting all by itsef. This thing sped through like a bullet, and now it's being propelled in spite of the slow-down? That is intriguing. I wish badly there was enough of a heads-up on things like this to allow for us Earthlings to send a probe in enough time. Ef... [More]
No tail, or even the luminous halo called a coma have been seen with Oumuamua, not even when it was nearest the Sun, when these should be the most conspicuous. It was not understood to be a comet.  Interesting that now, a change in the object's course through space is found. This was discernible, even over a relatively short course of observations. Was a very low level of cometary activity  sufficient to alter the object's course, to this degree?
It's worth remembering that the object is said to be tumbling on all three axes. How would a single, or multiple, out gassing points generate a smooth and continuous change in speed. Surely the overall effect would be to cancel out any net push in one direction ?Â
Yeah, the tumbling could diminish the heat point so it diminish the tail at the same time. But the evaporating face and trust will always be on the sun side whatever the tumbling.
Good point, but would there be a latency effect where maximum heating happens past the point of direct solar alignment? I tend to think of this object, due to rotation, heating proportionally though it's mass which would drive out-gassing in areas well past an axis aligned on the sun? Â
Actually, comets have been known to change course, due to outgassing. It's not an unreasonable possibility in this case, either. The matter is not settled, though. Jim Oberg, who is quite skeptical of 'extraterrestrial' claims, having debunked many, is not so sure about this one. He cites the apparently rapid increase in the object's velocity as asking a lot of a barely outgassing comet, especially one whose tail and coma have never even been seen.       Â
The researchers who wished to explain the acceleration of Oumuamua as due to outgassing from a comet published a letter in the science journal Nature. In it, they admitted that a number of suppositions had to be made, in order for their hypothesis to work. They said that it must be assumed that Oumuamua contains several materials unusual in comets, for the outgassing to be sufficient to accelerate the comet to the degree observed. Â
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