The past of the interstellar object Oumuamua was more interesting than astronomers assumed.
New simulations show that an amazing chunk of space rock could have been torn apart by a star – the remnants caked in the shape of a cigar that we discovered in October 2017.
If so, the new findings could answer some of the most pressing questions about the specific properties of this keen space traveler.
'Oumuamua is primarily known for being the first stone known to enter the solar system from somewhere else – our first known interstellar visitor. We first learned about this in October 2017, but soon other features of it became apparent.
First, the form. Most asteroids and comets are potato-like, but Oumuamua is long and slender — 400 meters in length, about eight times its width. It also has a red hue, similar to an asteroid baked by cosmic radiation, dry, predominantly rocky and metallic.
But acceleration from the Sun was also observed, faster than could be explained by gravity. This behavior is more consistent with the comet's outgassing, which provides acceleration, since the volatile ice sublimates when the comet is near the sun.
So, it is still not entirely clear whether Oumuamua is an asteroid or a comet.
Its properties are so unusual that some have suggested that the stone was an alien probe. (There is no evidence for this.)
Now researchers from the Chinese Academy of Sciences and the University of California at Santa Cruz have determined how the strange object could have formed. Not only is this process completely natural (again, there are no aliens here), it may explain some of Oumuamua's strange properties.
“We have shown that interstellar objects like Oumuamua can be formed by extensive tidal fragmentation as they approach their host stars and then ejected into interstellar space,” said astronomer and astrophysicist Douglas Lin of the University of California, Santa Cruz.
Tidal interactions are gravitational interactions between two bodies. When a small body approaches a larger body – like a star, or a black hole, or even a large planet – intense gravity can change it in a process called tidal interaction. An example is the tide that Jupiter inflicted on Comet Shoemaker-Levy 9 in 1992.
Shoemaker Levy 9 shattered into pieces that collided with Jupiter, but simulations by Lin and his colleague Yun Zhang of the Chinese Academy of Sciences showed that a very different result is possible with the participation of a star.
(NAOC / Y. Zhang)
First, an object flying at the correct distance from a star – a piece of rock such as a planetesimal – is fragmented when tidal stresses tear it apart. Then, when it turns, these fragments melt and stretch into an elongated shape. Finally, as it moves away from the star, it recombines, cools and solidifies, which ensures the structural stability of the newly transformed object.
Since Oumuamua's discovery last year, a second interstellar object has been discovered, Comet 2I / Borisov. As our technological capabilities develop, we are expected to find even more interstellar objects visiting our solar system.
The study was published in the journal Nature Astronomy.
