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Oumuamua's strange space object may be a fragment of a dead planet



A free translation (with few additions) of a very good article by Nadia Drake .

You may have already heard about the asteroid Oumuamua (1I / 2017 U1), which was called either an alien spaceship or a space chip. From the moment he first appeared in the solar system, astronomers are trying to determine its origin.

In a new work, scientists from the National Astronomical Observatory of China and the University of California at Santa Cruz, USA, showed that the first of the known interstellar objects that came from outside the solar system could get its oblong shape when the planet was torn apart by a distant star.

An unusual visitor made his journey through the solar system at the end of 2017. This is a small rocky object that was born in a star system located somewhere far, far away from us.

Oumuamua got its unusual name thanks to astronomers working at the Haleakal Observatory in Maui (Hawaii). Translated from Hawaiian, the name of the asteroid means "the first messenger from afar." And this messenger immediately suggested several interesting puzzles . Originally it was considered a comet. The interstellar “alien” had an atypical form for asteroids and moved so unusual that hypotheses about its artificial origin began to appear. Oumuamua looked like an elongated, cigar-shaped object (its length exceeds its width by almost ten times) - in our solar system such forms have not yet been seen.

Computer modeling helped to reveal the history of the origin of this strange interstellar object: a certain planet was torn to pieces by a too close approaching star, leaving behind a mass of long thin fragments. Some of these fragments went into interstellar space. And millions, and perhaps billions of years later, Oumuamua reached our solar system. Scientists have established three possible types of home systems for Oumuamua, and their work explains both the elongated shape and the curious movement of the interstellar visitor.

“Oumuamua caused us many problems in terms of understanding and explaining its origin,” says Yun Zhang , a scientist at the French observatory and author of the study,published in Nature Astronomy. "Before our study, no one could offer a clear explanation of the unusual shape of the asteroid."

A riddle from the far corners of the universe


Astronomers have always suspected that interstellar objects fly through our solar system. Finding such objects was only a matter of time. But there was an opinion that these objects would be similar to Borisov’s comet , looking albeit unusual, but similar in composition to our comets.

“With Borisov’s comet, we received exactly what we expected from the interstellar guest. Everything about him is completely ordinary, ”says Greg Laughlin , professor of astronomy at Yale. "And this is a striking contrast with Oumuamua, which has literally nothing ordinary."

Instead of being icy and like a comet, Oumuamua looks rocky and dry, like an ordinary asteroid. It is too small and dull for us to see the surface, so astronomers concluded about the shape of the object, based on the reflection of light during movement. A strange elongated shape provoked a lot of theories about its origin. And when astronomers observed the movement of Oumuamua, they noticed strange accelerations that were attributed to water vapor escaping from under the surface. However, Yun Zhang's research provides a better understanding of the secret of the interstellar traveler.

How to make a space cigar


Zhang and her colleague Douglas Lin appreciated the likelihood that Oumuamua came from a system with planets or planetesimals orbiting a small, dense central star. An object that has sufficient gravity to destroy worlds that are too close, and at the same time not fry them to a crisp.

The team using a high-performance computer simulated the trajectory of three types of objects rotating around this star: planetesimals 800 meters wide, long-period comets and larger objects like super-earth.

Zhang and Lin found that if any of these objects were within a radius of 350 thousand km. from the star, it will begin to rotate, stretch and collapse under the influence of gravity. A star acts mercilessly, tearing objects that come close and scattering them around interstellar space. Depending on the composition of a torn planet, some of its fragments may take an elongated shape similar to the one acquired by Oumuamua.

Simulation also showed that in this process objects should be formed that repeat the first interstellar guest not only in shape, but also in other characteristics (dry surface, rocky composition, water ice under the surface and even features of movement). When the parent world is torn to pieces, the heat of the star melts the resulting fragments and evaporates any water on the surface. But patches of ice buried deep inside the fragments remain. And this may explain the hypothetical jets of water vapor that pushed Oumuamua as it approached our sun. Astronomers call the calculations of the state of the asteroid convincing, since they explain the strange properties of the interstellar guest, which can give new knowledge about the formation of planets in other galaxies. Astronomers predict the fate of the "alien":the asteroid will fall apart.

A cigar or a pancake?


However, there are other theories of the origin of the asteroid. Michelle Bannister of the University of Canterbury, New Zealand, who also studies interstellar objects, has done a great job studying Oumuamua. In her opinion, the comet, and not the super-earth, should have been the parent body for this object. But she, along with Professor Laughlin, offers a new riddle: is Oumuamua really an object in the form of a cigar? Based on an article published last summer , they propose considering a different version: Oumuamua has a pancake-like shape. As an analogy, Bannister cites an object in the external solar system called MU69, or Arrokot . It is similar to over- filled pita.

If this theory is confirmed, then the true origin of Oumuamua will still remain shrouded in mystery. And scientists will have to look for an explanation of the origin of not the “chips”, but the cosmic “pancake”.

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