In 2017, for the first time in human history, it was discovered that “foreign visitors” broke into the solar system. It was an unusually long and narrow celestial body that was very fast and seemed to “accelerate” itself. The position is more erratic than the comet, but there is no tail of the comet. Some Harvard scientists even speculated that it was an alien sailing ship.

And a study published in the evening of Nature Astronomy on April 13th proposes a unified interstellar visitor Oumuamua all the weirdness Possible explanation for the place. Omomo’s predecessor was a rocky super-earth, or has not yet become a planet, and was torn apart because it was too close to the star. One of them happened to pass by our solar system. Under the porous surface, it is deep in water ice.

The two authors of the paper are Zhang Yun from the National Astronomical Observatory of the Chinese Academy of Sciences and Lin Chao, a professor in the Department of Astronomy at the University of California, Santa Cruz, and a visiting professor at the Institute of Advanced Studies, Tsinghua University.


Messenger from afar

“Omomo” was discovered by the Pan-Star Survey Telescope in Hawaii on October 19, 2017, and it was dark red The body is unusually long and narrow, with an aspect ratio of more than 6, like a cigar.

The International Astronomical Union will name it 1I / Oumuamua, I stands for interstellar celestial bodies, and Omomo has become the first human record in this category. Oumuamua means “distant messenger” in Hawaiian language, not only saying it came from afar, but also describing it as fast.

Scientists estimate that Omomo entered the solar system at a speed of 25.5 kilometers per second, and then reached 44 kilometers per second. After just two months, the earth The most sensitive telescope on the Internet is also difficult to see its figure.


Ao Momo has a long and narrow shape, like a cigar

What is more intriguing is that Omomo ’s trajectory is erratic and cannot be completely explained by gravity. In other words, it seems to have additional “power”.

This happens to comets: comets are rich in ice material, sublimated by solar radiation, leaving a long misty comet tail behind them. Therefore, the Chinese people call the comet a broom star. This “broom” tail, like a jet propeller, provides extra acceleration for the comet.

Omomo accelerated when approaching the sun, which seems to be explained by the comet mechanism.

However, preliminary observations show that Omomo ’s appearance is more like an asteroid than a comet, and there is no evidence of comet activity.

Avi Loeb, a theoretical physicist at Harvard University who has always had a big brain hole, took the opportunity to throw out his “interstellar light sail” hypothesis, that Omo may be a A spaceship made by an alien civilization is pushed forward by the photon, just like a sailboat is agitated by the wind.

The American Institute for Search for Extraterrestrial Civilizations (SETI) said that no artificial radio signal was found on Aomo.


A unified interpretation

It can be said that the previous hypothesis about Omomo often missed each other, and it is difficult to explain one point while explaining one point.

Zhang Yun and Lin Chao have established a model that can take into account many rare features of Omomo, including its unusually flat shape and lack of misty coma , And the non-gravitational acceleration that occurs when flying across the sun.

Their model shows that if Omomo ’s mother is within hundreds of thousands of kilometers from the star and is dominated by the star ’s strong gravitational field, The star’s tidal force twists and then disintegrates. The parent body will then produce many very flat rotating fragments, which have enough kinetic energy to escape the planetary system.


simulating the tidal tearing process and fragments at different distances Shape

The surface of the parent body will become very hot during this process, and most of the volatile substances will evaporate. But the author believes that under the porous surface of Omomo, its deeper layer may retain water ice and sublimate as it swept the sun, thus explaining the non-gravitational acceleration, but there is no obvious jet phenomenon.

This parent may be a kilometer-level star (equivalent to the nebula of a planetary embryo), or a “super-Earth” (a rocky planet much larger than Earth) ), Initially orbiting a low-mass star or white dwarf star.

Link to the paper: https://nature.com/articles/s41550-020-1065-8