Cracking the Oumuamua Code: Alien Spaceship or Natural Phenomenon?

In 2017, a mysterious comet called ‘Oumuamua ignited the imaginations of scientists and the public. It was the first known visitor from outside our solar system, didn’t have a bright coma or a dusty tail like most comets, and had a distinctive shape—something between a cigar and a waffle—and its smaller size more asteroid than a comet.

However, in a way that astronomers can’t explain, it’s drifting away from the sun baffled scientists and led some to speculate that it was an alien spacecraft.

Now, a UC Berkeley astrochemist and an astronomer at Cornell University says the comet’s mysterious deviations from its hyperbolic path around the Sun can be explained by a simple physical mechanism believed to be common to many icy comets: the release of hydrogen as the comet warms. in the sunlight

What set Oumuamua apart from other well-studied comets in our solar system was its size: It was so small that its gravitational deflection around the Sun was altered slightly by the small jolt produced when hydrogen gas was ejected from the ice.

Most comets are dirty snowballs that periodically approach the Sun from the outer reaches of our solar system. As the comet is heated by sunlight, it expels water and other molecules, forming a bright halo or coma and tails of gas and dust around it. The ejected gases act as spacecraft engines, providing the comet with a small thrust that slightly changes its orbit from the elliptical orbits typical of other Solar System objects such as asteroids and planets.

When discovered, Oumuamua had no coma or tail, and was too small and too far from the sun to capture enough energy to extract too much water; Was it a hydrogen iceberg released by H? ₂ ? A big fluffy snowflake pushed by the light pressure of the sun? A light sail created by an alien civilization? Spaceship under its own power?

Jennifer Bergner, an associate professor of chemistry at the University of California, Berkeley, who studies chemical reactions in icy rocks in the cold vacuum of space, thinks there may be a simpler explanation. He raised the issue with his colleague Darryl Seligman, now a National Science Foundation postdoctoral fellow at Cornell University, and they agreed to work together to test the issue.

“A comet traveling through the interstellar medium is mainly prepared by cosmic radiation, and as a result hydrogen is formed. Our thinking is, if this is happening, could it be trapped in the body where it enters the solar system and releases hydrogen when it heats up? – Bergner said. “The force needed to explain non-gravity acceleration can it produce quantitatively?

Surprisingly, he discovered that experimental studies published in the 1970s, 80s and 90s showed that when high-energy particles similar to cosmic rays hit the ice, molecular hydrogen (H2) was produced in large quantities and remained in the ice. _ice . In fact, cosmic rays can penetrate tens of meters into the ice, turning a quarter or more of the water into hydrogen.

“For a comet several kilometers in diameter, the outgassing will be through a very thin envelope relative to the mass of the object, so you wouldn’t expect it to be a noticeable effect, both in terms of composition and any acceleration.” – said. “But because ‘Oumuamua is so small, we really believe it generates enough power to provide that acceleration.”

The slightly reddish comet is believed to measure about 115 by 111 by 19 meters. Although their relative size was pretty accurate, astronomers couldn’t be sure of the true size because it was too small and too far away to be detected by telescopes. The size had to be estimated from the comet’s brightness and how the brightness changed as the comet fell. To date, all comets observed in our solar system (short-period comets from the Kuiper belt and long-period comets from the more distant Oort cloud) range in diameter from about 1 kilometer to hundreds of kilometers.