The first interstellar object ever discovered in our solar system, known as ‘Oumuamua, has generated enormous interest and controversy since it was spotted in October 2017.
Now, a pair of scientists have presented a robust natural explanation that accounts for ‘Oumuamua’s strangest behaviors, including its puzzling speed boost as it hurtled through the solar system. The new research suggests that the object’s many years in interstellar space left it with an abundance of molecular hydrogen, which was transformed into gas in the presence of the Sun.
This specific mechanism could finally thread the needle between the acceleration of ‘Oumuamua and the lack of hallmark signs of so-called “outgassing” events that are associated with similar speed bursts observed in solar system objects. To that end, the “mechanism can explain many of ‘Oumuamua’s peculiar properties without fine-tuning” and “provides further support that ‘Oumuamua originated as a planetesimal relic broadly similar to Solar System comets,” according to a study published in Nature.
“Given the information that we have, I think that this is our best hope of explaining ‘Oumuamua without having to resort to more sensational ideas, or, as we might say in the science community, ‘fine-tuned’ ideas,” said Jennifer Bergner, an assistant professor of chemistry at the University of Berkeley who led the study.
Darryl Seligman, a postdoctoral researcher at Cornell University and the co-author of the study, also adds:
The takeaway is that it closes the book on the five-year long fierce debate about what ‘Oumuamua was. But it has completely opened up what these interstellar objects are going to tell us about planet formation. It’s the beginning of an entirely new field. It’s important to note that non-gravitational accelerations are not, by themselves, strange. If you sublimate ice off of the comet, it’s like a rocket effect. Ice heats up, sublimates, and produces this outflowing coma and tail, and that’ll push the comet away from the coma.
Darryl Seligman said that it was very surprising that the amount of energy that ‘Oumuamua received from the Sun was not enough to create acceleration by releasing water or CO2. This is very surprising because almost every comet in the solar system is mainly composed of water.
The natural explanation for ‘Oumuamua’s strange movements cuts against a theory forwarded by Harvard astronomer Avi Loeb, who recently completed work at the Pentagon’s UFO investigations department. Loeb believes that the object was actually an alien artifact. It may sound strange, but Loeb’s approach is more rigorous than that of a typical alien hunter. He and his colleagues denied reports of UFOs over Ukraine, and recently confirmed the presence of the first known interstellar object on Earth using classified government data.
Loeb says the new analysis doesn’t disprove his theory, because he thinks ‘Oumuamua’s acceleration would require the hydrogen to completely evaporate.
Earlier research led by Seligman proposed that ‘Oumuamua was in fact made up of extremely rare solid hydrogen—making it the first observed example of a “hydrogen iceberg” — and that this hydrogen boiled off the surface, giving the object its distinctive shape and providing the observed speed boost without a coma.
This hypothesis intrigued Jennifer Bergner, who realized that radiation from cosmic rays could have seeded ‘Oumuamua with a store of so-called “amorphous” ice, a more chaotic version of the typical crystalline ice seen in most comets. This unique composition could account for the specific way that the object blasted out hydrogen that it had accumulated while traveling between stars, while leaving no trace of observable dust.
Next-generation telescopes, such as the Vera Rubin Observatory in Chile, will discover many more interstellar objects. As shown in another recent study led by Darryl Seligman, scientists have already observed a number of so-called “dark comets” that exhibit non-gravitational acceleration without comas.
“You could argue that the comets and the asteroids in the solar system have told us more about the solar system’s formation and evolution than the planets themselves have. In some sense, you could make the same argument that potentially the interstellar comments could tell us more about exoplanets than measurements of exoplanets as far away as they are, because you get to look up closer like the building blocks of exoplanets,” Seligman concluded.