Astronomers have discovered the oldest comet in the solar system

Comet Borisov was discovered in August 2019 by astronomer Gennady Borisov. The trajectory with which it moved through the solar system indicated that it was an interstellar object not bound by gravity to any star. It was the second interstellar object discovered by scientists - the first is the asteroid Oumuamua. But Oumuamua was already spotted en route from the solar system, so astronomers had little time to study it. Borisov's comet was discovered earlier and could be observed more similarly, according to phys.org.

Researchers at the European Southern Observatory in Chile used a system of powerful telescopes to determine the properties of cometary dust, and found that Borisov's comet is emitting about 200 kilograms of dust per second. It also turned out that comet Borisov has much more carbon monoxide than comets in our solar system usually have, but it is unevenly distributed: the celestial body is a "pebble" united into one whole.

As it turns out, Comet Borisov is unlike any object in our solar system, with the exception of Comet Hale-Bopp, a relic of the early solar system that made a lot of noise in the late 1990s. Until its last appearance, Comet Hale-Bopp is believed to have passed our Sun only once and therefore was hardly exposed to solar wind and radiation. In composition, it is a cloud of gas and dust from which the solar system formed about 4.5 billion years ago.

However, comet Borisov turned out to be even more pristine than comet Hale-Bopp. The light from it is much more polarized than the light reflected from any other comet, and the coma is remarkably uniform. This proves that before Borisov's comet flew past the Sun in 2019, it never interacted with other stars and is an intact relic formed from a cloud of gas and dust. As for the similarities between Comet Borisov and Hale-Bopp, it suggests that Comet Borisov's stellar system and our own early solar system were likely quite similar.

Studying comet Borisov and similar objects can help in understanding other stellar systems. Comets and asteroids around other stars are too far away, and interstellar objects such as Borisov's comet turn out to be a link between our solar system and other systems.

The research is published in the journal Nature Communications.