Comet 2 L / Borisov: More original than anything else – the solar path of the interstellar segment may be its first encounter

Pure: The passage of interstellar comet 2l / Borisov over our Sun may be the first stellar encounter for this piece. Because it is more original than any comet known in our solar system. Astronomers have concluded that with the strong polarization of the light that reflects it – it speaks in favor of the comet’s nearly windless surface, they report in Nature Communications.

In August 2019, astronomers discovered the interstellar body 2 Anna / Borisov The mass, which was less than a kilometer in size, was just approaching the inner solar system. After a short time, observations showed that it was an exoplanet guilty He should have acted. Like some “local” comets, the 2l / Borisov also survived its passage near the sun Not safeIn March 2020, a piece of the block of ice broke off.

This is what the 2l / Borisov deck might look like. © ESO / M. Kormesser

Polarization reveals the state

But before Borisov left our solar system slightly damaged, astronomers took the opportunity to learn more about its structure. A team led by Stefano Panolo from the Armagh Observatory in Ireland observed the comet in the winter of 2019/2020 using the FORS2 instrument on the European Southern Observatory’s Very Large Telescope (VLT) in Chile. This indicates the polarization of the light reflected by the comet.

“The arrival of 2I / Borisov from interstellar space represents the first opportunity to study comet formation from another planetary system,” explains co-author Ludmilla Kolokolova of the University of Maryland. “This way we can verify whether the material of this comet differs in any way from that of our original variants.”

Similarities with Hale-Bopp

Indeed: “The 2I / Borisov polarization is very different from what we observe with comets in our solar system,” astronomers report. The interstellar visitor light showed a remarkably strong polarization. Typically, this is an indication of a very clear surface that has not yet been exposed to the elements on comets that have been altered by the stellar winds.

In the solar system, an object has been observed for the first time approaching at least the interstellar guest in this respect: Comet Hill-Bopp. “At the time it was measured in the 1990s, the Hale-Bopp curve was steeper and longer than any other comet seen before,” explains Bagnolo and colleagues. So astronomers assume that Hale-Bopp first flew through our Sun before its last passage.

The first completely pure comet

But as the 2I / Borisov measurement data showed, the interstellar comet has a more extreme polarization curve than Hale-Bopp. The researchers concluded that this part of the iceberg could be original and little changed from the original comet. “2I / Borisov could be the first truly pure comet ever seen,” says Panolo.

For 2l / Borisov, a passage through the Sun in December 2019 could be the first symptom: Astronomers say: “Comet 2I / Borisov may never have approached the Sun or any other star before.” As a result, it has never been exposed to stellar winds and its surface is barely exposed to the elements. The comet may still carry the particles from which it was formed in its extrasolar environment.

These are the new findings about the interstellar visitor 2l / Bvorisov.© ESO

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He grew up on the edge of his home system

Polarimetry also provided preliminary indications of the environment: “The fact that the two comets are remarkably similar to each other indicates that the composition of the environment in which 2I / Borisov was formed was not very different from the environment in the early Solar System,” co-author Alberto Celino of the Turin Physics Observatory Astrological.

So it could be that an interstellar comet formed on the icy outer edge of its original system. But exactly where it comes from is open. Similar to interstellar Asteroids Oumuamua However, astronomers believe that the 2l / Borisov was thrown from its original orbit around a space star due to gravitational perturbation or collision. (Nature Communications, 2021; Doi: 10.1038 / s41467-021-22000-x)

Coyle: European Southern Observatory (ESO)

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