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Interstellar Comet Borisov May Make It Out Of The Solar System Largely Intact After All


Comet 2I/Borisov on December 9, just after its perihelion, or closest approach to the Sun, and before the drama happened. NASA, ESA, and D. Jewitt (UCLA)

Just like many break-ups, Comet 2I/Borisov’s is complicated.

Earlier this year, the first interstellar comet visitor appeared to brighten considerably (a cometary outburst), suggesting that it was breaking apart on its exit from our Solar System. Further images of Borisov in late March showed an extended core and a separated chunk of its nucleus – a complete fragmentation looked on the cards.


However, according to a new analysis published on pre-print server arXiv, these events were not as dramatic as first thought and resulted in only a partial break-up of the cosmic object. For all parties involved, this is the perfect compromise. Borisov looks set to continue its journey largely intact, whilst the debris shed in its outbursts can be probed to understand the interstellar comet’s composition.

After the rock’s closest pass to the Sun in early December, astronomers suspected it may have fallen foul, as other comets in the Solar System do, to the star’s heat. Comets are like dirty snowballs, made up of frozen gases, rock, and dust that on a close encounter with the Sun can melt and fragment, spewing out gas and dust in the process and leaving a gaseous trail behind. Although Borisov has been shown to have many similarities and differences to comets in our Solar System, scientists feared the Sun’s stress may have been enough to tear it apart.

But, having revisited the data from the cometary outbursts in March, a team led by David Jewitt, a UCLA professor of planetary science and astronomer, found that only a small proportion of the comet’s mass was lost.

In the earliest events (between March 4 to 12), around 20 million kilograms (44 million pounds) were estimated to have been shed. This seems like a lot but pales in comparison to its suspected 300-billion-kilogram (660-billion-pound) nucleus. The further chunk spotted in late March had a mass of around 120,000 kilograms (265,000 pounds), which the team believes also broke off in the initial outbursts. In fact, its delayed appearance in images gave the team a clue as to its origin.


“Overall, our observations reveal that the outburst and splitting of the nucleus are minor events involving a negligible fraction of the total mass,” the authors wrote in the paper. “[Comet] 2I/Borisov will survive its passage through the planetary region largely unscathed.”

Discovered in August last year, Comet Borisov is only the second-ever interstellar object detected in our Solar System. The other being ‘Oumuamua, which was first spotted in 2017. Both rocks are high on astronomer’s agendas to help understand how such objects form around stars other than our own.

[H/T: ScienceAlert]

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