The interstellar comet 2I/Borisov is starting to brighten, suggesting it may be breaking apart as it makes its way out of our solar system.
The comet was first spotted in August last year, and astronomers have been keenly following it ever since. A team in Poland was the outbursts from the comet in early March, more than doubling its brightness. That suggests it is emitting material after being heated by the sun during its close approach in December 2019.
“Changes in brightness indicate that the comet has changed in activity,” says Michele Bannister at the University of Canterbury in New Zealand, who is part of a team using the Very Large Telescope (VLT) in Chile to observe the object. “That can be due to the sun’s heat penetrating the comet and reaching material that’s a bit more volatile, [or] the comet could be developing a weakness that could lead to eventual breakup.”
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As 2I/Borisov is the first comet from another star to be found in our solar system, astronomers weren’t sure how it would behave. Gases and water detected on the object suggest it is similar to our own comets, but outbursts of the kind being seen now weren’t guaranteed at all, says Bannister.
Such events are scientifically fascinating, because they can reveal fresh material from the object’s subsurface that hasn’t been exposed to space before. “You can see whatever was inside the nucleus of the comet,” says Cyrielle Opitom at the Royal Observatory, Edinburgh in the UK. “It might mean that we are observing [its] real composition.”
The comet is now in front of the bulk of our galaxy’s stars in the night sky, making observations difficult. Yet observatories like the Hubble Space Telescope could look for signs of fragmentation in the coming weeks, while the comet should remain visible to telescopes for at least another few months.
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