Hubble Gives Us Our Best Look Yet At Interstellar Comet Borisov

Comet 2I/Borisov as seen by Hubble. NASA, ESA, and D. Jewitt (UCLA)

Comet 2I/Borisov is the second interstellar object that we have caught visiting the Solar System and thanks to Hubble we now have the best view of it yet. The image highlights the tail and the dusty coma around the nucleus, which, at 1 kilometer (0.6 miles) across, is too small to be seen by the space telescope.

The comet was discovered on August 30, 2019, by Crimean astronomer Gennady Borisov (and named after him). The discovery comes two years after astronomers spotted ‘Oumuamua, an interstellar asteroid that whizzed through the Solar System.

"Whereas 'Oumuamua appeared to be a rock, Borisov is really active, more like a normal comet. It's a puzzle why these two are so different," leader of the Hubble team David Jewitt of the University of California, Los Angeles (UCLA), said in a statement.

The similarity between Comet Borisov and comets in our own Solar System is quite striking. Ignoring its orbit and speed, it could easily pass for one of ours. Its similarities to our comets have been remarked upon following several observations and in a recent Nature Astronomy paper. However Borisov formed, it seems the processes that lead to comets must be relatively common.

"Though another star system could be quite different from our own, the fact that the comet's properties appear to be very similar to those of the Solar System's building blocks is very remarkable," said Amaya Moro-Martin of the Space Telescope Science Institute in Baltimore, Maryland.

Hubble photographed the comet when it was about 420 million kilometers (260 million miles) away. It is still getting closer and brighter but it's so speedy (moving at 180,000 kilometers/110,00 miles per hour) that its trajectory is not majorly affected by the Sun.

Hubble and many other telescopes will keep an eye on the comet as it continues to move through the Solar System. It should remain visible to our observatory until the first months of 2020, although observations might be extended.  

"New comets are always unpredictable," said Max Mutchler, another member of the observing team. "They sometimes brighten suddenly or even begin to fragment as they are exposed to the intense heat of the Sun for the first time. Hubble is poised to monitor whatever happens next with its superior sensitivity and resolution."

Comet Borisov will reach its closest point to the Sun on December 7, when it will be roughly 300 million kilometers (190 million miles) from our star.

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