Hubble snaps one of the fastest comets ever seen whizzing past the sun

13 Dec 2019

The Hubble Space Telescope. Image: NASA/ESA

The Hubble Space Telescope has seen an interstellar comet whizz past the sun at an incredible speed.

Once again, the NASA and ESA Hubble Space Telescope has spotted comet 2I/Borisov travelling through the solar system, going past the sun on its way back to interstellar space. It travelled at speeds of more than 175,000kph, making it one of the fastest comets ever seen, and it remains one of only two objects known to have passed through our solar system.

The interstellar comet was spotted by Hubble last October approximately 420m km from Earth, but two images were later taken in November and December at a closer distance, giving us a better sense of its details and dimensions.

The December image was taken at the comet’s closest approach to the sun – approximately 298m km from Earth – where it was subjected to intense heat after millions of years of extreme cold.

The nucleus, an agglomeration of ice and dust, is still too small to be resolved. However, the bright central portion spotted in the latest image is a coma made up of dust leaving the comet’s surface. By the end of this month, it will have made its closest approach to Earth at a distance of 290m km.

Comet Borisov lit up as it made its closest approach to the sun.

The photo taken by Hubble of comet 2I/Borisov on 9 December 2019 as it travelled at more than 175,000kph. Image: NASA/ESA/D Jewitt (UCLA)

Surprising discovery

“Surprisingly, our Hubble images show that its nucleus is more than 15 times smaller than earlier investigations suggested it might be. The radius is smaller than half a kilometre,” said astronomer David Jewitt, whose team photographed Borisov.

“This is important because knowing the size helps us to determine the total number, and mass, of such objects in the solar system and in the Milky Way. Borisov is the first known interstellar comet, and we would like to know how many others there are.”

The comet was discovered by Crimean amateur astronomer Gennadiy Borisov on 30 August this year, after which astronomers around the world determined it was of interstellar origin.

Until now, all catalogued comets have come either from a ring of icy debris at the periphery of our solar system, called the Edgeworth-Kuiper belt, or from the Oort cloud at its outermost regions.

While 2I/Borisov may be one of the very few interstellar comets to be spotted, it’s believed there may be thousands of visitors at any given time that are too faint to be seen by modern-day telescopes.

Colm Gorey was a senior journalist with Silicon Republic