Exocomets are probably born the same way as comets in our solar system

Observations of comets orbiting the star Beta Pictoris have revealed their range of sizes, which suggest that they probably form via a series of collisions just like comets that orbit the sun


28 April 2022

Artist’s impression of exocomets orbiting the star Beta Pictoris

ESO/L. Calada

Comets throughout the universe may be remarkably similar to the ones in our own solar system. The first measurement of the sizes of exocomet nuclei – the icy masses of rock that makes up the main body of comets – shows that these rocks orbiting distant stars probably formed the same way as the ones orbiting the sun.

The first exocomes ever detected, found in 1987, orbit a star about 63 light years away called Beta Pictoris. Alain Lecavelier des Etangs at Sorbonne University in France and his colleagues examined news of Beta Pictoris taken by the Transiting Exoplanet Survey Satellite (TESS) to determine the sizes of these balls of ice and stone.

They found that the comet nuclei range from 3 to 14 kilometers in diameter. This is the first time we have measured the sizes of comets beyond the solar system, and the proportion of comets at each size matches up with the distribution we’ve observed in the solar system.

“There are many, many more small objects compared to big objects [around Beta Pictoris], and this is exactly what we observe in the solar system, and it’s what we expect for bodies produced by fragmentation,” says Lecavelier des Etangs. That means that these comets were likely formed when larger objects smashed into one another and broke up into lots of little pieces. “We suspected that these are very common processes, and comets are normal byproducts of planetary formation,” says Lecavelier des Etangs.

This tells us that the way planets formed in the solar system is probably similar to how they form around other stars, and it also paints a picture of what it would be like to exist in a relatively small and young planetary system.

“If you were on a planet orbiting Beta Pictoris the sky would be full of comets in every direction – it’s like seeing comet Hale-Bopp every two days,” says Lecavelier des Etangs. “It’s spectacular – I would love to be there.”

Journal reference: Scientific ReportsDOI: 10.1038/s41598-022-09021-2

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