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6 Exocomets Seen Near A Distant Star

S u m m a r y :
The dusty tails of 6 comets outside of our solar system, orbiting a star found 800 light years away from us, have been identified by a team of scientists and amateur astronomers. The findings are published in the Monthly Notices of the Royal Astronomical Society.

Exocomets Beyond Our Solar System

Six exocomets—comets found outside of our solar system—have been discovered orbiting a star located 800 light years away from Earth. The discovery was made by a team of scientists from Massachusetts Institute of Technology (MIT) working in concert with other institutions, and amateur astronomers. The researchers analysed data from NASA’s stellar observatory Kepler Space Telescope. Their findings mark the first time objects of such small sizes have been spotted using a technique called transit photometry which is meant to capture the falls in intensity of the light of a star; decreases in intensity indicate transits or the crossings of other objects, like planets or comets, in front of a star.

An artist’s conception of a view from within the Exocomet system KIC 3542116. Photo Credits: Danielle Futselaar.

The Smallest Objects

This was how the comets were spotted: their passing in front of the star blocked one-tenth of 1% of the latter’s light, revealing the comets’ tails, the trails of gas and dust. The comets, made up of ice and dust and travelling at speeds of around 100,000 miles per hour, were comparable in size to Halley’s Comet, putting them in the list of the smallest objects found beyond our solar system.

“It’s amazing that something several orders of magnitude smaller than the Earth can be detected just by the fact that it’s emitting a lot of debris,” says MIT’s Saul Rappaport. “It’s pretty impressive to be able to see something so small, so far away.”

Kepler’s data has been used before to successfully identify over 2,400 exoplanets, most of which orbiting stars in the constellation Cygnus. The smallest of these are around one-third the size of Earth.

The Man Behind the Discovery, Amateur Astronomer Thomas Jacobs

It all started in March when amateur astronomer Thomas Jacobs from Bellevue, Washington, scanned through Kepler’s data; he is a member of Planet Hunters, a citizen scientist project that allows amateurs to look for exoplanets by looking into Kepler’s data to spot what computers might have missed. He eventually noticed several light patterns that stood out.

“Looking for objects of interest in the Kepler data requires patience, persistence, and perseverance,” says Jacobs. “For me it is a form of treasure hunting, knowing that there is an interesting event waiting to be discovered. It is all about exploration and being on the hunt where few have travelled before.”

Finding the Comets

Jacobs found three single transits around a faint star named KIC 3542116, located 800 light years from us; he had initially identified assymetric light curves. When Rappaport and other scientists were alerted of his findings, they interpreted the data, and went on to spot the other three transits.

“We sat on this for a month, because we didn’t know what it was — planet transits don’t look like this,” Rappaport recalls. “Then it occurred to me that, ‘Hey, these look like something we’ve seen before.'”

Rappaport explains that the asymmetry resembles disintegrating planets that have long trails of debris; however, they ruled out the possibility of it being planets because the latter would have had repeated transits, and Jacobs had not found any periodic pattern that would allude to planets.

They, thus, confirmed that the objects were comets: these would only transit the star until they get vapourised when coming too close to it. So, yea, sad news: the comets already vapourised out of existence.

“We thought, the only kind of body that could do the same thing and not repeat is one that probably gets destroyed in the end,” Rappaport says.

“The only thing that fits the bill, and has a small enough mass to get destroyed, is a comet.”

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