Amateur astronomer discovers exocomets in Kepler data

Exocomets are smallest objects ever found orbiting a star other than the Sun.
By Laurel Kornfeld | Nov 02, 2017
An amateur astronomer who reviewed data collected by NASA's Kepler exoplanet hunting telescope through the citizen science Planet Hunters program discovered unusual dips in a star's light that scientists at MIT and other universities determined to be caused byexocomets.

The comets orbit a faint star approximately 800 light years from Earth.

This marks the first time that the transit method, which measures the dimming of a star's light as a planet passes in front of it, discovered extremely small objects.

In contrast to the smallest exoplanets yet discovered, approximately one-third the size of the Earth, exocomets are tiny, making them very difficult to find.

Thomas Jacobs of Bellevue, Washington, an amateur astronomer and co-author of a paper on the discovery published in the Monthly Notices of the Royal Astronomical Society, began studying four years of exoplanet data collected by the initial Kepler mission, which included more than 200,000 stars and graphs showing the intensity of the light they emitted.

Planet Hunters engages volunteers to find patterns in Kepler data that computer algorithms missed, which could indicate the presence of exoplanets.

On March 18 of this year, he came upon three unusual light patterns, individual transits across the star KIC 3542116. Unlike planet transits, which occur at regular intervals, single transits indicate an object that passes in front of the star just once.

He then reported his findings to Saul Rappaport, a professor emeritus at MIT's Kavli Institute for Astrophysics and Space Research, and Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics.

"We sat on this for a month because we didn't know what it was--planet transits don't look like this," Rappaport said. "Then it occurred to me that, 'Hey, these look like something we've seen before.'"

Unlike the light curves of transiting planets, those Jacobs found were asymmetrical and resembled those of planets that disintegrate after coming too close to their star, leaving behind long debris trails that block very small amounts of the star's light.

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

Three more comet transits around the same star were subsequently found by the researchers.

From the data, scientists estimate the comets were about the size of Halley's Comet in our solar system and traveled about 100,000 miles per hour before coming too close to the star and being vaporized.

Their gas and dust tails blocked approximately one percent of the star's light as they transited.

"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," Rappaport noted.

Jacobs credits his finding to patience and perseverance. "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 traveled before."



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