UT astronomers find evidence of exocomet tails 800 light-years away

Jennifer Liu

UT astronomers found evidence of six exocomets, or comets outside Earth’s solar system, 800 light-years away, using NASA’s Kepler space telescope.

Comets are small, icy solar system bodies of frozen gases, rock and dust, according to NASA. The tails of these exocomets were detected using a technique called transit photometry, which requires taking pictures of stars over and over, said Andrew Vanderburg, a NASA Sagan Fellow at UT.

Kepler took pictures of around 200,000 stars every 30 minutes for four years, yielding a total of 60,000 images for every star, he added. Kepler is located in space above the Earth’s atmosphere and is able to measure the changes in brightness of stars very precisely, Vanderburg said. 

“With data from the Kepler mission, it is relatively straightforward to measure a star’s brightness with a precision of .01 percent,” MIT physics professor Saul Rappaport said. He was the primary author of a paper detailing these findings that was published late October in the Monthly Notices of the Royal Astronomical Society. 

These brightness measurements were analyzed for periods of time and found that a star, KIC 3542116, dimmed briefly. This dimming, or transit, indicated that an exocomet passed between the star and the telescope. 

It can be hard to see how the evidence of something as small as exocomet tails can have such a big impact on astronomy, Vanderburg said. Comets are very important in the history of our solar system, however. 

“As we learn more about the comets in other solar systems, and where they are found at different stages in the formation and evolution of those solar systems, we may learn new things about how comets behaved in our own solar system long ago, when they might have been affecting how our own planet is today,” Vanderburg said.

For example, the presence of water on Earth may have come from comets impacting Earth during a phenomenon called the Late Heavy Bombardment, Vanderburg added.

In addition, learning about comets and asteroids around other solar systems can help astronomers determine whether our solar system is special in some ways or typical compared to others. 

Rappaport was the first person to notice and try to explain the unusual transits that the researchers saw in 2012.

Vanderburg first met Rappaport while he was a graduate student at Harvard, and they’ve worked together on various projects ever since. He introduced Rappaport to other astronomers at UT who worked on the high-resolution imaging of stars. 

The most challenging part of this discovery was convincing themselves that the transits were real, Vanderburg said. They concluded that the transits were definitely astrophysical and not due to some data glitch, after running tests and consulting Jon Jenkins from NASA, who is probably the world’s expert on Kepler data, according to Vanderburg.

Their next step was determining what caused the transits. The shape of the transits were similar to “disintegrating planets,” or planets that vaporize and fall apart.

As planets are being vaporized by a star, a comet-like tail comes off the planets, Vanderburg said. The researchers took inspiration from these disintegrating planets and they realized that these transits were shaped almost exactly like transits of real comets. 

The researchers said they would like to know if similar signatures can be seen in the stars around those which they first saw the transits of the exocomets. 

“If we can see these signatures, that will confirm that the transits we saw were almost certainly due to exocomets, and also that these other signatures that had been seen by other astronomers, are indeed due to exocomets as well,” Vanderburg said. “We’d know that we’re definitely on the right track.”