Scientists from MIT and other institutions, working closely with amateur astronomers, have spotted the dusty tails of six exocomets - comets outside our solar system - orbiting a faint star 800 light years from Earth.
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These cosmic balls of ice and dust, which were about the size of Halley's Comet and traveled about 100,000 miles per hour before they ultimately vaporized, are some of the smallest objects yet found outside our own solar system.
The discovery marks the first time that an object as small as a comet has been detected using transit photometry, a technique by which astronomers observe a star's light for telltale dips in intensity.
Such dips signal potential transits, or crossings of planets or other objects in front of a star, which momentarily block a small fraction of its light.
In the case of this new detection, the researchers were able to pick out the comet's tail, or trail of gas and dust, which blocked about one-tenth of 1 percent of the star's light as the comet streaked by.
"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 Saul Rappaport, professor emeritus of physics in MIT's Kavli Institute for Astrophysics and Space Research.
"It's pretty impressive to be able to see something so small, so far away."
Rappaport and his team have published their results this week in the Monthly Notices of the Royal Astronomical Society.
The paper's co-authors are Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics; several amateur astronomers including Thomas Jacobs of Bellevue, Washington; and researchers from the University of Texas at Austin, NASA's Ames Research Center, and Northeastern University.
"Where few have traveled"
The detection was made using data from NASA's Kepler Space Telescope, a stellar observatory that was launched into space in 2009. For four years, the spacecraft monitored about 200,000 stars for dips in starlight caused by transiting exoplanets.
To date, the mission has identified and confirmed more than 2,400 exoplanets, mostly orbiting stars in the constellation Cygnus, with the help of automated algorithms that quickly sift through Kepler's data, looking for characteristic dips in starlight.
The smallest exoplanets detected thus far measure about one-third the size of the Earth. Comets, in comparison, span just several football fields, or a small city at their largest, making them incredibly difficult to spot.
However, on March 18, Jacobs, an amateur astronomer who has made it his hobby to comb through Kepler's data, was able to pick out several curious light patterns amid the noise.
Jacobs, who works as an employment consultant for people with intellectual disabilities by day, is a member of the Planet Hunters - a citizen scientist project first established by Yale University to enlist amateur astronomers in the search for exoplanets.
Members were given access to Kepler's data in hopes that they might spot something of interest that a computer might miss.
In January, Jacobs set out to scan the entire four years of Kepler's data taken during the main mission, comprising over 200,000 stars, each with individual light curves, or graphs of light intensity tracked over time.
Jacobs spent five months sifting by eye through the data, often before and after his day job, and through the weekends. ■