A few days before it went silent, the Kepler space telescope “gave” astronomers information about three new exoplanets. The research, carried out with the help of citizen amateur astronomers, is published in the journal Monthly Notices of the Royal Astronomical Society.

More than 5,000 planets have been confirmed beyond our solar system, and more than half were discovered by NASA’s Kepler space telescope.

Just before it went silent in October 2018, the telescope continued to record the brightness of stars, and a team of scientists from the Massachusetts Institute of Technology and the University of Wisconsin sifted through its last week’s high-quality data and found three stars, in the same place of the sky, the brightness of which seemed to fade for a while. As they found, two of the stars “host” a planet, while the third a “candidate” planet that has not yet been verified.

The researchers presented their observations to the Visual Survey Group, a group of amateur and professional astronomers who look for exoplanets in satellite data.

The team spent a few days efficiently examining the light curves of about 33,000 stars recorded by Kepler. It was data collected by the telescope just one week before it began to run out of fuel.

Even with this little data, the team was able to detect a unique transit in three different stars.

Professional astronomers then looked at the telescope’s latest, lower-quality observations, taken in its last eleven days of operation, to see if they could detect additional transits of the same three stars, evidence that a planet is periodically orbiting its star. This research confirmed the two planets.

One planet is K2-416 b which is about 2.6 times the size of Earth and orbits its star about every 13 days. The second, K2-417 b, is a slightly larger planet that is just over three times the size of Earth and orbits its star every six and a half days. Both planets are about 400 light years from Earth.

The planet candidate (EPIC 246251988 b) is the largest of the three at nearly four times the size of Earth, orbits its star in about ten days, and is located just over 1,200 light-years from Earth.

“We found perhaps the last planets ever discovered by Kepler, in data taken while the spacecraft was literally running on fumes,” says Professor Andrew Vanderberg of the Massachusetts Institute of Technology.