Astronomers from the Massachusetts Institute of Technology and the University of Wisconsin, Madison, with the help of citizen scientists, have discovered the last three planets viewed by the Kepler Space Telescope before the eclipse. The research is published in Monthly Notices of the Royal Astronomical Society.
More than 5,000 planets are confirmed to exist outside our solar system. More than half were discovered by NASA’s Kepler Space Telescope. For more than nine and a half years, the probe tracked Earth, scanning the sky for periodic dips in starlight that could signal the presence of a planet passing in front of its host star.
For the last few days, the telescope has been constantly recording the brightness of the stars as it ran out of fuel. On October 30, 2018, its fuel tanks ran out and the spacecraft was officially retired.
A team of astronomers, led by Professor Andrew Vanderburg and Elyse Incha, combed through the telescope’s last week of high-quality data and spotted three stars in the same part of the sky that appeared to have briefly darkened. The researchers found that two of the stars each host a planet, while the third hosts a “candidate” planet that has yet to be verified.
The two confirmed planets are K2-416b, a planet about 2.6 times the size of Earth that orbits its star approximately every 13 days, and K2-417b, a slightly larger planet that is slightly more than three times the size of Earth . and it orbits its star every 6.5 days. Because of their size and proximity to their stars, both planets are considered “hot mini-Neptunes”. They are located about 400 light years from Earth.
The planet candidate is EPIC 246251988 b — the largest of the three planets, nearly four times the size of Earth. This Neptune-sized candidate orbits its star in about 10 days and is slightly further away, 1,200 light-years from Earth.
Vanderburg and Incha presented the challenge to the Visual Survey Group, a team of amateur and professional astronomers who search for exoplanets in satellite data. They scan the thousands of recorded light curves of each star by eye, looking for characteristic dips in brightness that signal a “transit,” or possible passage of a planet in front of its star.
Astronomers spent several days efficiently looking at light curves recorded by Kepler from about 33,000 stars. The team only worked with a week’s worth of high-quality data from the telescope before it began to lose fuel and focus. Even in this short window of data, the team was able to record a single transit in three different stars.
Incha and Vanderburg then looked at the telescope’s latest, lower-quality observations, taken over the last 11 days of operation, to see if they could pick up more transits of the same three stars—evidence that the planet was regularly orbiting its star.
This search revealed a second transit for K2-416b and K2-417b, confirming that they each host a planet. The team also detected a similar decrease in brightness for K2-417b in data taken of the same star by NASA’s Transiting Exoplanet Survey Satellite (TESS), a mission led and operated by MIT. Data from TESS helped confirm a candidate for a planet around this star.
“We found probably the last planets ever discovered by Kepler in data taken when the spacecraft was literally running on fumes,” says Professor Vanderburg. “The planets themselves are not particularly unusual, but their atypical discovery and historical significance make them interesting.”
“These two are definitely planets,” Incha says. “We also followed up with ground-based observations to rule out all kinds of false-positive scenarios, including interference from background stars and nearby stellar binaries.”
“These are the last planets observed chronologically by Kepler, but every bit of the telescope’s data is incredibly useful,” says Incha. “We want to make sure that none of this data goes to waste because there are still many discoveries to be made.”
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Reference: https://ras.ac.uk/news-and-press/news/astronomers-discover-last-planets-seen-kepler-space-telescope
