NASA’s Kepler space telescope was responsible for the discovery of over 2,700 confirmed extrasolar planets, more than half of the total number of exoplanets known today. These discoveries took place during both Kepler’s primary mission, when it spent 4 years staring at the same part of the sky, and its extended K2 mission, when a mechanical failure forced it to observe different parts of the sky along the ecliptic. At the very end of the mission, when Kepler was exhausting the last of its fuel reserves, it collected a short set of observations known as K2 campaign 19. Now, University of Wisconsin-Madison astronomer Elyse Incha and colleagues have found evidence for three exoplanets in the campaign 19 dataset.
Incha et al. found three new exoplanets in the K2 campaign 19 dataset. Image credit: NASA / JPL-Caltech / K. Walbolt.
“’These are fairly average planets in the grand scheme of Kepler observations,” said Dr. Incha, lead author of a paper published in the Monthly Notices of the Royal Astronomical Society.
“But they’re exciting because Kepler observed them during its last few days of operations.”
“It showcases just how good Kepler was at planet hunting, even at the end of its life.”
Dr. Incha and her colleagues worked with the Visual Survey Group, a collaboration between citizen scientists and professional astronomers, to scan K2 campaign 19 dataset for exoplanets.
They hunted for signals of transiting worlds over all light curves in the dataset and spotted three stars, in the same part of the sky, that appeared to dim briefly.
They determined that two of the stars each host a planet, while the third hosts a planet candidate that has yet to be verified.
One of the two validated planets, K2-416b, is about 2.6 times the size of the Earth. This planet orbits its parent star, K2-416, once every 13 days.
The second planet, K2-417b, is just over three times Earth’s size and circles its star, K2-417, once every 6.5 days.
For their size and proximity to their stars, both planets are considered hot mini-Neptunes. They are located about 400 light-years away from Earth.
“The second transits for those two planets helped us confirm their discovery,” said Dr. Andrew Vanderburg, an astronomer with the Kavli Institute for Astrophysics and Space Research at MIT.
“No one had found planets in this dataset before, but our collaboration was able to find three.”
“And we’re really pushing up against the last few days, the last few minutes, of observations Kepler collected.”
The planet candidate, EPIC 246251988b, is the largest of the three worlds at almost four times the size of the Earth.
This Neptune-sized candidate orbits its star, EPIC 246251988, in around 10 days, and is slightly farther away, around 1,200 light-years from Earth.
“These discoveries demonstrate Kepler’s exoplanet detection power, even when it was literally running on fumes,” the authors said.
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Elyse Incha et al. 2023. Kepler’s last planet discoveries: two new planets and one single-transit candidate from K2 campaign 19. MNRAS 523 (1): 474-487; doi: 10.1093/mnras/stad1049
