Astronomers unearth the last alien worlds observed by the Kepler Space Telescope

On October 30, Kepler was officially retired due to the fact it was out of fuel and could no longer maintain its Earth-trailing orbit.

Since that time, a team of astronomers led by Professor Andrew Vanderburg and Elyse Incha has poured over data from the telescope's last week of observations. The astronomers behind the observations initially presented the final Kepler Space Telescope data to citizen scientists from the Visual Survey Group, a team of amateurs and professional astronomers who hunt for exoplanets in satellite data. Together, they highlighted three separate stars in the Kepler data whose light appeared to dim periodically.

They have now determined that two of the stars host exoplanets, while the third likely also hosts a planet, though follow-up observations are required.

"We have found what are probably the last planets ever discovered by Kepler, in data taken while the spacecraft was literally running on fumes," Professor Vanderburg explained in the press statement. "The planets themselves are not particularly unusual, but their atypical discovery and historical importance makes them interesting."

"Still a lot of discoveries to be made"

The two confirmed planets are K2-416 b and K2-417 b and both are approximately 400 light-years away from Earth. K2-416 b is roughly 2.6 times the size of the Earth and it orbits its star roughly once every 13 days. K2-417 b, meanwhile, is about three times Earth's size and its year is only 6.5 days long. Both planets are described as "hot mini-Neptunes" due to their size and proximity to their stars.

The unconfirmed planet has been designated the name EPIC 246251988 b. It is the largest of the three at almost four times the size of the Earth and is located some 1,200 light-years from Earth.

"These are the last chronologically observed planets by Kepler, but every bit of the telescope's data is incredibly useful," Incha said. "We want to make sure none of that data goes to waste, because there are still a lot of discoveries to be made."

Study abstract:

The Kepler space telescope was responsible for the discovery of over 2700 confirmed exoplanets, 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 yr 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. So far, no planets have been discovered in this data set because it only yielded about a week of high-quality data. Here, we report some of the last planet discoveries made by Kepler in the Campaign 19 dataset. We conducted a visual search of the week of high-quality Campaign 19 data and identified three possible planet transits. Each planet candidate was originally identified with only one recorded transit, from which we were able to estimate the planets’ radii and estimate the semimajor axes and orbital periods. Analysis of lower-quality data collected after low fuel pressure caused the telescope’s pointing precision to suffer revealed additional transits for two of these candidates, allowing us to statistically validate them as genuine exoplanets. We also tentatively confirm the transits of one planet with TESS. These discoveries demonstrate Kepler’s exoplanet detection power, even when it was literally running on fumes.