NASA's Kepler Mission K2 team announced the discovery of another new world today, two months after the Kepler spacecraft ran out of fuel on October 30th, and ended its mission after nine years, during which it discovered 2,600 confirmed planets around other stars - the bulk of those now known - along with thousands of additional candidates astronomers are working to confirm.
HD 21749b orbits a star, about the size of the sun, 53 light years away. That is fast by Earth standards, but the other two planets include Pi Mensae b with a 6.3-day orbit and LHS 3844b that orbits its star at a blistering pace of once every 11 hours. The team, however, needed at least three transits to claim the discovery of a candidate planet and they did not find a third signal in the observations they reviewed. It's very hard to find small planets that orbit farther from their stars, and are therefore cooler. "If confirmed, it will be the smallest planet we have found to date", study co-author Chelsea Huang, a colleague of Dragomir's at the MIT Kavli Institute, said today during a briefing at the American Astronomical Society's winter meeting in Seattle.
Its size, three times that of Earth, makes it a sub-Neptune - but it's also 23 times as massive as Earth.
Scientists said the system may hold an additional planet that is about the size of Earth that has an orbit of only eight days.
The new world, known as K2-288Bb, could be rocky or could be a gas-rich planet similar to Neptune.
"We think this planet wouldn't be as gaseous as Neptune or Uranus, which are mostly hydrogen and really puffy", Dragomir said. "The planet likely has a density of water, or a thick atmosphere".
Researchers have also detected evidence of a second planet, with a shorter, 7.8-day orbitin the same planetary system, though it is yet to be confirmed.
The exoplanet, known as K2-288Bb, is about twice the size of Earth and orbits within the habitable zone of its star, meaning liquid water may exist on its surface.
Since it launched in April 2018, TESS, an MIT-led mission, has been monitoring the sky, sector by sector, for momentary dips in the light of about 200,000 nearby stars. K2-288Bb orbits this smaller and dimmer star every 31.3 days.
The planet is in the K2-288 system, which contains a pair of dim, cool M-type stars that are 5.1 billion miles apart, about six times the distance between Saturn and the sun.
To complicate matters, the star itself is relatively active, and Dragomir wasn't sure if the single transit she spotted was a result of a passing planet or a blip in stellar activity. "But we had this one transit, and knew something was there".
As it turned out, though, the team wasn't actually analyzing all of the data. "TESS found as many in its first month".
Astronomers are now conducting follow-up observations on more than 280 exoplanet candidates.
He continued: "Re-orienting Kepler relative to the Sun caused minuscule changes in the shape of the telescope and the temperature of the electronics, which inevitably affected Kepler' sensitive measures in the first days of each campaign".
The Trappist-1 star system, which hosts a record seven Earth-like planets, was one of the biggest discoveries of 2017.
The discoveries of a new planet and several supernovae are exciting enough and what's to come should give us even more information about the phenomena already discovered. More than a dozen universities, research institutes, and observatories worldwide are participants in the mission.