Astronomers Have Discovered a Super Earth in the Habitable Zone

Using data from NASA's Kepler space telescope, two NASA interns and a team of amateur astronomers have found a new 'super Earth'. Roughly twice the size of Earth, and known as K2-288Bb, the new world is located within its star's habitable zone, raising hopes it could contain life. It is 226 light-years away in the constellation Taurus, and could be rocky or could be a gas-rich planet similar to Neptune, NASA says. Its size is rare among exoplanets - planets beyond our solar system.

“It's a very exciting discovery due to how it was found, its temperate orbit and because planets of this size seem to be relatively uncommon,” said Adina Feinstein, a University of Chicago graduate student, who is also the lead author of a paper describing the new planet accepted for publication by The Astronomical Journal.

The planet lies in a stellar system known as K2-288, which contains a pair of dim, cool stars separated by about 5.1 billion miles (8.2 billion kilometers) - roughly six times the distance between Saturn and the Sun. The brighter star is about half as massive and large as the Sun, while its companion is about one-third the Sun's mass and size, NASA says.

The new planet, K2-288Bb, orbits the smaller, dimmer star every 31.3 days. The discovery was made made when, in 2017, Feinstein and Makennah Bristow, an undergraduate student at the University of North Carolina Asheville, worked as interns with Joshua Schlieder, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. 

They searched Kepler data for evidence of transits, the regular dimming of a star when an orbiting planet moves across the star's face. Examining data from the fourth observing campaign of Kepler's K2 mission, the team noticed two likely planetary transits in the system. 

But scientists require a third transit before claiming the discovery of a candidate planet, and there wasn't a third signal in the observations they reviewed. However, it later turned out the team wasn't actually analyzing all of the data. In Kepler's K2 mode, which ran from 2014 to 2018, the spacecraft repositioned itself to point at a new patch of sky at the start of each three-month observing campaign.

Astronomers were initially concerned that this repositioning would cause systematic errors in measurements, so ignored the first few days of observations.On re-examining it, they found the data needed to confirm the exoplanet.   The re-processed data were posted directly to Exoplanet Explorers, a project where the public searches Kepler's K2 observations to locate new transiting planets. 

In May 2017, volunteers noticed the third transit and began an excited discussion about what was then thought to be an Earth-sized candidate in the system, which caught the attention of Feinstein and her colleagues.

“That's how we missed it - and it took the keen eyes of citizen scientists to make this extremely valuable find and point us to it,” Feinstein said.

The team began follow-up observations using NASA's Spitzer Space Telescope, the Keck II telescope at the W. M. Keck Observatory and NASA's Infrared Telescope Facility (the latter two in Hawaii), and also examined data from ESA's (the European Space Agency's) Gaia mission.