The newfound planet K2-288Bb, illustrated here, is slightly smaller than Neptune.
NASA's Goddard Space Flight Center/Francis Reddy
  • Scientists have used data from NASA's Kepler space telescope to discover a new planet that is twice as large as Earth.
  • Kepler died in October 2018, nine years after it launched.
  • The exoplanet, called K2-288Bb, is within its star's habitable zone, which means liquid water could exist on its surface.

Astronomers have discovered a planet twice the size of Earth, and it's within a zone that could allow liquid water to exist on its surface.

The finding comes from data from NASA's Kepler space telescope, which ran out of fuel in October 2018.

K2-288Bb, as the new planet is called, is located within its star's habitable zone, which is why liquid water is a possibility.

Its size is unusual for an exoplanet (the term for a planet that orbits a star outside our solar system). Few planets that orbit close to their stars are more than 1.5 times as large as Earth, yet K2-288Bb is estimated to be roughly 1.9 times the size of our planet.

"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," University of Chicago graduate student Adina Feinstein, the lead author of a paper on the discovery, said in a NASA news release.

According to NASA, the planet is half the size of Neptune and could be gas-rich, though it's possible that it's rocky instead. K2-288Bb is located in the Taurus constellation and is about 226 light-years away.

The new planet orbits the smaller of two cool stars in the stellar system called K2-288. These stars are about 5.1 billion miles apart, and the dimmer one is one-third as massive as the sun. NASA said the brighter star is half the size of the sun.

An illustration of NASA's Kepler space telescope.

Kepler, which died nine years after launching into space, has discovered more than 2,600 confirmed planets. About 50 of them may be the same size and temperature as Earth.

Data from Kepler has helped scientists determine whether a given planet has a solid surface, like Earth, or a gaseous one, such as Jupiter. Narrowing the options down in that way increases the odds of finding Earth-like planets that may harbour life.

Since Kepler is no longer hunting for planets, NASA is now hoping that a new space telescope will aid in the search: the Transiting Exoplanet Survey Satellite (TESS). TESS began its two-year mission in April 2018, and scientists say it will examine 200,000 nearby stars as it looks for rocky, Earth-size planets.

"We learned from Kepler that there are more planets than stars in our sky, and now TESS will open our eyes to the variety of planets around some of the closest stars," Paul Hertz, the director of NASA's astrophysics division, said in March 2018. "TESS will cast a wider net than ever before for enigmatic worlds."

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