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Kepler and star and planets
An artist’s conception shows NASA’s Kepler telescope observing four planets as they pass across the disk of their parent star. The comparative sizes of the spacecraft and the star are not to scale. (Credit: NASA / JPL)

Astronomers say they’ve confirmed the existence of 104 worlds to add to the list of extrasolar planets detected by NASA’s Kepler K2 mission, and at least two of them appear to be potentially habitable super-Earths.

The two prospects are among four planets orbiting K2-72, a red dwarf (or M dwarf) star that’s 181 light-years away in the constellation Aquarius.

All four of the planets are between 20 and 50 percent wider than Earth. They all come closer to K2-72 than Mercury comes to our own sun. But because the red dwarf is so much cooler than our sun, the worlds known as K2-72c and K2-72e lie in the star system’s habitable zone. That means it’s conceivable that liquid water could exist on those planets.

K2-72c makes a complete orbit of its sun every 15 Earth days and is thought to be about 10 percent warmer than Earth. K2-72e is farther out: It has a 24-day orbit and should be about 6 percent cooler than Earth.

Study leader Ian Crossfield, who works at the University of Arizona’s Lunar and Planetary Laboratory, said he couldn’t rule out the possibility of life arising in such red dwarf environments.

“Because these smaller stars are so common in the Milky Way, it could be that life occurs much more frequently on planets orbiting cool, red stars rather than planets around stars like our sun,” Crossfield said today in a news release.

The K2-72 planets, and 100 other worlds, were on a list of 197 initial planet candidates taken from the K2 mission’s database. The Kepler space telescope detected those candidates by spotting telltale dips in the intensity of starlight from their parent suns. However, other means had to be employed to confirm that they were really planets and not some other type of phenomenon, such as a double-star system.

Follow-up observations were made using Earth-based telescopes, such as the North Gemini telescope and the Keck Observatory in Hawaii, the Automated Planet Finder in California and the Large Binocular Telescope in Arizona. The confirmation for the 104 planets is reported in a research paper published online as part of the Astrophysical Journal Supplement Series.

The Kepler spacecraft suffered a serious breakdown in its navigational system in 2013, and for a while it looked as if the mission was lost. But engineers soon came up with a clever fix that allowed the Kepler team to resume their planet-hunting ways over a wider swath of the sky. The revived mission was dubbed K2.

“The K2 mission allows us to increase the number of small, red stars by a factor of 20, significantly increasing the number of astronomical ‘movie stars’ that make the best systems for further study,” Crossfield said.

If Kepler hadn’t had its breakdown, K2-72’s planets would never have been detected.

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