sciencetech-blog

comments

Despite being crippled in space, Kepler has managed to discover a star that hosts three Earth-sized planets.

The outermost planet orbits in the 'Goldilocks' zone - a region where surface temperatures could be moderate enough for liquid water and perhaps life to exist.

At a distance of 150 light years, the star ranks among the top 10 nearest stars known to have transiting planets.

Scroll down for video 

After the Kepler Space Telescope lost two if its four reaction wheels, it was unable to point accurately enough for long observations. Despite being hobbled in space, Kepler has managed to discover a star that hosts three planets only slightly larger than Earth

The star, EPIC 201367065, is a cool red M-dwarf about half the size and mass of our own sun.

Its distance means it's bright enough for astronomers to study the planets' atmospheres to determine whether they are like Earth's atmosphere and possibly conducive to life.

'A thin atmosphere made of nitrogen and oxygen has allowed life to thrive on Earth,' said Ian Crossfield, the University of Arizona astronomer who led the study.

'But nature is full of surprises. Many exoplanets discovered by the Kepler mission are enveloped by thick, hydrogen-rich atmospheres that are probably incompatible with life as we know it.'

This cartoon shows the three newly discovered extrasolar planets (right) casting shadows on their host star that can been seen as eclipses, or transits, at Earth (left). Earth can be detected by the same effect, but only in the plane of Earth's orbit (the ecliptic)

The three planets are 2.1, 1.7 and 1.5 times the size of Earth.

The outermost planet, at 1.5 Earth radii, is the smallest of the group and orbits far enough from its host star that it receives levels of light from its star similar to those received by Earth from the sun. 

'Most planets we have found to date are scorched. This system is the closest star with lukewarm transiting planets,' Eric Petigura a UC Berkeley graduate student who made the discovery.

'There is a very real possibility that the outermost planet is rocky like Earth, which means this planet could have the right temperature to support liquid water oceans.'

University of Hawaii astronomer Andrew Howard said that extrasolar planets are discovered by the hundreds these days, though many astronomers are left wondering if any of the newfound worlds are really like Earth.

The newly discovered planetary system will help resolve this question, he said.

'We've learned in the past year that planets the size and temperature of Earth are common in our Milky Way galaxy,' Professor Howard said.

'We also discovered some Earth-size planets that appear to be made of the same materials as our Earth, mostly rock and iron.'

The next step will be observations with other telescopes, including the Hubble Space Telescope, to take the fingerprint of the molecules in the planetary atmospheres.

If these warm, nearly Earth-size planets have puffy, hydrogen-rich atmospheres, Hubble will see the tell-tale signal.

The Goldilocks zone is the belt around a star where temperatures are ideal for liquid water to pool on a planet

Kepler: NASA's mission to find habitable planets

The discovery is all the more remarkable, the researchers said said, because the Kepler telescope lost two reaction wheels that kept it pointing at a fixed spot in space.

Kepler was reborn in 2014 as 'K2' with a clever strategy of pointing the telescope in the plane of Earth's orbit, the ecliptic, to stabilise the spacecraft.

Kepler is now back to mining the cosmos for planets by searching for eclipses or 'transits,' as planets pass in front of their host stars and periodically block some of the starlight.

'This discovery proves that K2, despite being somewhat compromised, can still find exciting and scientifically compelling planets,' said Professor Petigura.

Kepler sees only a small fraction of the planetary systems in its gaze: those with orbital planes aligned edge-on to our view from Earth. Planets with large orbital tilts are missed.

A census of Kepler planets that the team conducted in 2013 corrected statistically for these random orbital orientations, and concluded that one in five sun-like stars in the Milky Way Galaxy have Earth-size planets in the habitable zone.

Accounting for other types of stars as well, there may be 40 billion such planets galaxy-wide.

 Kepler sees only a small fraction of the planetary systems in its gaze: those with orbital planes aligned edge-on to our view from Earth. Planets with large orbital tilts are missed. Pictured is an artist's impression of an Earth-like planet orbiting a star that has formed a planetary nebula