Astronomers find possible near-Earth-like planet in archived Kepler data

Most of the exoplanets found by the Kepler space telescope are Neptune-size worlds orbiting close to their host stars where temperatures are too extreme for water, a key ingredient for life, to exist as a liquid (bottom left). Nearly all the Earth-size planets found in habitable zones orbit close to small red dwarf stars that may, or may not, be conducive to life (bottom right). KOI-456.04, while larger than Earth, orbits in the sweet spot of a very Sun-like star (upper right). Image: MPS/René Heller (adapted by Astronomy Now)

Astronomers have found evidence for an exoplanet less than twice the size of Earth orbiting a very Sun-like star at a distance almost identical to Earth’s, completing one orbit every 378 days in the heart of the host sun’s habitable zone where temperatures would be conducive to the presence of liquid water and, possibly, life.

The planet, dubbed KOI-456.04, was found using a novel statistical analysis of archived data from NASA’s now-retired Kepler space telescope, not by direct observation of the host star’s dimming as the planet transited the disc of its host as viewed from Earth. But the researchers say they have high confidence – 85 percent – the world actually exists.

If so, KOI-456.04 would represent one of the closest analogues of the Earth-Sun system yet found, a planet receiving 93 percent of the sunlight Earth enjoys.

“KOI-456.04 is relatively large compared to many other planets that are considered potentially habitable,” said René Heller, lead author of a study describing the system. “But it’s the combination of this less-than-double the size of the Earth planet and its solar-type host star that make it so special and familiar.”

Located some 3,000 light years from the Sun in the constellation Lyra, the star in question, known as Kepler-160, has a surface temperature of 5,200 degrees Celsius and a very Sun-like luminosity. The presumed exoplanet has a radius 1.9 times that of Earth and receives roughly the same levels of sunlight in similar colours.

Most terrestrial, roughly Earth-size worlds found to date orbit small red dwarf stars. Planets orbiting in the habitable zones of such stars are much closer to their hosts, bathed in infrared radiation, possibly subjected to sterilising solar flares and gravity-driven tidal heating that could trigger bouts of global volcanism.

“The full picture of habitability … involves a look at the qualities of the star, too,” says Heller.

About 4,000 exoplanets have been discovered to date by observing a star’s wobble as the gravity of one or more planets tug them from side to side or by monitoring a star’s brightness for the tell-tale dimming that occurs when a planet moves in front of its host as viewed from Earth. The Kepler space telescope used the latter transit methodology.

Kepler-160 was already known to host two large exoplanets orbiting close to their star. Heller, co-author Michael Hippke and researchers with the Max Planck Institute for Solar System Research, the Sonneberg Observatory, the University of Göttingen, the University of California in Santa Cruz and NASA developed an improved search algorithm to tease out data indicating the presence of two previously undetected exoplanets.

One of those, Kepler-160d, was suspected earlier based on a subtle distortion in one of the confirmed planet’s orbit. The other was KOI-456.04.

“Our improvement is particularly important in the search for small, Earth-sized planets”, Heller said. “The planetary signal is so faint that it’s almost entirely hidden in the noise of the data. Our new search mask is slightly better in separating a true exoplanetary signal from the noise in the critical cases.”

Direct confirmation could come from the European Space Agency’s Plato mission or from next-generation space and ground-based telescopes.