One in Five Stars Has Earth-sized Planet in Habitable Zone

W. M. Keck Observatory press release

Scientists from University of California, Berkeley, and University of Hawaii, Manoa, have statistically determined that twenty percent of Sun-like stars in our galaxy have Earth-sized planets that could host life. The findings, gleaned from data collected from NASA’s Kepler spacecraft and the W. M. Keck Observatory, now satisfy Kepler’s primary mission: to determine how many of the 100 billion stars in our galaxy have potentially habitable planets. The results are being published November 4 in the journal Proceedings of the National Academy of Sciences.

Early HR8799
Artist’s rendering of the planetary system HR 8799 at an early stage in its evolution. Credit: Dunlap Institute for Astronomy & Astrophysics
“What this means is, when you look up at the thousands of stars in the night sky, the nearest sun-like star with an Earth-size planet in its habitable zone is probably only 12 light years away and can be seen with the naked eye. That is amazing,” said UC Berkeley graduate student Erik Petigura, who led the analysis of the Kepler and Keck Observatory data.

“For NASA, this number – that every fifth star has a planet somewhat like Earth – is really important, because successor missions to Kepler will try to take an actual picture of a planet, and the size of the telescope they have to build depends on how close the nearest Earth-size planets are,” said Andrew Howard, astronomer with the Institute for Astronomy at the University of Hawaii. “An abundance of planets orbiting nearby stars simplifies such follow-up missions.”

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Super-Earth Detected in Habitable Zone of Nearby Star

W. M. Keck Observatory press release

An international team of scientists has discovered a potentially habitable super-Earth orbiting a nearby star. With an orbital period of about 28 days and a minimum mass 4.5 times that of the Earth, the planet orbits within the star’s “habitable zone,” where temperatures are neither too hot nor too cold for liquid water to exist on the planet’s surface. The researchers found evidence of at least one and possibly two or three additional planets orbiting the star, which is about 22 light years from Earth.

The researchers used public data from the European Southern Observatory and analyzed it with a novel data-analysis method. They also incorporated new measurements from the W. M. Keck Observatory’s High Resolution Echelle Spectrograph (HiRES) and the new Carnegie Planet Finder Spectrograph at the Magellan II Telescope. Their planet-finding technique involved measuring the small wobbles in a star’s motion caused by the gravitational tug of a planet.

The team includes UC Santa Cruz astronomers Steven Vogt and Eugenio Rivera and was led by Guillem Anglada-Escudé and Paul Butler of the Carnegie Institution for Science. Their work will be published by Astrophysical Journal Letters, and the manuscript will be posted online at

The host star is a member of a triple-star system and has a different makeup than our sun, with a much lower abundance of elements heavier than helium, such as iron, carbon, and silicon. This discovery indicates that potentially habitable planets can occur in a greater variety of environments than previously believed.

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