NASA’s Kepler Spies 3 New “Goldilocks” Planets

Relative sizes of the newly discovered habitable-zone planets and Earth. Left to right: Kepler-69c, Kepler-62e, Kepler-62f and Earth (except for Earth, these are artists’ renditions). Image credit: NASA Ames/JPL-Caltech

NASA’s Kepler Mission proves once again that Earth has relatives or at least good friends. The agency announced the discovery today of three new super-Earth-size planets around two different stars. All three are rocky planets orbiting within their host stars’ “Goldilocks Zone”, a region neither too hot nor too cold but just right for liquid water to exist on a planet’s surface.

The diagram compares the planets of the inner solar system to Kepler-62, a five-planet system about 1,200 light-years from Earth in the constellation Lyra. The three inner planets orbit so close to the host star, they’re too hot to be in the Goldilocks Zone. Credit: NASA Ames/JPL-Caltech

Two of the new planets – Kepler-62e and 62f – circle the star Kepler-62 along with three other planets for a total of five in the system; Kepler-69c, the third super-Earth, orbits Kepler-69 along with one additional planet. Kepler-62 is only 2/3 the size of the sun, 1/5 as bright and resides 1,200 light years away in the constellation Lyra the Harp. Kepler-62 is slightly smaller and less luminous than the sun and lies 2,700 light years from Earth in Cygnus the Swan.

The diagram compares the planets of the inner solar system to Kepler-69, a two-planet system about 2,700 light-years from Earth in the constellation Cygnus. The two planets of Kepler-69 orbit a star that belongs to the same class as our sun, called G-type. Credit: NASA Ames/JPL-Caltech

Here are the specs on the super-Earths, defined as planets with masses greater than Earth but less than that of the planets Uranus and Neptune which are about 15 times more massive than Earth:

* Kepler-69c — 70% larger than Earth, the smallest yet found in the habitable zone of a sun-like star. It circles its sun in 242 days with an orbit similar to that of Venus.

* Kepler-62e —  60% larger than Earth, orbits every 122 days in the the habitable zone’s inner edge.

* Kepler-62f — 40% larger than Earth, the smallest known habitable zone exoplanet, orbits every 267 days.

Although some 871 exoplanets have been discovered to date only 10 have been found in their host stars’ habitable zones. Since mission start on April 8, 2009, Kepler has detected 2,740 candidates of which 122 have been confirmed. Planets are becoming as common as rabbits it would seem.

Kepler watches for dips in a star’s brightness when a planet transits or crosses in front of it.

Kepler uses the transit method to spy its new planets, keeping a constant eye on more than 150,000 stars in Cygnus and Lyra just waiting for a planet to transit or pass in front of one of them. The resulting dip in the brightness of the star reveals the planet’s size relative to its host. Based on information we read in a star’s light using a spectrograph, we can estimate the star’s size and then calculate the planet’s size. Three successful transits are required to become a planet candidate. Earth-based telescopes then perform follow-up observations to confirm Kepler’s results.

The significance of today’s announcement is simple. With every new potentially habitable planet discovered, we learn more about how Earth fits in. How long will our blue globe remain unique as planet finding turns from trickle to torrent?

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3 Responses

  1. WolfGF

    Any idea why are we studying such distant stars first? Or have we determined that some of the closest stars, like Alpha Centauri, don’t have planets in the Golilocks zone?

    1. astrobob

      Kepler is only one of many instruments used in hunting exoplanets. It’s designed with a wide field of view to simultaneously observe as many stars as possible at one time (observations are made every 30 minutes of more than 150,000 stars.) Some of the stars will happen to be close, others far. It stares at a piece of the Milky Way – rich in stars – far from the plane of the planets so it never has to deal with the sun coming into the field of view or the majority of asteroids.

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