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NASA’s Kepler Mission Discovers Bigger, Older Cousin to Earth

artist's concept depicts one possible appearance of the planet Kepler-452b,

In a press conference this morning (2015 July 23), NASA's Kepler team announced discovery of planet Kepler-452b which has the closest match of planet characteristics to Earth: 60% larger than Earth, orbiting a Sun-like star in a 385 day orbit period, that puts it in the star's habitable zone. [Kepler confirmed planet count is now 1030.]

The team also announced a new Kepler planet catalog with 4696 planet candidates (521 more than previous catalog).

Exoplanet missions

Notes from the Press Conference [taken by Alan Gould, Kepler Mission Education Team]:

  • John Grunsfeld, astronaut and associate administrator for NASA's Science Mission Directorate in Washington
  • Jon Jenkins, Kepler data analysis lead at NASA's Ames Research Center in Moffett Field, California
  • Jeff Coughlin, Kepler research scientist at SETI Institute in Mountain View, California
  • Didier Queloz, co-discoverer of first exoplanet in 1995, professor of astrophysics at Cambridge University, United Kingdom

John Grunsfeld introduced with context of the significance of this discovery in terms of the age old question--one that as children we ask as we lie gazing up at the stars: do those stars have planets with life like Earth does? He also set the context of Kepler Mission as just the first step in a series of future missions to find other planets like Earth:

  • Transiting Exoplanet Survey Satellite (TESS)
  • James Webb Space Telescope (JWST)
  • Wide-Field Infrared Survey Telescope (WFIRST-AFTA)
  • New Worlds Telescope (large Starshade occulter to block the light of stars to observe their planets)

small, habitable planets in the last six years.

Jon Jenkins gave details of the discovery of Kepler-452b which he said is the closest analog to the Earth-Sun system to date in terms of the type of star and the placement of the planet in this system. He mentioned that in December of 2011 we found Kepler-20e which was smaller than Earth, but very close to its star--way to hot for life. Later there was Kepler-22b that was in the habitable zone of a Sun-like star, but twice the size of Earth. Kepler-186f was very near the size of Earth and in the habitable zone of its star, but the star is an M-dwarf, much cooler than the Sun.

size and scale of the Kepler-452 system compared alongside the Kepler-186 system and the solar system

Kepler-452b orbits a star very similar to the Sun, and the planet is about 60% larger than Earth, with a surface gravity 2x that of Earth, and a slightly better than even chance of being a rocky planet, with an atmosphere likely thicker than Earth's, and possibly with active volcanoes. Its 385 day orbit puts it at a distance from its star that would be suitable for the existence of liquid water.

A diagram showed that Kepler-452b may be about 1.5 billion years older than Earth, giving that much more time for life to have evolved there.

Age of Kepler-452b compared with Earth

Jeff Coughlin announced the release of the latest Kepler catalog of planets (the 7th release) that has 4696 planet candidates, 12 of which are small planets in their stars' habitable zone, and 521 more than the previous catalog release. He told of how the planet-finding automation software had become more and more refined to permit not the first automation step that had been used in the past, but automating the second step of reassessment that in the past had been done by painstaking human analysis.

Kepler's dozen small planets in habitable zone

There are more great results yet to come: the full archive is available for new observations and discoveries and an 8th catalog will be produced in about a year.

Didier Queloz remarked that it is now 20 years since the discovery of 51 Peg b (Oct 6, 1995), and that in the early 20th century there was even a theory that formation of planets is caused by stellar collisions and would be very rare, since stellar collisions are rare. Kepler discoveries prove that wrong and that most stars have planets.

Artist concepts of 51 Peg b and Kepler-452b

More comments made in Question and Answer period:

Artwork depicting the appearance of Kepler-452b is based on advice from planetary scientist Bill Moore.

Uncertainty in age of Kepler-452b is large: about ± 2 billion years.

The previous "closest cousin" of Earth was Kepler-186f, but it was orbiting a star much smaller and cooler than the Sun (an M dwarf star).

Jon Jenkins said that the planet would be "pretty much like home in terms of the sunshine you'd experience."

In answer to the question "Could we survive in gravity 2x Earth's?" ...Jenkins said it's likely we could adapt, and Grunsfeld commented that astronauts coming back from space say "gravity really sucks" but they quickly adapt. We'd get stronger everyday. [Of course life that evolved on the planet, if there is any, would be adapted from the get-go.]

new planet candidates from the seventh Kepler planet candidate catalog that are less than twice the size of Earth and orbit in the stars' habitable zone
The star is a little bigger and brighter than the Sun, so it's good that the planet is slightly farther from its star than Earth is from the Sun.

Distance to Kepler-452b: about 1400 light-years.
It's mass is not known, since the star is too dim for there to be radial velocity measurements made, but estimates from similar planets are that it might be about 5 Earth masses ±2.

About 15-25% of planets are roughly Earth size. Smaller planets are way more common than the larger planets.

Regarding the K2 Mission that has been in operation since not too long after the primary mission ended with failure of 2 of the 4 reaction wheels needed for precise aiming, Jenkins said that its performance has been phenomenal. "It's the best worst thing that could possibly have happened." The first 4 K2 campaigns are successfully done and we're about to start on Campaign 5. Campaign 9 will focus on the Milky Way galactic bulge and there will be special efforts involving micro-lensing observations.

Data used in Kepler-452b discovery spanned from June 2009 to May 2013, very nearly 4 years of data.

Ground-based followup of stars is crucial. In the case of Kepler-452b, when it was first identified as a planet candidate, it was computed to have a radius 1.1 times Earth, but subsequent ground based observations of the star indicated the star was significantly larger, resulting in the computed planet radius going up from 1.1 to 1.6 Earth radii.

In response to a question about what are the chances we can travel to the planet, the answer was that Kepler provides only a first step. TESS will identify Earth-size planets closer to Earth.

Artist impression of the surface of Kepler 452b.
Artist impression of the surface of Kepler 452b. With a radius 60% larger than Earth, the planet has a better than even chance of having a rocky composition, and is likely to have a thick atmosphere and a significant amount of water. Because we can’t yet measure the mass of Kepler 452b, astronomers rely on models to estimate a range of possible masses, with the most likely being 5 times that of Earth. Such a massive rocky planet would likely still have active volcanism. Kepler 452b is orbiting a close cousin of our Sun, but one that is 1.5 billion years older. In the scenario depicted here, the planet is just entering a runaway greenhouse phase of its climate history. The increasing energy from its aging sun could be evaporating any oceans, leaving behind large lakes ringed with mineral deposits. Kepler 452b could be giving us a preview of what the Earth will undergo more than a billion years from now, as the Sun ages and grows brighter.
Credit: Danielle Futselaar - SETI Institute

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