Kepler releases new catalog of planet candidates

Mar 06, 2012 By Michele Johnson
The histogram summarizes the findings in the Feb. 27, 2012 Kepler Planet Candidate catalog release. The catalog contains 2,321 planet candidates identified during the first 16 months of observation conducted May 2009 to September 2010. Of the 46 planet candidates found in the habitable zone, the region in the planetary system where liquid water could exist, ten of these candidates are near-Earth-size. Credit: NASA Ames/Wendy Stenzel

Since science operations began in May 2009, the Kepler team has released two catalogs of transiting planet candidates. The first catalog (Borucki et al, 2010), released in June 2010, contains 312 candidates identified in the first 43 days of Kepler data. The second catalog (Borucki et al, 2011), released in February 2011, is a cumulative catalog containing 1,235 candidates identified in the first 13 months of data.

Today the team presents the third catalog containing 1,091 new planet candidates identified in the first 16 months of observation conducted May 2009 to September 2010. These are the same candidates that the team discussed at the Science Conference held at Ames Research Center in December 2011.

Here are the highlights of the new catalog:

• Planet candidates smaller than twice the size of Earth increased by 197 percent, compared to 52 percent for candidates larger than twice the size of Earth.

• Planet candidates with orbital periods longer than 50 days increased by 123 percent, compared to 85 percent for candidates with orbital periods shorter than 50 days.
Since the last catalog was released in February 2011, the number of planet candidates identified by Kepler has increased by 88 percent and now totals 2,321 transiting 1,790 stars.

The cumulative catalog now contains well over 200 Earth-size planet candidates and more than 900 that are smaller than twice Earth-size. Of the 46 planet candidates found in the habitable zone, the region in the planetary system where liquid water could exist, ten of these candidates are near-Earth-size.

The number of planetary systems found with more than one planet candidate also has increased. Last year, 17 percent, or 170 stars, had more than one transiting planet candidate. Today, 20 percent, or 365, stars have more than one.

"With each new catalog release a clear progression toward smaller planets at longer orbital periods is emerging, " said Natalie Batalha, Kepler deputy science team lead at San Jose State University in California. "This suggests that Earth-size planets in the habitable zone are forthcoming if, indeed, such planets are abundant."

Nearly 5,000 periodic transit-like signals were analyzed with known spacecraft instrumentation and astrophysical phenomena that could masquerade as transits, which can produce false positives. The most common false positive signatures are associated with eclipsing binary stars- a pair of orbiting stars that eclipse each other from the vantage point of the spacecraft.

The Kepler space telescope identifies by repeatedly measuring the change in brightness of more than 150,000 stars in search of planets that pass in front, or "transit," their host star. Kepler must record at least three transits to verify a signal as a planet.

The findings are published in the "Planetary Candidates Observed by Kepler III: Analysis of the First 16 Months of Data". The catalog is available at the Kepler data archive at the Space Telescope Science Institute and can be downloaded from the NASA Exoplanet Archive.

NASA's Ames Research Center in Moffett Field, Calif., manages Kepler's ground system development, mission operations and science data analysis. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., managed the Kepler mission's development.

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More information: For information about the Kepler Mission, visit: www.nasa.gov/kepler

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User comments : 6

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baudrunner
not rated yet Mar 06, 2012
Gravity is a function of mass, so the fact that a planet is much larger than Earth should not preclude the existence of life upon it. Were gravity a function of volume, I would have to revisit my personal understandng of the fundamental nature of reality.
Deathclock
1 / 5 (1) Mar 06, 2012
Yes, and mass is a function of volume and density... Unless your giant planet is made of gas it will have very high gravity compared to Earth. If it is made of gas then that certainly doesn't preclude the possibility of life, but it won't be recognizable to use.
nkalanaga
5 / 5 (1) Mar 06, 2012
Gravity is proportional to Mass (M) / radius squared (R^2)
Volume (V) is proportional to R^3
For a constant density V = M
Therefore gravity would be proportional to V/(R^2)= (R^3)/(R^2) = R. Twice the radius, twice the gravity.

In the real world, given the same material, at planetary scales, density increases with mass, although the increase is relatively slow. Thus, increasing the radius will cause gravity to increase slightly faster. But, for more-or-less Earth-sized rock/metal planets, gravity = radius is a good lower limit.
TopherTO
5 / 5 (1) Mar 06, 2012
I like planets.
Birger
not rated yet Mar 07, 2012
The problem with bigger planets is that volume increases faster than area...There is a risk that oceans get too thick for any volcanic islands to reach the surface.

Also, if the internal heat builds up fater than it can be lost, the system will stabilise with rather small tectonic plates creating different conditions than on the young Earth. See the book by John S. Lewis: "Worlds Without End".
nkalanaga
not rated yet Mar 07, 2012
Both true, at least according to current theories. On the other hand, in simulations, the water content of "Earth" varied from 0.01 to 100 times actual, even given the same starting conditions. So we still don't know if Earth is "normal", or drier/wetter than normal, for a planet of its size and location. If we're wetter than most planets our size, larger planets may have shallower oceans than expected.

Internal heat, on the other hand, is likely to be similar for all planets of a given size, so that could be a bigger problem. If it is a problem, which we still don't know, as we only have one tectonically active planet to study.

But, given our current knowledge and theories, Birger is right.