The number of confirmed exoplanets found by the Kepler space telescope has increased again, by 41. The planets, which orbit 20 different stars, range in size from about the same size as Earth to more than seven times Earth’s radius.
Not too long ago, the Kepler space telescope discovered the first exoplanet which orbited two binary stars (a circumbinary star system). Such planets had been thought possible, but this was the first confirmed detection of a world reminiscent of the planet Tatooine in the Star Wars films, a planet with a double sunrise and double sunset.
As the number of exoplanets being found by the Kepler space telescope continues to grow into the thousands, it can start to feel overwhelming (in a good way though). So many worlds found so far, and many more, probably millions, waiting to be discovered.
The Kepler planetary candidates are of a wide variety, orbiting different kinds of stars. Some are large gas giants like Jupiter or Saturn, and others are small and rocky, like Earth. The most current observations now suggest that they are common in the universe, maybe even outnumbering the stars themselves.
The Kepler space telescope has been finding a wide variety of alien worlds, as well as solar systems that they reside in. In our own solar system, the planets are in nice, neat orbits which are aligned with the Sun’s equator, consistent with the idea that they formed from a relatively flat, spinning disk of gas and dust around the Sun billions of years ago.
So far, other solar systems found haven’t tended to follow that pattern. Did that mean our solar system was a fluke? But now, Kepler has found one, about 10,000 light-years away. Scientists at MIT, the University of California at Santa Cruz and other institutions made the discovery from analysis of Kepler data.
The longer the Kepler mission keeps searching for exoplanets, the more amazing discoveries it makes. The Kepler mission team just released their third catalogue of new planetary candidates – 1,091 to be exact. This bring the total number of planetary candidates found by Kepler so far to 2,321, which orbit 1,790 stars. Confirmed planets so far now number 760, from Kepler and other telescopes.
These are the same candidates which had been previously discussed at the Kepler Science Conference last December, but now the official catalogue is available to the public.
A primary goal of Kepler is to find out how many planets among the stars being studied are Earth-sized and how many orbit within a star’s “habitable zone” where it would be possible for liquid water to exist. Ideally, planets which fit both criteria would be the “holy grail” of the mission.
Over 200 Earth-sized planets have now been added to the catalogue, and over 900 planets that are less than twice the size of Earth. There are also 46 planets in the habitable zone, and of these, ten are Earth-sized.
With the latest results, the number of planets found that are less than twice the size of Earth increased by 197%. Planets larger than twice the size of Earth, however, increased by 52%. This confirms the earlier trends seen that smaller rocky planets outnumber larger gas or ice giants.
There are also more multi-planet systems being discovered; 20% of the stars studied compared to 17% last year.
One of the Earth-sized planetary candidates found would seem to be of particular interest – KOI-494.01. It is still awaiting final confirmation, but the data so far support it being a real planet. It is estimated to have a mass 15% greater than Earth and a radius only 5% greater. The mean surface temperature is now estimated to be only about 1 ºC (33.8 ºF) cooler than on Earth. The estimated mean surface temperature (Ts) of KOI-494.01 is listed at 287 K (14 ºC / 56.93 ºF). Not bad!
According to the Earth Similarity Index (ESI), an estimated measure of how similar a planet is to Earth, KOI-494.01 now has an ESI rating of 99%. In the previous catalogue, it was listed at 97%. The confirmed planet with the highest rating so far is Gliese 667Cc, at 85%.
There is also a growing list of other Earth-sized candidates with ESI ratings close to that of KOI-494.01. See the summary lists here, updated March 3, 2012.
According to Natalie Batalha, Kepler deputy science team leader at San Jose State University in California, “With each new catalog release a clear progression toward smaller planets at longer orbital periods is emerging. This suggests that Earth-size planets in the habitable zone are forthcoming if, indeed, such planets are abundant.”
The updated findings continue the trend of exoplanets which are smaller like Earth, some of which orbit in their stars’ habitable zones. While these are likely to be of a wide variety, depending on other factors like composition, star type, etc., the discovery of planets like KOI-494.01 is an encouraging sign that there may indeed be other worlds out there similar to our own.