exploring alien worlds

Is Kepler getting close to finding another Earth?

Size comparisons of Kepler planetary candidates. Credit: NASA Ames/Wendy Stenzel

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.

This article was first published on


  1. I understand from the news media that KOI-494.01 has an orbit of 25 days. That is really fast. Wouldn’t it has an affect on the habitability of the planet?

    • The human race uses mostly caborn combustion to convert 4 tons of matter per year to energy to provide power for its planet wide industry. The sun which masses 2,000 trillion trillion tons converts 19,565 trillion tons of hydrogen into helium each year. This produces converts 134.8 trillion tons of matter to energy each year which is radiated into space. 61,163 metric tons of that energy is intercepted by the Earth each year.To send the equivalent of Yuri Gagarin or John Glenn to Canopus (310 ly) or Deneb (350 ly) at one gravity requires 8,000 tonnes to 10,000 tonnes of massenergy to move a 10 metric ton capsule one way. It requires between 64 million and 100 million metric tons of massenergy to send the capsule on a two way journey without tapping into the destination’s energy sources. There are several things we can say about this. (1) WE MUST USE SOLAR SYSTEM RESOURCES TO TRAVEL TO THE STARS: Increasing our handling of energy and resources on Earth will not provide the 2,000 fold increase in the needed levels for star travel as easily as tapping into the resources of the Solar system. (2) WE MUST LIFE IN SPACE TO TRAVEL TO THE STARS: Building space colonies that mass about 40 tons to 100 tons per resident and living in space long-term, processing local resources at the destination, whether the colony returns or not, pays huge dividends in energy reduction. (3) WE MUST USE ADVANCED ENERGY TECHNOLOGIES: Chemical combustion and fusion will do little to assist us in traversing the interstellar gulfs. There are three near term technologies that process enough energy to take us to the stars. (3a) Solar pumped laser and laser light sail Light sails have infinite specific impulse. Lightweight concentrators with thin disk lasers operating near the Sun, convert their weight into usable energy every year. This is sufficient to send considerable payloads to the stars. (3b) Anti-matter fired photon rockets Anti-matter flashes into energy with high efficiency when combined with normal matter. Anti-matter is produced in large quantities in certain solar flares. Capturing anti-matter on an industrial scale is possible with an appropriately designed satellite. Such satellites convert solar energy to anti-matter at a rate approaching 10 tons of massenergy per year for each ton of satellite. (3c) Synthetic black holes Famous physicist Stephen Hawking showed that through the Unruh effect, black holes had a temperature. The smaller the black hole, the higher the temperature. Black holes ranging from a few grams to a few kilograms are highly efficient high temperature sources of energy for this reason. Collections of synthetic black holes, if they can be made, convert matter efficiently to energy and are in many ways vastly superior to the other methods, once they are manufactured. These can convert 100+ tons of massenergy in a year for each ton of satellite.(4) USE SELF-REPLICATING MACHINERY TO PROCESS MATERIALS AND ENERGY IN SPACE. To produce infrastructure that processes 2,000+ times as much massenergy as all of humanity processes today, is an astoundingly tall task to accomplish. The only way this can be achieved in time periods that are short is to use self-replicating machinery to do it.(5) SOLVING ALL OUR SHORTAGES ON EARTH AND SENDING ALL PEOPLE TO THE STARS AT THE SAME TIME IS A SMALL DIFFERENCE TO SELF REPLICATING MACHINES. Let’s imagine that we have a 1 metric ton self replicating machine system that has to process 1 million metric tons of asteroidal material to collect a ton of massenergy and that 8,000 tons of massenergy to power a 10 ton probe to Deneb. This means that the 1 ton self replicating machine system would have to multiply its total size by 8 billion times. This requires LN(8e+9)/LN(2) = 32.9 doubling periods.If a doubling period is 1 week, then it takes only 33 weeks of operation for the probe to complete its task. Along the way it processes more energy and material than has been processed by humanity throughout its history. Along the way, it easily without breaking a sweat, solves all our energy and material supply problems.Now, lets suppose that we wish to increase this further by 8 billion times again to create a space colony for every single man woman and child on Earth. We then need; LN(64e+16)/LN(2) = 65.8 doubling periods. We’ve only ADDED 33 more weeks. For a trip that will take over 300 years star time, this is of little consequence.8,000 tons of massenergy times 8 billion people is 64 trillion tons of massenergy dividing this over 10 years 6.4 trillion tons per year is 4.75% of the total solar output. (5) SENDING EVERYONE TO THE STARS PROVIDES IMMEDIATE BENEFIT TO ALL: People ask, if it takes 320 years to fly to Deneb and 320 years to fly back, why should we do it? If people are offered a luxurious lifestyle of adventure and possibility traveling to Deneb to stay there, and when they return to Earth they find it 1,000 years more advanced than it is today the benefits are immediate and long lasting to all. (6) DEPOPULATING THE EARTH WITH STAR TRAVEL USING OFF-WORLD RESOURCES IS MORE HUMANE THAN OTHER METHODS: The world has 7 billion people on it. Their numbers are growing at 1.14% per year. Birth rates are 2.08% per year. Advancing medical science see the possibility of longevity treatments that end and reverse the aging process. We may already be well beyond our carrying capacity, no matter how we screw down living standards and conserve. Learning how to live off-world and make use of off-world resources to travel to the 700,000 stars within 350 light years of Earth, is the only humane way to proceed to reduce population levels on Earth.(7) THOSE IN TRANSIT DO NOT REPRODUCE: Suspended animation has made great advances in the past year. It is possible to place animals and people into suspended animation for extended periods. High acceleration travel between the stars involves significant time dilation. For these reasons those in transit will not be reproducing at the same rate as those on Earth do. For this reason it is of paramount importance to begin a program of interstellar colonization immediately and make its results freely available to all who wish leave Earth and travel beyond 100 light years from Earth.

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