Kepler 22b: Why it is Almost Certainly NOT Habitable
by Rich Deem


NASA has made an announcement of finding the first "earth-like" planet in the middle of the star's habitable zone through the Kepler satellite, which finds planets through stellar dimming during transits. To date (2011), over 700 extrasolar planets have been confirmed to exist, although Kepler has a potential list of over 2,000 more. The current announcement probably had the widest news coverage of any recent NASA statement. This page examines the claims, along with distortions by the media, and NASA artists themselves.

Parent star

Stars and planets are given names according to the following convention. A star's name usually includes some numbers identifying it. The planets being discovered by the Kepler mission are being numbered sequentially by discovery. Stars are labeled with the number followed by the letter "a." So, the "name" of the star around which the new earth-like planet is revolving is designated as Kepler 22a.1 Planets are numbered with subsequent letters, beginning with "b." So, the newly discovered planet is designated as Kepler 22b. Unlike the last announcement of the last "earth-like planet," Gliese 581g, within its small star's habitable zone, this one is orbiting a near solar-twin. Small stars, like Gliese 581a, exhibit lower energy spectral emissions, which are not conducive as strong supporters of photosynthesis. In addition, their weak emissions require planets to be located very close to the parent star to be within the habitable zone, resulting in tidal locking (one side of the planet always faces the star). Stars larger than the Sun burn much more quickly, with rapid escalation of stellar luminosity, which continually moves the habitable zone further and further away from the star. So, realistically, only stars that are nearly solar twins would be conducive to harboring life. Kepler 22a happens to be such a star, which is why scientists were so excited to find a rocky planet orbiting around it.

Habitable zone

NASA's definition of the habitable zone is very generous. For example, using our own solar system, they say that Venus and Mars are both within the habitable zone. However, according to the inverse square law, the solar irradiance received by Venus should be nearly twice that of earth. Even with Earth's relatively thin atmosphere, it would be uninhabitable, due to overheating, if located as close as the orbit of Venus. However, since Venus has a thick greenhouse atmosphere, surface temperatures are in excess of 460°C—even higher than Mercury, the closest planet to the Sun. If the earth were located toward the outer limits of the Sun's habitable zone, beyond the orbit of Mars, it would a frozen ball of ice. Planet Kepler 22b is located near the inner part of Kepler 22a's habitable zone, so it's likely to be much warmer than the claimed 72°F in news stories.2

Planet Kepler 22b

Although declared to be "earth-like," Kepler 22b is actually 2.4 times more massive than earth. This increased mass likely impacts the atmospheric content of the planet. Planets must possess a minimal mass in order to retain an atmosphere. For example, Mars has only 10% the mass of the earth, and almost no atmosphere. Extensive evidence indicates that it once had a thicker atmosphere and large bodies of water on its surface. However, because of its reduced gravity, it lost nearly all of that atmosphere and water due to the actions of the solar wind. The earth originally had a much denser atmosphere that was mostly blasted into space during the collision that formed the Moon. Had it not been for this fortuitous collision, the earth would have had an atmosphere similar to Venus (81% the mass of the earth), which has an atmosphere 80 times denser than earth's. NASA scientists have assumed that Kepler 22b has an atmosphere similar to earth's. This assumption is almost certainly wrong, unless the planet experienced a large collision event, similar to earth's, early in its history. With at least 2.5 times the mass of earth, the planet would likely have an atmosphere much denser than Venus, making life there extremely unlikely. Such a dense atmosphere would contribute to a large greenhouse effect, which would raise temperatures dramatically. If Kepler 22b ever had water, it probably doesn't now, having been evaporated and blown away by Kepler 22a's solar wind. The artist's impression (right) is almost certainly wrong, since even NASA scientists admitted in their December 20, 2011 news conference that Kepler 22b most likely has a very dense atmosphere compared to earth (not the thin, wispy clouds we see in the diagram).

Conclusion Top of page

The Privileged PlanetThe newly confirmed planet Keppler 22b has been advertised as being an earth-sized planet within the habitable zone of its star, with an average temperature of 72F. What the new media does not tell you is that the temperature assumptions are based upon the planet having an atmosphere identical to earth's. The assumption is extremely unlikely. First, the earth's atmosphere is very thin for the size of planet, having achieved such a thin atmosphere due to the collision that formed earth's moon. Since Kelper 22b is 2.4 times more massive than earth, it most likely has an atmosphere as dense or denser than Venus. With such a thick atmosphere, any water on the planet would be in the form of superheated steam or boiled off completely. I wouldn't plan on moving there any time soon. If you do, remember to take lots of sunblock!

Rare EarthRare Earth: Why Complex Life is Uncommon in the Universe by Peter D. Ward and Donald Brownlee

A secular book that recognizes the improbable design of the earth. Paleontologist Peter D. Ward and astrobiologist Donald Brownlee examine the unusual characteristics of our galaxy, solar system, star, and Earth and conclude that ET may have no home to go to. Surprisingly, the authors conclude that the amazing "coincidences" are the result of good luck and chance.

The Creator and the CosmosThe Creator and the Cosmos by Dr. Hugh Ross

A classic book for modern Christian apologetics and science, recently updated with fully one third of the book updated. Dr. Ross presents the latest scientific evidence for intelligent design of our world and an easy to understand introduction to modern cosmology. This is a great book to give agnostics, who have an interest in cosmology and astronomy.

References Top of page

  1. NASA's Kepler Mission Confirms Its First Planet in Habitable Zone of Sun-like Star. Kepler Mission News, December 5, 2011.
  2. On newly discovered Earth-like planet, it's 72 degrees. Florida Today, December 6, 2011.
  3. Leslie Mullen. 2010. Doubt cast on existence of possibly habitable alien planet, Astrobiology Magazine.

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