On January 11, 2012, astronomers working with the European Southern Observatory (ESO) announced that most stars in our Milky Way Galaxy have planets. They used gravitational microlensing to analyze how common planets may be around stars. After six years of observation involving millions of stars, they concluded "that stars are orbited by planets as a rule, rather than the exception." While other techniques are biased towards detecting planets close to their stars (such that 17 to 30 percent of Sol-type stars have been found to have such inner-orbit planets), gravitional lensing has found reveals the fraction of planets at farther orbits. In their survey of planets within 0.5 to 10 AUs of their host star, the astronomers found that 17 +6/-9 percent of observed stars had Jupiter-class planets (of 0.3 to 10 Jupiter masses), 52 +22/-29 percent had Neptune-class planets (of 10 to 30 Earth-masses), and that 62 +35/-37 percent had super-Earths of 5 to 10 Earth-masses, which is consistent with the conclusion that an average star in the Milky Way should have one or more planets within an orbital distance of 0.5 to 10 AUs, and that there may be some 10 billion Earth-sized planets in the galaxy (ESO press release; Anil Ananthaswamy, New Scientist, January 11, 2012; Jason Palmer, BBC News, January 11, 2012; and Cassan et al, 2012).

Martin Kornmesser, ESO



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A planet detection effort using
gravitational microlensing suggests
that most stars in our galaxy have
planets in orbit around them, of
which many are super-Earths (more).

On December 5, 2011, astronomers working on the Kepler Mission announced their first confirmation an extra-Solar, super-Earth-sized planet orbiting within the "habitable zone" of a distant Sun-like star (spectral class G5), which was discovered using Kepler. Located around 620 light-years away around a star somewhat smaller, cooler, and roughly 25 percent dimmer than Sol which was designated "Kepler-22," planet "b" is estimated to have about 2.38 (+/- 0.13) times Earth's diameter and has an orbital period around Kepler 22 of about 290 days (with an average orbital distance of around 0.85 +/- 0.02AUs). Scientists have not yet been able to determine whether Kepler-22 b has a predominantly rocky, gaseous, or liquid composition (NASA news release; Kepler briefing and discoveries; and science news).

Unknown artist, Kepler, Ames, JPL,
Caltech, NASA



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Kepler 22b is a super-Earth candidate with
around 2.4 times Earth's diameter that orbits
a G5 star within its habitable zone (more).

On December 5, 2011, on the opening of its inaugural science conference at NASA's Ames Research Center, the Kepler Mission team announced 1,094 new planetary candidates, bringing the running total of potential planet discoveries to 2,326. Of those Kepler planetary candidates, 207 are roughly Earth-size, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size, and 55 are larger than Jupiter. Based on Kepler observations conducted from May 2009 to September 2010, the planet findings show a dramatic increase in the numbers of smaller-size planet candidates, where Earth-size and super-Earth-size candidates have increased in number by more than 204 and 136 percent, respectively, since the last Kepler announcement in February 2011. The new data indicate that planets from one to four times the size of Earth may be abundant in our galaxy. Thus far, Kepler has found 48 planetary candidates in their host star's habitable zone (of which 10 are near Earth-size), but this number is a decrease from the 54 reported in February 2011 only because the Kepler team is now applying a stricter definition of what constitutes a habitable zone around stars to account for the warming effect of planetary atmospheres, which would move such a zone away from the star, outwards in orbital distance resulting in longer orbital periods (NASA news release; and Kepler Press Conference slides -- in pdf).

Unknown artist, Kepler, Ames, JPL, Caltech, NASA



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As Kepler 22 is slight smaller and cooler than
our Sun, Sol, its habitable zone is slightly
smaller and located closer to the star than the
habitable zone around our own Sun (more).

© Lynette Cook (Artwork from
Extrasolar Planets - Collection III,
used with permission)


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Like Gliese 581 g, Gliese 667 Cc is
believed to be a super-Earth that orbits
Gliese 667 C within the red dwarf
star's habitable zone (more).

On September 12, 2011, astronomers working with the High Accuracy Radial velocity Planet Searcher (HARPS) at the European Southern Observatory (ESO) announced the discovery of 16 super-Earths (including HD 85512 b discussed below) among 50 newly detected extra-Solar planets (ESO science release; and Mayor et al, 2011).

© ESO



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Like Gliese 581 d, HD 85512 b orbits just
within its host star's habitable zone and so
may have liquid surface water on its surface
under favorable atmospheric conditions.

Martin Kornmesser, ESO



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HD 85512 b has some 3.6 Earth-masses
and appears to orbit near the estimated
inner edge of the habitable zone around
its host star, where liquid water, and
possibly life, may exist under favorable
conditions (more).

On June 10, 2011, a team of astronomers submitted a preprint which revealed the detection of a possible cold super-Earth around a low-mass star around 9,900 +/- 1,100 light-years away in Constellation Scorpius (17:48:5.06-35:00:19.8) using the gravitational microlensing method. It was first detected on June 1, 2009 by the Microlensing Observations in Astrophysics (MOA) collaboration with the 1.8-meter telescope at the Mount John University Observatory in New Zealand. Designated MOA-2009-BLG-266L b, the planet has a mass of around 10.4 +/- 1.7 Earth-masses and orbits its host star at a semi-major axis of 3.2 +1.9/-0.5 AUs with an orbital period of 7.6 +7.7/-1.5 years. MOA-2009-BLG-266L, the host star has only some 0.56 +/- 0.09 of a Solar-mass. Measurement corroboration of the planet's mass as well the microlensing parallax were undertaken with the Deep Impact / EPOXI spacecraft, which was in a Heliocentric orbit (around our Sun, Sol). The planet's mass and orbital distance are around the theoretical threshold values needed to accrete a substantial gas envelope of hydrogen and helium like Uranus (Muraki et al, 2011; and the Extrasolar Planet Encyclopaedia entry for MOA-2009-BLG-266L b).

On May 23, 2011, astronomers on the Kepler Mission announced confirmation of another planet in the Kepler-10 system, designated Kepler-10c. It's existence was "validated using a combination of a computer simulation technique called 'Blender' and NASA's Spitzer Space Telescope. Kepler-10c appears to be a super-Earth class planet with 2.2 times Earth's radius, and it orbits the star every 45 days (which is longer than Kepler-10b's eight-day orbit and so must have a longer orbital distance). Although also a super-Earth class planet, Kepler-10b has only 1.4 times Earth's radius and has been determined to be one of the smallest rocky planets detected thus far. Both Kepler-10b and 10c, however, are calculated to be "blistering hot worlds" (Kepler news release; Fressin et al, 2011; and Francois Freesin's PowerPoint presentation slides).

Unknown artist, JPL, SSC, Caltech, NASA


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A new super-Earth "c" has been detected
in the Kepler 10 system around 560
light-years away, which should be a
"blisteringly hot" world (more).

On March 8, 2011, two astronomers analyzing the first four months of data from NASA's Kepler Mission submitted a pre-print with an initial estimate that the 1.4 (+/- 0.5) to 2.7 (+/- 0.9) percent of the Sun-like stars (of FGK spectral types) in the Kepler sample of nearly 155,500 may host Earth- and super-Earth sized planets with orbits within their host star's habitable zone (Catanzarite and Shao, 2011). The variance in the estimates depended on the use of a conservative versus a more conventional definition of habitable zone (Kasting et al, 1993; and ExoPlanet Task Force, 2008 report in pdf, pp. 102-103). Their calculations suggested that Kepler will eventually find a total of 12 such "Earth-analog" planets after three to four years of observation, and that four of these planets have already been detected. The astronomers expect that this estimate of Earth-analog planets can be refined as Kepler's data set grows to 3.5 to six years of observations (Catanzarite and Shao, 2011; and Victoria Jaggard, National Geographic News, March 29, 2011).

David A. Aguilar, CfA,





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A March 2011 study estimates that
1.4 to 2.7 percent of the Sun-like
stars (of spectral classes FGK) in
the 155,500 sample being observed
by NASA's Kepler Mission may
host Earth- or Super-Earth sized
planets in habitable orbits (more).

In 2010, model simulations of rocky super-Earths between two and 10 Earth-masses indicated that high pressures could keep their cores solid instead of molten, which would prevent a protective magnetic field from forming protecting developing surface life from stellar radiation. Without a magnetic field generated by a rotating molten metallic core, the atmosphere of such a planet would also face progressive erosion by the stellar wind of its host star. Other scientists caution that the interiors of super-Earth may still get hot enough to melt their iron cores despite the pressure due to other factors not yet considered by the model simulation (New Scientist, November 6, 2010; and Morard et al, 2010).

On May 23, 2011, astronomers on the Kepler Mission announced confirmation of another planet in the Kepler-10 system, designated Kepler-10c. It's existence was "validated using a combination of a computer simulation technique called 'Blender' and NASA's Spitzer Space Telescope. Kepler-10c appears to be a super-Earth class planet with 2.2 times Earth's radius, and it orbits the star every 45 days (which is longer than Kepler-10b's eight-day orbit and so must have a longer orbital distance). Although also a super-Earth class planet, Kepler-10b has only 1.4 times Earth's radius and has been determined to be one of the smallest rocky planets detected thus far. Both Kepler-10b and 10c, however, are calculated to be "blistering hot worlds" (Kepler news release; Fressin et al, 2011; and Francois Freesin's PowerPoint presentation slides).

Unknown artist, JPL, SSC, Caltech, NASA


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A new super-Earth "c" has been detected
in the Kepler 10 system around 560
light-years away, which should be a
"blisteringly hot" world (more).

On January 10, 2011, astronomers working with NASA's Kepler space telescope announced the discovery of a rocky super-Earth of only 1.4 Earth-diameters across and around 4.6 Earth-masses, at the 217th Annual Meeting of the American Astronomical Society. Designated "Kepler-10b," the planetary candidate was already catalogued as Kepler Object of Interest or (KOI) 72.01. It orbits an aged, spectral type G star (KIC 11904151) of 0.895 Solar-mass and 1.06 Solar-diameter with around 1.00 Solar luminosity, which is estimated to be at least 7.4 billion years old. The Kepler-10 system lies around 560 light-years away in the northwestern corner of Constellation Cygnus.

Kepler Mission, NASA





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Kepler 10b appears to
be a rocky planet that
is probably denser
than Earth (more).

With a torch orbit around its host star that takes only about 20 hours (84 percent of an Earth day) to complete, Kepler 10b has an average orbital distance of only 0.017 AU from its host star and so has a tidally locked, synchronous orbit. Hence, the planet has a perpetually daylight side with a fequilibrium surface temperature of around 2,840 degrees Fahrenheit (1,560 degrees Celsius), which is hotter than molten lava and sufficient to melt iron. Kepler 10b was detected using the transit method from more than eight months of data collected by the spacecraft between May 2009 and early January 2010 and confirmed by radial velocity measurements, and there evidence for another planet (KOI 72.02) in an outer orbit with a period around 45.3 days (Kepler news release; images, animations, and discovery page; and Batalha et al, 2011).

Tim Pyle, Kepler Mission, NASA




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The planetary candidate KOI 377.03 (or Kepler-9d),
a super-Earth orbits too close to its host star to be
potentially habitable (more).

Kepler Mission, NASA




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The Kepler Mission has detected the
possible transits of several hundred
potential super-Earth- and Earth-sized
planets around distant stars (more).