Super-Earth
First in habitable zone
### First in habitable zone

In April 2007, a team headed by [Stéphane Udry](/wiki/St%C3%A9phane_Udry "Stéphane Udry") based in Switzerland announced the discovery of two new super\-Earths within the [Gliese 581 planetary system](/wiki/Gliese_581_planetary_system "Gliese 581 planetary system"), both on the edge of the [habitable zone](/wiki/Habitable_zone "Habitable zone") around the star where liquid water may be possible on the surface. With [Gliese 581c](/wiki/Gliese_581c "Gliese 581c") having a mass of at least 5 Earth masses and a distance from [Gliese 581](/wiki/Gliese_581 "Gliese 581") of 0\.073 [astronomical units](/wiki/Astronomical_unit "Astronomical unit") (6\.8 million mi, 11 million km), it is on the "warm" edge of the habitable zone around Gliese 581 with an estimated mean temperature (without considering effects from an atmosphere) of −3 degrees Celsius with an [albedo](/wiki/Albedo "Albedo") comparable to [Venus](/wiki/Venus "Venus") and 40 degrees Celsius with an albedo comparable to Earth. Subsequent research suggested Gliese 581c had likely suffered a [runaway greenhouse effect](/wiki/Runaway_greenhouse_effect "Runaway greenhouse effect") like Venus.

[thumb\|upright\=1\.5\|right\|Mass and radius values for transiting super\-Earths in context of other detected exoplanets and selected composition models. The "Fe" line defines planets made purely of iron, and "H2O" for those made of water. Those between the two lines, and closer to the Fe line, are most likely solid rocky planets, while those near or above the water line are more likely gas and/or liquid. Planets in the Solar System are on the chart, labeled with their [astronomical symbols](/wiki/Astronomical_symbols "Astronomical symbols").](/wiki/File:Exoplanet_Mass-Radius_Scatter_Super-Earth.png "Exoplanet Mass-Radius Scatter Super-Earth.png")


How do the masses and radii of super-Earths like Gliese 581c compare to other detected exoplanets?