Majestic relative of Earth found

The discovery of the most Earth-like planet found to date outside the Solar System was announced today[1]. At least five times the mass and 1.5 times the diameter of our home planet, the discovered exoplanet takes 13 days to complete a year around its mother star - the red dwarf Gliese 581. Most notably, however, the temperature of this planet is predicted to be in the range 0...40 degrees Celsius, opening up the possibility of there being liquid water on it!

Most of the more than 200 planets found so far around stars other than the Sun have had more in common with the gas giants (Jupiter, Saturn, Neptune, Uranus) than the rocky, or Earth-like planets (Mercury, Venus, Earth, Mars) of the Solar System. However, the hunt for other Earths is on and today's announcement certainly marks the most significant discovery so far on that quest, showing for a fact that planets quite similar to ours exist around other normal stars.

Red dwarfs, with masses and temperatures around and below half that of the Sun, are the most abundant type of stars in the Universe and most of the 150 billion or so stars in our Galaxy fall into this category. They radiate less energy than the Sun, which is why the newly discovered planet potentially has conditions similar to Earth even though it's eleven times closer to its mother star than the Earth-Sun distance. Most importantly, however - Gliese 581, at a distance of 20.5 light-years, is one of the closest neighbors of the Sun (the closest is Alpha Centauri at 4.4 light-years and the diameter of the Galaxy is ~100000 light-years). This goes to show how difficult it is to discover exoplanets around even the nearest stars, but also implies that red dwarfs further away from us are likely to harbor planets as well. And there are many, many red dwarfs out there.

As for this particular planet, it is not known yet whether it's tidally locked (always keeping the same side to its parent star, exactly like the Moon is tidally locked to the Earth and always keeps the same side visible to us), which is quite possible for a planet so close to its star and would have unknown consequences for its climate and habitability. Nothing certain is known about the atmosphere, if any, of this planet, nor the composition - but observational astronomers and engineers will be working hard to get at that information in the coming years - years, which will undoubtedly reveal a plethora of new planets to study and send our imaginations running wild.

PS. Wow! :)

References:
[1] "Astronomers Find First Earth-Like Planet in Habitable Zone", ESO Press Release, 2007.04.25