April 26, 2007
Astronomers have discovered the most Earth-like planet outside our Solar System to date, an exoplanet with a radius only 50 percent larger than the Earth and capable of having liquid water.
Using the ESO 3.6-m telescope, a team of Swiss, French and Portuguese scientists discovered a super-Earth about 5 times the mass of the Earth that orbits a red dwarf, already known to harbour a Neptune-mass planet. The astronomers have also strong evidence for the presence of a third planet with a mass about 8 Earth masses.
This exoplanet - as astronomers call planets around a star other than the Sun - is the smallest ever found up to now  and it completes a full orbit in 13 days. It is 14 times closer to its star than the Earth is from the Sun.
However, given that its host star, the red dwarf Gliese 581 , is smaller and colder than the Sun - and thus less luminous - the planet nevertheless lies in the habitable zone, the region around a star where water could be liquid!
"We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid," explains Stephane Udry, from the Geneva Observatory (Switzerland) and lead-author of the paper reporting the result.
"Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky - like our Earth - or covered with oceans," he adds.
"Liquid water is critical to life as we know it," avows Xavier Delfosse, a member of the team from Grenoble University (France). "Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra-terrestrial life. On the treasure map of the Universe, one would be tempted to mark this planet with an X."
For more information:
- New 'super-Earth' found in space
- Swiss Scientist: Search for Life Next
- Found 20 light years away: the New Earth
- Earth-like planet found that may support life
- Planet of Promise: Small, Rocky World Could Harbor Life
- New Earthlike planet discovered Gliese 581c See Video!
- Astronomers Find First Earth-like Planet in Habitable Zone See Video!
In April 2007 around this red dwarf the first Earth-like exoplanet has been discovered, Gliese 581 c. This has 1.5 times the diameter and 5 times the mass of Earth and orbits its star every 13 days in a distance of 0.07 AU. Probably the planet has a surface temperature which allows liquid water. This discovery is a real sensation and an important step to the finding of alien life.
Another planet d with 8 times Earth's mass, an orbit period of 84 days and a distance of 0.25 AU, probably has life-friendly temperatures as well.
In April 2009 Gliese 581 e was discovered, the so far lightest exoplanet with only 1.9 times the mass of Earth. With an obit period of 3.14 days it is too close to its star for life.
Already longer known is a planet b with 16.6 times the mass of Earth, which orbits the star every 5.4 days.
Age: 4.3 billion years
Distance: 20.4 light-years
Spectral class: M3.5
Visual magnitude: 10.56
Luminosity: 0.002 * Sun
Mass: 0.33 * Sun
Radial velocity: -9.4 km/sec
Digital artwork Don Dixon