In the News this month... and finally
Artists impression of the Gliese 581 system. Gliese 581 e (foreground) is only about twice the mass of our Earth. The Gliese 581 planetary system now has four known planets, with masses of about 1.9 (planet e, left in the foreground), 16 (planet b, nearest to the star), 5 (planet c, centre), and 7 Earth-masses (planet d, with the bluish colour). The planet furthest out, Gliese 581 d, orbits its host star in 66.8 days, while Gliese 581 e completes its orbit in 3.15 days. CREDIT: ESO/L. Calçada
The discovery of the lightest exoplanet found so far was announced at the Joint European and National Astronomy Meeting at the University of Hertfordshire on the 21st of April. This is the fourth planet discovered in the Gliese 581 system, orbiting a star located 20.5 light years away in the constellation Libra. The planet, known as Gliese 581 e, has a mass just 1.9 times that of Earth and orbits its parent star in just 3.15 days. The team, led by Michel Mayor of Geneva Observatory, have been searching for planets using the HARPS spectrograph on ESO's 3.6-metre telescope at La Silla in Chile for more than four years.
By refining the orbit of the planet Gliese 581 d, first discovered in 2007, a team of astronomers has shown that it lies well within the habitable zone, where liquid water oceans could exist. This diagram shows the distances of the planets in the Solar System (upper row) and in the Gliese 581 system (lower row), from their respective stars (left). The habitable zone is indicated as the blue area, showing that Gliese 581 d is located inside the habitable zone around its low-mass red star. CREDIT: ESO
The same study found that one of their previous planetary discoveries is located within the habitable zone of Gliese 581, a low mass red dwarf star. While the mass of this planet means it is unlikely to be a rocky, Earth-like planet, its location in the habitable zone means there could be liquid water on its surface. The results of the study have been submitted for publication in the journal Astronomy and Astrophysics (PDF).