Near Earth-sized planet discovered by Scientists
By Tim Longwell
The discovery was announced Tuesday April 21, 2009 at the JENAM conference during the European Week of Astronomy & Space Science, which took place at the University of Hertfordshire, UK. The research team made up of M. Mayor, S. Udry, C. Lovis, F. Pepe and D. Queloz (Geneva Observatory, Switzerland), X. Bonfils, T. Forveille , X. Delfosse, H. Beust and C. Perrier (LAOG, France), N. C. Santos (Centro de Astrofisica, Universidade de Porto), F. Bouchy (IAP, Paris, France) and J.-L. Bertaux (Service d’Aéronomie du CNRS, Verrières-le-Buisson, France), have been observing the Gliese 581 system — located only 20.5 light-years away in the constellation Libra (“the Scales”) for well over four years using the HARPS spectrograph attached to the 3.6-meter European Southern Observatory (ESO) telescope at La Silla, Chile, have discovered in this system the lightest exoplanet found so far: Gliese 581 e 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 Earth-masses while completing it’s orbit in 3.15 days. The planet furthest out, Gliese 581 d, which orbits its host star in 66.8 days as defined by the team at ESO. Additionally the team of astronomers has shown that it lies well within the habitable zone, around its low-mass red star, where liquid water oceans could exist, based on a diagram by Franck Selsis, Univ. of Bordeaux.
According to ESO Gliese 581 d is probably too massive to be made only of rocky material, but astronomers speculate that it is an icy planet that has migrated closer to the star. The new observations were made with the HARPS exoplanet hunter and have revealed that the planet is in the habitable zone, where liquid water could exist. It could thus be covered by a large and deep ocean and is so the first serious “water world” candidate, according to astronomers.
Michel Mayor, well-known exoplanet researcher from the Geneva Observatory, who led the European team to this stunning breakthrough, announced the discovery Tuesday April 21, 2009, stating; “The holy grail of current exoplanet research is the detection of a rocky, Earth-like planet in the ‘habitable zone’ — a region around the host star with the right conditions for water to be liquid on a planet’s surface”
Co-author Xavier Bonfils from Grenoble Observatory made the comment; “With only 1.9 Earth-masses, it is the least massive exoplanet ever detected and is, very likely, a rocky planet”.
With the discovery of Gliese 581 e, the planetary system now has four known planets, with masses of about 1.9 (planet e), 16 (planet b), 5 (planet c), and 7 Earth-masses (planet d).
As for the new information regarding Gliese 581 d, team member Stephane Udry observed; we can speculate that it is an icy planet that has migrated closer to the star, ‘d’ could even be covered by a large and deep ocean — it is the first serious ‘water world’ candidate,”
The planets are located by observing “the gentle pull of an exoplanet as it orbits the host star which introduces a tiny wobble in the star’s motion, only about 7 km/hour,” about the same speed as a brisk walk, “can just be detected on Earth with today’s most sophisticated technology. Low-mass red dwarf stars such as Gliese 581 are potentially fruitful hunting grounds for low-mass exoplanets in the habitable zone. Due to such cool stars being relatively faint and their habitable zones close in to their parent star, the gravitational tug from any orbiting planet found there would be stronger, making the telltale wobble more pronounced.” None the less, “detecting these tiny signals is still a challenge, and the discovery of Gliese 581 e and the refinement of the orbit of Gliese 581 d were only possible due to HARPS’s unique precision and stability,” states ESO
“It is amazing to see how far we have come since we discovered the first exoplanet around a normal star in 1995 — the one around 51 Pegasi,” says Mayor. “The mass of Gliese 581 e is 80 times less than that of 51 Pegasi b. This is tremendous progress in just 14 years.”
The astronomers are very confident that they can do better still. “With similar observing conditions an Earth-like planet located in the middle of the habitable zone of a red dwarf star could be detectable,” says Bonfils. “The hunt continues.”