New potential locations for life in other planetary systems |
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New potential locations for life in other planetary systems
The conditions for the development of life on extra-solar planets might be more extended than previously thought. A team of astronomers has computed that a solar-mass star, in its last red-giant phase, can heat up the surface of planets previously frozen. This will bring physical conditions favorable for life, in systems excluded until now.
Astronomers searching for life on exoplanets usually just transpose to other planetary system the situation in our own Solar System. They are then led to search for life on planets located at about 1 Astronomical Unit from a star more or less similar to the Sun.
An international team of astronomers, composed of Bruno Lopez (Observatoire de Nice), Jean Schneider (Observatoire de Paris, LUTH) and William Danchi (NASA, Goddard Space Flight Center), has recently realized that the emergence of life on a more distant planets is possible within the red giant phase of the parent star. They estimate that more than 150 red giant stars are close enough - within 100 light years - to be good targets for upcoming or proposed missions such as the Darwin (ESA) or Terrestrial Planet Finder (NASA) proposals.
There is a common consensus that the development of life on a planet, as we know it on Earth, requires the presence of liquid water. The planet must therefore lie in what is called the "habitable zone" where the planet, heated by its parent star, acquires a temperature suitable for liquid water: too cloe to the star, the water would boil, too far from the star water would freeze. For a a star similar to the Sun, the habitable zone has a radius of about 1 AU.
But, as Lopez and his colleagues have realized, if a planet sits far outside the habitable zone and is thus too cold for having liquid water, during the read giant phase of the star, the habitable zones extends significantly and can reach the planet, making it suited for the development of life. Morover, The authors realized that the interplanetary migration of small sized material, from dust to comets, may serve as an appropriate vehicle to seed the planet with life coming from an inhabited planet at 1 AU.
Figure 1: A solar-mass star grows in size and luminosity in its red-giant phase. The heat increases now at a distance where planets were frozen before: the ice melts and oceans can develop, creating therefore a site favorable to life. (Credit NASA)
Click on the image to see the movieBefore ambitious missions such as Darwin and TPF, to be launched between 2015 and 2020, the european French-led CoRoT mission, to be launched in 2006, will search for Earth-like planets around 60,000 stars.
Reference
Can Life develop in the expanded habitable zones around Red Giant Stars?
Bruno Lopez (1), Jean Schneider (2), William C. Danchi (3)
(1) Nice Observatory, (2) Paris Observatory (LUTH), (3) NASA - Goddard Space Flight Center
Astrophysical Journal, in press astro-ph/0503520
NASA Press release
Contact
Bruno Lopez (Observatoire de Nice)
Jean Schneider (Observatoire de Paris, LUTH)