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Astronomers search for life
21/02/2006 10:01 - (SA)
St Louis - United States astronomers have come up with a short list of five stars in the Milky Way galaxy that are most likely to support extraterrestrial life.
The stars were chosen based on criteria including size, composition, age and colour, that would make them similar to the sun and enable planets resembling earth to orbit them, said Margaret Turnbull of the Carnegie Institution of Washington.
"These are places I would want to live if God were to put our planet around another star," Turnbull said on Saturday at a conference of the American Association for the Advancement of Science (AAAS) in Saint Louis, Missouri.
The list was developed to guide the use of the National Aeronautics and Space Administration's (Nasa) new powerful orbiting observatories, or the Terrestrial Planet Finder, which will search for earth-like planets.
Extensive research
"There are 400 billion stars in the galaxy, and obviously we are not going to point the Terrestrial Planet Finder at every one of them," Turnbull said.
Among the most promising sun-like stars is beta CVn, about 26 light years from earth in the constellation Canes Venatici. One light year is equivalent to 9.5 billion kilometres.
Turnbull and her colleagues initially set out to select a dozen stars that were sufficiently close to the earth's solar system and most likely to send extraterrestrial signals.
In 2003, after a painstaking study of nearly 120 000 stars, the team of astronomers came up with a catalogue of 129 "habitable stellar systems".
Another star on the short list, Pegasus 51, became famous in 1995 when Swiss astronomers discovered the first planet outside the solar system in its orbit, a giant planet resembling Jupiter.
A star named 16 Sco, a popular target for planet searches, also made the list. The star is located in the Scorpion constellation near the center of the Milky Way and is virtually a twin of the sun, according to Turnbull.
List just a starting point
To be considered as potential homes for intelligent life to evolve, stars must be at least three billion years old.
Turnbull said the list was merely a starting point and it remained difficult to rank stars as more or less likely to shelter life.
"There are inevitable uncertainties in how we understand these stars," she said. "If I took the top 100, it would be very difficult for me to tell which is the best."
The list will provide potential targets for the Terrestrial Planet Finder, which was originally set to be launched in 2016 but has been postponed due to federal budget constraints.
Research for the list was sponsored by Nasa and the privately funded Search for Extraterrestrial Intelligence (Seti) organisation. The institute was created in 1984 by the renowned astronomer Carl Sagan, who died in 1996.
- AFP
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