Most likely host star for advanced life named
http://www.newscientistspace.com/article/dn8744-most-likely-host-star-for-advanced-life-named.htmlRoxanne Khamsi, St. Louis
Margaret Turnbull, Carnegie Institution of Washington
SETI Institute
AAAS Annual Meeting
Astronomers searching for advanced life beyond Earth should focus their attention around beta CVn, a binary star roughly 26 light years away that resembles our Sun.
The recommendation comes from a shortlist of likely life-bearing systems compiled by Margaret Turnbull, at the Carnegie Institution of Washington, and presented at the annual meeting of the American Association for the Advancement of Science in St Louis, Missouri, US.
She adds that researchers looking for any kind of life – including basic forms that could not send communications to Earth – should take a particularly close look around another star, epsilon Indi A.
Both of the stars share similar traits, Turnbull says: "They're mature, very stable, calm stars. They're stars that are acting like they're taking care of someone."
Planetary picks
Turnbull began her analysis by looking at thousands of stars in a catalogue of stellar distances measured by the Hipparcos mission. In 2003, she had narrowed the list down to 30 stars that might harbour planets in so-called "habitable zones".
One star, 37 Gem, topped the list at that point. But Turnbull has now refined the criteria, meaning 37 Gem does not make the new shortlist of 10 stars. She says 37 Gem is simply further away from the now higher-ranking stars, making it more difficult for scientists to observe clearly.
The rationale for the stellar shortlist, says Turnbull, is to answer the question of "which stars are the absolute best ones for us to spend our telescope time on?" And she notes: "This all comes down to what we know about life on Earth."
Metal poor
One example of the criteria she uses to draw up the list is the distance between planets and their parent stars - being too far from the star would mean water would freeze but being too close would mean it would boil off.
In assessing which stars might have nearby planets with advanced life, Turnbull also threw out stars that are very young: "On Earth it took billions of years for technology to arise, so I don't want stars that are less than a couple billion years old, and I chose three billion years as the cut-off."
Beta CVn and epsilon Indi A both met her criteria, but because the former is older she thinks it has a better chance of hosting advanced life.
Turnbull also disregarded stars likely to be too metal poor – lacking the iron, nickel and silicon which facilitate life on Earth. "A star that forms out of a metal-poor cloud is not likely to be able to form metal-rich planets around it," she says.
Phone message
The projects looking for life include the Search for Extraterrestrial Intelligence (SETI), in which scientists examine radio transmissions from stellar neighbourhoods for signs of intelligent life.
Finding such a sign would be an extraordinary and perhaps portentous discovery. But the SETI institute's Margaret Race believes we would plenty of time to consider any response, as it would probably come from a distant galaxy. "If we find something far away it's sort of like your telephone message machine giving you an answer message," she says. "I can decide if I want to respond and when I want to respond."
A planned life-hunting project is NASA's Terrestrial Planet Finder, would look for life by imaging forms potentially habitable planets. That might reveal life that does not deliberately send any signals off their home planet.
But the mission, which some anticipated would launch in 2014, has been postponed due to cuts in NASA's science budget proposed by US President George W Bush on 6 February 2006. "TPF is essentially shelved," says Turnbull.
The budget cuts would mean that NASA's 2007 budget for astrobiology would be 50% of that in 2005, according to Jill Tarter of the SETI Institute.
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