Margaret Turnbull of the Carnegie Institution of Washington released her "top 10" list of potential stars to the American Association for the Advancement of Science. They will be the first targets of NASA's Terrestrial Planet Finder, a system of two orbiting observatories scheduled for launch by 2020.
"There are 400 billion stars in the galaxy, and obviously we're not going to point the Terrestrial Planet Finder ... at every one of them," said Turnbull.
Turnbull's list includes 51 Pegasus, where in 1995 Swiss astronomers spotted the first planet outside our solar system, a Jupiter-like giant.
Others include 18 Sco in the Scorpio constellation, which is very similar to our own sun; epsilon Indi A, a star one-tenth as bright as the sun; and alpha Centauri B, part of the closest solar system to our own.
"The truth is when looking at these so-called 'habstars,' habitable solar systems, it is hard to really rank them. I don't know enough about every star to say which one is the absolute best one," Turnbull said.
She said NASA once had a policy of what to do, whom to call, and how to announce the news if someone detected a signal of intelligent life from space.
She said life on Earth is all so similar -- based on DNA made up of specific building blocks -- that it is likely to have had a single origin. Life elsewhere may be built from different ingredients, or structured very differently, she said.