By Ron Cowen
Surveying the distant universe is a daunting task, but spotting stars even a few tens of light-years from our solar system isnt easy either. Most are much less massive than the sun, and many emit less than 1 percent as much light.
Faint, nearby stars in the southern sky represent an unexplored trove because most surveys have been conducted in the north, notes Todd J. Henry of Georgia State University in Atlanta. At a meeting of the American Astronomical Society in Washington, D.C., last month, Henrys team unveiled 12 previously unknown stars in the southern sky that lie within 33 light-years of Earth.
Eleven of these are extremely low-mass stars called red dwarfs. One is a star just 18 light-years away, making it the 55th closest star to the sun. Three others are locked in a gravitational embrace 24.6 light-years from Earth.
The teams ongoing survey focuses on faint stars that drift across the sky. The relatively rapid motion indicates the stars are close by. To measure the distances to these neighbors, the researchers rely on parallax, the apparent shift in position of nearby stars as Earth moves around the sun.
Finding more of the suns neighbors not only provides a more accurate map of nearby space but reveals fresh targets where we can look for planets and, ultimately, for life on those planets, Henry says.
Astronomers used to believe that planets orbiting dwarf stars, such as those in Henrys survey, would be poor candidates for harboring life. A dwarf star emits so little heat and light that any planet with a temperature high enough for water to remain liquid–a requirement for life as we know it–would have to orbit the star extremely closely.
A closely orbiting planet would always have the same side pointing toward its parent star. The uneven heating that would result from such an orientation could doom life. However, if such a planet had a thick, heat-absorbing atmosphere, it could redistribute the stars heat, notes Jonathan I. Lunine of the University of Arizona in Tucson.
