A team of planet hunters from the University of California (UC) Santa
Cruz, and the Carnegie Institution of Washington has announced the
discovery of a planet with three times the mass of Earth orbiting a
nearby star at a distance that places it squarely in the middle of the
star's "habitable zone."
This discovery was the result of more than a decade of observations
using the W. M. Keck Observatory in Hawaii, one of the world's largest
optical telescopes. The research, sponsored by NASA and the National
Science Foundation, placed the planet in an area where liquid water
could exist on the planet's surface. If confirmed, this would be the
most Earth-like exoplanet yet discovered and the first strong case for
a potentially habitable one.
To astronomers, a "potentially habitable" planet is one that could
sustain life, not necessarily one where humans would thrive.
Habitability depends on many factors, but having liquid water and an
atmosphere are among the most important.
The new findings are based on 11 years of observations of the nearby
red dwarf star Gliese 581using the HIRES spectrometer on the Keck I
Telescope. The spectrometer allows precise measurements of a star's
radial velocity (its motion along the line of sight from Earth), which
can reveal the presence of planets. The gravitational tug of an
orbiting planet causes periodic changes in the radial velocity of the
host star. Multiple planets induce complex wobbles in the star's
motion, and astronomers use sophisticated analyses to detect planets
and determine their orbits and masses.
"Keck's long-term observations of the wobble of nearby stars enabled
the detection of this multi-planetary system," said Mario R. Perez,
Keck program scientist at NASA Headquarters in Washington. "Keck is
once again proving itself an amazing tool for scientific research."
Steven Vogt, professor of astronomy and astrophysics at UC Santa Cruz,
and Paul Butler of the Carnegie Institution lead the Lick-Carnegie
Exoplanet Survey. The team's new findings are reported in a paper
published in the Astrophysical Journal and posted online at: