MAUNA KEA, Hawaii (June 13th, 2005) Data obtained at the W. M. Keck Observatory has resulted in the discovery of the most earth-like world to ever be discovered—but it’s not likely to hold that record for long.

The discovery centers around the smallest extrasolar planet to ever be discovered and the first in a new series of rocky, terresterial planets orbiting stars other than our sun. It took more than 150 observations of this star to obtain the necessary data for this result.

“Today’s results are an important step toward answering one of the most profound questions that mankind can ask: Are we alone in the universe?” said Michael Turner, head of the Mathematical and Physical Sciences directorate at the National Science Foundation (NSF), which provided partial funding for the research.

The newly-discovered planet orbits a red dwarf star named Gliese 876, which is just one-third the mass of the Sun, and is located about 15 light years from Earth.

This new planet is a very unusual world—more than seven times the mass of the Earth, orbiting its star in just two days at a distance of just .021 astronomical units, or less than one-tenth that of Mercury’s orbit inside our own solar system.

The discovery follows recent improvements to Keck’s high-resolution spectrometer (HIRES) which provided the crucial new data.

“It is the higher precision data from the upgraded HIRES that gives us confidence in this result,” said team member Paul Butler of the Carnegie Institution of Washington.

Theoretical astronomer Jack Lissauer of NASA’s Ames Research Center, and post-doctoral researcher Eugenio J. Rivera of UCO/Lick have been analyzing Keck data on the Gliese 876 system to model the unusual motions of the two known planets, and three years ago got an inkling that there might be a smaller, third planet orbiting the star. In fact, if they hadn’t taken account of the resonant interaction between the two known planets, they never would have seen the third planet.

“We had a model for the two planets interacting with one another, but when we looked at the difference between the two-planet model and the actual data, we found a signature that could be interpreted as a third planet,” Lissauer said.

A three-planet model consistently gave a better fit to the data, added Rivera. “But because the signal from this third planet was not very strong, we were very cautious about announcing a new planet until we had more data,” he said.

The team now has convincing data for the planet orbiting very close to the star, at a distance of about 10 stellar radii. That’s less than one-tenth the size of Mercury’s orbit in our solar system.

A paper detailing their results has been submitted to The Astrophysical Journal. Authors include Steven Vogt, of the University of California, Santa Cruz; Paul Butler of the Carnegie Institution of Washington; Geoffrey Marcy of the University of California, Berkeley; Jack Lissauer of NASA’s Ames Research Center; Gregory Laughlin of the Lick Observatory at UCSC; Debra Fischer of San Francisco State University and Timothy M. Brown of NSF’s National Center for Atmospheric Research in Boulder, Colorado.


The news was announced by the National Science Foundation. A copy of the press release may be obtained at:
NSF Press Relese (html)

The W. M. Keck Observatory ( is managed by the California Association for Research in Astronomy (CARA), a non-profit scientific partnership of Caltech, the University of California, and NASA.