Smallest extra-solar planet is three times more massive than Earth

Washington, June 3 : Astronomers have discovered an extra-solar planet that is only three times more massive than our own, the smallest yet detected outside our solar system and has the smallest host star yet detected.

The international research team that found this planet was led by David Bennett of the University of Notre Dame in the US.

The star that the planet orbits itself is not large, perhaps as little as one twentieth the mass of our Sun, suggesting to the research team that relatively common low-mass stars may present good candidates for hosting Earth-like planets.

"Our discovery indicates that that even the lowest mass stars can host planets," said Bennett. "No planets have previously been found to orbit stars with masses less than about 20 percent that of the Sun, but this finding indicates that even the smallest stars can host planets," he added.

The astronomers used a technique called gravitational microlensing to find the planet, a method that can potentially find planets one-tenth the mass of our own.

The gravitational microlensing technique, which came from Einstein's General Theory of Relativity, relies upon observations of stars that brighten when an object such as another star passes directly in front of them.

"This discovery demonstrates the sensitivity of the microlensing method for finding low-mass planets, and we are hoping to discover the first Earth-mass planet in the near future," said Bennett.

Using standard nomenclature, the star hosting the newly discovered planet is dubbed MOA-2007-BLG-192L.

It resides 3,000 light years away and is classified as either a low-mass hydrogen burning star, one that sustains nuclear reactions in its core as our Sun does, or a brown dwarf, an object like a star yet without the mass to sustain nuclear reactions in its core.

The researchers were unable to confirm which category the star fits into due to the nature of the observations and the margin of error.

Researchers in New Zealand made the initial measurements of the new planet and its star using the new MOA-II telescope at the Mt. John Observatory.

Researchers in Chile made follow-up observations using high angular resolution adaptive optics images at the Very Large Telescope at the European Southern Observatory.

Data from the observations was analyzed by scientists around the world hailing from five continents.

"This discovery is very exciting because it implies Earth-mass planets can form around low-mass stars, which are very common," said Michael Briley, NSF astronomer. "It is another important step in the search for terrestrial planets in the habitable zones of other stars," he added.

ANI