Planet Discovered with Only 3 Times the Mass of the Earth

Most of the planets found to date have been massive and orbiting their parent stars at a fraction the orbit of Mercury – the hot jupiters. They’re interesting to astronomers, but the big goal is going to be finding Earth-mass planets orbiting other stars. To do this, astronomers are looking for less massive stars, where the effects of gravity from a smaller, Earth-sized planet will be easier to spot. Today, an international team of astronomers announced they have found a planet with only 3 times the mass of the Earth orbiting a tiny star that can barely support nuclear reactions.

The announcement of this new planet, known as MOA-2007-BLG-192Lb, was made at the 212th meeting of the American Astronomical Society held in St. Louis from June 1-5, 2008. Researchers from several universities, including the University of Notre Dame presented their findings.

The star is known as MOA-2007-BLG-192L, and it’s located about 3,000 light-years away. It’s probably not actually a star, with only 6% the mass of our own Sun. These objects are classified as brown dwarfs, because they don’t have enough mass to sustain nuclear reactions in the core. I say “probably” because the uncertainty of the observations might put it into the very low end of a hydrogen-burning star.

Researchers found the planet and star using the gravitational microlensing technique. This is where two stars line up perfectly from our point of view here on Earth. As the two stars begin to line up, the foreground star acts as a lens to magnify and distort the light from the more distant star. By watching how this brightening happens, astronomers can learn a tremendous amount about the nature of both the foreground and background star.

In this case, there was an additional gravitational distortion from the planet orbiting the foreground star MOA-2007-BLG-192L, which astronomers were able to tease out in their data.

This technique demonstrates the gravitational microlensing might be one of the best ways to find Earth-mass planets. In fact, the researchers think the technique will turn up the first one. Here’s David Bennett, from the University of Notre Dame: “I’ll hazard a prediction that the first extra-solar Earth-mass planet will be found by microlensing. But we’ll have to be very quick to beat the radial velocity programs and NASA’s Kepler mission, which will be launched in early 2009.”

Unfortunately, the lensing events can only happen one time. The foreground star will probably never be seen again since it was only revealed by the two stars lining up. Astronomers have to work fast to get all their data collected.

Original Source: University of Notre Dame News Release