Another New Exoplanet Found.

This lunchtime perusal of the Sky and Telescope web site revealed this interesting story about an exoplanet that, while more massive than Earth, appears to be closer to Earth's mass than most previously discovered exoplanets.

January 25, 2006 Three international groups have teamed up to discover what is probably the lowest-mass exoplanet ever found around a normal star. The planet's mass is between 3 and 11 times that of Earth, with a most likely mass of 5.5 Earths. The previous record-holder, which orbits the red-dwarf star Gliese 876, contains about 7.5 Earth masses. The only known exoplanets with lower masses are four objects orbiting a pulsar — the collapsed core of a massive star that went supernova.

The newfound planet was the third exoplanet discovered by gravitational microlensing — an effect predicted by Einstein's general theory of relativity that occurs when two objects line up almost perfectly with Earth. In this case, a foreground red-dwarf star passed in front of a background star and acted as a gravitational lens. The red dwarf's gravity redirected some of the background star's light toward Earth, causing the background star to brighten threefold and then fade over the course of 1½ months. A planet orbiting the red dwarf acted like a secondary lens, causing a slight additional brightening and fading that lasted about 30 hours.

The OGLE (Optical Gravitational Lensing Experiment) group, which is led by Andrzej Udalski (Warsaw University Observatory, Poland), first noticed the brightening of the background star on July 11, 2005. OGLE alerted two other groups, PLANET and MOA, and all three began monitoring the star continuously with telescopes around the world. They detected a characteristic brightening that peaked on July 31st. As the background star was fading on August 9th, the teams observed a 30-hour brightening and fading caused by the planet, which has been named OGLE-2005-BLG-390Lb. The PLANET group, led by Jean-Philippe Beaulieu (Paris Astrophysical Institute), made the most sensitive and critical observations on August 9th and 10th.

Unfortunately, the microlensing method detects the host star and planet only through their gravity. About all that can be said right now is that the system is roughly 22,000 light-years away in the direction of the galactic center, the planet lies roughly 2.6 astronomical units from the star (which would put it in the asteroid belt in our solar system), and it probably takes about 10 years to complete one orbit. Since the star radiates only about 1 percent the energy of the Sun, the planet must have a surface temperature of about –220°C (–364°F), which is almost certainly way too cold for life.

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22,000 light-years is about 2/3 the distance the Sun is from the center of the Milky Way. Not that we'd be heading off to Gliese 876 soon either, even at a distance of a mere 15 light-years. Christ, NASA's New Horizons Pluto mission will take until 2015 to perform its flyby of that planet and it's moons, and Pluto is within astronomical spitting distance at about three billion miles (4.8 billion kilometers), so it's pretty much a lock that if anyone lives on these worlds, they are gonna have to come visit us is they want to make their presence felt because we ain't going anywhere right now.