New Planet Points the Way for ET Hunters

By Eliza Strickland | June 3, 2008 1:02 pm

exoplanetIn a solar system far, far away, around a small and dim star, orbits a small planet, just three times the size of Earth.

The astronomers who discovered the small planet don’t know much else about it yet, but the basics are enough to get them excited. Extraterrestrial life is thought to have the best chance of surviving on planets with a similar mass to that of Earth, orbiting small stars.

This “exoplanet,” which goes by the romantic name MOA-2007-BLG-192Lb, is the second smallest planet ever spotted outside our solar system. The very smallest planet yet discovered is believed to be sterile, as it orbits a neutron star that emits blasts of radiation.

Lead astronomer David Bennett of the University of Notre Dame cautioned that the newly discovered planet is not an ideal candidate for extraterrestrial life. The star it orbits appears so small and dim that it’s likely a brown dwarf, a “failed” star which can’t maintain the nuclear fusion reaction that makes our own sun a source of warmth and light.

At the announcement at an American Astronomical Society meeting, Bennett said that the surface of the planet is probably rather dark and could could be frozen solid, like Pluto on the edge of our solar system. However, a slight chance remains that it could be habitable, researchers said.

Nicholas Rattenbury, a co-author from the University of Manchester and Jodrell Bank, told BBC News: “Our best ideas about how planets form suggests the planet could have quite a thick atmosphere. This atmosphere could act like a big blanket, keeping the planet warm. So even though there’s very little energy coming from its host star, hitting the planet and warming it up that way, internal heat coming from within the planet could be warming up the surface. This has led to some speculation that there could, possibly, be a liquid ocean on the surface of this planet” [BBC News].

Whether or not the orb has ever been home to liquid oceans and some squiggly form of life, Bennett said the discovery of the small planet around the small star has encouraged his team to hunt for similar systems. “The fact that we’re finding outer planets around low-mass objects is an indication that planets are forming in these low-mass systems,” the University of Notre Dame physicist said. Many such systems are relatively nearby and would be easy places to take the next step—the search for life [National Geographic News].

The research team used telescopes in New Zealand and Chile to make their observations, and used a technique called gravitational microlensing to identify the planet. 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 (relative to an observer, in this case on Earth). The gravity of the passing star acts as a lens, much like a giant magnifying glass. If a planet is orbiting the passing star, its presence is revealed in the way the background star brightens [National Science Foundation].

Image: NASA’s Exoplanet Exploration Program


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