Smallest Planet Outside Solar System Found

January 31, 2006 -- An international group of scientists found the smallest planet yet detected orbiting around a normal star outside our solar system. Its detection fuels the hope of discovering more planetary systems in the future. The planet is five times the size of Earth and orbits a red dwarf every 10 years.

The planet was found indirectly by observing the motion of stars. When one star passes in front of another, the gravity of the front star bends the light of the star behind it, acting like a lens and focusing the light, a phenomenon called gravitational microlensing. Additional brightening can reveal the presence of a companion planet to the front star that would otherwise be too faint for telescopes to detect.

None of the roughly 160 known planets outside our solar system have been directly imaged because they are too dim and close to their stars to be seen. Because the chances of witnessing a microlensing effect are unpredictable and rare, astronomers improve their odds by having monitoring teams watch 100 million stars every night.

Several National Research Council reports deal with astronomical discovery. Astronomy and Astrophysics in the New Millennium recommends major astronomy initiatives, including the use of microlensing and other techniques to search for other planetary systems. The Atacama Large Millimeter Array (ALMA): Implications of a Potential Descope advises that a 60-element array would be greatly superior to any current or planned comparable instruments and would revolutionize millimeter and submillimeter astronomy, which could be used for planetary discoveries.

Assessment of Options for Extending the Life of the Hubble Space Telescope: Final Report recommends steps to ensure continuation of the extraordinary scientific output of the Hubble Space Telescope, which has collected other evidence of planets orbiting stars. The letter report Review of Science Requirements for the Terrestrial Planet Finder concluded that the Terrestrial Planet Finder project should remain ranked third among NASA's major missions and sixth overall in its research priority, but the current accelerated schedule for one of the project's missions does not leave enough time for vital precursor missions and proceeding would disrupt the balance of NASA’s space science portfolio.

• Astronomy and Astrophysics in the New Millennium (2001)
• Astronomy and Astrophysics in the New Millennium: Panel Reports (2001)
• The Atacama Large Millimeter Array (ALMA): Implications of a Potential Descope (2005)
• Assessment of Options for Extending the Life of the Hubble Space Telescope: Final Report (2005)
• Review of Science Requirements for the Terrestrial Planet Finder: Letter Report (2004)

• Hubble Press Release
• OGLE monitoring team
• PLANET monitoring team
• RoboNet monitoring team
• MOA monitoring team