The exoplanet express just keeps on rolling: The European Space Agency (ESA) today announced the discovery of the smallest known planet orbiting a normal star other than the sun. The newly discovered extrasolar planet, or exoplanet, which appears to be terrestrial (that is, not a gas giant like Jupiter), has a radius less than twice that of Earth.

The exoplanet has been dubbed COROT-Exo-7b after the European satellite COROT, which located it. The space telescope revealed the exoplanet by monitoring how the light from its parent star dimmed as the planet transited, or passed in front of the star during orbit (see brightness graph, not to scale, at left). Most of the 300-plus exoplanets so far discovered have been found using this method or by observing the wobbling of stars induced by the gravitational pull of orbiting bodies.

Mass-wise, the new planet appears to be in the lower echelon, with something less than 11 Earth-masses, but seemingly less massive planets with unresolved dimensions have been found. A better estimate of the mass of COROT-Exo-7b will require further analysis of its terrestrial makeup and hence its density.

As with most known exoplanets, COROT-Exo-7b appears too extreme to harbor life. According to the ESA, the planet sticks close to its star, completing an orbit every 20 hours, and so is very toasty—1,800 to 2,700 degrees Fahrenheit (1,000 to 1,500 degrees Celsius). The discovery is being submitted for publication in the journal Astronomy & Astrophysics.