To compare alien planets, Dr. Mendez at the Planetary Habitability Laboratory and his colleagues are creating an Earth Similarity Index that ranks worlds by their resemblance to our own planet, on a scale from zero to one, based on their mass, radius, density and surface temperature.

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We're now on track to go from zero -- zero commercial-scale biofuel refineries to 19 by the year 2012, and from no commercial-scale power plants operating carbon capture to five by the year 2015.

WHITEHOUSE: Meeting with Governors on Energy Policy

Binzel recently created a 10-point scale for estimating the threat of a near-Earth asteroid, with zero indicating no chance of an Earth impact and 10 indicating a certain Earth impact with severe, global damage.

CNN: Scientists reduce odds of Earth-asteroid collision