Thousands of planets will likely be discovered in the next few years, and a new system is needed to better classify the ability of those worlds to support life. In a paper to be published in the December 2011 issue of Astrobiology, co-author David Catling from the Department of Earth and Space Sciences and colleagues propose a new system that classifies some planets as either similar to Earth or not similar but capable of harboring life. That is different from the current system, which is dominated by the notion that Earth serves as the best model of conditions suited to the emergence of life on other worlds.