Now, a team of scientist is suggesting an alternative equation based on a planet's chemistry and its "origin of life"-type events.
"It has somewhat of the methodology of the Drake Equation because it's trying to compute some parameter that might help you evaluate the prevalence of life in the cosmos," said astronomer Seth Shostak, with the SETI Institute in Mountain View, Calif., and who was not involved in the study.
SETI is an acronym for The Search for Extraterrestrial Intelligence.
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The new study is based on the idea that life's origin on early Earth, and presumably other planets, was not a one-shot process.
The idea is that there were "lots and lots of experiments going on and it may be that they actually helped one another, though not deliberately ... Some molecule that's made over here by accident and which isn't alive may help that molecule over there, which also is not alive, take another step toward something that is alive," Shostak said.
"They're just trying to put all that into some mathematics so that it gives you some idea of the probability that all that will work. That's my take on it," Shostak said.
Origin of life-type events, "may be the critical difference between cosmic environments where life is potentially more or less abundant but, more importantly, points to constraints on the search," SETI researchers Caleb Scharf, with Columbia University, and Leroy Cronin, with the University of Glasgow, write in the new study.
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Their research also points out that if planets in a star system swap spit, so to speak, with meteorites from one body landing on the other, chances of life arising on either or both of those worlds is higher than for planets in more isolating conditions.
The new equation also could have practical results, especially when combined with the search for potentially habitable exoplanetary systems, Scharf and Cronin said.
The study is published in this week's edition of the Proceedings of the National Academy of Sciences.
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