Earth is now on the edge of the habitable zone for life

Earth is pretty good at supporting life, but according to a new estimate of what constitues a planetary "habitable zone," it looks like our planet (and perhaps many others) is only barely in the right place.

Two decades ago, before astronomers were finding potential alien planets all over the galaxy, Penn State University researcher James Kasting developed the original definition of a habitable zone, the area in a solar system in which a planet can contain liqud water. Too close to a star and any water that could be on the planet will vaporize. Too far and it will freeze. Planets like Earth are in that just-right position relative to their stars to support life. 

Kasting's original estimates placed the habitable zone between 0.96 astronomical units (or AU, the distance between the Earth and the sun) and 1.67 AU. Now, using updated databases known as HITRAN (high-resolution transmission molecular absorption) and HITEMP (high-temperature spectroscopic absorption parameters), which measure planets' absorption parameters of water and carbon dioxide, a Penn State University research team that includes Kasting has determined that those estimates were wrong. 

See, when Kasting made his original calculations, he didn't have all these new exoplanets to add to his data. Now that we've seen other potentially habitable planets out there, we've added to these databases, both of which help indicate whether a planet has the right atmospheric conditions to hold liquid water. Based on all that new data, researchers have now determined that the habitable zone is actually between 0.99 and 1.7 AU, putting Earth right on the edge of being too hot for water.

But obviously, Earth does support life quite well. The question is how this will affect all those other exoplanets out there waiting to be explored. Some of them have just become too hot for life, while others have just moved into the habitable zone after decades of being deemed too cold. 

"This will have a significant impact on the number of planets that are within habitable zone," said lead researcher Ravi Kumar Kopparapu. 

So this week science has, in some ways, completely changed how we view the search for life on other planets. Now we have to see if all those planets in the habitable zone show us anything interesting.

(Via NBC News)

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