New 'Habitability Index' Ranks Exoplanets for Potential to Host Alien Life

Tuesday, 13 October 2015 - 12:34PM
Astrobiology
Alien Life
Tuesday, 13 October 2015 - 12:34PM
New 'Habitability Index' Ranks Exoplanets for Potential to Host Alien Life
As telescopes become more and more powerful, astronomers will be able to investigate a plethora of exoplanets, and essentially won't know where to begin searching for of extraterrestrial life. Now, researchers from the University of Washington have devised a new "habitability index," in order to guide the search for alien life based on near-future observations of exoplanet atmospheres.

Usually, when astronomers are searching for extraterrestrial life, the main criterium is its location relative to its star, or whether it lies in the "Goldilocks zone." The Goldilocks zone is the area in which a planet is close enough to its star that the planet isn't frozen and hostile to life but far enough away that it can potentially host liquid water. 

Opening quote
"That was a great first step, but it doesn't make any distinctions within the habitable zone," said lead author Rory Barnes. "Now it's as if Goldilocks has hundreds of bowls of porridge to choose from."
Closing quote


The Kepler Space Telescope has allowed for the detection of thousands of exoplanets, and the technology is only getting more advanced. But there are already far too many exoplanets to investigate individually; even though telescopes are getting more powerful, their usage is extremely expensive and painstaking, so the limited resources need to be directed somehow if we are to have any hope of finding alien life. In the new paper by Barnes and Victoria S. Meadows, the researchers detail a means of comparing and ranking exoplanets for their potential to host alien life in order to guide this search. 

Opening quote
"Basically, we've devised a way to take all the observational data that are available and develop a prioritization scheme," said Barnes, "so that as we move into a time when there are hundreds of targets available, we might be able to say, 'OK, that's the one we want to start with.'"
Closing quote


The index allows astronomers to input a variety of different values into a form, which will then output the probability that the exoplanet can host liquid water. The factors include the planet's estimated rockiness and a phenomenon called the "eccentricity-albedo degeneracy," which compares the energy reflected back into space (albedo) to the circularity of its orbit, which determines how much energy the planet receives from its host star. If the planet's orbit is more elliptical, or eccentric, rather than circular, it will receive more energy from its host star, so planets at the outer edge of the "Goldilocks zone" would need a more elliptical orbit in order to be habitable, while planets at the inner edge would need a higher albedo in order to cool the planet's surface so it's not too hot for liquid water.

While Kepler has detected thousands of exoplanets, the habitability index will be most useful in a few years, once the James Webb Telescope is launched. This state-of-the-art technology will allow us to measure the atmospheric composition of exoplanets for the first time, which means we'll be able to calculate habitability more accurately than ever before. But we need a means to prioritize certain exoplanets over others, which is where the habitability index comes in.

Opening quote
"This innovative step allows us to move beyond the two-dimensional habitable zone concept to generate a flexible framework for prioritization that can include multiple observable characteristics and factors that affect planetary habitability," said Meadows. "The power of the habitability index will grow as we learn more about exoplanets from both observations and theory."
Closing quote


Via Space.com.
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Astrobiology
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