Study Finds Earth's Probability of Being Habitable Is 82%

Tuesday, 09 February 2016 - 10:41AM
Astrobiology
Earth
Alien Life
Tuesday, 09 February 2016 - 10:41AM
Study Finds Earth's Probability of Being Habitable Is 82%
Astronomers from the University of Washington have devised a new habitability index, based on a planet's appearance when it's transiting its star, and according to this metric, Earth's probability of being habitable is 82%. This not only means that alien astronomers from a faraway galaxy would be approximately 80% sure Earth is habitable, but that there are several exoplanets that have already been discovered which are "more likely to be habitable" than Earth.

In the study, researchers synthesized a new habitability index called the "habitability index for transiting exoplanets" ("HITE"), which ranks exoplanets in order to prioritize the ones that are most likely to be habitable for further research. Factors that impact a planet's HITE include common criteria for determining habitability, such as the size of the planet and distance from the star, but also includes the overall energy equilibrium of the planet, which tells us whether the planet is warm enough to emit energy into space.

The index also includes the eccentricity of the planet's orbit, and entails a penalty for orbits that have a large radius. This planetary behavior is helpful for determining habitability in the long term, because solar systems with eccentric orbits are more likely to destroy each other. But in the short term, it's not very relevant, so the researchers used the HITE without taking into account the eccentricity (a metric they call H′) in order to rank exoplanets.

Opening quote
"Basically, we've devised a way to take all the observational data that are available and develop a prioritization scheme," lead author Rory Barnes told Universe Today, "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

Using this index, they found that Earth's H′ is only .82, meaning that from the vantage point of another galaxy, Earth would only appear to be 82% likely to be habitable. This is interesting in itself, but more significantly, there are many exoplanets already discovered that have similar habitability indexes, including Kepler 442-b (.84) and KOI 6108.01 (.87), and are worth a closer look for alien life. Funnily enough, there are several planets that have significantly higher habitability rankings than Earth, including KOI 5737.01 (.92), KOI 7235.01 (.93), and KOI 3456.02 (.96).

Opening quote
"This does not mean these planets are 'more habitable' than Earth," the authors wrote in their paper, "it means that an Earth twin orbiting a solar twin that is observed by Kepler would not have the highest probability of being habitable."
Closing quote

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