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For an exoplanet to be in the habitable zone around its star — at to the lowest degree as how we define it — information technology needs to have enough atmospheric pressure to support liquid water on the surface. You can decide this, given enough information about the exoplanet, based on how much energy it receives from its parent star and how far abroad it is in orbit, and then past comparing that with what life needs to flourish.

This has been the basis for a lot of research into finding alien life on other worlds, likewise as on other moons within our own solar arrangement. Using the NASA'southward Kepler space telescope, astronomers have been finding thousands of possible exoplanets around other stars, and often more one for a given star. At present researchers from both the Australian National University and the Niels Bohr Found in Copenhagen accept figured out how probable information technology is for stars in the Milky way to have planets in the habitable zone, where liquid water could be nowadays, and the event is pretty astounding: from one to three per star.

The photo at the top of this story (Credit: NASA/Kepler) shows the habitable zone (in green) for dissimilar types of stars, meaning that liquid water could potentially be on the surface. The red areas are too hot for that, and the blue areas are too cold for information technology.

Kepler Exoplanet NASA

Here's what we know then far: Nosotros've found over ane,800 exoplanets around stars in the Milky way. Scientists have at present establish that each star has from two to six planets, at to the lowest degree that nosotros can find via information from Kepler, if non more than that. (We're even already looking for the beginning exomoon around an exoplanet.) The trick is teasing out from the data which of those planets are far enough from their parent star to be in the habitable zone, and whether there are others not showing in the data that could skew the results. To do so, the research team employed the Titius-Bode constabulary, which 18th-century astronomers originally used to calculate the position of Uranus before Sir William Herschel officially discovered information technology in 1781.

In uncomplicated terms — meaning those that this author can understand — the law states that there's a progressive ratio betwixt the orbital periods of planets in a given solar system. Information technology means that if yous know, say, how long it takes for Mercury and Venus to orbit our Sun, and then y'all can effigy out on paper how long the other planets take, and then figure out if one should be there that isn't there.

The researchers used this method to predict, for 151 planetary systems, where there were likely to be more planets than what was already showing in the Kepler data. Then they evaluated which ones would be in the habitable zone based on those calculations, and arrived at the one-to-three number per organization.

"Using T-B's law, we tried to predict where there could be more planets farther out in the planetary systems," Steffen Kjær Jacobsen, a PhD pupil at the Niels Bohr Institute at the University of Copenhagen, said in a statement. "But nosotros only fabricated calculations for planets where there is a practiced chance that you can encounter them with the Kepler satellite." The researchers and then made note of some "Goldilocks" planets that they're hoping Kepler will find in the future as information technology continues to sweep the heavens. And, maybe at some point fifty-fifty soon, we'll find out for sure whether there actually is life beyond world.