Life on other planets more widespread

Planets previously considered uninhabitable may be able to sustain life according to research from the University of Aberdeen

Earth-sized planets can support life at least ten times further away from stars than previously thought, according to academics at the University of Aberdeen.

A new paper published in Planetary and Space Science claims cold rocky planets previously considered uninhabitable may actually be able to support life beneath the surface.

The team, which included academics from the University of St Andrews, challenge the traditional 'habitable zone' – i.e. the area of space around a star, or sun, which can support life – by taking into consideration life living deep below the ground.

"The traditional habitable zone is also known as the Goldilocks zone," explains PhD student Sean McMahon.

"A planet needs to be not too close to its sun but also not too far away for liquid water to persist, rather than boiling or freezing, on the surface.

"But that theory fails to take into account life that can exist beneath a planet's surface. As you get deeper below a planet's surface, the temperature increases, and once you get down to a temperature where liquid water can exist – life can exist there too."

The team created a computer model that estimates the temperature below the surface of a planet of a given size, at a given distance from its star.

"The deepest known life on Earth is 5.3 km below the surface, but there may well be life even 10 km deep in places on Earth that haven't yet been drilled.

"Using our computer model we discovered that the habitable zone for an Earth-like planet orbiting a sun-like star is about three times bigger if we include the top five kilometres below the planet surface.

"The model shows that liquid water, and as such life, could survive 5km below the Earth's surface even if the Earth was three times further away from the sun than it is just now.

"If we go deeper, and consider the top 10 km below the Earth's surface, then the habitable zone for an Earth-like planet is 14 times wider."

The current habitable zone for our solar system extends out as far as Mars, but this re-drawn habitable zone would see the zone extend out further than Jupiter and Saturn.

The findings also suggest that many of the so-called "rogue" planets drifting around in complete darkness could actually be habitable.

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White Dwarfs hold the key to detecting Life on other Planets

Because it has no source of energy, a dead star—known as a white dwarf—will eventually cool down and fade away but circumstantial evidence suggests that white dwarfs can still support habitable planets, says Prof. Dan Maoz of Tel Aviv University's School of Physics and Astronomy.

Now Prof. Maoz and Prof. Avi Loeb, Director of Harvard University's Institute for Theory and Computation and a Sackler Professor by Special Appointment at TAU, have shown that, using advanced technology to become available within the next decade, it should be possible to detect biomarkers surrounding these planets—including oxygen and methane—that indicate the presence of life.

Dan Maoz

Published in the Monthly Notices of the Royal Astronomical Society, the researchers' "simulated spectrum" demonstrates that the James Webb Space Telescope (JWST), set to be launched by NASA in 2018, will be capable of detecting oxygen and water in the atmosphere of an Earth-like planet orbiting a white dwarf after only a few hours of observation time—much more easily than for an Earth-like planet orbiting a sun-like star.

Their collaboration is made possible by the Harvard TAU Astronomy Initiative, recently endowed by Dr. Raymond and Beverly Sackler.

Faint light, clear signals
"In the quest for extraterrestrial biological signatures, the first stars we study should be white dwarfs," said Prof. Loeb.

Prof. Loeb

Prof. Maoz agrees, noting that if "all the conditions are right, we'll be able to detect signs of life" on planets orbiting white dwarf stars using the much-anticipated JWST.

An abundance of heavy elements already observed on the surface of white dwarfs suggest rocky planets orbit a significant fraction of them.

The researchers estimate that a survey of 500 of the closest white dwarfs could spot one or more habitable planets.

The unique characteristics of white dwarfs could make these planets easier to spot than planets orbiting normal stars, the researchers have shown.

Their atmospheres can be detected and analyzed when a star dims as an orbiting planet crosses in front of it.

James Watt Space Telescope - JWST

As the background starlight shines through the planet's atmosphere, elements in the atmosphere will absorb some of the starlight, leaving chemical clues of their presence—clues that can then be detected from the JWST.

When an Earth-like planet orbits a normal star, "the difficulty lies in the extreme faintness of the signal, which is hidden in the glare of the 'parent' star," Prof. Maoz says.

"The novelty of our idea is that, if the parent star is a white dwarf, whose size is comparable to that of an Earth-sized planet, that glare is greatly reduced, and we can now realistically contemplate seeing the oxygen biomarker."

In order to estimate the kind of data that the JWST will be able to see, the researchers created a "synthetic spectrum," which replicates that of an inhabited planet similar to Earth orbiting a white dwarf.

They demonstrated that the telescope should be able to pick up signs of oxygen and water, if they exist on the planet.