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12271Our Closest Star System Alpha Centauri B Could Harbor 'Superhabitable' Worlds"

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  • derhexerus
    Mar 28 6:16 PM
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      URL to an interesting post from The daily Galaxy blog

      (Madness takes its toll. Please have exact change)

      Researchers have concluded superhabitable worlds will tend to orbit orange dwarfs and be slightly older and two to three times more massive than Earth. This could make orange dwarf Alpha Centauri B, the member of the closest stellar system to the sun, an ideal target for searches of a superhabitable world, especially since it may host an Earth-mass planet.

      So-called "superhabitable" worlds are intriguing astrobiologists such as René Heller at McMaster University in Hamilton, Canada, who recently co-published a paper in the Jan. 16 issue of Astrobiology examining the prospects for habitable worlds that are very unlike Earth. One such planet might even exist around the stellar system closest to Earth Alpha Centauri B.

      There is life virtually everywhere there is liquid water on Earth. As such, the search for extraterrestrial life has focused on so-called habitable or "Goldilocks" zones — distances around stars at which a planet receives neither too much nor too little heat from its star to possess oceans of liquid water on its surface. (The moons of planets in the habitable zones of stars could potentially host surface water as well, opening up the possibility of inhabited moons.)

      Since Earth is the only inhabited world known, this planet has usually been the focus of studies on habitability. For instance, NASA's Kepler space telescope and the CoRoT satellite from the French National Center for Space Studies and the European Space Agency were aimed at detecting planets roughly the mass and diameter of Earth.

      However, Heller reasoned that worlds other than Earth-like ones could offer conditions suitable for life to emerge and evolve. Some planets and moons could be even better than Earth-like planets at offering such conditions. Heller was inspired by this idea after reading a question from his colleague John Armstrong at Weber State University in Ogden, Utah, submitted via an online live chat in 2012 at AbGradCon, a conference organized by and for early-career astrobiologists. The query asked what experts thought could make an exoplanet — a planet that orbits a star outside the solar system — an even more habitable planet than Earth.

      "It was this question that inspired me to start some research," Heller said.

      Instead of looking for rocky planets about the size and mass of Earth in roughly the same orbit as this planet, Heller catalogued a list of properties that could help make a world habitable. He then reasoned what kinds of planets or moons best fit these criteria.

      "Our study implies that searches for extrasolar inhabited worlds — planets or moons — should better not focus on the most Earth-like planets," Heller said.

      Past research by Heller and his colleagues found that planets and moons do not have to lie within habitable zones as they are conventionally described to possess surface water, nor do worlds within habitable zones necessarily have surface water. A key factor underlying habitability, besides the amount of light a world receives from its star, is how much that world gets heated by tidal forces.

      The tides that Earth experiences are caused by the gravitational pull of the moon and sun. Our tides pale in comparison to what we see elsewhere in the solar system — for instance, the gravitational pull Europa experiences from Jupiter leads to tidal forces roughly a thousand times stronger than what Earth feels from our moon.

      Tidal forces not only flex the surface of Europa, but heat it as well. Heller and his colleagues found tidal heating could render other rocky bodies habitable even outside the normal confines of a habitable zone, and make worlds within the conventional definition of a habitable zone uninhabitable.

      Heller also considered how much room a planet or moon might have to accommodate life. Other worlds might have more surface area than Earth, possessing a wrinklier surface or larger diameter. Moreover, planets with the same amount of land area as Earth but broken up into smaller continents might be more habitable, while continents that are too large (such as Earth's past continent Gondwana about 500 million years ago) might have vast, inhospitable deserts in their interiors. In addition, Earth's shallow waters have a greater biodiversity than its deep oceans, so planets with shallower waters may be superhabitable.

      Past research also suggests desert planets much like the world depicted in the science fiction classic "Dune," might also be a more common type of habitable planet in the galaxy, rather than watery planets such as Earth. Water vapor is a greenhouse gas that traps heat, and too much water vapor in a planet's atmosphere can actually render it too hot for life, as was the case with Venus. As such, even worlds with vast deserts could be more hospitable to life than many watery planets, if these desert planets also had many scattered oases of water in their deserts that could support life.