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article imageBillions of planets in habitable zone of red dwarfs in Milky Way

By JohnThomas Didymus     Apr 29, 2012 in Science
A new estimate of habitable planets orbiting red dwarf stars, considered the most common in our galaxy, indicates there may be "tens of billions" of rocky planets like our Earth in the Milky Way galaxy alone and about 100 in the Sun's neighborhood.
According to PhysOrg, the new result from ESO’s HARPS planet finder shows that rocky planets about the size of our Earth are very common in the habitable zones around red dwarfs.
The new study concluded that the tens of billions of planets could have liquid water. According to the study, this fact dramatically increases our chances of finding extraterrestrial life in our galaxy.
Red dwarfs are a type of stars that are fainter, cooler and less massive than our Sun. Our Sun is a typical Class G star. Red dwarfs generally have longer life spans than Class G stars. Astronomers estimate that red dwarfs make up 80 percent of stars in the Milky Way galaxy.
Space.com reports that red dwarfs had previously not been considered viable candidates for planets bearing life because they are small and dim and consequently their habitable zone is a narrow band around the star. The habitable zone of a star is the region of space around the star where the surface of an orbiting planet can hold liquid water. According to Space.com, Seth Shostak, senior astronomer at the Search for Extraterrestrial Intelligence Institute (SETI), in Mountain View, California, said: "The habitable zone would be very, very small. Consequently, the chances that you would actually find any planet at the right distance from the sun to be attractive to life was likely to be small, too."
Physorg reports that the new study concluded, after analysis of data obtained from the European Space Agency's HARPS Spectrograph on the 3.6-metre telescope at ESO's La Silla Observatory in Chile, that 41 percent of red dwarfs may have planets concealed in their habitable zone. The study was based on a sample of 102 red dwarfs. Space.com reports Shostak said: "The number of habitats might increase by a factor of 8 or 10."
According to Physorg, Xavier Bonfils, leader of the team at the IPAG ( Observatoire des Sciences de l'Univers de Grenoble, France), said: "Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet. Because red dwarfs are so common — there are about 160 billion of them in the Milky Way — this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone."
According to Space.com, one of the problems with planets orbiting close to a red dwarf, as far as search for extraterrestrial life is concerned, is the intensity of radiation close to a red dwarf. A planet orbiting within the habitable zone of a red dwarf would be bombarded with powerful radiation, especially when storms erupt from the star. Such storms expose the surface of the planet to levels of radiation harmful to life.
But even under such conditions, if the planet has a magnetic field, life may survive on the surface of the planet. Alternatively, if the planet has oceans then life could survive and evolve underwater, with the water shielding the life forms from harmful radiation.
Space.com identifies another problem with planets orbiting close to red dwarf stars as the phenomenon of tidal locking. Tidal locking keeps one side of a planet facing its star permanently, and causing this side alone to receive most of the heat from the star. But some researchers have found that other planets in the system could exert gravitational influence that prevents tidal locking.
Shostak also told Space.com that if a planet experiencing tidal locking has an atmosphere, wind could move hot atmosphere to the cooler and darker side and help warm the cool side, while, at the same time, the hot side gets cooled. Shostak said: "Clearly, if it's too cold on one side and too hot on the other, somewhere in the middle there's that lovely Goldilocks zone where everybody wants to build their condos."
But even with these problems, the increase in estimate of potentially habitable planets still improves our chances of finding extraterrestrial life. Shostak said: "SETI is looking for Mr. Right or maybe Ms. Right, depending on your point of view. It helps to find out that there's 10 times as many candidates as there were before."
More about Alien life, habitable worlds, extraterrestrial life, habitable zone, billions of planets
 
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