Billions And Billions….
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Artist’s impression showing a sunset as seen from the super-Earth exoplanet Gliese 667. Image Credit: ESO/L. Calçada
New research from the ESO’s HARPS mission provides evidence that small, rocky, Earth-sized planets are extremely common, especially in the habitable zones around faint red dwarf stars. Based on this new research, an international team places an estimate of tens of billions of these worlds in our galaxy alone, and possible hundreds of billions in our cosmic neighborhood. The team’s research is based on direct measurements of the frequency of exoplanets around red dwarf stars, which are reported to make up over three-quarters of the stars in our Galaxy.
Regarding their research, team lead Xavier Bonfils (IPAG, Observatoire des Sciences de l’Univers de Grenoble) states, “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.”
Over a period of six years, the team performed a survey of over one hundred red-dwarf stars. During the course of the study, nine “super-Earth” exoplanets were discovered, two of which were in the “habitable zone” of their parent star. From information gathered, the team was also able to estimate the distance at which the exoplanets orbited their parent star, as well as the mass of the detected exoplanets. After combining the data, the team then determined how common different types of exoplanets are around red dwarf stars. Interestingly enough, and not entirely surprising, red dwarf stars are found to have fewer “gas giant” (such as Jupiter) exoplanets. In fact, the teams research estimates roughly 12% of red dwarfs have a “gas giant” orbiting them.
Given the high number of red dwarf stars near (cosmically speaking) our solar system, the team’s estimates place about one hundred “super-Earth” exoplanets within about ten parsecs (~32 light years). Being in a star’s “habitable zone” doesn’t necessarily mean life can exist on such worlds. Team member Stéphane Udry (Geneva Observatory) adds, “The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to the star than the Earth is to the Sun. But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely.”
Gliese 667Cc is one exoplanet discovered in the HARPS survey – the second planet in a triple star system. Orbiting in the near-center of its host star’s habitable zone, the world is more than four times heavier than Earth, but is the closest known “twin” to Earth. Given the distance between Gilese 667Cc and its parent star, conditions may be right for liquid water on its surface. Gilese 667Cc is the second “super-Earth” exoplanet inside the habitable zone of a red dwarf discovered by the HARPS survey – Gliese 581d was announced in 2007 and confirmed in 2009.
“Now that we know that there are many super-Earths around nearby red dwarfs we need to identify more of them using both HARPS and future instruments. Some of these planets are expected to pass in front of their parent star as they orbit — this will open up the exciting possibility of studying the planet’s atmosphere and searching for signs of life,” concludes team member Xavier Delfosse.
Source:ESO Press Release
Ray Sanders is a Sci-Fi geek, astronomer and blogger. Currently researching variable stars at Arizona State University, he writes for Universe Today, The Planetary Society blog, and his own blog, Dear Astronomer
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