Number of Habitable Planets Increases By Billions, Study Finds

Norman Byrd's picture

There are billions of planets out there that are yet to be discovered. Of those, only a fraction will be habitable by human standards. But to that fraction, a new study says planets circling red dwarf stars should be added, because they, too, have a "Goldilocks Zone" of habitability.

Red dwarf stars are everywhere. In fact, they make up over 80 percent of the stars in the Milky Way galaxy. And around those stars, like most stars, planets revolve. However, where once it was thought that planets would have to be inordinately close to the red stars in order for said planets to be warm enough for liquified water yet would be too close to be safe from radiation bombardment, scientists now say that conditions could exist in a rather small "Goldilocks Zone" whereby the planets might be able to sustain an environment conducive to living organisms. Under the right conditions, that is. And those parameters have increased the potential number of habitable planets by billions.

A six-year study involving 102 red dwarfs revealed that rocky worlds -- like Earth -- are common. In fact, according to European Southern Observatory’s HARPS planet finder, there should be four super-Earths to be found around every ten red dwarfs.

“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,” HARPS team leader Xavier Bonfils of the Observatoire des Sciences de l’Univers de Grenoble, France, noted, according to Astrobiology Magazine. “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.”

So what does this mean for the possibility of finding life on worlds circling red dwarf stars?

Seth Shostak, senior astronomer at SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, Calif. told Space.com, "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."

This would increase the potential number of habitable worlds in the Milky Way about 8-10 times, he said. Increasing the potential number also increases the odds of finding worlds with extraterrestrial life.

As for conditions being right (along with the planets being located within the Goldilocks Zone) to support living organisms, scientists entertain several scenarios where life could survive, even under the brutally harsh radiation of a red dwarf. A magnetic field wrapping a planet could shield living organisms, as well as could bodies of water. As for planets that suffered tidal locking (where one side of planet always faces the star), conditions could exist that circulate atmospheres to keep the planet shielded and cool enough to support life.

The study adds to the increasing parameters whereby habitable zones continue to expand. In a September report in Astrobiology Magazine, researchers from NASA and Tokyo University noted that the habitable zone around stars increased up to three times when considering a much drier, much more Mars-like planet. The study suggested that there might be far more habitable planets in the universe with conditions like that of Arrakis, the fictional desert planet in the Frank Herbert science fiction classic novel Dune, than there are waterworlds.

There is also the consideration that life might evolve outside of conditions usually considered for viability, in conditions that give rise to alien organisms not akin to carbon-based life. Such an idea was postulated last year by MIT planetary science doctoral student Renya Hu and his colleagues, Sara Seager and William Bains. The team detailed their findings at the American Astronomical Society in Boston in May, noting that it was possible that life could evolve that breathed sulfur molecules.

Such studies indicate that the parameters of the concept of habitability itself might be expanded, thereby also increasing the number of worlds that might sustain some form of alien life.

(photo credit: G. Bacon, NASA, Wikimedia Commons)

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