Exoplanets In Our Own Back Yard?
February 6, 2013

Earth’s Twin In Our Own Back Yard? Six Percent Of Red Dwarfs Have Habitable Planets

Lee Rannals for redOrbit.com - Your Universe Online

Astronomers using NASA's Kepler space telescope have found that six percent of red dwarf stars have habitable, Earth-like planets.

Red dwarfs are considered to be the most abundant stars in our galaxy, so it is feasible that one of these Earth-like planets could be just 13 light-years away, when taking into account the astronomers new research published in The Astrophysical Journal.

The Harvard-Smithsonian Center for Astrophysics (CfA) team said they thought they would have to search vast distances to find an Earth-like planet, but now they have determined another Earth could be "in our own backyard."

An average red dwarf is just one-third as large and one-thousandth as bright as the Sun, and despite their dimness, they make great candidates to look for Earth-like planets. Astronomers believe that there could be a total of at least 75 billion red dwarfs in our galaxy.

Because the light from the star is smaller, an Earth-sized world would block out more of the star's disk. Also, since the star itself is cooler than our sun, the planet could sit much closer, and would be more likely to transit in front of it from our perspective here on Earth.

For the study, CfA astronomers reanalyzed stars from a catalog of 158,000 Kepler targets, helping to calculate more accurate sizes and temperatures. What they found was that nearly all of those stars were smaller and cooler than previously thought.

Since the size of a transiting planet is determined relative to the star size, shrinking the star shrinks its planet. The team found that at least 60 percent of red dwarfs have planets smaller than Neptune. However, most were not quite the right size or temperature to be considered "Earth-like," bringing the amount of planets closer to our Earth at about six percent of all red dwarf stars.

"We now know the rate of occurrence of habitable planets around the most common stars in our galaxy," said co-author David Charbonneau of CfA. "That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought."

About 75 percent of the closest stars to our very own solar system are red dwarfs, and, according to the research, since six percent of those should host habitable planets, then the closest Earth-like planet to us could be just 13 light-years away.

Because red dwarfs live longer than Sun-like stars, astronomers say that it could raise some interesting possibilities that life on these planets would be older, and more evolved, than on Earth.

"We might find an Earth that's 10 billion years old," Charbonneau said.

On the other hand, research recently reported by redOrbit this week, and published in the journal Monthly Notices of the Royal Astronomical Society, suggests that these "Earth-like" planets that have been observed, are actually more like "mini-Neptunes."

Dr. Helmut Lammer of the Space Research Institute (IWF) at the Austrian Academy of Sciences told redOrbit that out of the seven super-Earths observed, they actually ended up looking more like mini-Neptunes, with rocky cores surrounded by hydrogen, or hydrogen-rich volatiles.

So while the Harvard astronomers research could be true, nothing yet, according to Lammer, considered to be Earth-like is at all like our own planet.

“I expect that there are more Earth-like exoplanets are out there, but so far we know only the radius or the mass of such exoplanets or exoplanet candidates,” Lammer told redOrbit. “If we don´t know both parameters we cannot calculate the density.”

He said it is only a matter of time before observers discover the size and mass of actual Earth-like planets, so maybe astronomers need to be looking at these red dwarfs to do so.