THE search for faraway planets that could harbour life is getting warmer. A handful of red-dwarf stars have been found with rings of dusty debris around them that appear to be the signature of planet formation.
The finding is significant because though such small, dim stars were not thought to be likely places to find Earth-like planets, any planets around them are relatively easy to find. Until now, only six red dwarfs had been found with the telltale discs of dusty debris, common around sun-like stars, that are thought to be kicked up by small bodies crashing into each other during the formation of planets.
Now the orbiting Spitzer Space Telescope has found another nine red dwarfs with dusty discs in the NGC 2547 star cluster, 1400 light years from Earth. 鈥淩ed dwarfs with discs seem to be more common than was thought,鈥� says Jan Forbrich of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who led the study.
Advertisement
Habitable planets around these red dwarfs should be easier to find because the gravitational tug of a planet on a star as lightweight as a red dwarf would make it wobble by a relatively large amount, enough to be detected from Earth. This 鈥渞adial velocity鈥� method tends to find planets that are in tight orbits. The same is true of the 鈥渢ransit technique鈥�, which looks for the telltale drop in brightness when a planet passes in front of its star. If they were orbiting bright, sun-like stars, such close-in planets would be too hot to have liquid water on their surfaces, but a dim red dwarf might give them just the right temperature.
From the way the temperature of the dust varies, Forbrich鈥檚 team concludes that it is not far from the parent stars, although the measurements are not sensitive enough to calculate an exact distance. 鈥淚t could very well be in the habitable zone,鈥� Forbrich says.
The find is welcome news, says Jonathan Lunine of the University of Arizona in Tucson, who was not involved in the study. He recently led a committee on exoplanet research that recommended red dwarf surveys be made a high priority. 鈥淓arth-sized planets around red dwarfs are easier to find. Here鈥檚 some low-hanging fruit that we ought to try to pluck,鈥� Lunine says.
鈥淓arth-sized planets around red dwarfs are easier to find. Here鈥檚 some low-hanging fruit that we ought to try to pluck鈥�
Astronomers have already started scrutinising other red dwarfs for planets, and seven of the diminutive stars have so far been known to harbour planets. One of them, Gliese 581, has a planet eight times the mass of Earth near the outer edge of the habitable zone, which may just be warm enough for liquid water if it has an atmosphere that provides a strong greenhouse effect.
Astrobiology 鈥� Learn more in our out-of-this-world .
