Toasty planet discovered in Earth's cosmic backyard
BY SPACEFLIGHT NOW
Posted: July 18, 2012
The infrared element of NASA's Great Observatory series, the Spitzer Space Telescope, has discovered a new planet just 33 light-years away that is the nearest world beyond our solar system, found thus far, that is smaller than our own.
The discovering team believes the world has no atmosphere and its landscape may be volcanic or molten.
"We have found strong evidence for a very small, very hot and very close-by planet with the help of the Spitzer Space Telescope," said Kevin Stevenson, a recent Ph.D. graduate from the University of Central Florida.
The hot new planet candidate was found unexpectedly in Spitzer observations. Stevenson and his colleagues were studying the Neptune-sized exoplanet GJ 436b, already known to exist around the red-dwarf star GJ 436. In the Spitzer data, the astronomers noticed slight dips in the amount of infrared light streaming from the star, separate from the dips caused by GJ 436b. A review of Spitzer archival data showed the dips were periodic, suggesting a second planet might be blocking out a small fraction of the star's light.
This technique, used by a number of observatories including NASA's Kepler space telescope, relies on transits to detect exoplanets. The duration of a transit and the small decrease in the amount of light registered reveals basic properties of an exoplanet, such as its size and distance from its star. In UCF-1.01's case, its diameter would be approximately 5,200 miles, or two-thirds that of Earth.
UCF-1.01 would revolve quite tightly around GJ 436, at about seven times the distance of the Earth from the Moon, with its "year" lasting only a day-and-a-half in Earth days. Given this proximity to its star, the world would orbit far closer than the planet Mercury is to our Sun.
If the roasted, diminutive planet candidate ever had an atmosphere, it almost surely has evaporated. UCF-1.01 might therefore resemble a cratered, mostly geologically dead world like Mercury.
In addition to UCF-1.01, Stevenson and his colleagues noticed hints of a third planet, dubbed UCF-1.02, orbiting GJ 436. Spitzer has observed evidence of the two new planets several times each. However, even the most sensitive instruments are unable to measure exoplanet masses as small as UCF-1.01 and UCF-1.02, which are perhaps only one-third the mass of the Earth. Because knowing the mass is required for confirming a discovery, the paper authors are cautiously calling both bodies exoplanet candidates for now.
Of the approximately 1,800 stars identified by Kepler as candidates for having planetary systems, just three are verified to contain sub-Earth-sized exoplanets. Of these, only one exoplanet is thought to be smaller than the Spitzer candidates, with a radius similar to Mars, or 57 percent that of Earth.
"I hope future observations will confirm these exciting results, which show Spitzer may be able to discover exoplanets as small as Mars," said Michael Werner, Spitzer Project Scientist at NASA's Jet Propulsion Laboratory. "Even after almost nine years in space, Spitzer's observations continue to take us in new and important scientific directions."