Astronomers using the Spitzer Space Telescope have discovered what they believe is a planet two-thirds the size of Earth.
This artist’s concept shows what astronomers believe is an alien world just two-thirds the size of Earth (NASA / JPL-Caltech)
Located only 33 light years away, the exoplanet candidate UCF 1.01 is close to its star, so close it goes around the star in 1.4 days. The planet’s surface likely reaches temperatures of more than 1,000 degrees Fahrenheit. The astronomers believe that it has no atmosphere, is only two-thirds the gravity of Earth and that its surface 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 Dr Kevin Stevenson of the University of Central Florida (UCF), lead author of a paper accepted for publication in the Astrophysical Journal. “This discovery is a significant accomplishment for UCF.”
The team was studying a hot-Neptune exoplanet, designated GJ 436b, already known to exist around the red-dwarf star GJ 436, when data revealed clues that led them to suspect there could be at least one new planet in that system, perhaps two.
The astronomers noticed slight dips in the amount of infrared light streaming from the star. A review of Spitzer archival data showed that the dips were periodic, suggesting that a planet might be blocking out a small fraction of light as it passed in front of GJ 436, as seen from Earth.
“I could see these faint dips in the starlight and I wanted to determine their source. I knew that if these signals were periodic, they could be from an unknown planet,” said Dr Stevenson, who is now a postdoctoral scholar at the University of Chicago.
With the finding of UCF-1.01, GJ 436 is likely now home to the first multi-transiting-planet system described by a mission other than Kepler. Of the 1,800 stars identified by Kepler as candidates for having planetary systems, only three are verified to contain sub-Earth size exoplanets.
The depth and duration of a transit reveals basic properties of an exoplanet, such as its size and distance from a host star. In UCF-1.01’s case, its diameter is estimated at 5,200 miles, or two-thirds that of Earth, placing the world among the smallest on record. The team also noticed hints of yet another potential planet dubbed UCF-1.02, but its period was impossible to estimate.
So why aren’t scientists calling UCF-1.01 a planet? A measured mass is needed to verify that these objects are planets, but even the most sensitive instruments currently available are unable to measure exoplanet masses this small.
“Despite the lack of a confirmed mass, the team is confident future observations will verify our findings,” said Prof Joseph Harrington of the UCF.
“I hope future observations will confirm these exciting results, which show Spitzer may be able to discover exoplanets as small as Mars,” said Dr Michael Werner, Spitzer Project Scientist at JPL. “Even after almost nine years in space, Spitzer’s observations continue to take us in new and important scientific directions.”
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Bibliographic information: Stevenson et al. 2012. Two nearby sub-Earth-sized exoplanet candidates in the GJ 436 system. Accepted for publication in ApJ; arXiv:1207.4245v1
