Astronomers using NASA's Spitzer Space Telescope have detected what they believe to be a planet that is just two-thirds the size of Earth — one of the smallest on record. The exoplanet candidate, known as UCF-1.01, orbits a red dwarf (spectral type M2.5 V) star called Gliese 436 (GJ 436), which is located just 33.1 light-years away. UCF-1.01 might be the nearest world to our solar system that is smaller than our home planet.
Exoplanets (extra-solar planets) orbit other stars. So far, only a handful have been found that are smaller than Earth. Spitzer has performed transit studies on known exoplanets, but UCF-1.01 is the first ever identified using the space telescope, suggesting a possible role for Spitzer in helping discover potentially habitable, terrestrial-sized worlds.
The potential planet is very small, very hot and very near to its parent star. A paper on the discovery has been accepted for publication in The Astrophysical Journal. The lead author of the paper is Kevin Stevenson from the Unversity of Central Florida in Orlando. His co-author is Joseph Harrington, also of the University of Central Florida, who is also the principal investigator of the research. The Astrophysical Journal may be visited online by CLICKING HERE.
The exoplanet candidate was found unexpectedly in Spitzer observations and may become the second known planet in the GJ 436 system. Stevenson and his colleagues were studying the Neptune-sized exoplanet GJ 436b, already known to orbit 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 orbiting the star and blocking out a small fraction of the star's light.
This technique of tracking dips in starlight, used by a number of observatories including NASA's Kepler space telescope. It relies on transits to detect exoplanets. The duration of a transit and the amount of the decrease in light 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 (8,400 kilometers). That would make the planet size about two-thirds that of Earth, or roughly half-way between Mars and Venus. UCF-1.01 would revolve quite tightly around GJ 436, at about seven times the distance of Earth from the moon, with its "year" lasting only 1.4 Earth days. Given this proximity to its star, far closer than the planet Mercury is to our sun, the exoplanet's surface temperature would be more than 1,000 degrees Fahrenheit (almost 600 degrees Celsius).
If UCF-1.01 ever had an atmosphere, it almost surely has evaporated. Some suggest its appearance might resemble a cratered, mostly geologically dead world like Mercury. But the researchers suggest that the extreme heat of orbiting so close to GJ 436 has melted the exoplanet's surface, and the planet might even be covered in magma.
In addition to UCF-1.01, the research team 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 Earth. Knowing the mass is required for confirming a discovery, so the researchers are cautiously calling both bodies exoplanet candidates for now.
Of the approximately 1,800 stars identified by NASA's Kepler space telescope 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. The researchers hope that future missions which are better designed for the task, will confirm their results. That being said, scientists are singing the praises of the nine-year-old Spitzer mission, which may be able to discover exoplanets as small as Mars.
And now, the mission particulars...
NASA's Jet Propulsion Laboratory (JPL), Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology (Caltech) in Pasadena. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. To learn more about Spitzer, visit http://www.spitzer.caltech.edu/ and www.nasa.gov/spitzer .
More information about exoplanets and NASA's planet-finding program is at planetquest.jpl.nasa.gov .
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