Small exoplanet may be covered in magma

Astronomers using NASA’s Spitzer Space Telescope have discovered what may be the nearest world to our solar system that’s smaller than Earth.

Called UCF-1.01, it’s just 33 light-years away, and is around two-thirds the size of Earth – making it the second-smallest exoplanet found.

“We have found strong evidence for a very small, very hot and very near planet with the help of the Spitzer Space Telescope,” says Kevin Stevenson from the University of Central Florida in Orlando. Identifying nearby small planets such as UCF-1.01 may one day lead to their characterization using future instruments.”

The hot new planet candidate was found almost by accident. Stevenson and his colleagues were studying the Neptune-sized exoplanet GJ 436b, already known to exist around the red-dwarf star GJ 436 when they 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 present.

UCF-1.01 appears to be about 5,200 miles across, and to revolve quite tightly around GJ 436 – at about seven times the distance of the Earth from the moon, with its year lasting only 1.4 Earth days.

Its temperature must be more than 1,000 degrees Fahrenheit, meaning that if it ever had an atmosphere, it almost surely has evaporated. While it might be a cratered, mostly geologically dead world like Mercury, there is another possibility:that the extreme heat of orbiting so close to GJ 436 has melted the exoplanet’s surface.

“The planet could even be covered in magma,” says Joseph Harrington of the University of Florida.

The team’s also noticed hints of a third planet, dubbed UCF-1.02, orbiting GJ 436, but hasn’t yet been able to confirm it.

“I hope future observations will confirm these exciting results, which show Spitzer may be able to discover exoplanets as small as Mars,” says Spitzer project scientist Michael Werner.

“Even after almost nine years in space, Spitzer’s observations continue to take us in new and important scientific directions.”