05/09/2012 01:01 EDT | Updated 07/09/2012 05:12 EDT

Super-Earth's light seen for the first time

Scientists have detected light from a so-called super-Earth for the first time, NASA says.

Super-Earths — planets that are larger than our own but lighter than giant planets like Neptune — have been discovered before through indirect measurements, but the planet 55 Cancri e is the first to have its infrared light measured directly. It's also the smallest planet to have its brightness measured directly.

55 Cancri e, which orbits a star visible to the naked eye, is relatively nearby at 41 light years. It's one of about 70 super-Earths that have been discovered so far, but their relatively small size makes them difficult to see.

NASA's Spitzer Space Telescope, which in 2005 was the first to detect light from any planet outside our solar system, made the observations. The U.S. agency says Spitzer's successes are laying groundwork for its upcoming James Webb Space Telescope, which will focus on potentially habitable planets.

55 Cancri e is decidedly not.

About twice as big as Earth, it orbits the star 55 Cancri in just 18 hours and has a perpetually sun-facing side that is about 1725 C.

Despite the high temperatures, it is still a waterworld — a planet with atmospheres extremely high in water vapour. High temperatures and pressures on waterworlds turn the water into states of matter that don't exist on Earth, such as hot ice or superfluid water.

Measurements suggest 55 Cancri e is a rocky planet, surrounded by water that is simultaneously liquid and gas, surrounded by steam.

"It could be very similar to Neptune, if you pulled Neptune in toward our sun and watched its atmosphere boil away," principal research investigator Michaël Gillon told NASA.

A study released earlier this year in the journal Astronomy & Astrophysics estimated that tens of billions of rocky planets in the Milky Way support liquid water.