Astronomers using NASA’s Spitzer Space Telescope have for the first time captured the light emanating from a super-Earth exoplanet.
Artist's concept of the planet 55 Cancri e (JPL / NASA)
The new study, which will be published in the Astrophysical Journal, reports the detection of infrared light from the super-Earth 55 Cancri e. The planet falls into a class of planets termed super Earths, which are more massive than our planet but lighter than giant worlds like Neptune. It is about twice as big and eight times as massive as Earth, and orbits a bright star, called 55 Cancri, in a mere 18 hours.
Previously, Spitzer and other telescopes were able to study the planet by analyzing how the light from 55 Cancri changed as the planet passed in front of the star. In the new study, the astronomers measured how much infrared light comes from the planet itself. The results reveal the planet is likely dark, and its sun-facing side has a temperature of more than 2,000 Kelvin.
The new information is consistent with a prior theory that 55 Cancri e is a water world: a rocky core surrounded by a layer of water in a “supercritical” state where it is both liquid and gas, and topped by a blanket of steam.
“It could be very similar to Neptune, if you pulled Neptune in toward our Sun and watched its atmosphere boil away,” said study co-author Dr. Michaël Gillon of Université de Liège in Belgium.
The 55 Cancri system is relatively close to Earth, at 41 light-years away. It has five planets, with 55 Cancri e the closest to the star and tidally locked, so one side always faces the star.
“When we conceived of Spitzer more than 40 years ago, exoplanets hadn’t even been discovered,” said Dr. Michael Werner, Spitzer project scientist at NASA’s Jet Propulsion Laboratory in Pasadena. “Because Spitzer was built very well, it’s been able to adapt to this new field and make historic advances such as this.”
In 2005, Spitzer became the first telescope to detect light from a planet beyond our solar system. To the surprise of many, the observatory saw the infrared light of a “hot Jupiter,” a gaseous planet much larger than the solid 55 Cancri e. Since then, other telescopes, including NASA’s Hubble and Kepler space telescopes, have performed similar feats with gas giants using the same method.
In this method, a telescope gazes at a star as a planet circles behind it. When the planet disappears from view, the light from the star system dips ever so slightly, but enough that astronomers can determine how much light came from the planet itself. This information reveals the temperature of a planet, and, in some cases, its atmospheric components. Most other current planet-hunting methods obtain indirect measurements of a planet by observing its effects on the star.
While 55 Cancri e is not habitable, the detection of infrared light from it is a historic step toward the eventual search for signs of life on other planets.
