An artist’s impression of the 55 Cancri system, with 55 Cancri e nearly lost
in the glare of its star. (Courtesy: NASA/JPL-Caltech)
By Tushna Commissariat
Exoplanetary scientists will rejoice to hear that NASA’s Spitzer Space Telescope has managed to detect and analyse the tiny amount of infrared light that comes directly from a super-Earth exoplanet for the first time. About a few dozen super-Earths – planets that are 2–10 times more massive than the Earth – have been officially detected and countless other possible candidates have been found.
The exoplanet in question – known as 55 Cancri e – belongs to the 55 Cancri star-system, which is a measly 41 light-years away from the Earth – a small distance by astronomical scales. Indeed, 55 Cancri is so bright and close that it can be seen with the naked eye on a clear, dark night. The system is known to have five planets, with 55 Cancri e being the closest to its parent star. The planet is about eight times more massive than the Earth, completes its orbit in a dizzying 18 h – the shortest orbit known for an exoplanet – and is tidally locked, so one side always faces the star.
Previous studies of the planet revealed that 55 Cancri e is an extreme exoplanet with a rocky core surrounded by a layer of water in a “supercritical” state – the water is heated to such a degree that it is somewhere in-between a liquid and a gas – and topped off by a blanket of steam. In the new study, Spitzer measured the amount of infrared light that comes from the planet itself by looking at the slight dip in total light intensity when the planet undergoes an occultation – that is, when it circles behind the face of its parent star. When viewed in infrared, the planet is brighter relative to its star as its scorching surface heat blazes in the infrared end of the spectrum. 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’s light. In this case, the data revealed that the star-facing side of the exoplanet is more than 2000 K – hot enough to melt metal.
“Spitzer has amazed us yet again,” says Bill Danchi, who works on the Spitzer programme in Washington, DC. “The spacecraft is pioneering the study of atmospheres of distant planets and paving the way for NASA’s upcoming James Webb Space Telescope to apply a similar technique to potentially habitable planets.”