Super Earth Rich in Steamy Water Vapour


NASA's Spitzer Space Telescope has found that exoplanet 55 Cancri e, which was first discovered in 2004, is less dense than previously reported; instead of a scorched, rocky world, water vapour and other gases likely steam from its molten surface.

The planet is the innermost of five known in the 55 Cancri system, which is just 40 light years from Earth, close enough and bright enough to be observed with the naked eye on a clear night. Orbiting at a distance 26 times closer to its star than Mercury does to our own Sun, and in less than 18 hours, 55 Cancri e claims the shortest time period known of any exoplanet. The planet's radius was found to be just over twice that of Earth, and has a mass equivalent to 7.8 Earths.

Approximately 40 light years from Earth, 55 Cancri e orbits a star – called 55 Cancri A – so closely that “You could set dates on this world by your wrist watch, not a calendar,” says UBC astronomer Jaymie Matthews.

55 Cancri e is the type of place exoplanetary scientists will be eager to “visit” with their telescopes, says Winn. “The brightness of the host star makes many types of sensitive measurements possible, so 55 Cancri e is the perfect laboratory to test theories of planet formation, evolution and survival.”

While the planet isn’t visible, even through a telescope, its host star, 55 Cancri A, can be observed with the naked eye for the next two months on a clear dark night.

The planet's surface is estimated to reach searing temperatures of at least 1,760 degrees Celsius, with its close orbit similar to the inferno-worlds CoRoT-7b and Kepler-10b. Yet its low density is more in line with the cool super-Earth GJ1214b, which suggests that around one-fifth of the planet's mass must therefore be light elements and compounds, like water, but that due to the high temperatures the water would exist in a super-critical state, that is, between a liquid and gas.

The Sptizer team speculates that 55 Cancri e began life as a gaseous Neptune-like planet far from its sun. Gravitational interactions between the five known planets in the system caused migrations, setting the planet on course to eventually death-spiral into the star.

The paper describing the new results has been accepted for publication in Astronomy & Astrophysics.

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