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Super-Earth temperature map created from Spitzer data

Artist's rendition of Exoplanet 55 Cancri e.

This illustration shows one possible scenario for the hot, rocky exoplanet called 55 Cancri e, which is nearly two times as wide as Earth. Image & Caption Credit: NASA/JPL-Caltech

Using data collected by NASA’s recently upgraded Spitzer Space Telescope, scientists have created the first-ever temperature map of a super-Earth exoplanet. The exoplanet is considered a “super-Earth” because it is large and rocky with approximately eight times Earth’s mass.

Located approximately 40 light-years from Earth, 55 Cancri e is twice as big as Earth and orbits very close to its Sun-like star, with an orbital period of just 18 hours.

Exoplanet 55 Cancri e (GIF)

CGI simulation of Exoplanet 55 Cancri e. GIF Credit: NASA/JPL-Caltech

While the close orbit makes 55 Cancri e extremely hot, Spitzer observations, conducted in the infrared over 80 hours, revealed extreme temperature differences on its two sides.

Because the planet orbits so close to its parent star, it is tidally locked to it by gravity; i.e., one side always faces the star and the other always faces away from it.

The configuration is similar to that of our Moon, which is tidally locked to Earth and always presents the same face to it.

For 55 Cancri e, tidal locking means that one side is continuously heated by the star while the other is perpetually dark and, therefore, cooler.

However, tidal locking is not the only reason for the huge temperature differences on the planet’s two sides. The fact that heat is not being distributed across the planet suggests that the planet lacks a massive atmosphere, and its dark side may be covered with hardened lava that cannot transport heat.

By observing multiple orbits of the planet around the star, scientists discovered a temperature difference of 2,340 degrees Fahrenheit (1,300 K; 1,282 °C) between its hot and cool sides, with the hot side measuring almost 4,400 degrees Fahrenheit (2,700 K; 2,427 °C) and the ‘cool’ side measuring 2,060 degrees Fahrenheit (1,400 K; 1,127 °C).

The large temperature differential means the planet is inefficient at distributing heat globally, said Brice-Olivier Demory of the University of Cambridge, England, and lead author of a study about the planet published in the March 30 issue of the journal Nature.

Exoplanet 55 Cancri e infrared data plot.

The varying brightness of an exoplanet called 55 Cancri e is shown in this plot of infrared data captured by NASA’s Spitzer Space Telescope. (Click to enlarge) Image & Caption Credit: NASA/JPL-Caltech/University of Cambridge

Because it is hotter than it should be, even in such a close orbit, 55 Cancri e may have an unknown, possibly internal heat source.

“Spitzer observed the phases of 55 Cancri e, similar to the phases of the Moon as seen from the Earth,” Demory explained.

“We were able to observe the first, last quarters, new and full phases of this small exoplanet. In return, these observations helped us build a map of the planet. This map informs us which regions are hot on the planet.”

Unlike 55 Cancri e, planets with thick atmospheres and winds transport heat efficiently across their surfaces.

Lava flows on the planet’s surface may also play a role in its huge temperature variations.

“The day side could possibly have rivers of lava and big pools of extremely hot magma, but we think the night side would have solidified lava flows like those found in Hawaii,” noted Michael Gillon of the University of Liege in Belgium.

Spitzer also discovered that the planet’s hottest spot is not directly beneath the star as expected but somewhat shifted, meaning there may be some heat recirculation on its day side.

Extremely hot lava flows on the day side could also be responsible for the shift.

Spitzer was not initially designed for such high-precision observations, but recent upgrades have enhanced its sensitivity in measuring brightness changes of exoplanets.

Scientists plan to investigate further 55 Cancri e with the James Webb Space Telescope, scheduled for launch in October 2018.

“We still don’t know exactly what this planet is made of – it’s still a riddle,” Demory said. “These results are like adding another brick to the wall, but the exact nature of this planet is still not completely understood.”

Video Courtesy of Cambridge University


Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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