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Hot super-Earth, 55 Cancri e, found to have an atmosphere

Artist's concept of 55 Cancri e with Atmosphere. Image Credit: NASA

The super-Earth exoplanet 55 Cancri e, depicted with its star in this artist’s concept, likely has an atmosphere thicker than Earth’s but with ingredients that could be similar to those of Earth’s atmosphere. Image Credit NASA

Scientists analyzing data collected by NASA’s Spitzer Space Telescope have discovered that a hot super-Earth, which might have flowing lava on its surface, likely has an atmosphere.

Twice the diameter of Earth with about 8.63 Earth masses, 55 Cancri e, which is in a very close orbit around its star, was observed in the infrared with Spitzer between June 15 and July 15, 2013.

Because the planet orbits so close to its star, it is “tidally locked” to it, meaning one of its hemispheres always faces the star while the other always faces away from it. In 2016, scientists analyzing data collected during the Spitzer observations attributed the planet’s heat to lava flowing on its day side, reflecting stellar radiation into space.

While the lava initially flowed on the planet’s night side as well, it is believed that it eventually hardened there.

An artist's concept of the Spitzer space telescope. Image Credit: NASA/JPL-Caltech

Artist’s concept of the Spitzer Space Telescope. Image Credit: NASA/JPL-Caltech

This year, a second group of scientists conducted a more intensive study of the Spitzer data using improved computer models, which showed the flow of energy around the planet.

They determined its heat to be the product of an atmosphere rather than of flowing surface lava.

If lava were responsible for heating 55 Cancri e, the planet would have only localized hot spots directly above its lava lakes. For the lava to heat up the whole planet, it would have to cover every part of the surface, explained NASA Jet Propulsion Laboratory (JPL) astronomer Renyu Hu, co-author of a study on the findings published in The Astronomical Journal.

Even if the surface is completely covered in lava, the planet’s thick atmosphere would prevent astronomers from seeing it. Spitzer’s camera observed the planet in infrared light, which is capable of detecting and measuring heat.

With the improved computer model, the researchers compared changes in 55 Cancri e’s observed brightness with energy flow around the planet, concluding that the best explanation for those changes is an atmosphere containing some of the same volatile materials present in Earth’s atmosphere, including water, nitrogen, and oxygen.

In another key finding, they discovered that temperatures on the planet’s night side are warmer than previously thought. While dayside temperatures average about 4,200 degrees Fahrenheit (2,300 degrees Celsius), nighttime temperatures are still quite hot, ranging between 2,400 and 2,600 degrees Fahrenheit (1,300 to 1,400 degrees Celsius).

Extreme temperature differences between the day and night sides of tidally locked planets are typically found on worlds that do not have atmospheres.

“Scientists have been debating whether this planet has an atmosphere like Earth and Venus, or just a rocky core and no atmosphere, like Mercury,” Hu said. “The case for an atmosphere is now stronger than ever.”

Because the planet has a density similar to that of Earth, scientists believe it is rocky rather than gaseous.

Hu used a method he previously pioneered to study the surfaces and atmospheres of gaseous planets and adapted it to 55 Cancri e with the help of the University of California at Berkeley undergraduate Isabel Angelo, who is the paper’s lead author.

Angelo took part in the study during an internship at NASA JPL in Pasadena, California. Speaking at a seminar, she reported 55 Cancri e could be carbon-rich, with a large diamond in its interior.

Scientists are uncertain as to why the star has not stripped away the planet’s atmosphere, given the planet’s close orbit and the star’s high radiation emission.

“Understanding this planet will help us address larger questions about the evolution of rocky planets,” Hu emphasized.

As was noted on The Space Reporter, being rocky and having an atmosphere does not make 55 Cancri e habitable for life, as the planet is too hot to have liquid water on its surface.

 

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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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