A hot, rocky exoplanet called 55 Cancri e likely has an atmosphere thicker than Earth’s, with ingredients that could be similar to those of Earth’s atmosphere, according to a study by researchers from NASA’s Jet Propulsion Laboratory (JPL), Caltech, and the University of California, Berkeley.
This artist’s impression shows the super-Earth 55 Cancri e orbiting the Sun-like star 55 Cancri A. Image credit: NASA / JPL-Caltech.
55 Cancri e is one of five planets orbiting the Sun-like star 55 Cancri A that is located 40 light-years away yet visible to the naked eye in the constellation of Cancer.
Discovered in 2004, this planet has a radius twice Earth’s, and a mass 8 times greater, making it a so-called super-Earth.
55 Cancri e orbits its host star at a distance of 0.015 AU — about 25 times closer than Mercury is to our Sun — every 18 hours.
The planet is also tidally locked, meaning that it doesn’t rotate like Earth does — instead there is a permanent ‘day’ side and a ‘night’ side.
Based on a 2016 study using data from NASA’s Spitzer Space Telescope, astronomers speculated that lava would flow freely in lakes on the starlit side and become hardened on the face of perpetual darkness.
The lava on the dayside would reflect radiation from the parent star, contributing to the overall observed temperature of the planet.
Now, a deeper analysis of the same Spitzer data finds 55 Cancri e likely has an atmosphere whose ingredients could be similar to those of Earth’s atmosphere, but thicker.
Lava lakes directly exposed to space without an atmosphere would create local hot spots of high temperatures, so they are not the best explanation for the Spitzer observations.
“If there is lava on this planet, it would need to cover the entire surface. But the lava would be hidden from our view by the thick atmosphere,” said JPL/Caltech astronomer Dr. Renyu Hu.
Using an improved model of how energy would flow throughout the planet and radiate back into space, Dr. Hu and Dr. Isabel Angelo of JPL and the University of California, Berkeley, find that the night side of the planet is not as cool as previously thought.
The ‘cold’ side of 55 Cancri e is still quite toasty by Earthly standards, with an average of 2,400 to 2,600 degrees Fahrenheit (1,300 to 1,400 degrees Celsius), and the hot side averages 4,200 degrees Fahrenheit (2,300 degrees Celsius).
The difference between the hot and cold sides would need to be more extreme if there were no atmosphere.
“Scientists have been debating whether this planet has an atmosphere like Earth and Venus, or just a rocky core and no atmosphere, like Mercury. The case for an atmosphere is now stronger than ever,” Dr. Hu said.
“The atmosphere of this mysterious planet could contain nitrogen, water and even oxygen — molecules found in our atmosphere, too — but with much higher temperatures throughout,” the authors said.
“The density of the planet is also similar to Earth, suggesting that it, too, is rocky.”
“The intense heat from the host star would be far too great to support life, however, and could not maintain liquid water.”
The findings will be published in the Astronomical Journal (arXiv.org preprint).
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Isabel Angelo & Renyu Hu. 2017. A Case for an Atmosphere on Super-Earth 55 Cancri e. AJ, in press; arXiv: 1710.03342
