Today, astronomers have figured out the temperature of a super-Earth — one of the first studies to provide details on the climate of these planets. Not only does it show the planet is extraordinarily warm, it also creates new puzzles for researchers hoping to characterize this world.
The world's climate varies drastically between its dayside and its nightside
The world's climate varies drastically between its dayside and its nightside, according to the observations published this week in the journal Nature. On the planet's dayside, the temperature reaches about 4,400 degrees Fahrenheit (2,427 degrees Celsius). That’s more than twice as hot as the planet's dark side, which never sees sunlight; this shadowed region is 2,042 degrees Fahrenheit (1,107 degrees Celsius), hotter than most lava flows here on Earth. The exoplanet is so hot, in fact, that the researchers think that widespread volcanoes may be creating extra heat on this far away world.
Exoplanets that are between the size of our planet and Neptune (about 17 times the mass of Earth) are called super-Earths, and they’re probably common in our galaxy, if observations from NASA's planet-hunting spacecraft Kepler are any guide. Astronomers have been trying to study the atmospheres of known super-Earths, to learn more about how they formed — and to figure out if they could ever support life, according to Jacob Bean, an astronomer at the University of Chicago, who was not involved in the study. But these efforts have been difficult, as clouds often obscure these planets' atmospheres. "This paper presents interesting observations that are some of the first to detect something, anything, from a super-Earth atmosphere," Bean says.
The researchers were able to figure out these temperatures thanks to NASA's Spitzer Space Telescope, which observed infrared light coming from the exoplanet 55 Cancri e. The world 55 Cancri e is located about 40 light years away and is thought to be about twice the size of Earth. But unlike our planet, 55 Cancri e is tidally locked with its star, meaning one side is always bathed in light while the other side is always in darkness.
These observations prompt more questions about this exoplanet
These observations prompt more questions about this exoplanet. The wide variation in the planet's dayside and nightside temperatures indicates that 55 Cancri e is devoid of an atmosphere, according to study author Brice-Olivier Demory, an astrophysicist at the University of Cambridge. An atmosphere would help to spread heat across the entire surface of the planet, making temperatures similar across all regions. "If we had an atmosphere, we'd expect the nightside to be significantly hotter than what we’re seeing in our data," he said. But that directly contrasts a study that came out in February, arguing that 55 Cancri e has an atmosphere rich in helium and hydrogen. That study was the first time a super-Earth atmosphere had ever been characterized — and today’s research calls it into question.
It’s also unclear why 55 Cancri e is so hot. The planet is about 70 times closer to its star than the Earth is to the Sun, it’s true. But parts of the planet are even hotter than expected, given the world’s location. "We know the heat from the star is not enough to explain the hottest regions of the planet," says Demory. He argues that lava coming from volcanoes may be helping to heat up 55 Cancri e, but study authors aren’t sure where this heat source is coming from.
Fortunately, we may have more answers about this world soon, once NASA's James Webb Space Telescope launches in October 2018. That spacecraft, on track to be the most powerful space telescope ever built, will be able to characterize 55 Cancri e in much more detail. The results of today's research may inspire NASA to use James Webb to figure out what's really going on in the atmosphere of this super-Earth.