Astronomers have made a detailed map of a small, rocky “super Earth” revealing a planet that is almost entirely covered by lava, with a molten “hot” side and solid “cool” side. The international team of astronomers, led by the University of Cambridge, now has the most comprehensive “fingerprint” of a rocky planet outside our solar system.
The conditions on the hot side are so extreme that it may have caused the atmosphere to evaporate. The temperatures of each side of the planet vary widely, with the temperatures on the hot side reaching a scorching 2500 degrees Celsius, and the cool side being around 1100 degrees.
To examine the planet, known as 55 Cancri e, the researchers used data from NASA’s Spitzer Space Telescope. 55 Cancri e orbits a sun-like star, which is located 40 light years away in the Cancer constellation. This is the first time a map on how the conditions on a planet change during a complete orbit has been accomplished for a planet this small.
55 Cancri e is also known as a “super Earth,” and is a rocky exoplanet, which is about twice the size and eight times the mass of Earth. It also orbits its parent star; however, it is so close that a year only lasts just 18 hours.
The planet is also tidally locked, which means it only shows one side to its parent star (this is similar to our moon); so that means one side is permanently “day” and the other side is permanently “night.”
Since it is among the nearest super Earths whose composition can be studied, 55 Cancri e is among the best candidates for detailed observations of surface and atmospheric conditions on rocky exoplanets. Uncovering the characteristics of super Earths is difficult, since they are so small compared to the parent star and their contrast relative to the star is extremely small compared to larger, hotter, gas giant planets, the so-called “hot Jupiters,” according to a University of Cambridge statement.
Dr. Brice-Olivier Demory of the University’s Cavendish Laboratory, the paper’s lead author, said in a statement:
“We haven’t yet found any other planet that is this small and orbits so close to its parent star, and is relatively close to us, so 55 Cancri e offers lots of possibilities.
“We still don’t know exactly what this planet is made of — it’s still a riddle. These results are like adding another brick to the wall, but the exact nature of this planet is still not completely understood.”
Since its discovery in 2011, 55 Cancri e has been comprehensively studied. It was previously thought to be a water world, or perhaps even made of diamond, based on readings taken at different points in time. However, researchers now believe that it is almost completely covered by lava.
Study co-author Dr. Nikku Madhusudhan from the Institute of Astronomy at Cambridge, said:
“We have entered a new era of atmospheric remote sensing of rocky exoplanets.
“It is incredible that we are now able to measure the large scale temperature distribution on the surface of a rocky exoplanet.”
Looking at the new infrared measurements, the “day” side of the planet seems to be almost completely molten, while the “night” side is almost completely solid. Here on Earth our atmosphere aids in the re-circulation of heat, which keeps the temperature across the planet within a relatively narrow range. However, on 55 Cancri e the heat from the day side is not circulating to the night side, this is why the hot side stays hot and the cold side stays cold, the researchers explain.
Demory does give one possibility for this variation — it may be either a complete lack of atmosphere, or it may have been partially destroyed due to the strong irradiation from the nearby host star, saying:
“On the day side, the temperature is around 2500 degrees Celsius, while on the night side it’s about 1100 degrees — that’s a huge difference.
“We think that there could still be an atmosphere on the night side, but temperatures on the day side are so extreme that the atmosphere may have evaporated completely, meaning that heat is not being efficiently transferred, or transferred at all from the day side to the night side.
There is another possibility for the difference, and that may be because the molten lava on the day side moves heat along the surface, however, since lava is mostly solid on the night side, the heat may not moved around as efficiently.
What remains unclear is where exactly the “extra” heat on 55 Cancri e comes from in the first place, since the observations reveal an unknown source of heat that makes the planet hotter than expected solely from the irradiation from the star — but the researchers may have to wait until the next generation of space telescopes are launched to find out, according to the statement.
Demory and his colleagues plan to continue to study 55 Cancri e, hoping to find other secrets it may be holding. There is also the possibility that it may be surrounded by a torus of gas and dust, which could also account for some variations in the data.
The successor to Hubble and Spitzer, the James Webb Space Telescope will be launched in 2018. This will allow astronomers to look at planets outside our solar system with a totally new level of precision. The study was published in the journal, Nature.