A Planet of Two Surfaces

Artist depiction of 55 Cancri e orbiting its star. (Source: University of Texas, NSF, NASA, http://antwrp.gsfc.nasa.gov/apod/ap040901.html)

Searching for exoplanets, or planets around other stars, can be agonizing. The small, rocky ones, which are tantalizing as they most closely resemble Earth, are the hardest exoplanets to find because they are so small compared to their host stars. But astronomers are discovering more about these worlds, and recently, a team from the University of Cambridge completed the most detailed heat map of a small planet yet: a rocky exoplanet about twice the size of Earth and forty light years away known as 55 Cancri e. Orbiting very close to its star, 55 Cancri e is inhospitable to life but its close orbit has another effect: the planet’s rotation is locked such that the same hemisphere always faces the star, just as the same hemisphere of the Moon always faces the Earth. This splits the planet’s surface into two sides, one of permanent ‘day’ and the other permanent ‘night.’ According to a new study using infrared data from NASA’s Spitzer telescope, the temperature difference between these two sides on 55 Cancri e is as extreme as it gets, with the day side reaching 2500 degrees Celsius under the endless scorch, while the night side chills at a relatively frigid 1100 degrees. The day side is so hot that the surface pulses with riverlike flows and pools of molten lava, while the night side’s surface remains solid rock. The astronomers believe that with such a small distance between planet and star, the extreme stellar heat may have blasted off the planet’s atmosphere, cutting off any atmospheric circulation and thereby preventing heat from traveling from the hot side to the cool. Technology hasn’t caught up with the theory yet - researchers will have to wait for the next generation of space telescopes to get a look at the atmospheres of small worlds such as this one as they continue to hunt for more planets like Earth.

- Sean Faulk
Staff Writer, Signal to Noise Magazine
Graduate Student, Earth, Planetary, and Space Sciences

References:

Demory, BO., et al. (2016). A map of the large day–night temperature gradient of a super-Earth exoplanet. Nature. DOI: 10.1038/nature17169