An international group of astronomers using a 2-meter-class ground-based telescope has detected the shallow transit of a nearby exoplanet called 55 Cancri e.
This artist’s concept contrasts our Earth with 55 Cancri e. Image credit: NASA.
Discovered in 2004, 55 Cancri e is one of five planets orbiting the Sun-like star 55 Cancri that is located 40 light-years from our planet yet visible to the naked eye in the constellation of Cancer.
It falls into a class of planets termed super-Earths, which are more massive than our planet but lighter than giant worlds like Neptune. It has a radius twice Earth’s, and a mass eight times greater.
55 Cancri e is a toasty world that rushes around its star every 18 hours, in contrast to Earth’s 365 days. It orbits so closely – about 26 times closer than Mercury is to our Sun – that it is tidally locked with one face forever blisters under the heat of its host star.
The planet is proposed to have a rocky core surrounded by a layer of water in a ‘supercritical’ state, where it is both liquid and gas, and then the whole planet is thought to be topped by a blanket of steam.
Now, the astronomers led by Prof Ernst de Mooij from the University of Toronto have measured the passing of 55 Cancri e in front of its parent star using the 2.5-meter Nordic Optical Telescope in Spain. Previous observations of this exoplanet transit had to rely on space-borne telescopes.
During its transit, the planet crosses 55 Cancri and blocks a tiny fraction of the starlight, dimming the star by 1/2000th (or 0.05 percent) for almost two hours.
“Our observations show that we can detect the transits of small planets around Sun-like stars using ground-based telescopes,” said Prof de Mooij, who is the first author of a paper accepted for publication in the Astrophysical Journal Letters (arXiv.org preprint).
Until now, the transits of only one other super-Earth, GJ 1214b, had been observed with ground-based telescopes.
The Earth’s roiling air makes such observations extremely difficult. But the team’s success with 55 Cancri e raises the prospects of characterizing dozens of super-Earths likely to be revealed by upcoming surveys.
“It’s remarkable what we can do by pushing the limits of existing telescopes and instruments despite the complications posed by the Earth’s own turbulent atmosphere,” said co-author Prof Ray Jayawardhana of York University in Toronto, Canada.
“Observations like these are paving the way as we strive towards searching for signs of life on alien planets from afar. Remote sensing across tens of light years isn’t easy, but it can be done with the right technique and a bit of ingenuity.”
Next, the astronomers plan to search for water in the atmosphere of 55 Cancri e.
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E. J. W. de Mooij et al. 2014. Ground-Based Transit Observations of the Super-Earth 55 Cnc e. ApJL, accepted for publications; arXiv: 1411.7660
