For the first time, scientists have used a ground-based telescope to observe and measure a super-Earth, an exoplanet orbiting a nearby sun-like star.

Known as 55 Cancri e (55 Cnc e), the planet with twice the diameter of our own is about eight times as massive as the Earth. It orbits the relatively near 55 Cancri star, which is located just 40 light years away from the Earth and can be seen with the naked eye.  

Observing the movement of the exoplanet previously relied on space-borne telescopes such as the Microvariability and Oscillations of Stars telescope (MOST), Canada's first telescope, and NASA's Spitzer Space Telescope. However, Ernst de Mooij, from Queen's University in Belfast, U.K., and colleagues were able to detect 55 Cancri e's silhouette using the 2.5 meter Nordic Optical Telescope at the Roque de los Muchachos Observatory in Spain's La Palma Island.

Using the Nordic Optical Telescope, de Mooij and colleagues observed that 55 Cnc e blocks a tiny fraction of light as it crosses its host star, dimming the star by 1/2000th or 0.05 percent for nearly two hours, indicating that the exoplanet spans 16,000 miles in diameter and that it is about twice the size of planet Earth.

For their findings, which will be published in The Astrophysical Journal Letters, the researchers said that the measurements they have made using differential spectrophotometry are the same as the results obtained using space-based facilities.

"We report the first ground-based detections of the shallow transit of the super-Earth exoplanet 55Cnc e using a 2-meter-class telescope," the researchers wrote [pdf]. "The precision of our transit detection is comparable to that of the previously reported transit detections of this planet from space, with MOST and Spitzer, which reveals the great potential to do this type of science from the ground."

55 Cnc e is the smallest planet detected from the ground and raises hope that ground-based telescopes can be used for searching Earth-sized worlds that have the capability to support life.

"Our observations show that we can detect the transits of small planets around sun-like stars using ground-based telescopes," de Mooij said. "This is especially important because upcoming space missions such as TESS and PLATO should find many small planets around bright stars."

NASA's TESS mission is set for launch in 2017. The European Space Agency's PLATO mission, on the other hand, is scheduled for launch in 2024. Both missions will look for terrestrial planets orbiting nearby bright stars.

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