In an astronomical first, a ground-based telescope has observed a super-Earth planet passing in front of a bright, nearby Sun-like star.
The transit of the exoplanet 55 Cancri e is the shallowest detected from the ground yet, researchers said.
Since detecting a transit is the first step in analysing a planet’s atmosphere, this success bodes well for characterising the many small planets that upcoming space missions are expected to discover in the next few years.
The international research team used the 2.5-meter Nordic Optical Telescope on the island of La Palma, Spain, a moderate-sized facility by today’s standards but equipped with state-of-the-art instruments, to make the detection.
Previous observations of this planet transit had to rely on space-borne telescopes.
The host star, 55 Cancri, is located just 40 light-years away from us and is visible to the naked eye. During its transit, the planet crosses 55 Cancri and blocks a tiny fraction of the starlight, dimming the star by 1/2000th for almost two hours.
This shows that the planet is about twice the size of Earth, or 16,000 miles in diameter.
“Our observations show that we can detect the transits of small planets around Sun-like stars using ground-based telescopes,” said lead author of the study, Ernst de Mooij of Queen’s University Belfast in the UK.
“This is especially important because upcoming space missions such as TESS and PLATO should find many small planets around bright stars and we will want to follow up the discoveries with ground-based instruments,” he said.
TESS is a NASA mission scheduled for launch in 2017, while PLATO is to be launched in 2024 by the European Space Agency; both will search for transiting terrestrial planets around nearby bright stars.
“With this result we are also closing in on the detection of the atmospheres of small planets with ground-based telescopes,” said co-author Mercedes Lopez-Morales of the Harvard-Smithsonian Centre for Astrophysics (CfA).
“We are slowly paving the way towards the detection of bio-signatures in Earth-like planets around nearby stars,” said Lopez-Morales.
The planet 55 Cancri e is about twice as big and eight times as massive as Earth. With a period of 18 hours, it is the innermost of five planets in the system.
Because of its proximity to the host star, the planet’s dayside temperature reaches over 1700 degrees Celsius, hot enough to melt metal, with conditions far from hospitable to life.