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Earth-sized exoplanets' circular orbits may narrow down hunt for life

Amy Tyndall, News reporter
Jun 3, 2015, 16:04 UTC

Sen—A recent study has revealed 74 Earth-sized exoplanets that travel around their suns in circular orbits, something that was once thought to be a rarity in the Universe and possibly unique to our Solar System.

Smaller exoplanets are mostly detected via the transit method, which is the detection of a dip in the light coming from a distant star as a planet passes in front of it. In a paper published in the Astrophysical Journal, researchers from the the Massachusetts Institute of Technology (MIT) and Aarhus University in Denmark looked at Kepler data for 28 stars harbouring exoplanets, whose masses and radii had previously been measured through the study of their stellar pulsations. From this, they could calculate the duration of model transits for planets with circular orbits, then compare this value to the duration of real transits from the Kepler data.

Vincent Van Eylen, a visiting graduate student in MIT’s Department of Physics, and Simon Albrecht of Aarhus University, discovered that the two transit durations matched. This implies that each of the 74 Earth-sized exoplanets studied travel in circular orbits, and not in the eccentric orbits that are common amongst the gas giant exoplanets.

"We want to understand why some exoplanets have extremely eccentric orbits, while in other cases, such as the Solar System, planets orbit mostly circularly," Van Eylen said in a statement. "This is one of the first times we’ve reliably measured the eccentricities of small planets, and it’s exciting to see they are different from the giant planets, but similar to the Solar System."

This could be good news in a future search for life on other worlds. It is unlikely that any would be found on planets with eccentric orbits as the temperature and climate would vary too much as one moved very close to, then very far away from, its parent star. However, rocky planets possessing circular orbits would present far more stable conditions for life to emerge.