Cosmic

Closest exoplanet is remarkably Earth-sized

Closest exoplanet is remarkably Earth-sized

Published: 2015-10-23 | Original Article
Attribution By Ken Croswell

<strong>An Earth-mass planet orbiting α Centauri B</strong><br />Exoplanets down to the size of Earth have been found, but not in the habitable zone—that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water–carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star α Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth–Sun distance).
An Earth-mass planet orbiting α Centauri B
Exoplanets down to the size of Earth have been found, but not in the habitable zone—that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water–carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star α Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth–Sun distance).
In 2012, astronomers reported a planet orbiting Alpha Centauri B, an orange star that belongs to the closest star system to the sun, located a mere 4.3 light-years from Earth (artist's conception shown). But this detection, which must still be confirmed, left open a major question: Just how massive is this newfound neighbor of ours? The planet's gravity tugged its sun toward and away from us, inducing a tiny Doppler shift in the star, but deriving the planet's mass requires knowing whether we view its orbit around the star edge-on, face-on, or somewhere in between. If the orbit is edge-on, then the small Doppler shift means the planet has as little mass as Earth; but if the orbit is nearly face-on, then the planet could be as massive as Jupiter and still pull the star toward and away from us only slightly. Now, as other astronomers report in work submitted to The Astrophysical Journal, computer simulations of the planet's history indicate that the orbit isn't face-on, which in turn means the world is only one to three times as massive as Earth. This implies that the planet may have a terrestrial composition. Before you snap up any real estate here, though, be forewarned that the planet's day side is hot enough to melt lead.
nature11572.pdf
Attribution By Ken Croswell