Closest exoplanet is remarkably Earth-sized

ESO/L. Calçada/Nick Risinger (skysurvey.org)

Closest exoplanet is remarkably Earth-sized

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.

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