Our Nearest Neighbor Star Hosts an Earth-Mass Planet

An Earth-ish planet orbiting a red dwarf star would be the saddest thing. A perfect ball of rock, featuring plenty of carbon and water and methane, orbiting a dark star with no visible light, and stuck in tidal lock. That is, it orbits the star so close its own rotation would be married to its orbit: one half of the planet is always dark. Earth-mass planets are one thing — but having the right kind of sun is another. The European Southern Observatory announced yesterday afternoon the discovery of the first Earth-sized planet orbiting a Sunlike star, Alpha Centauri, a mere 4.5 light years away. Practically next door.

Only about three-and-a-half percent of stars in the Milky Way are G-type stars, e.g. stars like the Sun. Ten or so more percent are K-type, which are still pretty close to being Sunlike. Most stars, about 80 percent, are red dwarfs, which are smaller, cooler, and, crucially, dark. They don’t emit visible or ultraviolet light. Sunlike planets are the ticket if we’re going to find life, or places hospitable to life. Which is why finding an Earthsize planet orbiting one is very exciting, even if it is orbiting closer to its star than Mercury orbits the Sun, making it well outside the habitable range.

The hope, however, is that this scorched planet is part of a system, and there are other planets like it located more reasonable distances away. So we’re left with more hope than we started with: there are certainly others like this, probably a bottomless pit of them. The Kepler mission has already found 800 extrasolar planets.

But the Kepler mission also uses a different method of observation: measuring planetary transits, e.g. the dimming of a star as a planet passes in front of it. The ESO, using the HARPS instrument at the La Silla Observatory in Chile, looks at the star’s tilt as a planet tugs on it with its gravity. Due to its method of observation, the Kepler experiment finds planets very far away, while HARPS finds planets relatively nearby. The upshot of that is that the planets found by HARPS can possibly be observed even closer. It might be possible to do even atmospheric readings on a planet this close in, while most/many Kepler candidates will remain numbers.

Reach this writer at michaelb@motherboard.tv.