Big news today! A team of European astronomers announced the discovery of a planet orbiting Alpha Centauri. Located only 4.4 light years away, Alpha Centauri is a triple star and the closest star to the sun. It’s one of the few places where the sun holds its own as a first magnitude star in the constellation Cassiopeia. Not only is the new planet the closest extrasolar planet ever found, it’s also about the same size as the Earth, making it the lightest planet yet discovered orbiting a sun-like star.
Exoplanet surveys typically turn up massive planets because the big (and close-in) ones tug on their parent stars hardest. Astronomers use sensitive instruments called spectrographs to measure the slight changes in a star’s velocity induced by the circling planet. These tiny wobbles of the star toward and away from Earth can be measured and the planet’s mass determined.
In Alpha Centauri’s case, the team employed the super-sensitive HARPS spectrograph on the European Southern Observatory’s 142-inch (3.6 meter) telescope in La Silla, Chile for more than four years to reveal telltale velocity changes caused by an Earth-size planet orbiting Alpha Centauri B every 3.2 days.
The wobble is minute. The planet causes the star to move back and forth by no more than 1.1 mile per hour, about the speed of a baby crawling. Earth’s effect on our sun would be similar. Sadly, the planet is nowhere near a clement zone around the star; it orbits just 3.7 million miles from Alpha Centauri B, almost 10 times closer than Mercury to the sun. You could broil a steak there in a minute, but I doubt life could set up house on this heat-heavy world.
Alpha Centauri is a triple system with two bright components – Alpha Centauri A and B – and one more distant, fainter red dwarf called Proxima Centauri. A and B are separated by 13,000 times the distance between sun and Earth. From the new planet’s perspective, B would be far and away the dominate sun, while A would be brilliant pinprick of light off in the distance.
I’ve always wanted a planet to be found around Alpha Centauri if only because it feels so close to Earth. While Alpha Centauri Bb’s still over 26 trillion miles away, the news is most exciting. Of the 842 confirmed extrasolar planets found to date, it’s already my favorite. More about the discovery can be found HERE.