Astronomers at the University of Geneva have discovered a newly found planet, about the size of Earth, orbiting Alpha Centauri B, a nearby sun-like star roughly 4 light years away. It orbits around its star, which is about half the size of our Sun, in a dizzying 3.2 days. The new planet orbits its parent star about 10 times closer than Mercury so temperatures might be more than 2,240 degrees Fahrenheit, far too hot for liquid water to exist. Still, scientists are hopeful that more planets will be discovered a bit further out, some in the range that could indeed support life as we know it.
Astronomer Stephane Udry with Geneva University in Switzerland told reporters:
“Most of the low-mass planets are in systems of two, three, up to six or seven planets, so finding in our closest neighbor one Earth-mass planet … opens a really good prospect for detecting planets in the habitable zone in the system that is very close to us.”
The Alpha Centauri system is one of the brightest stars in the southern sky and the nearest system to Earth. It is actually a triple-star system consisting of two sun-like stars orbiting each other (Alpha Centauri A and B) and a third red component known as Proxima Centauri. Alpha Centauri B, the star the planet was discovered orbiting around, is very similar to the Sun but slightly smaller, less bright, and a bit cooler.
The planet was discovered using the HARPS (High Accuracy Radial Velocity Planet Searcher) instrument on the 3.6-meter telescope at ESO’s La Silla Observatory in Chile. Essentially, a planet orbiting a star causes the star to slightly shift towards and away from an observer on Earth – in other words, it wobbles. Using the Doppler effect, this wobble can be detected by observing a redshift (the shifting of the star’s spectrum towards longer wavelengths) and blueshift (the shift towards shorter wavelengths) of the star’s light. This shift is extremely small, no more than 51 centimeters per second, but can be measured using a high-precision instrument such as HARPS.
Discover magazine noted how difficult the find was:
“Scientists using Europe’s HARPS telescope spent four years trying to ferret out telltale signs of a small planet’s gravitational tug on light coming from Alpha Centauri B. The measurement is difficult because of variations in the star’s light caused by other phenomenon, such as flares and magnetic storms, similar to sunspots on the sun.”
There could be planets orbiting Alpha Centauri A too but since it is bigger and brighter, any small planets orbiting it would be harder to find.
Astronomer Debra Fischer of Yale University expressed her excitement:
“A rocky planet around Alpha Centauri, our nearest neighbor — this is incredible. If you were going to send a spacecraft anywhere, or a probe anywhere, that’s where you’d go first. And if you have evidence that there are rocky planets there, you’d be insane to skip that target.”