Earth-Like Planet Discovered In Nearest Star System Alpha Centauri B

An alien planet with a similar mass to the Earth has been discovered orbiting the nearest star system to the Earth, the Alpha Centauri system. This is also the first time that such a light exoplanet has been discovered orbiting a sunlike star.

A european team of researchers first detected the planet when using the HARPS instrument on the 3.6-metre telescope at the ESO’s La Silla Observatory located in Chile.

The Alpha Centauri star system is easily visible in the night’s sky, being located ‘only’ 4.3 light-years from the Earth. The single ‘star’ that we see is actually a triple star system, it’s composed of two sun-like stars orbiting very close to one another. These stars, Alpha Centauri A and B, are then orbited by a distant, and somewhat faint, red component called Proxima Centauri.

Since the beginning of the 1800’s researchers have been speculating about possible alien planets around these stars. Being the closest possible place to find alien life, they have been a focus of research since then. But until now, there hadn’t been any evidence that there were even planets there.

“Our observations extended over more than four years using the HARPS instrument and have revealed a tiny, but real, signal from a planet orbiting Alpha Centauri B every 3.2 days,” says Xavier Dumusque (Geneva Observatory, Switzerland and Centro de Astrofisica da Universidade do Porto, Portugal), the lead author of the research paper. “It’s an extraordinary discovery and it has pushed our technique to the limit!”

The researchers were able to detect the presence of the planet “by picking up the tiny wobbles in the motion of the star Alpha Centauri B created by the gravitational pull of the orbiting planet.” This effect is very subtle, causing no more than 51 centimetres per second of movement in the star. So far this is “the highest precision ever achieved using this method.”

There are a lot of similarities between the Alpha Centauri system and ours. The primary star, Alpha Centauri B, is only slightly dimmer and smaller than the Sun. And the planet itself has a mass only slightly more than the Earth’s. But even with those similarities, the differences are quite substantial. It orbits much closer to its star than Mercury does to our Sun. And it has essentially a second sun, though its orbit keeps it a bit further away and is consequently less bright.

“The first exoplanet around a Sun-like star was found by the same team back in 1995 and since then there have been more than 800 confirmed discoveries, but most are much bigger than Earth, and many are as big as Jupiter. The challenge astronomers now face is to detect and characterise a planet of mass comparable to Earth that is orbiting in the habitable zone around another star. The first step has now been taken.”

“This is the first planet with a mass similar to Earth ever found around a star like the Sun. Its orbit is very close to its star and it must be much too hot for life as we know it,” adds Stéphane Udry (Geneva Observatory), a co-author of the paper and member of the team, “but it may well be just one planet in a system of several. Our other HARPS results, and new findings from Kepler, both show clearly that the majority of low-mass planets are found in such systems.”

“This result represents a major step towards the detection of a twin Earth in the immediate vicinity of the Sun. We live in exciting times!” concludes Xavier Dumusque.

The research is published online in the journal Nature.

Source: European Southern Observatory

Image Credits: ESO/L. Calçada/N. Risinger (; ESO/L. Calçada/N. Risinger (

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top