Alpha Centauri, the closest star system to our Solar System, should harbour detectable Earth-like planets, according to a new study by astronomers at the University of Santa Cruz.

All-sky map showing the location of Alpha Centauri, the closest stellar system to the Sun, and one which may offer favourable conditions to terrestrial life. Image: NOAA.

Computer simulations of planet formation were performed to show that terrestrial planets are likely to have formed around one of the three stars in the system, Alpha Centauri B. Moreover, the planets would have formed in the 'habitable zone", where liquid water can exist on the planet's surface. Although many different simulations were performed, starting with a variety of different initial conditions, in every case a system of multiple planets evolved with at least one planet about the size of Earth.

The team are confident that a rocky, Earth-like planet could be detected around Alpha Centauri B using the existing Doppler detection method, which has already revealed the majority of the 228 known extrasolar planets. "If they exist, we can observe them," said Guedes, who is the first author on the paper describing the new findings. The Doppler method measures the shift in light from a star to detect the tiny wobble induced by the gravitational tug of an orbiting planet. Detecting small planets is particularly challenging because of the relatively small wobble induced in the parent star, and around five years worth of observations would be needed to detect an Earth-like planet around Alpha Centauri B. But this star offers favourable observing conditions because its position in the sky gives it a long period of observability from the Southern Hemisphere each year. An observation program using the 1.5 metre telescope at the Cerro Tololo Inter-American Observatory in Chile is planned to intensively study Alpha Centauri A and B in the hope to detect real planets similar to the ones that emerged in the computer simulations. "I think the planets are there, and it's worth a try to have a look," co-author Laughlin said.