Astronomers have discovered our nearest neighbouring exoplanet around our nearest star – α Centauri B, which is just 1.3 pc away. Using the HARPS instrument on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile, a team lead by Xavier Dumusque have been monitoring the Doppler motion of the star for 4 years. In this week’s edition of Nature, they have annouced their detection of a tiny signal from a planet orbiting α Cen B every 3.2 days at a distance of just 0.04 AU from the star. The team estimate the planet’s mass to be a little more than that of the Earth, making it the first exoplanet found with a mass similar to Earth around a Sun-like star.
An “Earth twin” will cause a radial-velocity variation of only a few tenths of a m/s on a Sun-like star, making such detections extremely challenging. α Cen Bb (the planet) induces a radial-velocity of just 0.5 m/s (or 1.8 km/hr, compared to the average human walking speed of 5 km/hr) on the star, making these observations the highest precision ever achieved using the Doppler method. At this precision, there are challenges removing the intrinsic stellar “jitter” that results from stellar oscillations, stellar rotation, and starspots. Furthermore, α Cen B is part of a triple system, comprising two Sun-like stars – itself and α Centauri A – in a binary system with a period of 79.91 years, and a dwarf star Proxima Centauri that orbits the binary at a distance of 12,300 AU.
The Swiss team are not the only group monitoring α Cen B, and two other teams using the Cerro Tololo Inter-American Observatory (CTIO) in Chile and the Mount John University Observatory in New Zealand, are now rushing to confirm – or not – these exciting results.
For more information, see
- Planet Found in Nearest Star System to Earth, ESO press release
- Alpha Centauri exoplanet is the closest ever – how was it found? The Conversation, Rob Wittenmyer
- An Earth-mass planet orbiting α Centauri B, Dumusque et al. (2012), Nature