It's also possible that other teams could find an exoplanet there before they do, but Anglada's team believes the risk is low. Several other searches at Proxima Centauri came up short, and they feel the chance of somebody using similar observational power is low.
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The team is pretty sure that they won't see planets of 2-3 times Earth's mass in the habitable zone of Proxima, but it's possible they can find something close to Earth's mass or smaller. HARPS looks at the gravitational wobbles a planet induces in its star. This technique only yields how long the orbit is and how eccentric it is, but not information such as density - something that is usually only possible using measurements if the planet passes in front of the star.
There aren't many nearby star or planet systems to us. Kapteyn's star is 13 light-years away and has two planets of about 5 and 7 Earth masses. Gliese 581 is also relatively close (20 light-years), with several planets being considered. Reports of a planet around Alpha Centauri, a close neighbor to Proxima Centauri, are currently under intense dispute.
The search is doing two new things: having HARPS stare at a star every day for two months, and also tying in with other systems to get photometry (light curves) on the star. The photometry reveals how active the star is, which can affect the certainty of the radial velocity predictions for obits.
HARPS has been a busy planet-hunting instrument, with some of its notable finds including finding planets close to Earth's size. The European Southern Observatory is also building the European Extremely Large Telescope, whose mirror is so big that it may be able to look at the atmospheres of larger planets.