It will have two telescopes mounted at opposite ends of a ten-metre boom, and will be able to measure astrometric wobbles as small as a millionth of an arcsecond.

ECONOMIST: A roadmap for planet-hunting

By using an entirely different planet-hunting approach, it should be able to plug this gap, and provide a means of calibrating the census figures resulting from the radial-velocity and astrometric searches.

ECONOMIST: A roadmap for planet-hunting

Astrometric and radial-velocity searches for planets are neatly complementary.

ECONOMIST: A roadmap for planet-hunting

Already, tests carried out with a prototype at the Palomar Observatory in California have achieved astrometric resolutions of 100 millionths of an arcsecond, and the improved atmospheric conditions in Hawaii will increase this by a factor of three.

ECONOMIST: A roadmap for planet-hunting

Viewed from ten light-years away, the sun's side-to-side astrometric wobble due to the effect of the earth is just one millionth of an arcsecond, or a twentieth of the tiniest angle that the Keck will be able to measure.

ECONOMIST: A roadmap for planet-hunting