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ESO 19/08 - Associated Images

16 June 2008
For Immediate Release

A Trio of Super-Earths

A harvest of low-mass exoplanets discovered with HARPS

Artist's impression of the trio of super-Earths discovered by an European team using the HARPS spectrograph on ESO's 3.6-m telescope at La Silla, Chile, after 5 years of monitoring. The three planets, having 4.2, 6.7, and 9.4 times the mass of the Earth, orbit the star HD 40307 with periods of 4.3, 9.6, and 20.4 days, respectively.

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The HARPS radial velocity measurements of HD 40307 are folded with the orbital periods of the three discovered planets: 4.3, 9.6, and 20.4 days, respectively. In each case, the contribution of the two other planets has been subtracted. The solid line shows the best fit to the measurements, corresponding to minimum masses of 4.2, 6.7, and 9.4 Earth masses. Note that the full span of the vertical axis is only 10 m/s! Error bars indicate the accuracy of the measurements.

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Schematic view from above of the orbits of the three super-Earths around their host star. The scale is in astronomical units (AU), the mean distance between the Earth and the Sun. All planets are thus well within the orbit of Mercury around the Sun (which has an orbital period of 88 days).

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