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<p>There was a very interesting article in Nature this week about a new technique that may enable people to measure the radial velocities imparted to Sun-like stars by Earth-sized planets. The news summary is at:</p><p> http://www.nature.com/news/2008/080402/full/452514b.html</p><p>and a free version of the paper is at:</p><p> http://arxiv.org/abs/0804.0955</p><p>The paper's abstract:<br />"Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60 cm/s (ref 1), which is sufficient to find a 5-Earth-mass planet in a Mercury-like orbit around a Sun-like star. To find a 1-Earth-mass planet in an Earthlike orbit, a precision of 5 cm/s is necessary. The combination of a laser frequency comb with a Fabry-Perot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration, with recent encouraging results. Here we report the fabrication of such a filtered laser comb with up to 40- GHz (1-A) line spacing, generated from a 1- GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb, or `astro-comb', is well matched to the resolving power of high-resolution astrophysical spectrographs. The astro-comb should allow a precision as high as 1 cm/s in astronomical radial velocity measurements."</p><p>So it looks like they've taken a big step toward being able to detect planets like the Earth orbiting other stars from the ground. This will also be really important for space missions like Corot and Kepler which hope to detect these planets via the transit technique. Previously it wasn't clear that any candidate new Earths found by these missions would be confirmable, now it seems like it might be possible. Also knowing both the mass and radius of these things will be key to inferring the properties of the planet.</p> <div class="Discussion_UserSignature"> </div>