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An artist's conception of the earthlike world, HD 85512 b (CREDIT: ESO/M. Kornmesser)

Today it was reported that HARPS, (High Accuracy Radial velocity Planet Searcher) a device operated from the European Southern Observatory’s station atop Mount la Silla in the Andes, has discovered 50 new exoplanets (planets which orbit stars other than the sun).  Sixteen of these new planets are “super-earths” rocky planets with a mass from 1 to 10 times that of our planet. One of these newly-discovered planets, HD 85512 b, is estimated to be only three-and-a-half times the mass of the Earth and it seems like it is located at the edge of the habitable zone, the orbital belt around a star where water can exist in liquid form.  This is only the second exoplanet discovered within the habitable zone, the first being Gliese 581 d.  Interestingly HARPS has disproved the existence of Gliese 581 g (which I wrote about last year) as a mathematical phantasm–so um, you might want to take that post with a grain of salt. The planet HD 85512 b orbits a star which is is approximately 35 light years from Earth.

In the eight years since the program has started, HARPS has discovered more than 150 exoplanets. HARPS discovers new planets by means of a mind-boggling technology: a spectrograph of stupendous precision is mounted on a 3.6 meter telescope in order to take painstaking observations of numerous nearby stars over a prolonged period of time.  A computer program then compares the tiny variances in the light emitted by these stars.  Stars with planets orbiting them undergo slight changes of radial velocity as the planets’ gravity tugs lightly at the stellar bodies. These shifts can be measured via Doppler shift and compared against the expected spectrographic signature caused by the stars relative drift toward or away from the observatory. Over many years the computer can thereby model the mass and approximate orbit of planets around stars (considering the math and the precise observations required for such calculations makes my hair stand on end).

Kepler, the NASA exoplanet discovery project uses an entirely different technology which involves measuring changes in brightness caused by the transit of a planet across a star’s glowing face.

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September 2011