Free Astronomy Magazine May-June 2016

6 PLANETOLOGY A bove and right, two ar- chive images (Palomar Ob- servatory Sky Survey) of the super-massive rocky planet BD+20594b (in the centre of the red circle, while its host star BD+20594 is in the black one). Below, the most recent picture of the same planet, ob- tained by the Las Cumbres Ob- servatory Global Telescope. [N. Espinoza et al./Pontificia Uni- versidad Católica de Chile] L ight curve of the transit of the super-Earth BD+20594b on the disk of the star BD+20594. The curve is based on photometric observations made by the Kepler space telescope during the K2 mission. [N. Espinoza et al./Pontificia Universidad Católica de Chile] scope and the HARPS spectrograph of ESO, have discovered that in the constellation of Aries, around the star BD+20594, about 500 light-years away, there is a planet 16 times more massive than the Earth, thus a size very similar to those of our gas planets Ura- nus and Neptune. Instead of having a dia- meter comparable to these (about 50,000 km), the new planet, called BD+20594b, has a diameter not much greater than half that size, and accordingly a very high average density, about 8 grams per cubic centime- tre, which indicates an essentially rocky composition; a surprising fact if we consider that according to the current models on planet formation, a super-Earth with this mass should not exist.