This exoplanet –the planet orbiting the star GJ 536- is not within the star’s habitable zone, but its short orbital period of 8.7 days and the luminosity of its star, a red dwarf which is quite cool and near to our Sun, make it an attractive candidate for investigating its atmospheric composition. During this research a cycle of magnetic activity similar to that of the Sun has been found, but with a shorter period, 3 years.
“So far the only planet we have found is GJ 536 b but we are continuing to monitor the star to see if we can find other companions”, says Alejandro Suárez Mascareño, who is the first author on the article. “Rocky planets are usually found in groups”, he explains, “especially round stars of this type, and we are pretty sure that we can find other low mass planets (other “superearths”) on orbits further from the star, with periods from 100 days up to a few years. We are preparing as programme of monitoring for transits of this new exoplanet to determine its radius and mean density”.
“This rocky exoplanet is orbiting a star much smaller and cooler than the Sun” comments Jonay Isaí González, “but, sufficiently nearby and bright. It is also observable from both the northern and southern hemispheres, so that it is a very interesting for future high stability spectrographs and in particular for the possible detection of another rocky planet in the habitability zone of the star”.
“To detect the planet”, states Rafael Rebolo “we had to measure the velocity of the star with an accuracy of the order of a metre per second. With the construction of the new instrument ESPRESSO, co-directed by the IAC, we will improve this accuracy by a factor of ten, and will be able to extend our search to planets with conditions very similar to Earth, around this and many other nearby stars”.
The planet has been detected in a joint effort between the IAC and the Geneva Observatory, using the HARPS (High Accuracy Radial velocity Planet Seeker) spectrograph on the 3.6M ESO Telescope at La Silla (Chile) and HARPS North, on the Telescopio Nacional Galileo (TNG) at the Roque de los Muchachos Observatory, Garafia (La Palma).
We report the discovery of a super-Earth orbiting the star GJ 536 based on the analysis of the radial-velocity time series from the HARPS and HARPS-N spectrographs. GJ 536 b is a planet with a minimum mass M sin $i$ of 5.36 +- 0.69 Me with an orbital period of 8.7076 +- 0.0025 days at a distance of 0.066610(13) AU, and an orbit that is consistent with circular. The host star is the moderately quiet M1 V star GJ 536, located at 10 pc from the Sun. We find the presence of a second signal at 43 days that we relate to stellar rotation after analysing the time series of Ca II H&K and H alpha spectroscopic indicators and photometric data from the ASAS archive. We find no evidence linking the short period signal to any activity proxy. We also tentatively derived a stellar magnetic cycle of less than 3 years.