Free Astronomy Magazine March-April 2022

50 MARCH-APRIL 2022 ASTRO PUBLISHING known exoplanets. Many exoplanets were discovered using the transit method – the measurement of minute differences in the emitted light, or its apparent magnitude, of a star as a planet passes in front of it (with respect to the observer). GJ 367 b was also discovered using this method, with the help of NASA’s Transiting Exoplanet Survey Satellite (TESS). With an orbital period of only one- third of an Earth day, GJ 367 b is a fast mover. “From the precise deter- mination of its radius and mass, GJ 367b is classified as a rocky planet,” reports Kristine Lam from the In- stitute of Planetary Research at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). “This places it among the sub-Earth sized terres- trial planets and brings research one step forward in the search for a ‘sec- ond Earth’.” GJ 367 b belongs to the ‘ultra-short period’ (USP) group of exoplanets that orbit their star in less than 24 hours. “We already know a few of these, but their origins are currently unknown,” says Savita Mathur, a re- searcher at the IAC and co-author of the article. Moreover, with a rota- tion period of 48 days for the star, “it is a very interesting system to study and understand the dynami- cal evolution of small rocky planets with this orbit,” explains the re- searcher. Following the discovery of this planet using TESS and the transit method, the spectrum of its star was then studied from the ground using the radial velocity method. This technique consists of measuring changes in the position and velocity of a star as it and a surrounding planet orbit their common centre of mass. The variation caused by the gravitational force of the two ob- jects is reflected in a shift in the spectrum of the observed star. In the case of GJ 367 b, the mass was deter- mined using the HARPS instrument on the European Southern Observa- tory’s 3.6m telescope. A n international team, includ- ing researchers from the In- stituto de Astrofísica de Ca- narias (IAC), has discovered an extra- solar planet with half the mass of the Earth that takes approximately eight hours to orbit its parent star, a red dwarf just under 31 light-years from Earth. Called GJ 367 b, it is one of the lightest among the nearly 5000 exoplanets known today. With a diameter of just over 9000 kilometres, this sub-Earth is slightly larger than Mars. The discovery not only demonstrates that it is possible to precisely determine the event the smallest, least massive exoplanets, but also provides a key to under- standing how terrestrial planets form and evolve. The study was pub- lished in the journal Science . A quarter of a century after the first discovery of an extrasolar planet, the focus has shifted to characteris- ing these planets more precisely, in addition to making new discoveries. At present, it is possible to construct a much more precise profile for most Astronomers discover an ultra-light and super-fast sub-Earth by IAC - Outreach Unit