An article accepted for publication in the journal “Astronomy & Astrophysics” reports the discovery of a super-Earth in the system of HD 164922, a star that’s slightly smaller and slightly less massive than the Sun. A team of researchers led by Serena Benatti of the Italian National Institute for Astrophysics, Palermo, used the HARPS-N spectrograph installed on the Galileo Telescope, on the Canary Islands, to collect the data which, together with others previously collected with other instruments, allowed to discover the exoplanet designated as HD 164922d. The discoveries of exoplanets are increasingly made thanks to software that performs an automatic analysis of data collected by various telescopes, but in this case it’s the prize for the tenacity of astronomers who put together the data of years of observations conducted with various instruments.
The observations of the HARPS-N spectrograph were conducted within the Global Architecture of Planetary Systems (GAPS) project which aims to discover low-mass exoplanets in star systems in which gas giants have already been found. The system of HD 164922, also known as Gliese 9613 or LHS 3353 or with other designations in various catalogs, is close in astronomical terms being 72 light-years from Earth. The star is ancient with an age estimated at almost 9.5 billion years, and in the past years two gas exoplanets orbiting it were discovered: in 2006 one with a mass comparable to Saturn’s and in 2016 a planet with a mass estimated at almost 13 times the Earth’s, which suggests that it’s a sub-Neptunian.
Previous studies of the HD 164922 system brought to light signals that weren’t associated with the two known exoplanets. Serena Benatti explained the great effort made by her team with over five years of observations that brought almost 700 radial velocity points thanks to the HARPS-N spectrograph. By adding the data collected in previous research, it was possible to simulate the activity of the star and the two known exoplanets on the computer.
However, it took almost five months of work to obtain the desired result, the discovery of a further exoplanet, cataloged as HD 164922d. According to the data, it’s at a distance from its star which is about one-tenth of the Earth’s from the Sun for a year that lasts about 12.5 Earth days and with an estimated mass at least four times the Earth’s.
The researchers also analyzed the dynamics of the orbits of the three exoplanets of the HD 164922 system, which are stable over time. This allows to identify other regions of that system where there might be another planet. The interesting thing is that an area is in that system’s habitable zone. Unfortunately, the signals don’t indicate the presence of other planets but it should be a super-Earth even more massive than HD 164922d or a gas planet to be detectable in the data.
The growing surveys in search of exoplanets sometimes make it relatively easy to find them, but in general they are the ones that pass in front of their star leaving visible traces. Research using the radial velocity method is more complicated, and the HD 164922d case is extreme. The patience and tenacity of the researchers made it possible to find a super-Earth after a very long research that also helps to better understand the evolution of a star system that is almost twice as old as the solar system.
