An international team of astronomers has discovered a close-in super-Earth exoplanet in the HD 164922 planetary system.

An artists impression of the super-Earth exoplanet HD 164922d. Image credit: Sci-News.com.

HD 164922 is a bright G9-type star located approximately 72 light-years away in the constellation of Hercules.

Also known as Gliese 9613 or LHS 3353, the star is slightly smaller and less massive than the Sun and is 9.6 billion years old.

HD 164922 is known to host two massive planets: the temperate sub-Neptune HD 164922c and the Saturn-mass planet HD 164922b in a wide orbit.

The sub-Neptune is 12.9 times more massive than Earth, and orbits the parent star once every 75.8 days at a distance of 0.35 AU (astronomical units).

The Saturn-like planet has a mass 0.3 times that of Jupiter and an orbital period of 1,201 days at a distance of 2.2 AU.

In a new study, Dr. Serena Benatti from the INAF Astronomical Observatory of Palermo and colleagues searched for additional low-mass planets in the inner region of the HD 164922 system.

The astronomers analyzed 314 spectra of the host star collected by HARPS-N (High Accuracy Radial velocity Planet Searcher for the Northern hemisphere), a spectrograph on the Telescopio Nazionale Galileo at the Roque de los Muchachos Observatory, La Palma, Canary Islands, Spain.

We monitored this target in the framework of the Global Architecture of Planetary Systems (GAPS) project focused on finding close-in low-mass companions in systems with outer giant planets, they said.

The team detected an additional inner super-Earth with a minimum mass of 4 times that of the Earth.

Named HD 164922d, the planet orbits the star once every 12.5 days at a distance of 0.1 AU.

This target will not be observed with NASAs Transiting Exoplanets Survey Satellite (TESS), at least in Cycle 2, to verify if it transits, the researchers said.

Dedicated observations with ESAs CHarachterizing ExOPlanet Satellite (CHEOPS) could be proposed, but they can be severely affected by the uncertainty on the transit time.

The teams paper will be published in the journal Astronomy & Astrophysics.

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S. Benatti et al. 2020. The GAPS Programme at TNG XXIII. HD 164922 d: a close-in super-Earth discovered with HARPS-N in a system with a long-period Saturn mass companion. A&A, in press; arXiv: 2005.03368

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