Two Additional Exoplanets Discovered in the Nearby Planetary System

An international team of astronomers have used the High Precision Radial Velocity Planet Hunter (HARPS) to perform radial velocity (VR) follow-up observations in the planetary system GJ 367. As a result, they have discovered two additional alien worlds that are at least four times more massive than Earth. The findings were reported on the arXiv preprint server. GJ 367, also known as TOI-731 or TIC 34068865, is a bright star with a spectral type of M1.0 V. It lies approximately 30.7 light-years distant and is about half the size and mass of the Sun. In 2021 a sub-Earth exoplanet named GJ 367 b was discovered. This planet has an ultra-short period, completing one orbit around its star in less than eight hours. It has a radius of about 0.72 Earth radii and an estimated mass of 0.55 Earth masses.

Led by Elisa Goffo of the University of Turin in Italy, the team of astronomers carried out an intensive radial velocity campaign using the HARPS spectrograph. They collected 371 high-precision measurements over nearly three years and combined these measurements with new observations from NASA’s Transiting Exoplanet Survey Satellite (TESS). The researchers discovered two low-mass companions in GJ 367 b. The closest planet to the star, designated GJ 367 c, has a minimum mass of 4.13 Earth masses and an estimated radius of 1.6 Earth radii. It completes one orbit around its host star every 11.5 days. The outermost planet, GJ 367 d, is at least six times more massive than Earth. It has an orbital period of approximately 34 days and an estimated radius of 1.7 Earth radii.

The study also refined the mass and radius determinations for GJ 367 b. It was found to have a mass of about 0.63 Earth masses and a radius of 0.7 Earth radii. The planet has an ultra-high density of 10.2 g/cm3, suggesting an iron core. The study authors note that GJ 367 is among a small group of well-characterized multiplanetary systems that host an ultra-short-lived exoplanet. GJ 367 b is the smallest and densest ultra-short-period planet known to date. Additional observations of this system and its planets could provide information about the formation of such systems.

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