Two now alien worlds.
Astronomers utilizing the High Accuracy Radial Velocity Planet Searcher (HARPS) have recently found two new exoplanets orbiting the GJ 367 star system, both at least four times heavier than Earth. This exciting discovery was shared publicly on the arXiv pre-print server on July 18.
The GJ 367 Planetary System
Situated roughly 30.7 light years away from us, GJ 367 (alternatively known as TOI-731 or TIC 34068865) is a bright, spectral type M1.0 V star. Its size and mass are roughly half that of our sun. Previously, it was known to host GJ 367 b, an ultra-short-period (USP) sub-Earth exoplanet, first discovered in 2021. This small, extrasolar body completes its orbit around the host star in under eight hours, with a radius approximately 0.72 times that of Earth and mass estimated at 0.55 Earth masses.
The Search for Additional Planets
Led by Elisa Goffo from Italy’s University of Turin, a team of astronomers now reports the presence of two more low-mass planets in the GJ 367 system. This breakthrough is the result of an intensive RV observational campaign using HARPS, supplemented with data from NASA’s Transiting Exoplanet Survey Satellite (TESS).
The scientists’ mission to ascertain planetary mass and radius and decipher the inner system architecture led them to gather 371 high-precision measurements over a span of nearly three years. “We combined our Doppler measurements with new TESS observations from sectors 35 and 36,” the researchers detailed in their paper.
Introducing the Newfound Exoplanets
The newly discovered planet, closer to the star and named GJ 367 c, boasts a minimum mass of 4.13 Earth masses and an anticipated radius of 1.6 times that of Earth. It takes this planet 11.5 days to orbit its host star. On the other hand, the outermost planet in the system, GJ 367 d, carries at least six times the mass of Earth. With an orbital period of approximately 34 days, its estimated radius is about 1.7 times that of Earth.
The study also honed in on the mass and radius measurements for GJ 367 b, revealing a mass of approximately 0.63 Earth masses and a radius of 0.7 Earth radii. This indicates an ultra-high density of 10.2 g/cm3, pointing towards an iron core.
The Significance of the GJ 367 System
Summarizing their findings, the researchers stated that GJ 367 belongs to a small group of thoroughly studied multiplanetary systems hosting a USP exoplanet, with GJ 367 b being the smallest and densest of all known USP planets. Hence, further scrutiny of GJ 367 and its planets could enhance our understanding of how such systems form.
The researchers concluded by highlighting the unique nature of this multiplanetary system, which hosts an ultra-high density, USP sub-Earth. They noted that the GJ 367 system would be an excellent target for future investigations into the formation and migration of USP systems.
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