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Two exoplanets discovered orbiting sun-like star

An international team of astronomers reports the discovery of two new exoplanets, a few times more massive than Earth, orbiting a sun-like star known as HD 35843. The finding was reported in a published May 1 on the arXiv pre-print server.

To date, NASA's Transiting Exoplanet Survey Satellite (TESS) has identified more than 7,600 candidate exoplanets (TESS Objects of Interest, or TOI), of which 622 have been confirmed by follow-up observations. The satellite's main aim is to complete a survey of about 200,000 of the nearest brightest stars, searching for transiting exoplanets—from small, rocky worlds to gaseous giants.

HD 35843, or TOI 4189, is a metal-poor G-dwarf star with a radius of approximately 0.9 solar radii and mass comparable to that of the sun. TESS observed this star between 2018 and 2022, which resulted in the detection of a transit signal in its light curve.

Follow-up ground-based observations conducted by a group of astronomers led by Katharine Hesse of the Massachusetts Institute of Technology (MIT) confirmed the planetary nature of this signal and also revealed the presence of an additional planet.

"We report the discovery and confirmation of two planets orbiting the metal-poor sun-like star, HD 35843 (TOI 4189)," the paper reads.

The confirmed exoplanet, designated HD 35843 c, is about 2.5 times larger and 11.3 times more massive than the Earth, which yields a density at a level of 3.8 g/cm³. The planet orbits its host every 46.7 days, at a distance of 0.25 AU from it. The estimated equilibrium temperature of HD 35843 c is 479 K, therefore it is one of the coolest alien worlds discovered with TESS.

The additional non-transiting planet that was identified by follow-up radial velocity measurements received designation HD 35843 b. It is closer to the parent star—at a distance of about 0.088 AU and its orbital period is approximately 9.9 days. The planet is estimated to have a mass of at least 5.84 Earth masses.

Based on the derived properties of the newly detected extrasolar worlds, the astronomers classified HD 35843 b as a super-Earth and HD 35843 c as a sub-Neptune exoplanet. It was noted that it is still too early to draw a final conclusion regarding the composition of HD 35843 c as it may be a "water world" or a rocky planet with a thick hydrogen atmosphere.

When it comes to the host star HD 35843, it has an effective temperature of 5,666 K and metallicity at a level of -0.27. The age of the star is estimated to be some 2.5 billion years.

The authors conclude that the high transmission spectroscopic metric (TSM) of HD 35843 c and relatively low temperature make it a promising target to conduct a follow-up atmospheric characterization study with the James Webb Space Telescope (JWST) in order to determine its exact composition.