Astronomers discover a new dense sub-Saturn exoplanet

An international team of astronomers has reported the detection of a new exoplanet orbiting a bright late F-type star. The newfound alien world, designated TOI-6038 A b, is about six times larger and nearly 80 times more massive than Earth. The finding is detailed in a paper published Jan. 4 on the arXiv preprint server .

NASA’s Transiting Exoplanet Survey Satellite (TESS) is conducting a survey of about 200,000 of the brightest stars near the sun with the aim of searching for transiting exoplanets. So far, it has identified nearly 7,400 candidate exoplanets (TESS Objects of Interest, or TOI), of which 591 have been confirmed so far.

Now, a group of astronomers led by Sanjay Baliwal of the Physical Research Laboratory (PRL) in Ahmedabad, India, reports the confirmation of another planet monitored by TESS. Baliwal’s team has identified a transit signal in the light curve of TOI-6038 A—a late F-type star about 578 light-years away. The planetary nature of this signal was validated by follow-up observations using the 2.5m telescope at the PRL Observatory in India.

“TOI-6038 A (TIC 194736418) was observed by TESS in Sectors 18 and 58. The Sector 18 (S18) observations were conducted between November 3 and November 27, 2019, while the Sector 58 (S58) observations took place from October 29 to November 26, 2022,” the paper reads.

Follow-up observations found that TOI-6038 A b has a radius of approximately 6.41 Earth radii and its mass is estimated to be 78.5 Earth masses, which yields a bulk density at a level of 1.62 g/cm³. The planet orbits its host every 5.83 days, at a distance of 0.069 AU from it. The equilibrium temperature of TOI-6038 A b was calculated to be 1,439 K.

Based on the internal structure modeling, the astronomers assume that TOI-6038 A b has a massive core with a mass of about 58 Earth masses, composed predominantly of dense materials such as rock and iron, which account for around 74% of the planet’s total mass. A modest hydrogen/helium envelope constitutes the remaining mass, which suggests a relatively thin atmosphere.

The derived properties of TOI-6038 A b make it a sub-Saturn exoplanet at the boundary between the Neptunian ridge and savanna. The so-called Neptunian desert and savanna mark the dearth of Neptune-like exoplanets on the shortest-period orbits and their modest occurrence at larger orbital distances. They are separated by a recently identified overdensity (ridge) of Neptune-like exoplanets in the 3–5 day orbital period range.

The parent star, TOI-6038 A, is part of a binary system with a K-type star, TOI-6038 B, separated by about 3,217 AU. TOI-6038 A has a radius of approximately 0.9 solar radii, while its mass is around 0.86 solar masses. The star, which is estimated to be 3.65 billion years old, has an effective temperature of 6,110 K, and its metallicity is at a level of 0.124 dex.

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