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Astronomers discover a super-Earth exoplanet orbiting a nearby star

Using NASA's Transiting Exoplanet Survey Satellite (TESS), an international team of astronomers has discovered a new super-Earth exoplanet that orbits a nearby M dwarf star. The newfound alien world, designated TOI-1846 b, is about two times larger and four times more massive than Earth. The finding was detailed in a paper June 23 on the arXiv preprint server.

Launched in April 2018, TESS has identified more than 7,600 candidate exoplanets (TESS Objects of Interest, or TOI), of which 636 have been confirmed so far. The satellite is conducting a survey of about 200,000 brightest stars near the sun, looking for transiting extrasolar worlds.

Now, a group of astronomers led by Abderahmane Soubkiou of the Oukaimeden Observatory in Morocco, reports that a transit signal has been identified in the star TOI-1846 monitored by TESS, which is located some 154 light years away. By conducting ground-based follow-up photometric and spectroscopic observations, they confirmed the planetary nature of this signal.

"We have validated TOI-1846 b using TESS and multicolor ground-based photometric data, high-resolution imaging, and spectroscopic observations," the researchers wrote in the paper.

According to the study, TOI-1846 b has a radius of about 1.792 Earth radii and is 4.4 times more massive than Earth, which yields a density at a level of 4.2 g/cm³. The planet orbits its host every 3.93 days, at a distance of some 0.036 AU from it. The equilibrium temperature of TOI-1846 b is estimated to be 568.1 K.

Based on the derived parameters, the astronomers concluded that TOI-1846 b is likely a water-rich super-Earth and belongs to the so-called "radius valley," a dip in occurrence in the radius distribution separating rocky super-Earths and gaseous sub-Neptunes. This dearth of planets is observed at around 1.8 Earth radii.

The researchers noted that radial velocity (RV) observations of TOI-1846 b should be conducted in order to unveil its composition. "These findings make TOI-1846 b well-suited for mass determination via RV observations. This could be possible with the MAROON-X instrument. (...) We find a TSM [transmission spectroscopy metric] of 47 for TOI-1846 b, which is below the ≈ 90 benchmark for small sub-Neptunes," the authors of the paper wrote.

When it comes to the parent star TOI-1846 (also known as TIC 198385543), it is about 0.4 times the size of the sun and its mass is approximately 0.42 solar masses. The star has an effective temperature of 3,568 K and is estimated to be 7.2 billion years old.