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Using NASA's Transiting Exoplanet Survey Satellite (TESS), astronomers from the University of California, Irvine (UCI) and elsewhere, have discovered two new exoplanets orbiting M-dwarf stars. The newfound alien worlds are similar in size to Jupiter and have Saturn-like densities. The finding was reported in a published Oct. 13 on the arXiv pre-print server .

TESS continues its ongoing survey of about 200,000 of the brightest stars near the sun, aiming to find transiting exoplanets. Since its launch in 2018, the telescope has identified more than 7,700 candidate exoplanets (TESS Objects of Interest, or TOI), of which 705 have been confirmed so far.

Now, a team of astronomers led by UCI's Shane O'Brien reports the detection of transit signals in the light curves of two M-dwarfs, namely TOI-5916 and TOI-6158, which are about half the size and mass of the sun each. O'Brien's team confirmed the planetary nature of these signals using ground-based photometry and radial velocity data.

"We report the discovery and confirmation of TOI-5916 b and TOI-6158 b as part of the Searching for GEMS [giant exoplanets around M-dwarfs] Survey. (...) Both systems were confirmed with ground-based photometry (Red Buttes Observatory and Swope, respectively) and radial velocity data from the Habitable-zone Planet Finder," the researchers wrote in the paper.

According to the study, TOI-5916 b has a radius of approximately 1.05 solar radii and its mass is 0.69 Jupiter masses, yielding a density at a level of 0.73 g/cm³. The planet orbits its host every 2.37 days, at a distance of some 0.028 AU from it. The equilibrium temperature of TOI-5916 b is estimated to be 716 K.

The second newfound exoplanet, TOI-6158 b, turned out to be smaller and less massive than TOI-5916 b, as its radius was measured to be 0.93 Jupiter radii, and its mass was calculated to be approximately 0.42 Jupiter masses.

The alien world has an orbital period of 3.04 days and a semi-major axis of 0.033 AU. The results indicate that TOI-6158 b has an equilibrium temperature of 636 K and a density of around 0.66 g/cm³.

Therefore, TOI-5916 b and TOI-6158 b are the latest additions to the relatively short list of 32 known GEMS and to the more common population of warm Jupiters. The scientists noted that both newly detected planets have Saturn-like densities, which generally seems to be a growing trend among GEMS.

When it comes to the parent stars, TOI-5916 and TOI-6158, they are both approximately two times smaller and less massive than the sun.

TOI-5916 has an effective temperature of 3,541 K and is located some 639 light years away, while TOI-6158's effective temperature was estimated to be 3,467 K and the distance to this star was measured to be about 592 light years.

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