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Warm Saturn-sized exoplanet discovered with TESS

Using NASA's Transiting Exoplanet Survey Satellite (TESS), an international team of astronomers has detected a new exoplanet orbiting a distant star. The newfound alien world, designated TOI-4994 b, is warm and slightly smaller than Saturn. The finding was reported in a published Dec. 3 on the pre-print server arXiv.

To date, TESS has identified more than 7,300 candidate exoplanets (TESS Objects of Interest, or TOI), of which 571 have been confirmed so far. Since its launch in April 2018, the satellite has been conducting a survey of about 200,000 of the brightest stars near the sun with the aim of searching for transiting exoplanets—ranging from small, rocky worlds to gaseous giants.

Now, a group of astronomers led by Romy Rodriguez of the Harvard–Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, has confirmed another TOI monitored by TESS.

They identified a transit signal in the light curve of TOI-4994—a G-type star about the size and mass of the sun, located some 1,079 light years away. The planetary nature of this signal was confirmed by follow-up observations using ground-based telescopes, including the Las Cumbres Observatory Global Telescope (LCOGT).

"A transit-like signal with a period of 21.5 days was first detected in Sector 12 of TESS and subsequently confirmed with follow-up photometry from the ground," the researchers explained.

The newly detected planet has a radius of about 0.76 Jupiter radii and its mass was estimated to be 0.28 Jupiter masses, which yields a Saturn-like density at a level of 0.78 g/cm³. TOI-4994 b orbits its host every 21.5 days at a distance of 0.15 AU from it, and its equilibrium temperature is some 717.6 K.

Therefore, the properties of TOI-4994 b are similar to those of Saturn and can be classified as a warm Saturn exoplanet. In general, the number of known warm Saturns is still relatively small as less than 20 planets of this type have been discovered to date, which makes TOI-4994 b a valuable addition to this sample.

The authors of the paper note that the properties of TOI-4994 b also suggest a history shaped by planet–planet scattering and a possible merger. However, further observations are required in order to confirm this. They add that the planet is a good candidate for follow-up stellar obliquity measurements.

When it comes to the parent star, TOI-4994 (also known as TIC 277128619), its radius is approximately 1.05 solar radii, while its mass is comparable to that of the sun. The star, which is estimated to be 6.3 billion years old, has an effective temperature of 5,640 K and its metallicity is at a level of 0.165 dex.