TESS discovers an ancient warm Jupiter-like exoplanet

Using the Transiting Exoplanet Survey Satellite (TESS), an international team of astronomers has discovered a new ancient and warm Jupiter-like extraterrestrial world orbiting a G dwarf star. The newly discovered exoplanet, designated TOI-5542 b, is the size of Jupiter — about 30% more massive than the Solar System’s largest gas giant. The result is reported in a paper published on September 29 on pre-print server arXiv.

TESS is conducting a survey of about 200,000 of the brightest stars near the Sun in search of passing exoplanets. So far it has identified nearly 6,000 possible exoplanets (TESS Objects of Interest or TOI), of which 256 have been confirmed so far.

Now, a group of astronomers led by Nolan Grieves of the University of Geneva in Switzerland has recently confirmed another TOI monitored by TESS. They report that a transit signal was identified in the light curve of a metal-poor G-dwarf named TOI-5542 (other designation TYC 9086-01210-1). The planetary nature of this signal was confirmed by follow-up observations using CORALIE and High Accuracy Radial Velocity Planet Searcher (HARPS) spectrographs.

“We report the discovery and characterization of warm Jupiter TOI-5542 b. The planet was first spotted by TESS as two separate transit events 375.6 days apart,” the researchers wrote in the paper.

The newly discovered exoplanet has a radius of about 1.01 Jupiter radii and a mass of 1.32 Jupiter masses, giving a density at the level of 1.6 g/cm³. It orbits its parent star every 75.12 days at a distance of 0.33 AU from it. The planet’s equilibrium temperature was estimated at 441 K, so astronomers classified it as warm Jupiter.

The host TOI-5542 is of spectral type G3V, has a radius of about 1.06 solar radii, and is 11% less massive than the Sun. The star has an effective temperature of about 5,700 K, a luminosity of about 1.05 solar luminosities, and is estimated to be 10.8 billion years old. The metallicity of TOI-5542 was measured to be approximately -0.21.

Noting that TOI-5542 is almost 11 billion years old, the researchers emphasized that its exoplanet is therefore one of the oldest known long-period warm Jupiters and one of the few with an estimated age.

“TOI-5542b is one of the oldest known warm Jupiters and it is cool enough to be unaffected by inflation due to incoming stellar flux, making it a valuable contribution in the context of studies of planetary composition and formation,” concluded the authors of the paper.

Given that TOI-5542 b has a circular orbit, researchers found it difficult to predict a formation or migration path for this planet. They hypothesize that it likely formed through disk migration or in situ formation than other mechanisms that leave a planet more likely to be in an eccentric orbit around its parent star.

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