TESS detects a warm Jupiter-like exoplanet that is thousands of years old

Gaia EDR3 catalog over-plotted on the TESS Target Pixel File of TOI-5542 for Sector 13. Credit: Grieves et al., 2022.

An multinational team of scientists has discovered a new ancient and warm Jupiter-like alien world circling a G-dwarf star using the Transiting Exoplanet Survey Satellite (TESS). The newly discovered exoplanet, TOI-5542 b, is nearly 30% more massive than Jupiter, the solar system's largest gas giant. The discovery is detailed in an article published on the arXiv pre-print server on September 29. TESS is surveying around 200,000 of the brightest stars near the sun in search of transiting exoplanets. It has discovered approximately 6,000 candidate exoplanets (TESS Objects of Interest, or TOI) thus far, with 256 verified.

Now, another TOI observed by TESS has been verified by a group of astronomers led by Nolan Grieves of the University of Geneva in Switzerland. They claim to have discovered a transit signal in the light curve of TOI-5542, a metal-poor G dwarf (other designation TYC 9086-01210-1). Follow-up studies with the CORALIE and High Accuracy Radial Velocity Planet Searcher (HARPS) spectrographs verified the signal's planetary nature.

We report the identification and characterisation of the warm Jupiter TOI-5542 b, the astronomers said in their publication. TESS discovered the planet for the first time as two separate transit occurrences 375.6 days apart. The newly discovered exoplanet has a radius of roughly 1.01 Jupiter radii and a mass of 1.32 Jupiter masses, resulting in a density of 1.6 g/cm3. It circles its parent star at a distance of 0.33 AU every 75.12 days. The planet's equilibrium temperature was predicted to be 441 K, hence it was categorized as a warm Jupiter by astronomers. TOI-5542's spectral type is G3V, it has a radius of roughly 1.06 solar radii, and it is 11% less massive than the sun. The star has an effective temperature of around 5,700 K, a brightness of about 1.05 solar luminosities, and an estimated age of 10.8 billion years. TOI-5542's metallicity was determined to be around -0.21.

Given that TOI-5542 is over 11 billion years old, the researchers stated that its exoplanet is one of the oldest known long-period warm Jupiters and one of the few with an age estimate. The scientists found that TOI-5542b is one of the oldest known warm Jupiters and is chilly enough to be untouched by stellar incident flux inflation, making it a useful addition to planetary composition and formation research. Because TOI-5542 b has a circular orbit, the researchers emphasized that predicting a creation or migration scenario for this planet is problematic. They believe it developed by disk migration or in situ formation, as these are more likely to leave a planet in an eccentric orbit around its parent star.

Journal Information: Nolan Grieves et al, An old warm Jupiter orbiting the metal-poor G-dwarf TOI-5542. arXiv:2209.14830v1 [astro-ph.EP], arxiv.org/abs/2209.14830