An international team of astronomers, led by Samuel H. C. Cabot of Yale University, found an ultra-hot Jupiter-type exoplanet while observing the TOI-1518 star with NASA's Transiting Exoplanet Survey Satellite (TESS) telescope. The study authors estimate that this exoplanet has high surface temperatures and is nearly twice as large as the largest gas giant in the Solar System.
This exoplanet is a gas giant like Jupiter, but with no clouds in the atmosphere.
The discovery came during observations of the star, which showed a traffic signal in the curve of light emitted by the star. Most exoplanets are discovered this way: when they pass in front of their stars, they cause a small reduction in their light, which can be seen in the light curves. So in the case of TOI-1518, a star roughly twice the size of the Sun, the researchers carried out observations with the Lowell Discovery Telescope's spectrograph to confirm that the signal was indeed planetary in nature.
The exoplanet in question is considered an "ultra-hot Jupiter", that is, it has characteristics similar to those of the largest planet in the Solar System, but with much higher temperatures and an orbital period below 10 days, so that it orbits the star very closely and has high surface temperature. According to the authors, TOI-1518b has a radius equivalent to 1,875 times that of Jupiter (for comparison, Jupiter's radius is approximately 69,911 km), and its mass can reach 2.3 gas giant masses — this estimate can be improved with future monitoring of the radial velocity of the system.
In addition, they estimate that the planet orbits the star every 1.9 days at 0.04 astronomical unit (AU) from it. Thus, the planet has an equilibrium temperature of 2,492 K, and the measured dayside temperature reached 3,237 K, which suggests the occurrence of thermal inversion. However, new spectroscopy observations will also be needed to confirm this.
The data indicate that the planet has an unaligned orbit, which the authors explain most often occurs with gas giants close to their stars. Finally, the team detected the presence of iron in the planet's atmosphere; by performing a cross-correlation analysis, they found neutral iron and point out that, so far, there have been only a few detections of iron on ultra-hot Jupiters.
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