March 25, 2023


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Hot days and cloudy nights on a heavy metal outer planet | Urania

Scientists used JWST to observe WASP-121b, a hot, spin-locked Jupiter that is notorious for the presence of heavy metals in its atmosphere. This study sheds new light on conditions on the planet’s night side and provides new evidence for metallic clouds.

Noteworthy exoplanet

WASP-121b seems to be in the news every time astronomers point a telescope at it. this Hot Jupiter It orbits its parent star every 30 hours, with one side permanently facing the star, keeping daytime temperatures high enough to even vaporize the gold there. Previous observations have already shown volatile metals such as iron, nickel and vanadium floating in the planet’s atmosphere.

One way to learn about the interesting atmosphere outer planets Like WASP-121b, it is a measurement of its phase curve, which is the total amount of light emitted and reflected by a planet and its host star when it completes its full orbit. Planetary phase curves can tell us a lot about how the temperature of a planet’s atmosphere changes between day and night. A previously measured phase curve of WASP-121b suggested that the night side of the planet might be cool enough for clouds to form over it. What is the new data from JWST Can you tell us about this hot metal world?

General on WASP-121b from a JWST perspective

In October 2022, a research team led by Thomas Mikal Evans (Max Planck Institute for Astronomy) used the JWST telescope to stare at this planetary system for 1.5 Earth days. The team used the JWST near-infrared spectrometer (NIR) in a special observational mode designed for obvious purposes, which allowed the scientists to collect data for 99% of the available observational time.

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light curve It shows deep depressions when a planet passes in front of a bright star, less deep depressions when a planet passes behind a star, and a gentle curve corresponding to the period when both star and planet are fully visible.

Metallic clouds at night

Michael Evans and co-authors condition modeled the system’s light curve and found that the warmest point in WASP-121b’s atmosphere lies a few degrees east of the point where its star is closest to the sub-point. Models of hot Jupiters like WASP-121b predict transitions that look much larger, closer to 10grades. The team suggested two possible reasons for this marked difference.

First, the planet’s atmosphere can be so hot that the gas ionizes, and the interaction between the ionized gas and the planet’s magnetic field slows the heat transfer to the east. Second, it is possible that the hottest point is actually farther to the east, but that clouds on the planet’s night side affect our interpretation of the resulting light curve.

Finally, a note about the night side of the planet. The team measured the temperature on this side of WASP-121b to be around 1,000 K. While that may sound like sweltering heat, it’s actually cold enough for some of the metal compounds common in Jupiter’s hot atmospheres to form liquid droplets — other words, WASP-121b could contain metallic clouds at night!

In addition to demonstrating these fascinating details of the WASP-121b phase curve, this study demonstrates the capabilities of the NIRSpec instrument. Next, the team plans to study the WASP-121b phase curve against wavelength to learn more about the planet’s nighttime atmosphere.

Agnes Nowak

more information:

Source: AAS

Pictured: A simulation of what WASP-121b might look like to our eyes under different lighting angles. Image credit: NASA/JPL-Caltech/Aix-Marseille University (AMU)