An Exoplanet Reaches 2400 C in One Hemisphere. Does it Really Rain Iron?

WASP-76b, an extremely hot Jupiter located 640 light years from Earth in the constellation Pisces, is called WASP-76b. It was famous for its hot iron that falls as rain, which it did a few years back. It is tidally linked to its star and can reach temperatures up to 2400 Celsius from its star-facing hemisphere, which is well above irons 1538C melting point.
Since its discovery in 2013, scientists have been studying the planet, and recent evidence suggests that it is even hotter than previously thought. Iron rain might not be so surprising, however.

Multi-year observations of WASP-76b have led to the discovery that WASP-76b may be even more hot than previously thought. The Astrophysical Journal Letters has published a new paper that is based on some of these observations. The paper's title is Detection of Ionized Calcium In the Atmosphere of Ultra-hot Jupiter WASP76b. Emily Deibert is a University of Toronto doctoral candidate.

Exoplanet research is a fascinating field. Astronomers are constantly looking for new ways to discover more exoplanets, and to begin studying their atmospheres. ExoGemSExoplanets using Gemini Spectroscopy is the basis of this new research. The ExoGemSExoplanets with Gemini Spectroscopy project uses Mauna Kea's Gemini North Telescope and a high resolution spectrograph to study the variety of exoplanet atmospheres. ExoGemS is designed to investigate at least 30 exoplanets that are of interest to astronomers. WASP-76b serves as the benchmark.

Remote sensing of many exoplanets will allow us to get a better picture of their true diversity, Ray Jayawardhana said. We'll be able to see whether they are hot enough to harbor iron rain or others with moderate climates.

Illustration of a Hot Jupiter close to its star. Image Credit: ESA/ATG medialab. CC BY -SA 3.0 IGO

Jayawardhana stated in a press release that it is amazing that we can learn so much with today's telescopes or instruments about the atmospheres of their physical properties, compositions, and wind patterns of planets orbiting stars hundreds and thousands of light-years distant.

WASP-76b was the subject of a study that suggested it could rain iron. While the dayside temperature can vaporize iron, the nightside temperature is cold enough that iron can condense into rain. Iron would condense into liquid near the terminator of the planet, and then fall to the surface.

This may be false, but we'll get to the truth. New research suggests that WASP76b may actually be more hot than previously thought. This is due to the discovery of rare spectroscopic lines of calcium ionized in the atmosphere.

Exoplanets have complex atmospheres. Astronomers study it from hundreds of light years away so conclusions may not be final. The authors state that WASP-76b probably has an escaping atmosphere. They also claim that hydrodynamics in the atmosphere may be affecting the spectrometry's ionized calcium lines. They write that a higher temperature would lead to an enhanced production of ionized Calcium and therefore to strong absorption characteristics.

Jayawardhana, Emily Deibert's adviser, stated that they were seeing so much calcium. Deibert stated that this spectral signature could be a sign of strong upper atmosphere winds on the exoplanet. Oder the exoplanet's atmospheric temperature is higher than we thought.

This figure is full of amazing detail. The dips are the three spectroscopic lines for ionized calcium. Image Credit: Deibert et al 2021.

Iron, which has attracted so much attention, could partly be responsible for the extreme heat in one of its forms. The atmosphere could also be affected by Mg and another form of iron. Metal photoionization, NLTE and other mechanisms that lead to temperature increases in ultra-hot Jupiter's atmospheres have been identified. "Non-local equilibrium" thermodynamic effects include overpopulation of species that are responsible for heating (e.g. Fe ii), and underpopulation for species that are responsible for cooling (e.g. Fe i. Mg).



__S.91__ and __S.92__



__S.98__, __S.99__, __S.100__


__S.107__ _______________________________________________

__S.113__ and __S.114__

__S.116__ and Fe clouds don't necessarily thrive in hot Jupiter atmospheres. Microphysics models show that Fe clouds can be trapped deep within the atmosphere because of its low nucleation rate.

A 2021 paper titled Decomposing Iron Cross-Correlation signal of the Ultra-Hot Jupiter WASP-76b In Transmission using 3D Monte-Carlo radiation transfer, also argues against iron rain., __S.120__, __S.121__

__S.123__. __S.124__. __S.125__

__S.127_______S.128____However, there is no signal from the nightside near the morning terminator. This indicates that atomic iron has not been absorbing starlight there. Temperature asymmetry could also explain the absence of an iron signal.

__S.131__, __S.132__, __S.133__