Metallic clouds found on sizzling Jupiter WASP-121 b because of the Hubble House Telescope

Artist’s rendering of the exoplanet WASP-121 b. This planet always has the same face as its star. This “day side” is therefore continuously lit and very hot, while the other, the “night side”, is constantly exposed to the coldness of space. Credit: Engine House VFX/MPIA.

Astronomers explore the unusual atmospheric conditions of a hot Jupiter-like exoplanet

An international group of astronomers, which includes Jake Taylor, a postdoctoral researcher at the Institute for Research on Exoplanets (iREx), has made a detailed measurement of the atmospheric conditions of a hot Jupiter-like exoplanet called WASP-121 b thanks to Hubble. Space Telescope. Due to tidal effects, this exoplanet always has the same face as its star. The team was able to study both the day side – the one that always faces the star – and the night side – the one that is never illuminated – for the first time! They were able to determine how water changes state as it passes from one side of the exoplanet to the other. While the metals and minerals in the air evaporate on the day side, which is very hot, the cooler night side features metallic clouds and showers of… gemstones! The study, published February 21, 2022 in the journal Nature astronomyis a major advance in the study of matter and energy exchanges in the atmosphere of exoplanets.

Studying the atmosphere of hot Jupiters

The first discovery of an exoplanet orbiting a Sun-like star more than 25 years ago introduced an exotic new class of planets: hot Jupiters. These are gas giant planets that look like Jupiter but are very close to their host star (only a few stellar diameters). Due to this proximity, in such a system, the star heats the planet to several hundred or even thousands of degrees Celsius. Of the roughly 5,000 known exoplanets, more than 300 are hot Jupiters.

Using the Hubble Space Telescope, an international team led by Thomas Mikal-Evans of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, studied the atmospheric properties of WASP-121b, a hot Jupiter. This exoplanet, discovered in 2015, is located in the constellation Pupa, at a distance of 855 light-years from Earth. The mass of WASP-121 b is about 20% greater than that of Jupiter, while its diameter is almost twice as large.

“We know of thousands of exoplanets, but it is only for a small fraction of them that we can study the atmosphere”, underlines Mikal-Evans. “So far, most studies have provided limited information, such as details of the chemical composition of these planets. or the average temperature of specific subregions of the atmosphere. »

First exploration of the night side of an exoplanet

The new observations have given astronomers the most detailed look yet into conditions on the night side of an exoplanet. Like all hot Jupiters, WASP-121 b revolves around itself at exactly the same time as it revolves around its star. The length of a day and a year are therefore the same on this planet, that is, 30 hours. Therefore, the side facing the star – the day side – always experiences the scorching heat of the star. The night side is constantly exposed to the coldness of space. By combining data from the day and night sides, the team obtained for the first time a global view of an exoplanet’s atmosphere.

Metallic clouds and gem rain

These are liquid showers of ruby ​​and sapphire that can fall into the atmosphere of the gas giant exoplanet WAPS-121 b. Credit: Wikimedia Commons (ruby, sapphire).

Rather than clouds of water like those on Earth, WASP-121b’s clouds are primarily composed of metals such as iron, magnesium, chromium, and vanadium. Previous observations have revealed the signature of these metals as gases on the dayside. New Hubble data indicate that on the night side, temperatures drop enough for metals to condense into clouds. Winds blowing eastward transport water vapor from the dayside to the nightside and also push metallic clouds from the nightside to the dayside, where it evaporates again.

Strangely, aluminum and titanium were not among the gases detected in WASP-121b’s atmosphere. A likely explanation is that these metals condensed and rained down into deeper layers of the atmosphere, which cannot be studied with observations. And this rain would be really very special, completely different from the rains that can be observed on the different bodies of the Solar System. Aluminum, for example, condenses with oxygen to form corundum, a species that, when it includes impurities of chromium, iron, titanium or vanadium, is known on Earth as ruby ​​or sapphire. Gemstone showers can therefore be common on the night side of WASP-121 b!

Perspectives with the James Webb Space Telescope

Jake Taylor, a postdoctoral fellow at the Institute for Research on Exoplanets (iREx), is a co-author of the study.

Jake Taylor, a NEAT postdoctoral fellow at iREx at the University of Montreal and co-author of the study, specializes in analyzing data from the atmosphere of exoplanets obtained through space telescopes. He helped establish the composition and structure of WASP-121b’s atmosphere using data from the Hubble Wide Field Camera 3.

“WASP-121b will soon be studied with the James Webb Space Telescope,” says Dr. Taylor. “These Hubble observations give us our first glimpse of what the NEAT GTO observation for WASP-121b will tell us about extreme weather conditions on this planet. »

NEAT is the James Webb Space Telescope’s observation program that uses Canada’s Guaranteed Observation Time (Guaranteed time observation; GTO) to study the atmosphere of a variety of exoplanets, including that of WASP-121 b. Jake joined iREx in 2021 specifically to work on this project.

By covering the region of infrared wavelengths, a type of light that Hubble is not sensitive to, the Webb telescope will allow the team to determine the amount of carbon in the atmosphere. This measurement could give clues to the mechanism and location of WASP-121 b formation in its star’s protoplanetary disk. The measurements will be accurate enough to know the wind speeds at different altitudes in the atmosphere!

Everyone at iREx and the international team is looking forward to learning more about WASP-121b with the Webb telescope!

To know more

The item ” Diurnal variations in the stratosphere of the ultra-hot giant exoplanet WASP-121b was posted on February 21, 2022 in Nature astronomy. In addition to Thomas Mikal-Evans (MPIA, Germany; MIT Kavli Institute, USA) and Jake Taylor (iREx, UdeM, Canada; University of Oxford, UK), the team includes 10 co-authors from the US, UK and India.


Adapted from an MPIA press release by

Dr. Markus Nielbock
Max-Planck-Institut für Astronomy Presse- und Öffentlichkeitsarbeit
MPIA-Campus Königstuhl 17 D-69117 Heidelberg
Such. +49(0)6221 528-134 Mobile +49(0)15678 747326

media contact
Marie-Eve Naud
Education and Extension Coordinator,
exoplanet research institute
University of Montreal

Nathalie Ouellette
exoplanet research institute
University of Montreal

scientific contacts
Jake Taylor
Post-Doctorate NEAT
University of Montreal, Montreal, Canada


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