This Extremely Extreme Exoplanet Has Metal Vapor Clouds And Rains Liquid Jewels

 

It rains liquid rubies and sapphires from a massive exoplanet 855 light-years away, which has clouds of liquefied metals.

Astronomers came at this conclusion by probing the exoplanet's atmosphere - the most extensive analysis of its kind to date, revealing for the first time the conditions and dynamics of the exoplanet's permanent night side.

"Despite the finding of thousands of exoplanets, due to the difficult nature of the observations, we've only been able to analyse the atmospheres of a small proportion," says astronomer Thomas Mikal-Evans of the Max Planck Institute for Astronomy in Germany.

"We're moving beyond taking isolated photos of specific sections of exoplanet atmospheres to studying them as the 3D systems that they are," he continues.

The exoplanet in question is one of the most well-known and studied exoplanets we've ever seen. It's called WASP-121 b, and it was discovered in 2015. It's a gas giant roughly 1.18 times Jupiter's mass and 1.81 times its size, orbiting its star in just 1.27 days. WASP-121 b became the first exoplanet with water in its stratosphere two years after it was identified.

WASP-121 b, on the other hand, is exceedingly unlikely to be livable. It's extremely hot on such a close orbit, with temperatures ranging from 1,500 to 3,000 Kelvin (1,227 to 2,727 degrees Celsius, or 2,240 to 4,940 degrees Fahrenheit).

WASP-121 b is classified as a hot Jupiter because of its size and proximity to its home star, WASP-121. Hot Jupiters are gas giant exoplanets with orbits of fewer than 10 days around their host stars. Over 300 of the over 5,000 identified exoplanets fall into this extreme category, but WASP-121 b has been dubbed a "prototype" for ultra-hot Jupiters.

WASP-121 b is similarly tidally locked with its star due to its close orbit. Tidal locking happens when an orbiting entity rotates at the same rate as it circles. That implies one side of the exoplanet is constantly facing its star, in perpetual sunlight, while the other side is always facing away, in perpetual darkness. Previous studies of WASP 121 b's atmosphere discovered heavy metal vapours in the day side's atmosphere.

Because the night side is about ten times darker than the day side, it's a little more difficult to investigate. Mikal-Evans and his team used the Hubble Space Telescope to examine two full orbits of WASP-121 b, integrating data from the day and night sides to understand how the atmosphere behaves worldwide to get more precise information on the entire exoplanet.

For the first time, they were able to see and rebuild an exoplanet's whole water cycle using this detailed, shifting spectrum of light.

Mikal-Evans notes, "We noticed this water feature and tracked how it altered at different areas of the planet's orbit." "That encodes information on how the planet's atmospheric temperature changes as a function of altitude."

The water cycle on Earth contains phase transitions as water passes through the phases of vapour, liquid, and solid (ice). Temperatures on WASP-121 b are too hot for either the solid or liquid phases of water, even at night. Instead, when temperatures approach 3,000 Kelvin during the day, the water molecules lose energy and light in infrared wavelengths. They may even break down due to the heat, breaking into hydrogen and oxygen.

The night side is significantly cooler, yet still extremely hot by Earth standards, with temperatures as low as 1,500 Kelvin. The huge temperature difference between the hemispheres causes a persistent pressure difference, which causes extreme westerly winds to whirl around the exoplanet, sweeping water molecules and atoms along with them.

"These winds are far quicker than our jet stream," adds MIT astrophysicist Tansu Daylan, "and can probably carry clouds over the entire planet in roughly 20 hours."

Temperatures are chilly enough on the night side of WASP-121 b to revert the water to a vapour condition before it is brought around to the day side again.

The water, on the other hand, would not condense into clouds. Instead, the team's findings demonstrate that nighttime temperatures on WASP-121 b are low enough for clouds to form from metals previously found in the planet's atmosphere. Vanadium, iron, chromium, calcium, sodium, magnesium, and nickel are among them, but aluminium and titanium aren't among them.

These elements may have condensed and sunk further into WASP 181 b's atmosphere, where they are no longer detectable, according to the study. Aluminum may react with oxygen to generate corundum, a crystalline form of aluminium oxide, there. Rubies and sapphires are formed on Earth when vanadium, iron, chromium, or titanium are combined with trace amounts of other metals.

That means magnificent diamonds could be showering down on WASP-181 b. Although it's possible that beautiful jewels are raining down on Neptune and Uranus as well — in either case, we'll never be able to collect them – WASP-181 b demonstrates the amazing variety that can exist among the various types of worlds out there.

More observations of WASP-181 b have already been scheduled on the recently launched James Webb Space Telescope. In order to learn more about how hot Jupiters develop, they're looking for carbon monoxide. We believe they can't be born close to their stars because gravity, radiation, and strong stellar winds should prevent the gas from clumping together, according to current planetary formation theories. Webb's observations might be able to shed some light on the situation.

Mikal-Evans explains, "That would be the first time we could measure a carbon-bearing molecule in this planet's atmosphere." "The amount of carbon and oxygen in the atmosphere can help scientists figure out where these kinds of planets emerge."

References:

• Mikal-Evans, T., Sing, D.K., Barstow, J.K. et al. Diurnal variations in the stratosphere of the ultrahot giant exoplanet WASP-121b. Nat Astron (2022). https://doi.org/10.1038/s41550-021-01592-w