2023-07-12 17:06:51
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The ESA space probe “Cheops” examines an already known exoplanet and discovers something surprising.
Marseille – The brightest planet in our night sky is Venus – the celestial body reflects regarding 75 percent of sunlight, while Earth only re-emits regarding 30 percent of the light. Now, for the first time, researchers have found a planet outside our solar system that can compete with the brightness of Venus: LTT9779 b. The exoplanet was discovered by NASA’s TESS spacecraft in 2020 and later studied further by ESA’s Cheops spacecraft.
It turned out that LTT9779 b reflects 80 percent of the light that falls on the exoplanet – it is the largest known “mirror” in the universe so far, according to one communication of the European Space Agency Esa. But why does the exoplanet, which is regarding the size of the planet Neptune, emit so much light? “Imagine a burning world near your star, with heavy metal clouds hovering overhead and titanium droplets raining down,” explains astronomer James Jenkins, co-author of a study on LTT9779 b that in the journal Astronomy & Astrophysics published became. The exoplanet is shrouded in metallic clouds made up mostly of silicate and metals like titanium.
Name:LTT9779 bType:Exoplanet (ultra-hot Neptune)Radius:4.7 times Earth’s radiusMass:29 times Earth’s massDuration of one year:19 hoursDiscovery:2019 by TESS
Most planets reflect little light
Most known planets have a low albedo—the technical term for the amount of light reflected off the object. That’s because they either have an atmosphere that absorbs a lot of light, or the planet’s surface is dark. Exceptions with a high albedo are ice worlds with bright surfaces or planets like Venus, which have a reflective cloud layer.
The high albedo of LTT9779 b came as a surprise to the researchers, because the side of the planet that faces its star is estimated to have a temperature of around 2000 degrees Celsius. Temperatures above 100 degrees Celsius do not actually allow clouds of water vapor to form, and 2000 degrees Celsius should be too hot even for clouds made of metal or glass. “It was really a mystery until we realized that we should think of this cloud formation as condensation in a bathroom following a hot shower,” explains Vivien Parmentier, a co-author of the study.
The researcher goes on to explain: “To fog a bathroom, you can either cool the air until the water vapor condenses, or you can run the hot water until clouds form, because the air is so saturated with water vapor that it just freezes can’t take anything anymore. Similarly, despite its high heat, LTT9779 b can form metal clouds because the atmosphere is oversaturated with silicate and metal fumes.”
Exoplanet LTT9779 b is a surprise for researchers
The exoplanet LTT9779 b is a surprise for the researchers for another reason: Due to its size and temperature, it is one of the “ultra-hot Neptunes” – but so far no other planet of this size or temperature class has been discovered so close to its star like LTT9779 b. It is located in the so-called “Neptune Desert”. “It’s a planet that shouldn’t exist,” says researcher Parmentier. “We assume that the atmosphere of such planets is blown away from their star, leaving bare rock behind.”
Artist’s rendering of exoplanet LTT9779b, which reflects regarding 80 percent of the light that falls on it. This makes it the largest known “mirror” in the universe. © Ricardo Ramírez Reyes (Universidad de Chile)
First author Sergio Hoyer (Marseille Astrophysics Laboratory) adds to the research team’s theory: “We believe that these metal clouds help the planet to survive in the hot Neptune desert. The clouds reflect the light and prevent the planet from getting too hot and evaporating. At the same time, the high metal content makes the planet and its atmosphere heavy and difficult to blow away.”
ESA probe “Cheops” has examined exoplanet LTT9779 b
The researchers owe the new findings regarding the exoplanet LTT9779 b to the ESA probe “Cheops”. This is the first space mission to re-observe and more accurately characterize known exoplanets. “Unlike large survey missions that focus on discovering new exoplanet systems, ‘Cheops’ is flexible enough to quickly focus on targets of interest and achieve coverage and precision that we often just can’t achieve by other means.” , explains Maximilian Günther, Esa project scientist for the Cheops project.
“Cheops” is only part of a three-part exoplanet mission. The Plato spacecraft is scheduled to follow in 2026 and study Earth-like planets that exist at potentially habitable distances from their stars. The “Ariel” space probe is also planned for 2029, which will specialize in the atmospheres of exoplanets. (tab)
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