2023-07-16 02:56:22
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The ESA probe “Cheops” examines the exoplanet LTT9779 b more closely and makes several surprising discoveries.
Marseille – Venus is the brightest planet in our night sky, reflecting about 75 percent of sunlight, compared to Earth, which reflects only about 30 percent of the light. Now, for the first time, a planet outside our solar system has been discovered that can compete with Venus in terms of brightness: LTT9779 b. In 2020, NASA’s TESS spacecraft discovered this exoplanet, and later it was further studied by ESA’s Cheops spacecraft.
It turned out that LTT9779 b reflects about 80 percent of the incident light, as in a Communication from ESA is called. This makes the exoplanet the largest known “mirror” in the universe to date. The cause of this intense light emission from the roughly Neptune-sized exoplanet is being investigated by astronomer James Jenkins, co-author of a in the journal Astronomy & Astrophysics published study via LTT9779 b. “Imagine a burning world near your star, with heavy metal clouds hovering overhead and titanium droplets raining down,” says the researcher. These metallic clouds, composed mostly of silicates and metals like titanium, surround the exoplanet.
Exoplanet (ultra-hot Neptune)4.7 times Earth’s radius29 times Earth’s mass19 hours2019 by TESS
Exoplanet LTT9779 b is a giant “mirror” in the Universe
The vast majority of known planets have a small amount of reflected light (called albedo). This is either because they have an atmosphere that absorbs a lot of light, or because the planet’s surface is dark. However, there are exceptions where albedo is high, such as icy worlds with bright surfaces or planets like Venus, which have a reflective cloud layer.
The extraordinarily high albedo of LTT9779 b particularly surprised the researchers because the side of the planet facing its star is estimated to have a temperature of around 2000 degrees Celsius. Under normal circumstances, temperatures above 100 degrees Celsius do not allow the formation of water vapor clouds, and at 2000 degrees Celsius clouds of metal or glass should not be possible either. “It was really a mystery until we realized that we should think of this cloud formation as condensation in a bathroom after a hot shower,” explains Vivien Parmentier, a co-author of the study.
Reflective exoplanet is shrouded in metallic clouds
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.”
Artist’s rendering of exoplanet LTT9779b, which reflects about 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)
The exoplanet LTT9779 b surprised the researchers for another reason: Due to its size and temperature, it is counted among the “ultra-hot Neptunes”. However, no other planet of this magnitude or temperature class has been discovered in such close proximity to its star as 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.”
Metal clouds help the planet survive in the “Neptune Desert”.
First author Sergio Hoyer (Marseille Astrophysics Laboratory) explains 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.”
The latest findings about the exoplanet LTT9779 b are the result of research carried out using the ESA probe “Cheops”. This space mission is a first as it focuses on re-observing and characterizing previously known exoplanets. Maximilian Günther, the ESA project scientist for the Cheops project, explains: “Unlike large survey missions that focus on discovering new exoplanet systems, ‘Cheops’ is flexible enough to quickly focus on interesting targets and create a cover and Achieving precision that we often just can’t achieve any other way.”
Machine assistance was used for this editorial-written article. The article was carefully checked by editor Tanja Banner before publication.
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