Using the James Webb Space Telescope (JWST), astronomers discovered that a scorching hot lava planet believed to be composed of diamond formed a second atmosphere after its star destroyed its first atmosphere.
The planet, known as 55 Cancri e, is located about 41 light-years from the solar system and is almost twice as wide as Earth and has a mass about nine times greater than our planet. Among the extrasolar planets, or “exoplanets,” that scientists have cataloged over the years, this world is classified as a “super-Earth.” This means it is larger than Earth but much lighter than planets like Neptune and Uranus. But for 55 Cancri e, comparisons with our world end there.
This exoplanet is so dense that astronomers have suggested that it consists mostly of carbon pressed into diamond. Additionally, the exoplanet is located just 1.4 miles (2.3 kilometers) from its sun-like star 55 Cancri A. This is equal to 0.01544 times the distance between the Earth and the sun. This closeness means that 55 Cancri e orbits its host star in about 17 Earth hours and has a scorching hot surface temperature of about 4,400 degrees Fahrenheit (about 2,400 degrees Celsius).
Thus, radiation from its star destroyed 55 Cancri e’s original or primary atmosphere, as has been seen on other rocky planets orbiting so closely around their stars. But new research shows that there is a thick layer of gas surrounding the planet, implying that it has “grown” a second atmosphere, and the scientists behind the discovery think they know how this happens.
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“We measured thermal emissions from this rocky planet, and the measurement shows that the planet has a significant atmosphere,” Renyu Hu, a researcher at the California Institute of Technology (Caltech) and a member of the team behind this discovery, told Space. .com. “This atmosphere is likely supported by outgassing from the rocky interior of 55 Cancri e, and we think this is the first measurement of a secondary atmosphere on a rocky exoplanet. This is very exciting.”
How did 55 Cancri e challenge its star?
55 Cancri e was discovered in 2004 due to the “wobble” it causes in the motion of its host star, as seen from our perspective of Earth. This is called the radial velocity exoplanet discovery method for exoplanet discovery. The world, originally named Janssen, was the first super-Earth found to orbit a distant main-sequence star, or a star still fusing hydrogen into helium in its core.
As the planet was studied in more detail, scientists also learned about its 0.7 Earth-day orbit and carbon composition. Later in 2016, the Hubble space telescope determined that the atmosphere of 55 Cancri e contained hydrogen and helium, during the first atmospheric survey of an exoplanet.
Two possible scenarios exist to explain the atmosphere of 55 Cancri e.
First, the super-Earth may be a lava world with a thin, vaporized silicate atmosphere on top. It would consist of the planet’s volatiles and chemical compounds such as carbon, nitrogen, hydrogen and sulfur that can be easily lost due to irradiation from its star. Or alternatively it could be a thick layer of the planet. secondary The atmosphere formed over time through volcanism.
To investigate which of these scenarios is correct, Hu and colleagues examined JWST observations of the planet as it passed behind the star 55 Cancri A, an event called a secondary eclipse. Data from two secondary eclipses at 55 Cancri e ruled out the possibility that it was a nearly bare lava world without a significant atmosphere.
There’s no doubt that the planet is a lava-covered hellscape, and the team even thinks it’s this molten nature that helps 55 Cancri e form its secondary atmosphere.
“55 Cancri e is so close to its host star that it receives a lot of heat in the form of radiation. This heat keeps the temperature on the planet very high,” Hu said. “At these temperatures, everything on the planet is molten. If it’s rock, there’s also molten lava, which helps with the outgassing process that supports the secondary atmosphere due to the molten surface.”
He explained that the gas dissolved in the global lava ocean of 55 Cancri and was constantly “bubbling” to form the secondary atmosphere.
The researcher added that the original atmosphere that 55 Cancri e will have since its formation around its star will consist mostly of hydrogen and helium. However, the composition of the secondary atmosphere that replaces the first remains unclear.
“The composition of the secondary atmosphere depends on what the underlying rock is made of,” Hu said. “If the rock is reduced too much [made of compounds that gain electrons and hydrogen]it can also form a hydrogen-helium atmosphere like the primary atmosphere. “But if the rock is more similar to the Earth’s mantle, water, carbon monoxide and carbon dioxide will dominate the secondary atmosphere.”
Hu added that although JWST observations of 55 Cancri e do not say for sure what the planet’s atmosphere consists of, the models used to explain the measurements support significant amounts of carbon dioxide and carbon monoxide.
Can the 55 Cancri e really create a secondary atmosphere?
55 Cancri e isn’t the only rocky planet orbiting this close to its host star, but Hu points out that it’s among the hottest planets of its kind. So does this mean that other scorching hot terrestrial worlds might also have developed secondary atmospheres? The team isn’t sure.
That’s because the 55 Cancri e has something quite unique.
“It’s a fairly large piece of rock, 1.8 times the size of Earth, which helps shield volatiles from stellar radiation,” Hu explained. “We would expect a very small rocky planet in a very close orbit around its star to lose its entire planetary variable budget and then become atmosphereless.”
This means that it is not just the distance between a planet and its star that determines whether one planet will retain its atmosphere and “grow” another, but also the size of that world. Hu noted that in both respects, 55 Cancri e appears to be “optimized” to replace the lost primary atmosphere with a secondary atmosphere.
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This analysis of 55 Cancri e would be impossible without JWST’s observing power and infrared sensitivity, making it ideal for characterizing the atmospheres of exoplanets, Hu said.
“We are definitely considering the next steps to study 55 Cancri e. We have some ideas about making measurements of the planet’s thermal emission not only during secondary eclipses, but also as the planet orbits the star,” Hu said. “This will give us information about the size of the atmosphere and the circulation within.”
The team’s research was published Wednesday (May 8) in the journal Nature.