The ???? ???search for a rocky world swaddled in a protective atmosphere somewhere else in space has eluded scientists, but the James Webb Space Telescope has found a strong case.
Webb, the leading infrared observatory run by NASA and the European and Canadian space agencies, has taken a closer look at super-Earth 55 Cancri e, an exoplanet blanketed in either carbon dioxide or carbon monoxide just 41 light-years away.
But to call it an "Earth-like world" would be misleading. Discovered 13 years ago in the constellation Cancer, the planet seems to orbit so close to its star, its surface is probably lava. And because it's hugging the star so tightly, chances are it isn't rotating either, with one side in constant darkness.
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Still, the discovery could be the best evidence scientists have found of a rocky planet's atmosphere outside Earth's own solar system. Such a finding, published in the journal Nature, bolsters experts' confidence that they'll eventually discover rocky worlds with hospitable atmospheres.
"Webb is pushing the frontiers of exoplanet characterization to rocky planets," said Renyu Hu, a researcher at NASA's Jet Propulsion Laboratory, in a statement. "It is truly enabling a new type of science."
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When exoplanets cross in front of their host star, the star’s light is filtered through that atmosphere. Molecules within the atmosphere absorb certain light wavelengths, or colors, so by splitting the star’s light into its basic parts — a rainbow — astronomers can use Webb to detect what light segments are missing and discern the molecular makeup of an atmosphere.
Scientists have found signs of atmospheres surrounding many exoplanets over the past 20 years, but all of them have been gas giant planets, like Jupiter, with thick atmospheres mostly composed of hydrogen.
Knowing what's in another planet's atmosphere is important. NASA has playfully called Earth's own atmosphere its "security blanket": Without it, the type of life flourishing on the planet wouldn't exist. This cocoon holds oxygen in the air and filters out harmful ultraviolet radiation from the sun, all while keeping our world warm and habitable. Furthermore, it creates pressure that allows liquid water to exist on Earth's surface.
NASA made a travel poster-inspired illustration of what the exoplanet 55 Cancri e might look like. Credit: NASA / JPL-Caltech illustration The first sign that 55 Cancri e could have a substantial atmosphere came from temperature readings based on the infrared light it radiates. If the planet is covered in dark molten rock with no atmosphere — or a very thin one of vaporized rock — the side in constant light should be about 4,000 degrees Fahrenheit.
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Instead, the researchers found a much lower temperature of about 2,800 degrees Fahrenheit.
"Webb is pushing the frontiers of exoplanet characterization to rocky planets," said Renyu Hu, a researcher at NASA's Jet Propulsion Laboratory. Credit: NASA GSFC / CIL / Adriana Manrique Gutierrez illustration "This is a very strong indication that energy is being distributed from the dayside to the nightside, most likely by a volatile-rich atmosphere," Hu said.
While 55 Cancri e would seem far too hot to support life as we know it, scientists think studying it could enhance their understanding of the primitive conditions of Earth, Venus, and Mars, which some believe were also once covered in magma oceans.
"Ultimately, we want to understand what conditions make it possible for a rocky planet to sustain a gas-rich atmosphere: a key ingredient for a habitable planet,” Hu said.