Scientists using NASA's Hubble Space Telescope have characterized the atmospheres of two of the most common type of planets in the Milky Way galaxy and found both may be blanketed with clouds.
The planets are GJ 436b, located 36 light-years from Earth in the constellation Leo, and GJ 1214b, 40 light-years away in the constellation Ophiuchus. Despite numerous efforts, the nature of the atmospheres surrounding these planets had eluded definitive characterization until now. The researchers described their work as an important milestone on the road to characterizing potentially habitable, Earth-like worlds beyond the solar system.
The two planets fall in the middle range in mass, between smaller, rockier planets such as Earth and larger gas giants such as Jupiter. GJ 436b is categorized as a "warm Neptune" because it is much closer to its star than frigid Neptune is to the sun. GJ 1214b is known as a "super-Earth" because of its size. Both GJ 436b and GJ 1214b can be observed transiting, or passing in front of, their parent stars. This provides an opportunity to study these planets in more detail as starlight filters through their atmospheres.
"Either this planet has a high cloud layer obscuring the view, or it has a cloud-free atmosphere that is deficient in hydrogen, which would make it very unlike Neptune," said Knutson of the California Institute of Technology in Pasadena, California. "Instead of hydrogen, it could have relatively large amounts of heavier molecules such as water vapor, carbon monoxide, and carbon dioxide, which would compress the atmosphere and make it hard for us to detect any chemical signatures."
Using Hubble, astronomers led by Laura Kreidberg and Jacob Bean of the University of Chicago took a closer look at GJ 1214b. They found what they consider definitive evidence of high clouds blanketing the planet and hiding information about the composition and behavior of the lower atmosphere and surface. The new Hubble spectra also revealed no chemical fingerprints in GJ 1214b's atmosphere, but the data were so precise they could rule out cloud-free compositions of water vapor, methane, nitrogen, carbon monoxide, or carbon dioxide for the first time.
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