Credit: NASA/JPL-CaltechĪstronomers were elated to find clear skies on a Neptune-size planet called HAT-P-11b in 2017. The illustrated view at left shows the high cloud layers of many Neptunian exoplanets that block the ability to detect molecules in the planets’ atmospheres. The view from this planet – were it possible to fly a spaceship into its gaseous layers – is illustrated at right. Scientists found clear skies on an exoplanet about the size of Neptune, using the combined power of NASA's Hubble, Spitzer, and Kepler space telescopes. The James Webb Space Telescope will be able to take a better look at exoplanet atmospheres after it launches in 2021. Neptunian exoplanets often have thick clouds that block any light from coming through, hiding the signature of the molecules in the atmosphere. NASA’s Transiting Exoplanet Survey Satellite (TESS) is designed to discover planets smaller than Neptune that transit stars bright enough to enable follow-up spectroscopic observations that can provide atmospheric compositions. By analyzing the amount of light blocked by the planet at different wavelengths, called spectroscopy, researchers can determine which molecules make up the atmosphere. The more light a planet blocks, the larger the planet appears. As starlight passes through a planet's atmosphere, atoms and molecules absorb light at certain wavelengths, blocking it from the telescope's view. Space telescopes like NASA’s Hubble (and formerly Spitzer) glean information about planet atmospheresby analyzing starlight.
It can be hard to tell a lot about distant planets’ compositions. We don’t know much about its composition, what it’s made of, or what elements are present in its atmosphere, but it’s in a similar orbit to its star as Uranus is to our Sun. Researchers discovered an ice giant exoplanet 25,000 light-years away in 2014. Since these three chemicals are typically found frozen as ices in the cold outer solar system, Uranus and Neptune are often referred to as "ice giants" (though their interiors are warm enough that the "ices" inside them are not frozen). While Uranus and Neptune are mostly composed of hydrogen and helium, both also contain water, ammonia, and methane. GJ 436 b is considered to be a “Warm Neptune,” because of its size and because it is much closer to its star than Neptune is to our sun.
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