Scientists Know Why Uranus Is So Pale - Nerdist
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Scientists Know Why Uranus Is So Pale

Uranus is hazy. Those extra particles dull the scattered light and make it look lighter blue than Neptune. Scientists have long wondered why the two planets are different colors. After all, they are of similar size, mass, and composition. They even spin at a similar rate, though in opposite directions. A new simulation shows that it snows more on Neptune, which clears out the atmosphere and makes it look a darker blue. 

The planet Uranus (left) is paler blue than Neptune (right)
NASA/ESA/A. Simon (Goddard Space Flight Center), and M. H. Wong (University of California, Berkeley) and the OPAL team

It’s not just any snow though. Uranus and Neptune both have atmospheres full of hydrogen sulfide and methane gas. Both of these are found on Earth, but in much smaller amounts. The diagram below shows that Uranus’ layer of these gases is larger. Because of the smaller band on Neptune, more movement occurs. This leads to more methane snow. 

It’s not just a mantra about optimism, the sky really is clearer after a storm. Rain and snow pull gunk out of the air on their fall to Earth. The same is true on Neptune and Uranus. Neptune gets more snow, thus there’s fewer particles hazing up the air. Just like Earth’s atmosphere, blue light is scattered on both Neptune and Uranus. This gives the planets an overall blue appearance. 

Comparison of atmospheres on Uranus and Neptune that shows Neptune's thinner layer which leads to more snow
International Gemini Observatory/NOIRLab/NSF/AURA, J. da Silva/NASA/JPL-Caltech/B. Jónsson

The video below is from the European Space Agency, which runs the Hubble Space Telescope with NASA. The researchers checked their simulation against data from Hubble and a few ground telescopes as well. The Journal of Geophysical Research: Planets published the research. 

We found this study on Gizmodo. There’s so much we don’t know about our own solar system still. The only trip we’ve taken past Uranus was by Voyager 2 in 1986. Recently, the National Academies of Sciences, Engineering, and Medicine listed probing Uranus as a priority

Melissa is Nerdist’s science & technology staff writer. She also moderates “science of” panels at conventions and co-hosts Star Warsologies, a podcast about science and Star Wars. Follow her on Twitter @melissatruth. 

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