Astronaut snaps strange iridescent clouds at the edge of space

Astronaut Matthew Dominick was going about 17,500 mph or so above Earth when he peered out his window and saw this remarkable view.

Dominick, who launched to the International Space Station in March as commander of NASA’s SpaceX Crew-8 mission, pulled out his camera and snapped the above photo. Taken on the Fourth of July, the image is as gobsmacking as any fireworks display back home. 

Below a thin curl of the moon is a lofty bed of so-called noctilucent clouds, floating in the calm before the riotous break of sunrise. These strange high-flying clouds at the edge of space — beguiling to scientists just two decades ago — are easy to observe from the station's orbit about 250 miles above Earth. 

"We have had so many great sunrises lately with amazing noctilucent clouds," Dominick said on X, formerly Twitter. "Probably taken a 1,000 images or so in the past week of them." 

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At least as far back as the 19th century, astronomers have gazed up at the sky and wondered about this kind of cloud, the highest in Earth's atmosphere. Rain clouds tend to form no more than 10 miles up, but noctilucent clouds hover some 50 miles above the planet's surface in a layer of the atmosphere known as the mesosphere. 

From the ground, people have often referred to them as "night-shining clouds," because their altitude allows them to keep reflecting sunlight well after sunset. In the summer, these iridescent clouds shimmer at dusk and dawn near the North and South Poles. 

Bright, mysterious noctilucent clouds appear over Edmonton, Alberta, in Canada in July 2011. Credit: NASA / Dave Hughes

How they formed remained a mystery until NASA's Aeronomy of Ice in the Mesosphere (AIM) mission in 2007. Scientists knew noctilucent clouds could vary with latitude and solar activity but didn't understand why. 

With a spacecraft orbiting 350 miles above Earth, researchers learned that the clouds happen when ice crystals condense on meteor smoke, tiny particles from shooting stars that burn up in the atmosphere. Perhaps even more surprising was that the ice within the mesosphere forms in a single continuous layer.

NASA's AIM mission took the first global image of iridescent polar clouds in June 2007. Credit: NASA

In its first year, the mission documented the "life cycle" of noctilucent clouds in the Northern Hemisphere, which started at the tail end of May and continued through August. The satellite, which was only slated for a two-year study, returned 16 years' worth of data before its battery died last year. 

Its observations led to many discoveries, including how events closer to the ground could trigger changes in the clouds, and how the icy layer in the upper atmosphere could cause eerie radar echoes in the atmosphere during the summer. Scientists appreciate the spacecraft's success, especially given the hurdles it overcame at the beginning of its mission: A broken receiver forced the NASA team to figure out how to reprogram it to communicate in Morse code. 

One of the more recent findings from the mission is how humans influence the clouds' formation. A 2022 study published in the journal Earth and Space Science found that morning rocket launches could actually create noctilucent clouds at farther distances from the poles, over southern Alaska, central Canada, northern Europe, southern Scandinavia, and south-central Russia. 

International Space Station crew see noctilucent clouds in the late hours over the southern tip of South Korea on July 1. Credit: Matthew Dominick / Earth Science and Remote Sensing Unit / NASA Johnson Space Center

Researchers compared the spacecraft's observations to the timing of launches south of 60 degrees north latitude. What they found was a strong correlation between morning launches and night-shining clouds in the relatively lower latitudes. 

Despite the end of the AIM mission, Cora Randall, deputy principal investigator, said in a statement that scientists will continue to make new discoveries based on the data. 

"There are still gigabytes upon gigabytes of AIM data to study," she said.