Last week, a SpaceX launch created a serendipitous and beautiful event over the Alaskan skies. In the midst of dancing green Northern Lights, a spiral cloud appeared in the sky. This is the result of the reentry stage of a Falcon 9 rocket taking satellites to orbit, including the first Earth observation satellite designed and operated by Kenya.
The spectacular images and footage have been taken by professional institutions and citizen scientists alike. They quickly spread on social media with a mixture of amazement, amusement, and curiosity about how such a structure formed.
Scientists at the Geophysical Institute were able to quickly work the answer and even shared a fantastic video of the spiral cloud quickly passing overhead as the rocket was coming back to Earth. The launch of the rocket took place in California and placed the satellites in polar orbit, this happened two hours earlier and the trajectory is consistent with the re-entry of the rocket.
“The cloud showed up after they had deployed all of their payloads, so it is likely either exhaust from a rocket burn to bring the second stage down over the Pacific, or perhaps dumping extra rocket fuel after that burn. The spiral pattern indicates that the second stage was spinning when it exhausted the gasses,” geophysicist Don Hampton, Poker Flat Rocket Range chief scientist, said in a statement. “Any water vapor would turn into ice at these altitudes, and the ice would reflect sunlight where the rocket was, and make a bright cloud visible on the ground in Alaska where the sun was well below the horizon. It looks really bright in those pictures, but it is likely just a few pounds of water.”
Exactly a year ago today, a similar spiral was spotted by another automatic camera. That time was over in Hawai’i and the camera in question was the Subaru-Asahi Star Camera. Its content is a continuous live stream of the night sky - a collaboration between the Asahi-Shimbun newspaper and the Subaru Telescope run by the National Astronomical Observatory of Japan.
So the clouds are just the consequences of a bit of icy material spinning away from a returning rocket. Who knew that angular momentum, water crystallization, and a bit of sunlight could create something so pretty?