The phenomenon was first noted earlier this year when SpaceX Falcon 9 rocket launches were connected with a “bleeding” red sky over Arizona and California. The red light was a type of aurora produced by rocket engines and deorbiting booster rockets interacting with the ionosphere.
That a burning rocket engine could punch a hole in the ionosphere is not new information for scientists, who have observed the phenomenon for decades. However, the concern comes from its increasing frequency.
Stephen Hummel, an astronomer and outreach program coordinator at McDonald Observatory in Texas, told US media the facility was seeing "2 to 5 of them each month.” The red orbs are “very bright” and "easily visible with the naked eye," he said.
Indeed, such incidents were widely reported over the summer, including one very bright post-launch aurora over the American Southwest.
The ionosphere is the highest layer of the Earth’s atmosphere, extending from 125 to 185 miles above the Earth’s surface and formed by the sun’s radiation, which strips atmospheric molecules of their electrons.
When rocket engines burn, their exhaust produces carbon dioxide and water vapor, which causes ionized oxygen atoms to recombine into oxygen molecules. Doing so “excites” them with lots of energy, causing them to emit light. It’s the same process that causes auroras, except that auroras are caused by solar radiation heating up the gases rather than recombining them.
SpaceX, a commercial space flight company owned by Elon Musk, gets steady work from US government contracts that keep the rockets flying on a regular basis, as does the company’s Starlink satellite internet system, which is based on thousands of satellites in low Earth orbit. In addition, the company’s rocket boosters are reusable, meaning they don’t just fall back to Earth, they carefully maneuver back to the launch pad after putting their payload into space. That involves many small rocket bursts to correct their flight, which produces the mini-auroras as they descend.
Hummel said the holes in the ionosphere don’t pose any danger to life on Earth, but said "their impact on astronomical science is still being evaluated.” The ionosphere is also used in some communication and navigation operations, such as shortwave radio, so there’s a potential for such “holes” to impact them as well.