If you ever spot a red spherical flash in the night sky, it’s likely from a Falcon 9 rocket. This occurrence has become so frequent that astronomers have affectionately dubbed it the “SpaceX auroras.”
They’re not true auroras. The bright SpaceX aurora in the image below was captured on Nov. 3, 2023, by photographer Stephen Hummel from the McDonald Observatory in West Texas. Although experts refer to this phenomenon as “auroras,” it’s actually a hole in the ionosphere caused by the reentry of a SpaceX rocket.
Hummel told the Spaceweather blog that the team at the McDonald Observatory observes two to five of these events every month due to the high frequency of SpaceX launches.
Holes in the ionosphere. SpaceX launches are known to create holes in the Earth’s atmosphere. It doesn’t occur during liftoff but at reentry, when the Falcon 9 rocket’s second stage reignites its engine to exit orbit and disintegrate in the Earth’s atmosphere.
Additionally, the phenomenon occurs at around 186 miles altitude in the ionosphere, the layer of ionized gas surrounding our planet. About 90 minutes after its launch, the Falcon 9’s second stage reignites its engine to deorbit, creating a time hole that emits a reddish glow.
Visible to the naked eye. The red hole is actually a chemical disturbance in the ionosphere. The rocket exhaust, which contains water vapor, can reduce local ionization by as much as 70%. This disturbance becomes visible because it emits a fluorescent red glow.
Although Falcon 9 ignites its engine for just two seconds (enough to propel it toward the ocean), it releases around 440 pounds of water and carbon dioxide. This results in a very intense glow that can be seen with the naked eye. According to the blog, the so-called SpaceX auroras can last up to 10 minutes.
They pose no threat. Scientists have long known that space launches can trigger these kinds of atmospheric effects. In 2005, a Titan rocket caused “severe ionospheric perturbations.” Fortunately, ionospheric holes close within a few minutes as the recombined gases reionize. As such, they pose no threat to the environment.
Why “SpaceX auroras”? Although this phenomenon can occur with different rockets, it’s primarily linked to SpaceX due to the high frequency of Falcon 9 launches. In 2023, SpaceX conducted more than 90 launches, which accounted for 80% of the total sent into orbit that year.
A significant portion of these launches involved Starlink satellites. SpaceX currently has more than 5,500 operational Starlink satellites and aims to increase this number to 12,000 in the coming years.
Image | Kelly Michals | Stephen Hummel
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