SpaceX's Falcon 9 rockets have flown nearly 90 times this year and now have astronomers worried about their impact on Earth's ionosphere. After launching its payload into space, Falcon 9 fires up its Merlin engines to orient itself and slow down in order to land on land or sea. Similarly, after the second stage completes its mission, it will start its engine and return to Earth.
These engines create holes in the ionosphere, a layer of electrically charged gases surrounding the Earth that plays a vital role in satellite communications. These holes produce red light that can further impact astronomy and astronomers' efforts to study the sky.
SpaceX's Falcon 9 is the world's only reusable medium-sized launch vehicle, and while the first stage booster lands on Earth after most missions, the second stage is not recovered. After completing its mission, once the Falcon 9's second stage has delivered its payload, the rocket fires its engines to lose altitude and burn up in the atmosphere, sometimes weeks after launch.
The ionosphere starts at 60 kilometers above the earth's surface and reaches a maximum of 300 kilometers. It is one of the highest regions of the atmosphere, and behind it, before the vastness of space begins, there is only one additional layer. Within the ionosphere, several layers are "ionized," which is the scientific term for charged particles. Particles within the ionosphere are excited due to their altitude, which exposes them to solar radiation. This radiation also helps humans on Earth because it helps radio waves travel farther.
Now, according to Stephen Hummel of the University of Texas at Austin Laboratory, the Falcon 9 second stage is punching a hole in the ionosphere. The exhaust from a rocket removes the charge from ionospheric particles, creating a blank space.
As part of its descent, the rocket's second stage fired its Merlin engines about an hour and a half after launch. The exhaust gas emitted by the engine mainly consists of water vapor, carbon dioxide and carbon monoxide. Hummel explained to Spaceweather that because the engine firing of the Falcon 9's second stage occurs higher in the ionosphere, it creates a larger hole due to the lack of overall atmospheric density.
While the researcher is unsure of the impact of these holes on astronomy, he worries that once SpaceX ramps up its launch tempo, voids may become more common than they are now. However, some researchers are excited because the rocket launch gives them the opportunity to observe the deionization of the ionosphere.
SpaceX has set a new record for launches in 2023, with one month left before the end of the year. The company is also developing the Starship rocket in Texas. If Starship is put into operation, the company will conduct more launches. SpaceX has also been criticized by astronomers for its Starlink satellites blocking the night sky, and the company has responded by upgrading its spacecraft to reduce reflections.