The atmosphere expands and contracts; watching objects in orbit reveals the extent
Astronomer and author, Dr. Tony Phillips, says he has found a way to turn SpaceX’s Starlink satellite constellation into a barometer.
Phillips runs spaceweather.com, which tracks solar flares, the solar wind, shifts in Earth’s geomagnetic field, and other phenomena.
On Tuesday, he published an article that opens “Starlink has many downsides.”
“The megaconstellation interferes with astronomy, pollutes the atmosphere with metallic re-entry debris, and has pushed Low Earth Orbit to the brink of the Kessler Syndrome.”
“On the other hand, it makes a terrific barometer.”
That’s because Earth’s atmosphere expand when it heats, often in response to increased radiation increases. Most satellites lose a few meters of altitude every day and when the atmosphere expands the rate at which their orbits decay can accelerate.
Phillips points out that the US Space Force tracks all artificial satellites and publishes data called “TLEs” about their orbits.
“Buried in each TLE is a drag term, called B* (‘B-star’),” Phillips wrote. “Here's the trick: the orbit model that reads a TLE assumes a fixed atmosphere. When the real atmosphere swells, the satellite slows down more than the model expects, and the fitted B* has to grow to keep the orbit matching the tracking. B* is where the air density ends up.”
The astronomer therefore collects and analyzes TLE data for 1,000 Starlink satellites, plus 107 of Planet Labs' SuperDoves, 391 Amazon Kuiper satellites, and 651 Eutelsat OneWeb birds. Each constellation orbits at different altitudes, but Phillips says he’s seen them all move in response to the same solar events.
“Using this new data stream, we can watch the atmosphere breathe,” he wrote. “Solar ultraviolet heats the thermosphere, and the sink rate tracks the sun's 10.7 cm radio flux with a two-day lag: the upper atmosphere takes about two days to answer a change in the sun. Big geomagnetic storms puff up the atmosphere faster than that and cause sharp spikes in the sink rate.”
Phillips allows that other scientists have used Starlink for similar studies, especially after the 2022 geomagnetic storm that dragged 40 of Elon Musk’s finest broadband birds to their doom.
“What's new here is a running, public, daily index with three independent constellations checking the answer,” Phillips wrote. “No instrument was launched for this. The swarm itself is the sensor, read from public tracking data.” ®