Satellites built to provide internet service, such as Starlink, can also help scientists map the almost invisible atmosphere at the edge of space, according to Scitech Daily.
Researchers at Kyoto University used data on orbital changes from about 1,200 Starlink satellites to map Earth's thermosphere, a thin and hard-to-observe region of the upper atmosphere. The analysis produced what the researchers describe as the first tomographic map of its kind, showing patterns of atmospheric density at an altitude of roughly 482 kilometers. The study was published in the journal Earth, Planets, and Space.
The researchers noted that although satellites in low Earth orbit travel through what looks like empty space, traces of atmosphere persist even hundreds of kilometers above the surface. Collisions with these sparse particles create drag, gradually lowering a spacecraft's speed and altitude.
The effect grows stronger when solar activity heats and expands the upper atmosphere. Geomagnetic storms can rapidly increase atmospheric density at the altitudes where satellites operate, altering predicted orbits and making collision avoidance harder.
Why the thermosphere is hard to observe
The authors said understanding how density changes in the thermosphere matters for tracking satellites, predicting atmospheric re-entries, planning maneuvers and assessing the paths of space debris. The thermosphere extends from 100 to 1,000 kilometers above Earth, and more than 99 percent of the upper atmosphere in that region consists of electrically neutral gas, compared with less than 1 percent for the charged particles of the ionosphere. While the ionosphere can be studied through its effect on radio signals, neutral particles leave a much weaker trace, so scientists usually rely on specialized instruments, models or measurements collected along individual satellite paths.
Turning Starlink into a sensor network
The Kyoto University team instead treated the Starlink constellation as a distributed network of moving atmospheric sensors. As each satellite moved through the thermosphere, air resistance caused it to lose small amounts of orbital energy. The researchers calculated these changes using publicly available orbital data known as ephemerides, then applied tomography, a mathematical method also used to reconstruct medical images, to estimate how atmospheric density varied by location.
This allowed the team to build a two-dimensional density map by latitude and longitude, unlike most previous spacecraft observations, which provided data only along a single satellite's path. The results largely matched density variations measured by the European Space Agency's SWARM satellites, providing independent verification of the reconstruction.
The researchers said it may eventually be possible to track thermosphere density in near real time, which could improve space weather forecasts, refine orbital predictions and help operators respond more effectively to solar storms that disturb the upper atmosphere.
