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Scientists have used data from roughly 1,200 Starlink satellites to create an unprecedented map of Earth’s upper atmosphere, revealing how thin air varies across a region about 300 miles above the surface.
Researchers at Kyoto University reconstructed the density of Earth’s thermosphere by analyzing tiny changes in the satellites’ orbits caused by atmospheric drag. The study, published in Earth, Planets and Space, represents the first tomographic analysis of thermospheric density using Starlink orbital data.
Although low Earth orbit appears nearly empty, spacecraft still encounter extremely sparse atmospheric particles hundreds of kilometers above Earth. Those collisions create drag that gradually removes orbital energy, causing satellites to lose speed and altitude.
The effect becomes more significant when solar activity heats the upper atmosphere. During geomagnetic storms, the thermosphere can expand and become denser at satellite altitudes, changing spacecraft trajectories and making collision avoidance more difficult.
The thermosphere extends from roughly 100 to 1,000 kilometers above Earth. More than 99 percent of the upper atmosphere in this region consists of electrically neutral gas, which is considerably harder to detect than the charged particles of the ionosphere.
The Kyoto University team turned that challenge into an opportunity. By examining detailed Starlink ephemeris data, researchers calculated how atmospheric drag affected individual satellites and then applied tomography, a technique commonly used to reconstruct medical images, to estimate atmospheric density across different geographic regions.
Combining observations from hundreds of satellites allowed the researchers to build a two-dimensional density map rather than relying on measurements along a single spacecraft’s path. The results also showed strong agreement with observations from the European Space Agency’s Swarm satellites, providing an independent check of the reconstruction.
Corresponding author Mamoru Yamamoto described the work as a multidisciplinary effort combining space science and engineering. The team says future versions of the technique could potentially provide near-real-time maps of thermospheric density.
Such information could improve orbital predictions, satellite maneuver planning, space weather forecasting, reentry estimates, and tracking of space debris. The research was supported by the Japan Society for the Promotion of Science.
