More than 1,200 Starlink satellites are now doing double duty as a giant scanner for Earth's upper atmosphere. Researchers in Japan have used their orbital data to create a new map of the thermosphere, the elusive layer that can slow satellites and complicate space traffic.
A clever use of public satellite data
The thermosphere sits between 100 and 1,000 kilometers above Earth. It is mostly neutral gas, making up over 99 percent of the upper atmosphere. The ionosphere, by contrast, is ionized and easy to track because it affects radio waves. The thermosphere is much harder to observe, which has made it a blind spot for scientists and engineers alike.
Kyoto University researchers found a workaround. They took publicly available orbital information from Starlink satellites and applied tomography, a technique often used in medical imaging, to the upper atmosphere. By measuring how atmospheric drag gradually decayed the satellites' orbits, they estimated thermospheric density around 1,200 satellites flying at 482 kilometers altitude.
A two-dimensional map at 500 kilometers
The team turned those measurements into a two-dimensional latitude-longitude snapshot of thermospheric density at roughly 500 kilometers above Earth. They say this is the first tomographic analysis of its kind. The density patterns matched observations from the European Space Agency's SWARM satellites, which measure atmospheric density along their paths.
The work builds on an earlier study by the same group. In that research, they estimated how thermospheric density changed over time and altitude using general orbital information. The new method goes further by producing a spatial map.
Why this matters for crowded orbits
Low Earth orbit is getting crowded with satellites and debris. Even thin traces of the upper atmosphere can create enough drag to alter a satellite's path. Accurate density measurements are essential for forecasting satellite motion and avoiding collisions. This new technique offers a way to monitor the thermosphere more closely, using data that is already being collected.
The researchers describe the work as a bridge between space science and space engineering. They hope deeper dialogue between those fields will lead to better tools for studying the upper atmosphere and for keeping space safe. The approach could sharpen satellite tracking and reduce the growing risk of collisions in increasingly crowded orbits.
