The achievement, published in the journal Earth, Planets and Space, turns routine orbital tracking of roughly 1,200 Starlink spacecraft into a two-dimensional latitude-longitude snapshot of atmospheric density at about 500 kilometers above Earth — a region where direct measurement has long frustrated scientists.
Why the thermosphere matters
The upper atmosphere between 100 and 1,000 kilometers is more than 99 percent electrically neutral gas, a layer scientists call the thermosphere. Thermospheric density dictates how much drag a satellite experiences, how quickly its orbit decays, and ultimately whether it stays safely separated from neighboring spacecraft or drifts into a collision course.
Despite its outsized role in space operations, the thermosphere is notoriously difficult to observe. The ionized fraction — less than one percent of the gas — interacts with radio waves and is comparatively easy to monitor from the ground. The neutral thermosphere, by contrast, offers no such convenient signal, leaving researchers with sparse data from dedicated missions like the European Space Agency’s SWARM satellites.
“This is a multidisciplinary study between space science and space engineering,” says corresponding author Mamoru Yamamoto. “Reading papers from both research fields, we realized that deeper dialogue between researchers from both fields is necessary.”
From medical imaging to atmospheric mapping
The Kyoto team borrowed tomography — the same mathematical technique that reconstructs cross-sectional images in CT scans — and applied it to the atmosphere. By tracking atmospheric drag through the slow decay of Starlink orbits at an altitude of 482 kilometers, the researchers estimated the density of the surrounding gas for each satellite.
Stacking those individual measurements produced a coherent two-dimensional picture of thermospheric density across latitude and longitude. The result showed strong agreement with independent SWARM observations, which measure density variations along their own satellite trajectories, validating the new approach.
This is not the group’s first attempt at remote atmospheric sensing. Earlier work used two-line element, or TLE, data — the general orbital summaries published for many satellites — to chart how thermospheric density varies with time and altitude. The new study extends that work horizontally, revealing the spatial structure of the thermosphere rather than just its vertical profile.
A crowded orbit demands better data
Low Earth orbit has grown congested as mega-constellations such as Starlink add thousands of spacecraft. Above that orbital traffic, the residual atmosphere still exerts enough drag to nudge satellites off their predicted paths over weeks and months. Accurate density forecasts are essential for collision avoidance, reentry planning, and sustaining the long-term safety of orbital operations.
The public availability of Starlink ephemeris data proved decisive. Traditional thermospheric measurements require dedicated satellites carrying accelerometers or mass spectrometers, missions that are expensive and few in number. By repurposing the orbital behavior of an existing constellation, the Kyoto team tapped a far denser and more frequently updated sensor network.
That density of measurement points matters because the thermosphere is dynamic. Solar activity heats and expands it, geomagnetic storms redistribute its mass, and seasonal winds shift its structure. A sparse set of sampling satellites can miss regional variations that a constellation-wide dataset captures.
What Happens Next
The method could mature into near-real-time monitoring of thermospheric density around active satellites, feeding directly into space-weather forecasting systems and operational collision-avoidance tools. As more mega-constellations deploy and publish ephemeris data, the spatial resolution of such maps should improve, potentially extending to altitudes beyond the 500-kilometer band examined in this initial report.
For space-weather agencies, the prospect is significant: a continuous, data-driven view of the thermosphere would complement physics-based models that currently rely on sparse measurements and solar proxies. For satellite operators, better density forecasts mean fewer unplanned maneuvers and tighter, safer spacing in an increasingly crowded sky. The Kyoto team’s next challenge is refining the technique to capture temporal changes — watching the thermosphere breathe as the sun drives it — and testing whether the approach scales to other constellations beyond Starlink.
— Priya Nair, science desk, AXO News