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A fleet of Starlink satellites is now helping scientists study a part of Earth’s atmosphere that has long resisted close observation.
Researchers at Kyoto University have found a new way to measure the Thermosphere, the thin and difficult-to-observe layer of atmosphere that stretches from about 60 to 620 miles above Earth’s surface.
Led by Mamoru Yamamoto at the university’s Research Institute for Sustainable Humanosphere, the team used public orbital data from roughly 1,200 Starlink satellites to build a detailed map of atmospheric density at an altitude of about 300 miles. It is the first time this method has worked using real satellite data instead of computer simulations.
The Thermosphere makes up more than 99% of Earth’s upper atmosphere. It consists of electrically neutral gas, which does not interact with radio waves the way the small ionized portion, called the Ionosphere, does. That difference makes the Ionosphere fairly easy to observe with radio-based instruments. The Thermosphere offers no such shortcut, so scientists have had to rely mostly on data collected directly by spacecraft passing through it.
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Even though the Thermosphere is extremely thin, it still creates enough drag to pull satellites off their intended paths slowly. Knowing how dense it is at a given time and location helps engineers predict where a satellite will actually end up, which matters more as low Earth orbit fills up with active satellites and debris.
Turning Satellite Drag Into a Measurement Tool
Every satellite passing through the Thermosphere experiences a small amount of drag from the surrounding gas. That drag causes its orbit to decay very slightly over time. By measuring this decay using orbital data that SpaceX makes publicly available for its Starlink satellites, Yamamoto’s team estimated atmospheric density around roughly 1,200 satellites flying at an altitude of about 482 kilometers, or 300 miles.
The researchers then applied Tomography, the same technique used to build three-dimensional images from CT scans in hospitals, to turn thousands of individual measurements into a single map. The result is a two-dimensional snapshot of thermospheric density across latitude and longitude, something that had not been demonstrated before using real satellite data.
Yamamoto described the project as sitting between two fields that do not always overlap. “This is a multidisciplinary study between space science and space engineering,” he said.
Checking the Results Against Independent Data
To confirm the map held up, the team compared it with measurements from the European Space Agency’s SWARM satellites, which track atmospheric density directly using onboard GPS. SWARM’s two satellites orbit both above and below the altitude Yamamoto’s team was studying, giving the researchers a useful way to check their work.
- Across 19 separate analyses using data collected between September 1 and 7, 2025, the Starlink-based estimates closely matched SWARM’s readings.
- On average, the estimates reached 95% of the values SWARM recorded, with individual results ranging from about 60 to 120%.
- The method also correctly located the Thermosphere’s density peak, matching the pattern predicted by an established atmospheric model used as a reference.
Why This Matters
Low Earth orbit is becoming more crowded every year, with thousands of active satellites and pieces of debris sharing the same limited space. Better data on thermospheric density improves predictions of how satellites drift over time. That helps operators avoid collisions before they happen.
The method could eventually support near real-time monitoring of atmospheric density around satellites. That kind of tracking would strengthen space weather forecasting and make satellite operations more predictable.
A Work in Progress
Yamamoto has been clear that the results are still preliminary. The current method captures broad, day-to-day patterns rather than small-scale changes, and it has a specific blind spot. Starlink satellites orbit at an inclination of 53 degrees, which leaves gaps in coverage near the poles. Closing those gaps will likely require adding data from satellites in other orbital shells and inclinations.
Even with those limits, the study is the first demonstration that this kind of tomographic mapping works using publicly available satellite data rather than simulations alone. It builds on earlier work by the same team, which used more basic orbital data to track how thermospheric density changes with altitude and time.
