Kyoto University develops new method to visualize atmospheric density data in the upper atmosphere

According to an ESA report, annual satellite launches increased dramatically from about 200 in 2015 to 2,700 in 2024. The G-Science Academies have likewise raised concerns about the growing risk of collisions involving satellites and space debris. In low Earth orbit, even the tenuous atmosphere at altitudes of several hundred kilometers exerts drag that affects satellite trajectories. Accurate data on atmospheric density, including when, where, and how much atmosphere is present, is essential for collision avoidance.

Specially Appointed Professor Mamoru Yamamoto at the Research Institute for Sustainable Humanosphere, Kyoto University demonstrated a new method to visualize atmospheric density at satellite altitudes using public orbit data of SpaceX's Starlink satellites. The findings were published as a rapid communication in Earth, Planets and Space.

The total number of Starlink satellites in Earth's orbit has reached approximately 10,000. For the purpose of avoiding collisions between Starlink satellites and other satellites, SpaceX publishes detailed orbit information called Ephemerides three times a day (approximately every 8 hours).

The research group studied atmospheric density at altitudes where satellites fly, using this public Ephemeris data. The atmosphere is drawn around Earth by gravitational force, possessing the highest density at the surface and decreasing exponentially as altitude increases. For example, at an altitude of 482 kilometers, because it is extremely thin at approximately one-trillionth of the surface, satellites continue to orbit Earth. However, because atmospheric drag attenuates orbital energy of satellites, they gradually fall. Starlink satellites are equipped with propulsion devices, and active satellites continue to maintain altitude by performing acceleration operations (maneuver operations).

In a paper published by the research group in April, using the general orbit information of Starlink satellites, by selecting only satellites that completed their roles and were naturally falling to examine their falling states, they clarified the altitude distribution of atmospheric density at altitudes of 200 to 600 kilometers. While this method was conventional, utilizing a large number of same-type satellites called Starlink was novel, succeeding in increasing the time resolution of atmospheric density data.

In the paper published this time, they performed analysis using Ephemeris information of Starlink satellites. By integrating atmospheric drag felt by a group of approximately 1,200 satellites flying near an altitude of 482 kilometers, they succeeded in capturing ultra-rarefied atmospheric density as a planar snapshot.

The data analysis technique used for this was tomography, the same as CT scans or MRI images that visualize cross-sections of the human body by slicing them, for example. In CT scans, attenuation when X-rays pass through the human body is measured from all directions, and cross-sectional photographs are generated by integrating them.

The research group obtained latitude and longitude distributions of density by integrating energy attenuation "felt" by numerous satellites orbiting the atmosphere. Results matched empirical models and actual measurements by other satellites extremely well. Both the data analysis method and results are world firsts.

The region where Earth's atmosphere connects to space is range-bound from altitudes of 100 to 1,000 kilometers and is called the upper atmosphere. While atmospheric density in the upper atmosphere is a fundamental parameter, because it is ultra-rarefied, observation methods were limited, and it was considered "full of mysteries" by the research community. Through this research, it was clarified that orbit information of Starlink satellites is useful for estimating atmospheric density around satellites.

Because Ephemeris data of Starlink satellites is updated as often as three times a day, atmospheric density data with dramatically higher temporal and spatial resolutions compared to conventional methods can be generated. This exerts a major impact on upper atmosphere research itself, leading to an important data supply in clarifying interactions between Earth's atmosphere and space.

The research group stated, "In the future, we would like to proceed toward constructing a real-time data service that instantly converts data into atmospheric density data after publication to publish it."

Yamamoto said, "We started this research upon learning in 2024 that the number of Starlink satellites had reached several thousand. Atmospheric density data of the upper atmosphere is crucially lacking research-wise as well, and this research is an important achievement filling that gap. The appeal of this research lies in having mixed knowledge of upper atmosphere science (geoscience) and satellite orbital mechanics (space engineering). By utilizing the latest AI technology, we were able to link two distant research domains together, quickly realizing efficient data processing."

Journal Information
Publication: Earth, Planets and Space
Title: Tomography of thermospheric density from Starlink Ephemeris: initial report
DOI: 10.1186/s40623-026-02509-5