Starlink satellites are usually discussed in terms of what they’re doing to the sky. Astronomer Tony Phillips has found a way to use them to learn something about it.
Phillips, who runs SpaceWeather.com, has turned the orbital data of hundreds of Starlink satellites into a daily measure of changes in Earth’s upper atmosphere. He calls it a “planetary barometer,” though it tracks air density rather than pressure. His planetary barometer relies on an ingenious observation, which Phillips explained in a blog post (as reported by The Register).
Here’s how a satellite becomes a weather instrument: Even hundreds of miles above Earth, there’s enough atmosphere to create drag. When energy from the sun heats the upper atmosphere, it expands, putting more particles in a satellite’s path. More drag means a satellite would lose altitude faster if it weren’t using its thrusters to stay in orbit.
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Phillips analyzes publicly available orbital records to estimate that effect. His daily “sink rate” asks how many meters a typical Starlink satellite at about 480 kilometers (roughly 300 miles) up would lose in a day with its thrusters off. So far in 2026, that figure has ranged from 19.7 meters on a quiet day in August to 127.6 meters during a major geomagnetic storm in January. That doesn’t mean Starlink satellites actually plunged that far on either day; the number is a way to show how much the atmosphere changed.
And Phillips isn’t relying on Starlink alone. He checks the pattern against satellites from Planet Labs, Amazon’s Kuiper network, and Eutelsat OneWeb. Planet’s SuperDoves are particularly useful because they have no thrusters: Their actual descent offers a check on the Starlink estimate. The index has limits, including orbital data that can blur sudden changes over several days.
Scientists have studied atmospheric drag using Starlink data before. Phillips’s contribution is a public number updated daily, offering a running look at conditions that matter for satellite orbits. Starlink’s crowded presence overhead remains a concern for astronomers. For this one purpose, though, all those satellites make it possible to watch the atmosphere change without launching anything new.
