Rubin’s huge eye could help defend Earth, but satellites are getting in the way

Early data from Vera C. Rubin Observatory, which began its 10-year survey of the southern sky in June, has already turned up a new dwarf galaxy orbiting the Milky Way and thousands of previously unknown asteroids. The observatory could also help spot asteroids that might one day threaten Earth — a task that may grow increasingly challenging as satellites fill the planet’s skies.

“Our primary goal for the Rubin Observatory is to be a discovery powerhouse,” Sarah Greenstreet, an assistant astronomer at the U.S. National Science Foundation, told the attendees of the Council for the Advancement of Science Writing’s New Horizons in Science briefing at the ScienceWriters2026 conference in Corvallis, Oregon, on Sept. 27.

By the end of the 10-year survey, Greenstreet said, Rubin is expected to find five million objects that have never been seen before — most of them asteroids and comets. While planetary defense is not one of Rubin’s primary goals, it flows naturally from the observatory’s effort to build a more complete inventory of the solar system.

In a study simulating direct asteroid impacts on Earth, researchers found that the Rubin Observatory can discover roughly 80% of large asteroids — those greater than 460 feet in diameter — about three years before the impact.

How early Rubin can warn about a potential impact depends on the object and what type of orbit it’s on, Greenstreet explained, but generally “the sooner we discover it the better.”

However, Rubin’s mission and its contribution to planetary defense is complicated by the rapid growth of satellite constellations in low Earth orbit. These satellites move quickly enough across the sky that they can cross the entire area of sky that Rubin covers within a 30-second picture, leaving bright streaks across the image.

“They are so bright that any of the light sources underneath them, like stars, galaxies or asteroids, are totally hidden,” she added.

About 16,000 satellites orbit Earth today and are projected to exceed 100,000 within this decade. Scientists predict that streaks will appear in 40% of images captured by Rubin during its 10-year mission. Greenstreet cautioned that “it is still too soon to know whether those predictions will hold.”

Until recently, the telescope had been undergoing engineering tests, observing scattered patches of sky at irregular times. That, Greenstreet said, won’t scale well to the full survey, which covers the entire sky every few days.Rubin’s leadership and its funders, the National Science Foundation and the Department of Energy, have been talking with satellite companies about joint policies that might serve both industry and astronomy. “So far, the discussions have been going really well,” Greenstreet said.

On the technical side, the team has removed satellite streaks by combining many exposures into a single deeper “co-added” image. “It’s not 100% successful,” she said. “But it’s been highly successful for us so far.”

Another strategy is dodging satellites altogether by programming the Rubin scheduler, which directs where the telescope points, to avoid parts of the sky where bright satellites are expected to pass. However, “most of the locations of satellites are not well known, or not made public to the point where we can successfully use this mitigation strategy,” said Greenstreet.