Some of the most important asteroid searches are done at exactly the time of night when satellite trails are hardest to avoid. That overlap is becoming a structural problem for planetary defense. Ground-based warning systems do not hunt only for large, long-known asteroids on leisurely orbits. They also scan for smaller near-Earth objects that can emerge late, brighten quickly and offer only days or weeks of notice. Systems such as ATLAS were built for that last-alert role, repeatedly sweeping broad areas of sky instead of staring deeply at one patch. The tradeoff is obvious: wide, fast surveys are efficient at catching fast movers, but they are also especially vulnerable to bright streaks crossing the detector.
The vulnerability is worst during twilight. That is when low-Earth-orbit satellites remain sunlit and highly visible, and it is also when astronomers look near the Sun’s direction to find objects whose orbits keep them hidden in daylight for most of their approach. A recent expert survey on planetary defense found that all 34 respondents were at least somewhat concerned about satellite overcrowding’s effect on asteroid detection, with 24% describing themselves as extremely concerned.
The technical reason is simple. Near-Earth object detection relies on comparing repeated images taken minutes apart and identifying the one point of light that shifts against a fixed background of stars and galaxies. Satellite trails do not merely spoil the pixels they cross. They can add glare, raise noise, create false candidates and, in moving-object pipelines, complicate the pattern-matching needed to link faint detections into a credible orbit. For facilities designed to revisit the sky on a strict cadence, the loss of even one needed exposure can break the chain.
The same issue has already become a major concern for wide-field observatories. Conservative simulations for the Vera C. Rubin Observatory have suggested that 30–40% of twilight exposures could be affected under large-constellation scenarios, with other studies noting even higher disruption at the beginning and end of the night. Rubin’s solar system programs are expected to discover millions of objects, but researchers working on near-Earth object searches have warned that contamination in one of the required image sets can cause a moving body to be missed entirely.
This matters because asteroid warning is divided by size and time. Large objects are often found years ahead, and the catalog of kilometer-scale near-Earth objects is already highly complete. The harder problem is the sub-140-meter population: common enough to matter, small enough to stay faint until late, and dangerous enough to cause severe regional damage. ATLAS is designed to provide roughly one week of warning for a 45-meter asteroid and three weeks for a 120-meter object, provided the incoming body is not too close to the Sun’s glare. That margin is narrow even before artificial light streaks enter the image stream.
The concern is no longer limited to telescopes on the ground. NASA-led modeling of future satellite populations found that if planned megaconstellations are fully deployed, roughly 39.6% of Hubble exposures could show at least one trail, while more than 96% of images from SPHEREx, ARRAKIHS and Xuntian could be contaminated. That does not directly disable planetary-defense surveys, but it removes the easy fallback idea that astronomy can simply migrate to orbit while low-Earth space fills with reflective hardware.
Mitigation proposals already exist: dimmer satellites, fewer orientation-induced flares, better reflectance testing, and far more accurate public orbit data so observatories can predict and avoid the brightest crossings. The difficulty is that avoidance costs observing time, and twilight surveys have little spare time to give away. For asteroid warning systems, that lost margin is the real hazard. The risk is not that every image becomes useless. It is that the most time-critical searches become less reliable in the brief windows when reliability matters most.
