Scientists use Earth’s shadow to hunt for alien probes

For decades, astronomers have searched for signs of extraterrestrial intelligence using radio telescopes and optical instruments, scanning the skies for artificial signals. Now, researchers are taking a different approach, this time looking much closer to home for alien artifacts that might already be in our solar system.

A new study published in the Monthly Notices of the Royal Astronomical Society describes an innovative method for detecting potential extraterrestrial probes near Earth. Their innovative approach: to use Earth’s shadow as a natural filter to eliminate interference from human-made satellites and space debris.

Modern skies are cluttered with thousands of satellites and millions of pieces of reflective debris, making it extremely difficult to spot anything unusual. This “contamination” poses a major challenge for anyone trying to identify non-human objects in space. Lead researcher Beatriz Villarroel from Stockholm University and her international team needed a way to filter out this noise.

This is why they turned to Earth’s shadow. Every night, Earth casts a cone-shaped shadow into space where direct sunlight cannot reflect off satellites or debris. This creates an ideal “clean” search zone. The shadow’s base spans roughly 8–9 degrees for objects at geosynchronous orbit, about 35,700 kilometers above Earth.

Human satellites typically don’t carry optical light sources, with rare exceptions like communication lasers or spacecraft thrusters. So any bright flashes or streaks detected within Earth’s shadow could potentially indicate something more exotic.

The researchers analyzed images from the Zwicky Transient Facility (ZTF), a telescope in California that systematically surveys the sky for changing objects. They examined more than 200,000 images, specifically focusing on those captured within Earth’s shadow.

Their automated search system, called NEOrion, detected thousands of candidates, including mysterious streaking objects and point source flashes. Most turned out to be meteors, aircraft, or known asteroids. However, one intriguing case emerged, an uncatalogued object moving much faster than typical asteroids and not found in any existing space object databases. Sadly however, the team was unable to confirm what it was, so it still remains a mystery.

The study also explores other innovative approaches, including examining pre-1957 astronomical photographs and analyzing the color spectra of suspicious objects to identify materials that have been weathered by long exposure to space.

While this proof-of-concept study didn’t definitively identify any alien technology, it demonstrates that systematic searches for extraterrestrial artifacts are now feasible using existing telescopes and new analysis techniques.

The researchers are developing the ExoProbe project, a network of telescopes designed specifically for this type of search, which will use multiple simultaneous observations to determine exact distances to mysterious objects.