Scientists from Pennsylvania State University and NASA’s Jet Propulsion Laboratory say that Earth’s space communications could be noticed by alien civilisations, according to a recent study. The research shows that when commands are sent to spacecraft like Mars rovers or orbiters, not all radio signals are absorbed. Some of these signals continue travelling through space, possibly forever.

“Humans are predominantly communicating with the spacecraft and probes we have sent to study other planets like Mars,” said Pinchen Fan, a graduate student in astronomy and astrophysics at Penn State and the first author of the study. He added that “a planet like Mars does not block the entire transmission, so a distant spacecraft or planet positioned along the path of these interplanetary communications could potentially detect the spillover; that would occur when Earth and another solar system planet align from their perspective. This suggests that we should look for alignment of planets outside of our solar system when searching for extraterrestrial communications.”

The study points out that these signals, while powerful and aimed at nearby planets, could be intercepted by intelligent life forms located along their path. Similarly, Earth could also detect alien signals if extraterrestrial civilisations send similar communications across space.

Published in the Astrophysical Journal Letters, the research opens new ways to search for intelligent life in space by listening for their transmissions, just as they might be listening to ours.

“Based on data from the last 20 years, we found that if an extraterrestrial intelligence were in a location that could observe the alignment of Earth and Mars, there's a 77% chance that they would be in the path of one of our transmissions, orders of magnitude more likely than being in a random position at a random time,” Fan explained. He added, “If they could view an alignment with another solar-system planet, there is a 12% chance they would be in the path of our transmissions. When not observing a planet alignment, however, these chances are minuscule.”

This research highlights a new perspective on interstellar communication and the possibilities of detecting or being detected by alien life.

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