Remember the “Wow!” signal? That high-energy radio signature occurred in 1977, when Earth was much “quieter” in the radio band. If it happened today, it probably wouldn’t even move the needle on the background noise of human radio chatter. Signals from satellites, radar and other human technology have crowded out extraterrestrial radio signals, limiting our ability to monitor the heavens for signals like the still-unexplained one received in 1977. What’s more, the ionosphere partially blocks lower-frequency radio signals, making them even harder to detect from the ground.

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