Detecting Extraterrestrial Civilizations That Employ an Earth-level Deep Space Network

A major aspect of the search for extraterrestrial intelligence (SETI) involves searching for electromagnetic transmissions from extraterrestrial sources, often using our own transmissions as a guide. Previous studies have suggested that humanity's most consistently detectable technosignatures were transmissions from our deep-space networks and interplanetary radar. In this study, we analyze NASA Deep Space Network logs to explore what strategies for selecting SETI targets and scheduling observations would enhance the chances of detecting such networks. Analyzing Deep Space Network uplink transmission logs over the last 20 yr, we find that these emissions were predominantly directed along the ecliptic plane, towards or directly away from the Sun, and towards other planets. The average duty cycle within the Earth Transit Zone is 20 times higher than that across all ecliptic latitudes. In the case of Mars, we find a species that is able to observe the Solar System for radio emission during an Earth-Mars conjunction in the past 20 yr would have had a 77% chance of observing during one of our transmissions, a $4\times10^5$-fold increase over intercepting our Deep Space Network transmission versus a random observer at a random time. These findings quantify how SETI searches might benefit from prioritizing edge-on exoplanet systems and aligning observation windows with exoplanetary conjunctions or planet-planet occultations because they significantly improve the likelihood of intercepting transmissions from any civilizations employing deep-space networks similar to our own.