A startling calculation has emerged from recent research: if an extraterrestrial intelligence were positioned to observe an alignment of Earth and Mars, there is a 77% chance they would be in the path of one of humanity’s deep space transmissions. It’s not a probability derived from speculation, but rather one inferred from two decades of NASA Deep Space Network communication logs-a consistent and powerful pattern in how Earth talks to its spacecraft. The finding reframes the search for alien technosignatures, suggesting that planetary alignments could serve as natural amplifiers for detecting civilizations with technology similar to our own.
The DSN is humanity’s interplanetary switchboard, comprising three large antenna complexes in California, Spain, and Australia. These dishes, some 70 meters in diameter, beam tightly focused radio signals-often in the X band at about 7.19 GHz-toward probes and rovers scattered across the solar system. With transmission powers as high as 20 kW and antenna gains of over 73 dBi, such signals are strong enough to be detectable from up to 23 light-years away by facilities like the Green Bank Telescope. Yet even the most tightly focused beams are not perfectly contained, and a fraction of their energy spills beyond the intended target into a detectable “spillover” cone in space as they travel millions of kilometers.
Researchers led by Pinchen Fan at Penn State have analyzed the DSN’s uplink patterns, correlating transmission times with the spacecraft ephemerides. The analysis demonstrated that 79% of all DSN transmissions over the past 20 years were sent within 5 degrees of Earth’s orbital plane-the ecliptic-because most interplanetary spacecraft operate along this flat geometry. Traffic is dominated by Mars-bound missions, with thousands of hours of contact given to the likes of Mars Reconnaissance Orbiter and Curiosity. That concentration means any observer whose vantage point coincides with the ecliptic at the time of an Earth-Mars conjunction would be far more likely to intercept a signal than at a random time.
It’s all about the geometry. Planetary systems, including our own, tend to be coplanar-the planets orbit in nearly the same plane. If Earth’s “dinner plate” view of the solar system aligns edge-on with another system’s plate, the focused beams to our spacecraft could pass directly through that system. It’s exactly the geometry used by the transit method for exoplanet detection, whereby astronomers look for the slight dimming of a star as a planet crosses in front of it. Systems found using transits are already in the right orientation for such interception and thus are prime targets for targeted SETI searches.
This alignment-based approach has been tried. In October 2024, Penn State and SETI Institute researchers used the Allen Telescope Array to scan the TRAPPIST-1 system, hosting seven transiting rocky planets through predicted planet–planet occultations. For 28 hours, they processed millions of narrowband signals and picked out 2,264 candidates during occultation windows. None were of extraterrestrial origin, but the experiment did prove the feasibility of synchronizing the observations with geometric alignments to maximize detection probability.
Other hotspots pop up in the transmission density maps made from the DSN. Signals congregate around the Sun–Earth Lagrange points L1 and L2, where the James Webb Space Telescope and other spacecraft station themselves. These regions peak in duty cycle, minutes of transmission per year,20 times higher than average across the sky. If alien civilizations put telescopes at their own Lagrange points, their communication patterns might spike similarly at planet–star conjunctions, offering another predictable window for detection.
Detectability depends not only on geometry but also on receiver sensitivity: a typical DSN X-band transmission from a 70-meter dish, integrated over 30 minutes, would be discernible from about 7 parsecs away with current Earth-based instruments. Much more powerful arrays, such as the upcoming Square Kilometer Array, could extend that range significantly, allowing searches for weaker, non-beacon signals comparable to those from our own spacecraft communications. The approach is thus a considerable departure from the more traditional SETI assumptions, which have been concerned primarily with searches for deliberate, high-power broadcasts; instead, it seeks the incidental technosignatures of routine interplanetary chatter.
The soon-to-launch NASA Nancy Grace Roman Space Telescope will add 100,000 new worlds to the catalog of transiting exoplanets. Many of those will contain multiple planets in coplanar orbits, dramatically increasing the total number of systems where planetary alignments might be exploited for SETI. Cross-referencing those discoveries with the detection radius of 23 light-years and ecliptic proximity allows researchers to create a prioritized target list that effectively mirrors the footprint of communication by the DSN.
This approach is not without its limitations. Restricting searches to alignment windows narrows the sky coverage-a point that SETI veteran Jean-Luc Margot has made, as he makes the case for broader surveys. Given the enormity of space and the limited resources of radio observatories, however, the gains that can be achieved by exploiting predictable geometric events are well worth the trade-off. “Using our own deep space communications as a benchmark, we quantified for the first time how future searchers for extraterrestrial intelligence could be improved by focusing on systems with particular orientations and planet alignments,” said Jason Wright of Penn State. Should alien civilizations be operating deep-space networks of their own, then the spillover from their planetary communications could be crossing our detectors now, provided we are searching in the right place and at the right time.
