If a distant civilization tracked its own interplanetary probes the way NASA tracks the Voyagers, Mars orbiters, and our other spacecraft, when and where would it be broadcasting, and could we catch it in the act?
That’s the question Pinchen Fan presented at IAUS404: Advancing the Search for Technosignatures in March 2026.
About the Presenter
Pinchen Fan is a PhD candidate in the Department of Astronomy and Astrophysics at Penn State University, and a visiting graduate student in the David A. Dunlap Department of Astronomy & Astrophysics at the University of Toronto. She serves as science principal investigator on a NASA Exoplanets Research Program grant supporting searches for infrared laser and radio technosignatures, and her broader research spans SETI, biosignatures, exoplanet characterization, and gravitational-wave astrophysics.
More About Fan’s Work in Advancing the Search for Technosignatures
Fan’s talk drew on a study, published in The Astrophysical Journal Letters in August 2025 with co-authors Jason T. Wright and JPL’s T. Joseph W. Lazio, that asks the question of what a Deep Space Network like our own might be broadcasting, and wether aliens could be detectable in the same way.
The team combed through 20 years of NASA Deep Space Network uplink logs, the communications sent to spacecraft like the Mars orbiters and Voyager probes, and mapped when and where those signals point.
The pattern is striking:
Most transmissions cluster within a few degrees of the ecliptic plane, the flat disk where the planets orbit
Signal duty cycle within the “Earth Transit Zone,” the narrow band from which an outside observer could see Earth cross the Sun, runs about 20 times higher than average
During Earth-Mars conjunctions, an outside observer would have had roughly a 77% chance of catching one of Earth’s transmissions, a jump of some 400,000-fold over a random look at a random time
The upshot for SETI: we may prioritize exoplanet systems seen edge-on, where transits are visible, and time observations around planetary conjunctions. With NASA’s Nancy Grace Roman Space Telescope expected to add roughly a hundred thousand new transiting exoplanets to the catalog, that target list is about to grow substantially.
Key Takeaways
Earth’s own deep-space communications cluster tightly around the ecliptic plane and toward the Sun
A civilization watching from the right angle, during the right planetary alignment, has a dramatically higher chance of intercepting a signal like ours
Edge-on, transiting exoplanet systems make the best SETI targets under this logic
The same reasoning extends to laser-based technosignature searches, not just radio
This approach adds a strategic layer to the broader technosignature search: rather than scanning everywhere, it argues for scanning smarter. Curious readers can find the full analysis, including the geometry behind the Mars conjunction calculation, in the published paper.
This video was included in the proceedings of the International Astronomical Union (IAU) symposium #404, Advancing the Search for Technosignatures, hosted by Blue Marble Space.
Thanks for joining us here with Planetary Perspectives, an editorial endeavor and science communication project from Blue Marble Space.
