Scientists engaged in the search for extraterrestrial life (SETI) have flipped the script, asking where alien civilizations would most likely detect evidence of humanity. By identifying the best vantage points for outsiders to notice Earth’s signals, researchers hope to refine strategies in the search for intelligent life.
The work was a collaboration between scientists at Penn State and NASA’s Jet Propulsion Laboratory, which analyzed how alien observers might detect Earth’s deep-space transmissions. The study, presented in The Astrophysical Journal Letters and at the 2025 Penn State SETI Symposium, examined when and where such observations would be most likely — and how those patterns could be reversed to improve SETI efforts.
The Deep Space Network and SETI
“SETI researchers often search the universe for signs of past or present technology, called technosignatures, as evidence of intelligent life,” said lead author Pinchen Fan, a graduate student in astronomy and astrophysics at Penn State’s Eberly College of Science. “Considering the direction and frequency of our most common signals gives insights into where we should be looking to improve our chances of detecting alien technosignatures.”
Using NASA’s Deep Space Network (DSN), which tracks communications between Earth and interplanetary spacecraft, the team compiled two decades of public transmission logs. By comparing the timing and direction of transmissions with the positions of spacecraft, the researchers built a detailed record of Earth-to-space communications. While other nations maintain similar networks, the focus was on NASA’s logs, as the agency has conducted more deep-space missions than any other.
“NASA’s Deep Space Network provides the crucial link between Earth and its interplanetary missions like the New Horizons spacecraft, which is now outbound from the Solar System, and the James Webb Space Telescope,” said co-author Joseph Lazio, project scientist at JPL. “It sends some of humanity’s strongest and most persistent radio signals into space, and the public logs of its transmissions allowed our team to establish the temporal and spatial patterns of those transmissions for the past 20 years.”
When reviewing the logs, the team focused on deep-space transmissions to space telescopes and other spacecraft, while ignoring low-Earth orbit communications, as their low power would make them far less likely to be detected by a distant civilization.
Where Our Signals Go
The most common targets for Earth-space transmissions were Mars, followed by Sun-Earth Lagrange points, positions in space where the Sun and Earth’s gravities keep telescopes in relatively fixed positions from an Earthly perspective.
”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 said.
“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.”
Reverse Engineering SETI
Based on their analysis, the researchers recommend identifying when exoplanets align with their host stars and targeting those opportunities in the search for technosignatures. Fortunately, this is something that astronomers are already largely doing, as the darkening of a star by a crossing exoplanet is one of the easiest methods for detecting such bodies.
“However, because we are only starting to detect a lot of exoplanets in the last decade or two, we do not know many systems with two or more transiting exoplanets,” Fan said. “With the upcoming launch of NASA’s Nancy Grace Roman Space Telescope, we expect to detect a hundred thousand previously undetected exoplanets, so our potential search area should increase greatly.”
Most of the transmissions examined occurred within about five degrees of Earth’s orbital plane, due to the flat layout of the solar system. Based on their calculations, such signals could be detectable up to 23 light-years away by a civilization with technology comparable to ours. To build on this, the team proposes cataloging exoplanets within 23 light-years whose orbital planes align edge-on with Earth.
Looking Out There
The researchers add that other methods of communication — such as laser-based systems now being tested by NASA — could also be detectable, though their spillover signals would be far narrower.
“Humans are pretty early in our spacefaring journey, and as we reach further into our solar system, our transmissions to other planets will only increase,” said co-author Jason Wright, professor of astronomy and astrophysics in the Penn State Eberly College of Science and director of the Penn State Extraterrestrial Intelligence Center.
“Using our own deep space communications as a baseline, we quantified how future searchers for extraterrestrial intelligence could be improved by focusing on systems with particular orientations and planet alignments,” Wright concluded.
The paper, “Detecting Extraterrestrial Civilizations that Employ an Earth-level Deep Space Network,” appeared in The Astrophysical Journal Letters on August 21, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.