- Humans use deep space communications to transmit information between Earth, space telescopes and spacecraft at other planets in the solar system.
- An alien civilization in another planetary system could most easily detect them when the planets – such as Earth and Mars – are in alignment from their vantage point.
- Likewise, scientists on Earth could search for similar alien communications when their planets are also in alignment, as seen from Earth.
How to find aliens: Look when their planets align
What is the best way to search for signals from alien civilizations? In a new study, researchers from Pennsylvania State University and NASA’s Jet Propulsion Laboratory in California suggest looking for transmissions among planets in candidate planetary systems. They said on August 21, 2025, that the study uses our own deep space communications as an analogy. This includes signals sent between Earth, space telescopes and interplanetary spacecraft. Most of those transmissions are part of the Deep Space Network (DSN). The researchers further say that the best chances of detecting the alien equivalent of a deep space network would be when the planets in their system are in alignment.
The study uses our own deep space communications as a baseline. Basically, the premise is that the patterns of communication in our own deep space transmissions can be used to search for similar kinds of transmissions in other planetary systems.
Astronomers could use this method for both radio and laser signals, both plausible types of alien technosignatures (any signs of advanced technology in various forms).
The researchers published their peer-reviewed analysis in The Astrophysical Journal Letters on August 21, 2025.
Analyzing the Deep Space Network
For the study, the researchers analyzed human-created deep space transmissions. NASA’s Deep Space Network (DSN), the largest of these, analyzed the network’s logs. The DSN is a system of ground-based facilities that permits two-way radio communications with human-made objects in space. The network acts as a relay to send commands to spacecraft and receive information they send back. The researchers matched the DSN logs with other information about spacecraft locations. This helped the researchers determine the timing and directionality of radio communications from Earth.
Joseph Lazio, project scientist at JPL and one of the three authors of the paper, said:
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. 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.
Fun new SETI study just dropped. ?
— Kiona N. Smith (@kionasmith07.bsky.social) 2025-08-24T01:39:50.378Z
Focus on deep space transmissions
The researchers focused on transmissions from Earth to deep space instead of spacecraft or satellites in low-Earth orbit. Those ones close to Earth have lower power and their signals would be much more difficult to detect by an alien civilization in another planetary system.
The results showed that most of the transmissions were directed toward spacecraft at Mars. Other primary transmissions were toward other planets in our solar systems. Others were to telescopes at the sun-Earth Lagrange Points. That’s where the gravity of both the sun and Earth keep the telescopes in a stable, fixed position in space.
Earth-Mars alignment
Using Mars as an example, the researchers found that the best chance to detect transmissions would be along the path between Earth and Mars. That is, when the two planets are aligned, from the perspective of an observer in another solar system. As first author Pinchen Fan, graduate student in the Penn State Eberly College of Science, explained:
Humans are predominantly communicating with the spacecraft and probes we have sent to study other planets like Mars. But a planet like Mars does not block the entire transmission, so a distant spacecraft or planet positioned along the path of these interplanetary communications could potentially detect the spillover; that would occur when Earth and another solar system planet align from their 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. 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.
Planetary alignments in the search for alien communications
Likewise, we could look for similar planetary alignments in other planetary systems to search for signals. Fan added:
This suggests that we should look for alignment of planets outside of our solar system when searching for extraterrestrial communications. SETI researchers often search the universe for signs of past or present technology, called technosignatures, as evidence of intelligent life. 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.
The research team found that an average DSN transmission could be detected up to about 23 light-years away. So the researchers suggest looking for planetary systems within 23 light-years. And ones that have orbital planes edge-on to Earth as seen from our vantage point.
Our solar system is fairly flat when seen edge-on. Most of the planets orbit in the same plane. The researchers liken this to looking at a dinner plate edge-on. Hence, most DSN transmissions follow that plane, only deviating to within 5 degrees at most. Therefore, it makes sense to look along that plane for DSN signals.
Radio and laser signals
The study focuses primarily on radio signals. But it also says that the same techniques could be used to look for laser signals. Lasers, notably, would have less spillover than radio signals. As a result, the transmissions would be more narrowly focused. The Search for Extraterrestrial Intelligence (SETI) has been expanding in more recent years to search for technosignatures other than just radio transmissions.
But whether radio or laser, using our own deep space communications as a baseline is a novel approach to the search for alien intelligence. According to co-author and astronomer Jason Wright:
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. 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.
Bottom line: A new study proposes a novel idea for how to find aliens: Look for their deep space communications when their planets are in alignment, as seen from Earth.
Source: Detecting Extraterrestrial Civilizations that Employ an Earth-level Deep Space Network
Via The Pennsylvania State University
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#planets #aligned