To Find Aliens We Should Look For Planetary Alignments, Scientists Say

Humans should look to planetary alignments outside of the solar system when searching for signatures of extraterrestrial communications, scientists say.

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The nascent search for radio transmissions from alien civilizations should focus not on planets, but on their alignments, according to new research from Penn State and NASA’s Jet Propulsion Laboratory.

The insight is based on analysis of humans’ deep space transmissions, the majority of which are between Earth and Mars. After all, there are 18 spacecraft in Mars orbit, seven currently active, while 10 landers and rovers are on its surface. NASA’s Deep Space Network — three vast dishes in California, Spain and Australia — sends some of humanity’s strongest and most persistent radio signals into space.

‘Spillover’ Signals

The theory, published this week in a paper in The Astrophysical Journal Letters, goes that if Earth is sending messages to Mars, any star directly behind Mars would receive spillover radio transmissions — and realize where they’re coming from. “Humans are predominantly communicating with the spacecraft and probes we have sent to study other planets like Mars,” said Pinchen Fan, graduate student in astronomy and astrophysics at Penn State Eberly College of Science, science principal investigator of the NASA grant supporting this research and first author of the paper. “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 spillover occurs when Earth and another solar system planet align from the perspective of an alien planet or spacecraft. “This suggests that we should look for alignment of planets outside of our solar system when searching for extraterrestrial communications,” says Fan.

Refining The Search

When it comes to finding aliens in the cosmos, there’s a need to restrict where to look. SETI — the search for extraterrestrial intelligence — has so far found no definitive radio signals sent by extraterrestrial intelligence — but is constantly refining where to look and how to detect them. There is no other choice because the cosmos is so vast — SETI is now decades old and has only examined a very tiny fraction of the universe for signals in limited frequencies and with limited sensitivity. According to NASA, if the Milky Way galaxy were an ocean, then SETI would have listened to the equivalent of a small swimming pool within it.

There may be other reasons to explain “The Great Silence” — the lack of any evidence for extraterrestrials — but all humans can do is be as clever as possible about where to look. “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,” said Fan.

Maximizing The Chances

The paper looked at 20 years’ worth of transmissions between Earth and Mars, as well as between Earth and spacecraft positioned around the sun or at Sun-Earth Lagrange points — such as where the James Webb Space Telescope is. “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,” said Fan. That’s orders of magnitude more likely than detecting our signals from a random position. “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.”

It’s hoped that NASA’s upcoming Nancy Grace Roman Space Telescope will reveal hundreds of thousands of previously undetected exoplanets — planets orbiting stars other than the sun — and reveal systems containing planets that align from Earth’s point of view.

Wishing you clear skies and wide eyes.