Chethana Janith, Jadetimes Staff
C. Janith is a Jadetimes news reporter covering science and geopolitics.
The method involves detecting alien messages while they’re whizzing between planets.
Since the first modern SETI (Search for ExtraTerrestrial Intelligence) studies tried to detect alien transmissions in the early 1960s, scientists on Earth have been on the alert for strange cosmic signals with no reasonable explanation. So far, they haven’t positively identified any signals as evidence of intelligent alien life among the stars, but the search continues.
Most SETI telescope searches aim to observe a vast expanse of sky or zero in on a specific star system or group of stars. They usually try to intercept signals that potential aliens could have aimed at Earth or those that pass close by. But what if aliens are transmitting messages from one exoplanet to another instead? If they exist, we may now have a way to eavesdrop on alien conversations, leveling up humanity’s search for intelligent life far from Earth.
Working with his team at Penn State University, astronomer Nick Tusay, a graduate student working on his Ph.D., came up with a new technique that tests indicate would detect alien radio chatter. From our Earthly point of view, we can observe when one exoplanet - a planet that is not part of our solar system - passes in front of and blocks another. This is called occultation. However, the occulting planet does not always completely cover the planet behind it. So, any message a hypothetical alien transmits from the occulted planet can spill over into space, and our radio telescopes could detect it.
“I want to be able to find or at least look for the kind of signals that we put out all the time, from an alien civilization going about its business doing its thing, not intending to signal anyone,” says Tusay, who led a study published in July 2024 in The Astronomical Journal
Tusay’s method of listening in on alien conversations during planet-planet occultations (PPOs) is designed to seek out narrowband radio signals. While there are many different types of radio waves that are emitted by objects such as quasars or pulsars, narrowband signals are glaringly artificial and are the type used by transmitters. We only know of one species that has been able to produce these signals, and that’s us. Humans send these signals into space when communicating with spacecraft via NASA’s Deep Space Network. The fact that these signals cannot occur naturally is an advantage for SETI, because if radio telescopes on Earth were to detect one coming from space, it would mean that it is definitely artificial.
Seth Shostak, Ph.D., Senior Astronomer at the SETI Institute and renowned SETI expert, agrees that narrowband signals would be a sure sign that someone out there is communicating, though not necessarily with us. There is always the possibility that extraterrestrials might be using a type of signal we cannot even fathom yet. However, Shostak, who is also an astrophysicist, believes it is likely aliens would use the same methods of communications that humans do.
“Maybe ether aliens have a different signaling system to what we can imagine, but the physics on their world are the same as the physics here,” he says. “Sending radio signals is something that they would probably do too, because it’s congruent with the physics the universe has.”
The more practical reason for relying on narrowband signals transmitted between planets is that we understand them, according to SETI historian Rebecca Charbonneau, Ph.D., author of Mixed Signals: Alien Communication Across the Iron Curtain. During the advent of SETI in the late 1950s and early 1960s, when the Space Race was taking off, humans were sending artificial signals into space. And they were already starting to wonder if there were intelligent beings out there who were doing the same.
“We’re highly influenced by our environment when it comes to thinking of what we might expect to see in other words, because radio is the primary mechanism with which humans have historically communicated,” says Charbonneau.
As our technology has evolved, we have shifted from radio to other modes of communication, such as fiber optics, internet, and cables buried deep beneath the ocean. This shift also means that radio signals from our telescopes may take a backseat to these newer types of signals. If intelligent aliens are looking for other life in the universe, then they may or may not be able to detect our variety of signals.
However, it’s possible that none of these signals may resonate with an advanced civilization, which could be millions - or possibly billions of years - older than ours; its members could be communicating in ways only science fiction could fathom. As a recent study published in The Open Journal of Astrophysics explores, it is possible that alien communications technologies are so advanced, they may be talking to each other using gravitational waves. These are ripples in spacetime, and physicists don’t yet fully understand them.
The problem is that - unlike narrowband radio waves - our science cannot distinguish between gravitational waves that are natural and those that may be artificial. That lack of knowledge still does not discourage Tusay. While he will not be developing the eavesdropping technique further, he plans to leave it in the literature as a proof of concept, so that future scientific progress may make the adjustments needed to pick up unnatural signals. Whether we could actually decode any type of signal from another civilization is an entirely different question, though.
“We probably won’t be able to decode it,” Shostak says. “But the modulation of the signal might [convey] something simple, such as what their planet looks like or what they look like. There might be something to learn by pointing antennas at the sky.”
Charbonneau thinks that, in addition to the possibility of alien messages remaining a mystery to us, identifying an errant PPO signal as alien will need rigorous scientific testing. It will also require us to question our own biases. We imagine and tend to look for signals and civilizations that are familiar to us on Earth, because after all, it’s all we know.
“We do need to continually do these searches until we find something,” Tusay says. “Not finding anything doesn’t necessarily mean that nothing is there.” Does that mean E.T. might phone another planet while we’re on the line?
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