To find aliens, scientists need to think like James Bond. In Quantum of Solace, Daniel Craig’s Bond goes to the opera, where he eavesdrops covertly on Quantum and its executives while they use the noise of Tosca to try to cover their conversation. Scientists searching for alien life believe they can do the exact same thing as Bond — but on the cosmic scale.
In fact, as part of the ongoing search for extraterrestrial life, eavesdropping on alien communication signals sent between one planet and another may be one of the easiest ways to find life. At least, that’s according to Evan Sneed, a researcher at Pennsylvania State University’s Department of Astronomy.
What’s new — Just like the villains’ chatter isn’t meant for Bond, these alien communication signals are specifically not meant for Earthlings’ ears. But that doesn’t mean we can’t listen in.
The communication signals Sneed and other researchers are interested in are those sent by an alien civilization’s operating systems on one planet to another in much the same way that NASA engineers on Earth communicate with their missions on Mars.
Jason Wright, a Penn State astronomer and director of the Penn State Extraterrestrial Intelligence Center who supervised the work for Sneed’s research, says the target planets don’t need to be habitable.
“Mars has no Earth life on it and we communicate with it, so life on the planets doing the transmitting or receiving is not actually necessary,” he tells Inverse.
If researchers are able to intercept this “spillover” communication data while it is in transit between planets, then it could help us learn our place in the universe and answer the question of whether we are alone.
Sneed presented his research at the annual meeting of the European Astronomical Society, which was held virtually in July 2021.
Digging into the details — The idea behind the search for spillover signals is inspired by a global network of antennas on Earth known as the Deep Space Network. NASA uses the network to communicate with the Perseverance rover and other ongoing missions on Mars.
The Deep Space Network uses radio frequency transmissions that travel through large antenna systems toward specialized receivers.
The network is made up of three deep-space communications facilities in three different locations across the world. Each facility is strategically placed approximately 120 degrees apart. One is located at Goldstone, in California's Mojave Desert, another is near Madrid, Spain, and the third is near Canberra, Australia.
Thing is, the signals the Deep Space Network beams out to spacecraft or planetary rovers tend to go beyond their target.
That’s because, by the time the signal makes it all the way to the satellite from Earth, the beam width is a lot wider than that target, Sneed says.
“What happens to that beam that spills over?” Sneed says in his presentation. “Can we turn this on its head and ask: Can we detect extraterrestrial deep space networks from this?”
How it works — In order to do this, the target planet and the observing planet (the one sending the signal and the one receiving it), and a third observing planet need to be aligned. This kind of alignment is a phenomenon known by astronomers as planet-to-planet occultation, whereby an occultation means the point when one object passes in front of another from an external observer’s point of view.
Both of the planets don’t necessarily have to be habitable. Rather, one could be a “service planet” the same way Mars could be characterized in relation to Earth. However, the planets do need to be near enough to Earth that they can be properly observed when in occultation — but in the vast universe, “near” is relative. These planets may be many light-years beyond the bounds of our own Solar System.
Sneed and his colleagues have narrowed down the shortlist of candidates to 20 star systems that they believe could be potential targets for eavesdropping scientists to aim their receivers toward.
One of the best candidates is TRAPPIST-1, a red dwarf star that has seven orbiting planets. Three of these worlds are located within the star’s habitable zone — a point of distance from the star that could feasibly enable life to flourish there as it does on Earth.
How scientists look for alien signals
One of the most robust scientific efforts to find alien signals is coordinated by SETI (Search for ExtraTerrestrial Intelligence), which is essentially a series of interrelated programs looking for intelligent life beyond our Solar System. Most of these programs do this by trying to detect radio signals coming from alien life.
The SETI Institute began operations on February 1, 1985, as a non-profit organization searching for narrow-band radio transmissions emitted by other planets. Narrowband transmissions are those that, like Earth radio signals, come in at specific frequencies and so are more likely than wideband transmissions to have come from an intelligent source.
Scientists at the Institute primarily use the ground-based Allen Telescope Array to try and find these signals, as well as ground-based optical telescopes for work on optical SETI programs.
This method is fundamentally passive, observing the cosmos to look for signs of life thriving upon other worlds not through specific exploratory missions but by casting a wide net in the hopes of stumbling upon something that may lead to such a targeted mission.
The recent study has not been published yet, and therefore the method is not fully developed.
In order to detect spillover signals using the SETI method, the planets not only need to be nearby but should also be well-studied, so that the observing scientists can distinguish their natural signals from ones that are being intentionally sent out by an intelligent civilization.
Wright says that does put some limitations on finding alien life.
“There is some bias because the systems we know about tend to be very close to their stars, so too hot for liquid surface water,” he says.
Another challenge lies within the signals themselves, he adds.
“The challenge is whether the signals are strong enough and whether we can distinguish them from our own transmissions,” he explains.
The chances that intelligent life is already developed somewhere near Earth, with transmitting radio signals being sent out, around the same time that Earth’s civilization is also brewing with technological advancement are rather slim considering our time and place in the vast universe.
But it is worth a try to sneak around and see if other planets are trying to communicate with one another the same way Earth is. And as our presence on Mars increases, so will our transmissions to the Red Planet which would increase the chances of Earth’s spillover radio signals being caught by an alien spy.
Abstract: Recent SETI surveys have increased the fraction of the cosmic haystack that has been analyzed by focusing on increasing the number of studied target systems and the total time each target is observed. However, few of these surveys have considered when is best to observe their targets; often instead relying on the assumption that technosignature targets are persistent and detectable over long timeframes. While several time-based search considerations exist within the SETI literature, relatively few have been further investigated nor used. However, advancements in our ability to detect and characterize exoplanets and their orbital dynamics give us an opportunity to search for technosignatures originating from exoplanets that have the solar system in their own transit zones. Inspired by the signals sent and received by the Deep Space Network, we present a method to eavesdrop on "spillover" communications by identifying when two or more exoplanets are collinear with Earth, a scenario known as a planet-planet occultation. This trategy is sensitive not only to deliberate transmission attempts, the subject of most SETI searches, but also to communications not intended for Earth.