Earth Could Soon Be More Detectable by Aliens, Study Says

We are all used to overhearing little snippets of cell phone conversations on the bus or at the store, but could aliens on nearby planets also eavesdrop on our mobile chatter? Scientists raised this intriguing question in a recent study that investigated whether any local extraterrestrials could detect radio waves emitted by base station towers that link the estimated 10 billion mobile devices on Earth.

The short answer to the question turned out to be no, because mobile communications don’t currently produce a strong enough signal to be spotted by aliens within 10 light years of Earth, unless they had extremely advanced instruments. However, the research revealed that the rise of mobile communications on Earth, in addition to other emerging technologies like 5G and large satellite constellations such as SpaceX’s Starlink, could make our planet stand out to aliens in the future.

For more than a century, scientists have speculated that extraterrestrial civilizations might be able to tune into the radio leakage produced by modern inventions, such as television broadcasts, radar systems, and satellite transmissions. For instance, researchers led by astronomer Woodruff Sullivan suggested that television leakage could potentially be received by aliens in a landmark 1978 study.  

Now, a team led by Ramiro Saide, a graduate student who studies exoplanet science at the University of Mauritius, have joined this tradition by focusing on an overlooked source of emissions—those made by modern mobile communication towers—which “represent a relatively new but growing contributor to the total radio-leakage associated with planet Earth,” according to a recent study published in the Monthly Notices of the Royal Astronomical Society.

“The nature of the Earth’s radio leakage has changed significantly since the pioneering work of Sullivan et al. (1978) was published over 40 years ago,” said Saide and his colleagues in the study. “For example, powerful TV transmissions are no longer a major contributor to the Earth’s leakage radiation with the rise of cable TV and the internet. In addition, mobile communication systems were unknown until the 1990s, and they currently represent a new and still growing component of the Earth’s human-generated radio emission.”

“As far as we know, no previous research has investigated the cumulative effect of the mobile tower emissions and the implication for eavesdropping and SETI more generally,” the researchers continued. “Our study provides some insight on what we might expect if there is a human-like civilization located elsewhere in the Milky Way with similar or indeed more advanced levels of radio telescope technology.”

Millions of cell phone towers have been rapidly constructed over the past 30 years to support the meteoric demand for mobile connectivity around the world. Radio leakage from these towers is very distinct from previous sources of emission, including television transmitters and radar systems, because of its higher frequencies, weaker signal strength, and vast geographic distribution, according to the new study.

The researchers calculated what all this mobile chatter might look like from the vantage point of three star systems in our local cosmic neighborhood: Alpha Centauri, HD 95735, and Barnard's star. They used OpenCellID, a database that contains tens of millions of crowdsourced data points from towers around the world, to build a profile of the mobile radio emissions that humans are sending into space. 

The results revealed that mobile emissions are far too weak to be picked up by alien civilizations, even if they were located in the nearest systems to the Sun. Likewise, we are not likely to overhear any extraterrestrial radio leakage produced by the alien version of a smartphone. 

However, Saide and his colleagues think that mobile platforms might produce a much more noticeable radio footprint in the future, given that they continue to rapidly proliferate around the world. The team also noted that other emerging technologies could also boost our signals to the universe, such as satellite megaconstellations like SpaceX’s Starlink. 

“Mobile systems are in their infancy, and the future development of this technology (e.g. 5G systems and beyond) suggests that this component of the Earth’s leakage will continue to increase in power over time,” the research said. “If the leakage can be detected, an extraterrestrial observer would be able to discern various details of the nature of our planet and the distribution of technology on its surface.”

Numerous companies including SpaceX are set to launch thousands of communications satellites into low-Earth orbit in coming years, which could similarly raise Earth’s profile, study co-author Michael Garrett from the University of Manchester said in a statement. 

“Current estimates suggest we will have more than one hundred thousand satellites in low Earth orbit and beyond before the end of the decade,” he said. “The Earth is already anomalously bright in the radio part of the spectrum; if the trend continues, we could become readily detectable by any advanced civilization with the right technology.”

While future research may shed light on how aliens might see Earth, Saide and his colleagues also emphasized that the study also offers a new way for us to see ourselves. 

“Our study draws attention to the fact that the leakage signature of the Earth has evolved quite rapidly over relatively short time scales,” the team concluded. “For the first time, our results highlight the significant leakage contributions being made via the rise of developing countries in the continent of Africa, as well as by countries such as Japan, Vietnam, China.”