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We’re phoning ET from home

In the 1982 movie E.T. the Extra-Terrestrial, an alien stranded on Earth had to “phone home” for his peers to come pick him up. In today’s world, however, we’re the ones phoning the aliens everyday, without even knowing it. When we use our cell phones, they ping off a network of cell phone towers worldwide, leaking radio signals into space. On May 2, 2023, the SETI Institute announced a new study that looked at how likely it would be for a nearby advanced civilization to detect those signals. It found that, at the moment, we’re still somewhat difficult to detect. But it also found that our signal will grow substantially in the coming years.

The new study looked at crowd-sourced data to simulate radio leakage from cell phone towers around the world. They took the viewpoint of an alien civilization nearby to Earth, such as Barnard’s Star, which is six light-years away.

Ramiro Saide of the University of Mauritius was the lead author of the study. The peer-reviewed journal Monthly Notices of the Royal Astronomical Society published the paper on February 6, 2023.

Measuring our signal to the aliens

Saide and his team made models of the radio leakage from mobile communication towers located around the globe. Specifically, the team noted the change in signals as Earth spins and the towers rise and set from the view of a specific star. They determined the dynamic power spectrum of Earth was around 4 gigawatts (GW). That’s summed over all cellular frequency bands. It’s similar to the power of 400 million LED light bulbs.

The team said that unless the alien civilization is much more advanced than ours, it would be difficult to detect the signals. However, the press release said:

… the detectability of our mobile systems will increase substantially as we move to much more powerful broadband systems.

More phone usage around the world

Overall, the increased use of cell phones around the world, such as in Africa, makes up for the decrease in powerful TV transmissions. Mike Garrett of the University of Manchester, another member of the study, said:

I’ve heard many colleagues suggest that the Earth has become increasingly radio quiet in recent years, a claim that I always contested. Although it’s true we have fewer powerful TV and radio transmitters today, the proliferation of mobile communication systems around the world is profound. While each system represents relatively low radio powers individually, the integrated spectrum of billions of these devices is substantial.

A look at the map below shows the location of cell phone towers located around the globe. Notably, Africa is bypassing the landline stage of development and moving into the digital age with cell phones.

We’re talking, but are aliens listening?

Nalini Heeralall-Issur, of the University of Mauritius, also participated in the study. Heeralall-Issur said:

Every day we learn more about the characteristics of exoplanets via space missions like Kepler and TESS, with further insights from the JWST. I believe that there’s every chance advanced civilizations are out there, and some may be capable of observing the human-made radio leakage coming from planet Earth.

The team plans to expand their research to include radars, new digital broadcast systems, Wi-Fi networks, the swarm of satellite constellations entering low-Earth orbit and more. Garrett said:

Current estimates suggest we will have more than 100,000 satellites in low Earth orbit and beyond before the end of the decade. 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.

Bottom line: A new study looked at whether aliens around nearby stars could detect the radio signals from Earth’s cell phone towers.

Source: Simulation of the Earth’s radio leakage from mobile towers as seen from selected nearby stellar systems

Via SETI