Radio waves from Earth have reached dozens of stars


When transiting exoplanets block stellar light, part of that light filters through the atmosphere. Energy and light interact with the molecules and atoms of that planet, and by the time that light reaches an astronomer’s telescope, scientists can determine whether it has interacted with chemicals like oxygen or methane.

A combination of those two, Kaltenegger says, is the fingerprint for life.

“What’s really interesting is people could have seen that the Earth was a habitable planet since about 2 billion years [ago], because of the oxygen buildup in the atmosphere,” she says.

The idea of studying transits to find out if we’re on someone else’s radar isn’t really new. Kaltenegger attributed much of her inspiration to a plan the SETI Institute, which pursues the search for extraterrestrial intelligence, had in the 1960s.

In 1960, a radioastronomer named Frank D. Drake was the first person to try to detect interstellar radio transmissions, focusing on two stars 11 light-years away and similar in age to our sun. Though that attempt was unsuccessful, scientists and amateur enthusiasts have continued to look for such signals ever since.

But whether the signals we send are getting through is another matter entirely. In the new study, Kaltenegger and Faherty reported that human-made radio waves had already swept over the 75 closest stars on their list.

Even though humans have been sending out radio waves for roughly 100 years, that’s nothing compared with Earth’s billions of years of planetary evolution.