As the exoplanet passes, it blocks stellar light, some of which is filtered into the atmosphere. Energy and light interact with the molecules and atoms of that planet, and when light reaches an astronomer’s telescope, scientists can determine if it has interacted with chemicals such as oxygen or methane.
A combination of these two, says Kaltenegger, is the fingerprint for life.
“What’s really interesting is that people might have seen that Earth was an habitable planet for about 2 billion years. [ago], due to the accumulation of oxygen in the atmosphere, ”he 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 his inspiration to a plan that the SETI Institute, which pursues the search for extraterrestrial intelligence, had in the 1960s.
In the 1960s, a radio astronomer named Frank D. Drake was the first person to attempt to detect it interstellar radio transmissions, staring at two stars 11 light-years away and similar in age to our sun. Although this test was not successful, scientists and amateur enthusiasts have continued to look for such signs ever since.
But whether the signals we send pass is another matter entirely. In the new study, Kaltenegger and Faherty reported that man-made radio waves had already swept the 75 stars closest to their list.
Although humans have sent radio waves for about 100 years, it is nothing compared to the billions of years of planetary evolution of the Earth.