When transiting exoplanets block starlight, some of that light filters through the atmosphere. Energy and light interact with molecules and atoms on this planet, and by the time the light reaches an astronomer’s telescope, scientists can determine if it has interacted with chemicals like oxygen or methane. .
A combination of these two, says Kaltenegger, is the fingerprint of life.
“What is really interesting is that people could have seen that the Earth has been a habitable planet for about 2 billion years. [ago], because of the build-up of oxygen in the atmosphere, ”she said.
The idea of studying transits to see if we’re on someone else’s radar isn’t exactly new. Kaltenegger attributed much of his inspiration to a plan by the SETI Institute, which continues the search for extraterrestrial intelligence, in the 1960s.
In 1960, a radio astronomer named Frank D. Drake was the first person to try to detect interstellar radio transmissions, focusing on two stars 11 light years apart and similar in age to our sun. Although this attempt failed, scientists and enthusiasts have continued to search for such signals ever since.
But whether the signals we send out are passed on is a whole different matter. In the new study, Kaltenegger and Faherty reported that man-made radio waves had already swept through the nearest 75 stars on their list.
Even though humans have been sending radio waves for about 100 years, this is nothing compared to Earth’s billions of years of planetary evolution.