When transiting exoplanets obscuring stellar light, part of this light flows through the atmosphere. Energy and light interact with that planet’s molecules and atoms, and by the time the light reaches an astronomer’s telescope, scientists can determine if it has reacted with chemicals like oxygen or methane.
The combination of these two, says Kaltenegger, is a lifelong imprint.
“What’s really exciting is that people can see that the Earth was a habitable planet about two billion years ago. [ago], due to the accumulation of oxygen in the atmosphere.
The idea of studying transit to see 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 radio astronomer named Frank D. Drake is the first person to try to find out interstellar radio transmission, focusing on two stars that are 11 light-years away and similar to the age of our Sun. Although this attempt was unsuccessful, scientists and hobbyists have continued to search for such signals ever since.
But whether the signals we send pass through is another matter entirely. In the new study, Kaltenegger and Fherty report that man-made radio waves have already swept through more than 75 stars closer to their list.
Although humans have been transmitting radio waves for nearly 100 years, this is nothing compared to billions of years of planetary evolution.