Some exoplanets have already benefited or will soon benefit from a direct line of sight to Earth according to a team of astronomers. With methods similar to ours, some civilizations, if they exist, could also detect signs of life in our atmosphere.
Over the past few years, several missions have been developed in the context of exoplanetary research, such as Kepler or TESS to name a few. But have you ever asked yourself the following question:could we be visible from the outside? In other words, if an extraterrestrial intelligence as developed as ours or more had the objective of probing the universe in search of life, could it fall on Earth?
A team of researchers led by Lisa Kaltenegger of Cornell's Carl Sagan Institute recently looked into the matter.
As part of this work published in Nature, the team focused on one of the most widely used methods on Earth to isolate the presence of exoplanets:that of transit. As a reminder, this method consists in measuring the curve of light emitted by the stars. Observed from Earth, periodic dips in luminosity sometimes testify to the passage of one or more planets in front of their host.
Furthermore, we can determine the size of these worlds approximately by the depth of the observed light curve. In this way, we can also exclude exoplanets that are unlikely to support life as we know it, such as gas giants.
That being said, for this study, the researchers relied on data from the European Space Agency's Gaia mission, which tracks the movements of billions of stars in the goal of generating a three-dimensional map of the Milky Way.
The researchers focused on a 10,000 year period . Concretely, these data have made it possible to isolate several star systems likely to have a direct view during the last 5,000 years and during the next 5,000 years within a radius of 100 parsecs (326 light years).
Researchers then discovered that many of these exoplanets can take advantage of a direct line of sight to Earth. Indeed, their analyzes show that a transit of our planet in front of the Sun could have been visible from 1,715 stellar systems over the last 5,000 years . More than three hundred additional star systems will also enter the land transit zone within the next 5,000 years .
The study also specifies that for about two-thirds of these stars, Earth transits would last at least ten hours. In addition, 868 of them will evolve over 10,000 years in areas with line of sight to Earth. Overall, the presence of the Earth does not really go unnoticed from our cosmic backyard.
Finally, the researchers add that if these worlds are indeed home to sufficiently advanced civilizations, these could theoretically be able to detect signs of life from their vantage point. The most obvious sign would probably be the detection of simultaneous presence of oxygen and methane in our atmosphere. This brings us back to the oxygenation of the Earth's atmosphere that took place about a billion years ago.
Whether these systems could actually harbor life remains to be seen. Of the samples counted, about two hundred stars resemble the Sun and more than a thousand are smaller, cooler and more unstable red dwarfs. The rest are a mix of smaller and larger stars, including seventy-five white dwarfs.
Based on estimates of the frequency of rocky planets found in the habitable zone of their stars, researchers estimate that more than 500 Earth-like planets have already benefited or will one day benefit from a direct line of sight towards the Earth in this perimeter of 326 light years.
