October 16, 2021

Could observers on exoplanets detect bio-signatures on Earth?

30 years ago, Carl Sagan described the Earth in the Voyager mission photo as a “pale blue dot” . There, our planet was recorded 6 billion kilometers away. This time, a pair of astronomers carried out a study where they propose a different view of the Earth: from the point of view of the exoplanets that exist relatively close to us, which one could have identified the Earth and the life that exists on it?

Lisa Kaltenegger, professor of astronomy and director of the Carl Sagan Institute and Joshua Pepper, professor of physics, identified 1,004 stars with NASA’s Transiting Exoplanet Survey Satellite (TESS) catalog , which may contain Earth-like planets in their habitable zones, where water can exist in a liquid state. All planets are 300 light-years from Earth, and are in locations that should allow the detection of chemical traces of life on Earth. “We propose to invert the point of view to that of the other stars and ask which other systems would Earth be seen as a planet in transit,” said Kaltenegger.

To say that a planet is in transit means that the planet in question is experiencing the observer’s view of another star – such as the sun, for example – and may reveal clues to the atmospheric composition of the other world. “If observers were looking outside, they could find signs of biosphere in the atmosphere of our Pale Blue Point,” she said. “We can even see some of the brightest stars in our night sky without binoculars or telescopes.”

Observing the transit is important for astronomers have identified planets from other systems, and the James Webb space telescope , due to be launched next year, will be essential for this. The secret to identifying these planets is in the plane of the Earth’s ecliptic, which is the orbit plane of our planet around the Sun. So, the exoplanets that could see Earth would be on the same plane, since they need to be places where the Earth can be observed by crossing the Sun and thus allowing observers to learn more about the Earth’s biosphere.

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Pepper points out that a very small number of exoplanets will be randomly aligned with the line of sight so that it is possible to observe their transit. “But all the thousand stars that we identified in our neighborhood could see the Earth moving through the Sun,” he comments. Still, for Kaltenegger, a planet with a vibrant biosphere like Earth’s could make researchers curious about whether or not there would be – something over there watching us back. “We just created the star map of where we should look first.”

The article with the results of the study was published in the Monthly Notices of the Royal Astronomical Society.

Source: Cornell University