When humanity speeds up its search for alien life, we have to bear in mind that E.T. may even be looking for us, too.
A recent analysis allows that case by discovering more than 1,000 neighboring stars that are favorably placed for detecting life on Earth.
"If observers were out there searching [from planets orbiting these stars], they would be able to see signs of a biosphere in the atmosphere of our Pale Blue Dot," study lead author Lisa Kaltenegger, an associate professor of astronomy at Cornell and director of the university's Carl Sagan Institute, said in a statement.
"And we can even see some of the brightest of these stars in our night sky without binoculars or telescopes," Kaltenegger said.
UNSPECIFIED: In this NASA digital illustration handout released on February 22, 2017, an artist's concept allows us to imagine what it would be like to stand on the surface of the exoplanet TRAPPIST-1f, located in the TRAPPIST-1 system in the constellation Aquarius. Because this planet is thought to be tidally locked to its star, meaning the same face of the planet is always pointed at the star, there would be a region called the terminator that perpetually divides day and night. If the night side is icy, the dayside might give way to liquid water in the area where sufficient starlight hits the surface. One of the unusual features of TRAPPIST-1 planets is how close they are to each other -- so close that other planets could be visible in the sky from the surface of each one. In this view, the planets in the sky correspond to TRAPPIST1e (top left crescent), d (middle crescent), and c (bright dot to the lower right of the crescents). TRAPPIST-1e would appear about the same size as the moon and TRAPPIST1-c is on the far side of the star. The star itself, an ultra-cool dwarf, would appear about three times larger than our own sun does in Earth's skies. The system has been revealed through observations from NASA's Spitzer Space Telescope as well as other ground-based observatories, and the ground-based TRAPPIST telescope for which it was named.
Earthly Transit
Astronomers also discovered several of the more than 4,000 exoplanets discovered to date using the "transit process," which describes the minor brightness dips induced from the observer's viewpoint as an orbiting world passes the face of its host star. NASA's groundbreaking Kepler Space Telescope used this technique to considerable benefit and is currently being used by its replacement, the Transiting Exoplanet Survey Satellite (TESS).
Soon, experts may also be able to look for possible indicators of existence in several close transiting planets' atmospheres. This search would be one of the several activities performed by, for example, NASA's $9.8 billion James Webb Space Telescope, expected to be unveiled late next year. And there will also be future ground-based megascopes, including the Massive Magellan Telescope performing such work.
In the new research, Kaltenegger and co-author Joshua Pepper, an associate professor of physics at Lehigh University, found Earth to be the target rather than the source of a transiting planet survey.
The researchers analyzed the TESS and European star-mapping Gaia spacecraft databases, checking for stars within 100 parsecs (about 326 light-years) associated with the ecliptic, the plane orbiting Earth around the sun. To see the Planet cross the face of the sun, some adjustments are necessary.
This search turned up 1,004 qualifying main-sequence stars that fuse hydrogen into helium in their centers, like our sun. And in a recent analysis released online in the journal Monthly Notices of the Royal Astronomical Society: Letters, Kaltenegger and Pepper wrote that 508 of those stars "guarantee a least 10-hour-long observation of Earth's passage" around the face of the sun.
New tool to search for E.T.
The latest findings deal with stars only. Scientists do not know how many planets flagged by Kaltenegger and Pepper circle the 1,004 suns, let alone how many of these structures harbor worlds that, as we know, might be conducive to existence.
As exoplanet hunters like TESS continue their mission, those figures should come into sharper view. And in the meantime and the future, the current research will serve as a signpost for astrobiologists, Kaltenegger said.
She added experts had just created the star map of where they should look first if they are looking for intelligent life in the universe that could find us and might want to get in touch.
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