1,004 Star Systems Can Directly See Earth—and So Can Their Aliens

Jennifer Leman
·4-min read

From Popular Mechanics

  • Astronomers search for transiting exoplanets, which zip in front of their stars and reveal clues about their atmosphere.

  • There are 1,004 stars in our galaxy that have a clear view of Earth's transit in front of the sun and could spot signs of life in our atmosphere.

  • Uh, we're waiting!

Since astronomers identified the first exoplanets in the 1990s, researchers have been scanning the distant worlds for signs of life. What if alien astronomers on these faraway planets are searching for us, too? And if they were, could they even see us?

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Now, researchers from Cornell and Lehigh universities have created a list of 1,0004 stars in distant galaxies that may have a clear view of Earth as it passes in front of the sun. All of these main-sequence stars, according to a statement from Cornell, lie within 300 light-years of Earth and may be home to untold numbers of exoplanets.

In Transit

Astronomers use the so-called "transit method" to hunt for distant exoplanets. As a planet crosses between Earth and its star, it causes a brief dip in that star's brightness. These temporary blips are picked up by planet-hunting telescopes like NASA's Kepler Space Telescope (RIP), Hubble Space Telescope, and Transiting Exoplanet Survey Satellite (TESS), as well as ground-based observatories like Chile's Extremely Large Telescope.

“Only a very small fraction of exoplanets will just happen to be randomly aligned with our line of sight so we can see them transit,” Lehigh astrophysicist Joshua Pepper said in the statement. “But all of the thousand stars we identified in our paper in the solar neighborhood could see our Earth transit the sun, calling their attention.”

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In recent years, observations of these far-off worlds have revealed stunning insight into the composition of their atmospheres and, in turn, shed light on their potential habitability. Some telescopes use spectroscopy to identify specific gas molecules in distance atmospheres.

In one such instance earlier this year, astronomers discovered that super-Earth K2-18b is shrouded in clouds of liquid water. Spotting traces of oxygen, methane, carbon dioxide, nitrogen, and other gases in these distant atmospheres could indicate they're ripe for life.

If any of the exoplanets surrounding those stars are home to advanced civilizations that are similarly scouring all corners of the universe for signs of life, there's a chance their telescopes could stumble upon our humble planet and detect the chemical signatures of life in our atmosphere.

Pepper and Kaltenegger, an astronomer at Cornell, used data from TESS and the European Space Agency's star-plotting Gaia satellite to develop the list of Earth-spotting stars. (It includes notables like GJ 357, which is home to GJ 357 d, a super-Earth just 31 light-years away.) The scientists published their findings in October's Monthly Notices of the Royal Astronomical Society.

Hot on Life's Trail

This could dramatically narrow the field in our own search for life on other worlds. If any exoplanets orbiting the stars on this list are found to be habitable, they're a shoe-in for further study. “If we’re looking for intelligent life in the universe, that could find us and might want to get in touch” Kaltenegger said, “we’ve just created the star map of where we should look first.”

Soon, TESS and Hubble will be joined by NASA's long-awaited James Webb Space Telescope. The $9.8 billion infrared telescope, which is scheduled to launch this spring after numerous delays, will devote a significant amount of time to peeling back the atmospheric layers of distant exoplanets.

There are other ways to sniff out life, too. Future Earth-based telescopes may soon be strong enough to pick up light sources on other worlds, National Geographic reports. If far-off civilizations are advanced enough, they may already have the technology to spot light emanating from our planet's bustling cities. Other technological clues, like our ever-expanding web of satellites, could capture the attention of extraterrestrial astronomers.

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