Smile, wave: Some exoplanets may be able to see us, too

Date:
October 21, 2020
Source:
Cornell University
Summary:
Three decades after astronomer Carl Sagan suggested that Voyager
1 snap Earth's picture from billions of miles away - resulting in
the iconic Pale Blue Dot photograph - two astronomers now offer
another unique cosmic perspective: Some exoplanets - planets
from beyond our own solar system - have a direct line of sight to
observe Earth's biological qualities from far, far away.



FULL STORY ========================================================================== Three decades after Cornell astronomer Carl Sagan suggested that Voyager
1 snap Earth's picture from billions of miles away -- resulting in the
iconic Pale Blue Dot photograph -- two astronomers now offer another
unique cosmic perspective: Some exoplanets -- planets from beyond our
own solar system - - have a direct line of sight to observe Earth's
biological qualities from far, far away.


==========================================================================
Lisa Kaltenegger, associate professor of astronomy at Cornell University
and director of Cornell's Carl Sagan Institute; and Joshua Pepper,
associate professor of physics at Lehigh University, have identified 1,004 main-sequence stars (similar to our sun) that might contain Earth-like
planets in their own habitable zones -- all within about 300 light-years
of Earth -- and which should be able to detect Earth's chemical traces
of life.

The paper, "Which Stars Can See Earth as a Transiting Exoplanet?" was
published in the Monthly Notices of the Royal Astronomical Society.

"Let's reverse the viewpoint to that of other stars and ask from which
vantage point other observers could find Earth as a transiting planet," Kaltenegger said. A transiting planet is one that passes through the
observer's line of sight to another star, such as the sun, revealing
clues as to the makeup of the planet's atmosphere.

"If observers were out there searching, they would be able to see signs
of a biosphere in the atmosphere of our Pale Blue Dot," she said, "And
we can even see some of the brightest of these stars in our night sky
without binoculars or telescopes." Transit observations are a crucial
tool for Earth's astronomers to characterize inhabited extrasolar planets, Kaltenegger said, which astronomers will start to use with the launch
of NASA's James Webb Space telescope next year.

But which star systems could find us? Holding the key to this science
is Earth's ecliptic -- the plane of Earth's orbit around the Sun. The
ecliptic is where the exoplanets with a view of Earth would be located,
as they will be the places able to see Earth crossing its own sun -- effectively providing observers a way to discover our planet's vibrant biosphere.

Pepper and Kaltenegger created the list of the thousand closest stars
using NASA's Transiting Exoplanet Survey Satellite (TESS) star catalog .

"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." Pepper
said. "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." "If we found a planet with a vibrant biosphere, we would
get curious about whether or not someone is there looking at us too," Kaltenegger said.

"If we're looking for intelligent life in the universe, that could find
us and might want to get in touch" she said, "we've just created the
star map of where we should look first." This work was funded by the
Carl Sagan Institute and the Breakthrough Initiative.


========================================================================== Story Source: Materials provided by Cornell_University. Original written
by Blaine Friedlander. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. L Kaltenegger, J Pepper. Which Stars Can See Earth as a Transiting
Exoplanet? Monthly Notices of the Royal Astronomical
Society: Letters, Volume 499, Issue 1, November 2020 DOI:
10.1093/mnrasl/slaa161 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201021140931.htm

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