Researchers at Northern Arizona University have proposed an innovative method to detect multicellular life on exoplanets: analyzing the shadows cast by trees. Published in the International Journal of Astrobiology on October 1, 2020, this hypothesis explores a promising new avenue in astrobiology.
The TESS satellite concluded its primary two-year mission in August 2020, contributing to two-thirds of the more than 4,200 exoplanets discovered to date. Despite these achievements, no signs of extraterrestrial life have been confirmed. The Northern Arizona University team suggests focusing on vertical photosynthetic multicellular life, such as trees, which cast distinctive shadows at high solar angles—differentiating them from single-celled organisms.
To validate their approach, the researchers modeled Earth as an exoplanet, home to about 3 trillion trees. These trees produce unique shadows unlike those from inanimate objects, based on the premise that abundant multicellular life would likely be vertical and photosynthetic.
Challenges remain in detecting these shadows remotely, especially since future telescopes may resolve exoplanets as just a single pixel. Using data from the CNES Polder instrument, the team analyzed Earth's cloud, aerosol, and tree shade patterns throughout the day, simulating one-pixel resolution. This method successfully distinguishes multicellular life signatures in higher-resolution scenarios but proves difficult at single-pixel scales.
The researchers emphasize the need for further studies to refine this technique for reliable use. While preliminary, it underscores the potential of tree shadows in the search for extraterrestrial life. Upcoming telescopes with higher resolution could provide the pixels needed to lend greater credibility to this approach.
