NASA has announced a new approach to the agency’s search for alien life on exoplanets, which involves trees’ shadows. The question of whether alien life exists somewhere out there has concerned scientists and philosophers for millennia, without any major progress so far.
Still, with the finding of more than 4,200 exoplanets and counting, the rush is on to verify whether complex, non-technical alien life actually exists in these faraway worlds. With the latest developments of telescopes able to directly view these planets, Northern Arizona University scientists are trying to use a new method to answer this question.
Multicellular Life on Exoplanets
The NASA-funded researchers have created a new interesting technique to determine whether basic life forms can be identified on exoplanets. To do so, the scientists turned to the shadows of one of Earth‘s most common multicellular life forms – trees.
Professor Chris Doughty, the lead author of the new study, explained: “Earth has more than three trillion trees, and each casts shadows differently than inanimate objects. If you go outside at noon, almost all shadows will be from human objects or plants, and there would be very few shadows at this time of day if there wasn’t multicellular life.”
The scientist suggests plenty of upright photosynthetic, multicellular life, such as trees, will throw shadows at high Sun angles; this, he believes, will likely differentiate them from single cellular life. Therefore, space telescopes will soon capture the kinds of shadows cast and should hypothetically determine whether there are similar life forms on exoplanets.
University of Arizona Ph.D. student Andrew Abraham, who took part in the research, said: “The difficult part is that any future space telescope will likely only have a single pixel to determine if life exists on that exoplanet. So, the question becomes: Can we detect these shadows indicating multicellular life with a single pixel?”
With only one pixel to work with, the researchers had to make sure any shadows observed by these telescopes were actually multicellular life, and not other structures, such as craters. Drones were used at various times of the day to determine whether craters did cast shadows differently to trees.
Shadows Viewed Through a Single Pixel
The scientists included high-tech imaging methods to confirm whether their theory would work on a large scale. By employing the Polarization and Directionality of Earth’s Reflectance (POLDER) satellite, the team was able to see the shadows on Earth at different Sun angles and times of the day.
The researchers also decreased the resolution to mimic how our planet would look like as a single pixel to an alien spectator as it orbits the Sun. Then, they compared this to data collected from Mars, Venus, and Uranus to see if Earth’s multicellular life was different.
They learned that the regions of the planet where trees grow in abundance, such as the Amazon forest, could be differentiated as multicellular life. However, when they observed Earth as a whole and a single pixel, distinguishing multicellular life was incredibly difficult.
Still, the potential for watching shadows could be a step closer to the answer than researchers have been before. Doughty said that the method remains valid in theory, and a future space telescope could manage to rely on the shadows found in only one pixel.
“If each exoplanet was only a single pixel, we might be able to use this technique to detect multicellular life in the next few decades,” he said. “If more pixels are required, we may have to wait longer for technological improvements to answer whether multicellular life on exoplanets exists.”
