The question of whether alien life exists has preoccupied philosophers and scientists for millennia, without any significant progress so far in finding an answer. However, with the discovery of more than 4,200 exoplanets and counting, the race is on to test whether complex, non-technological alien life really exists on these distant worlds.
But with the latest next generation of telescopes capable of directly viewing these planets, a team of Northern Arizona University researchers are attempting a novel approach to this question.
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 NASA-funded scientists have developed an intriguing new technique to determine whether basic forms of alien life can be detected on exoplanets.
To do so, the researchers turned to the shadows of one of Earth’s most common multicellular life forms — trees.
Professor Chris Doughty, lead author of the landmark new study, said in a statement: ”Earth has more than three trillion trees, and each casts shadows differently than inanimate objects.
NASA news: The space agency has turned to trees in their exoplanet alien life search
NASA news: The researchers turned to the shadows in their search for alien life
“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 researchers suggest abundant upright photosynthetic multicellular life – such as trees – will cast shadows at high sun angles.
This, the researchers believe, will probably distinguish them from single cellular life.
As a result, space telescopes will soon observe the types of shadows cast should theoretically determine whether there are similar life forms on exoplanets.
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University of Arizona PhD student Andrew Abraham, also involved 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?”
But with only one pixel to work with, the scientists had to ensure any shadows spotted by these telescopes were definitely multicellular life, not anything else, such as craters.
Professor Trilling said: ”It was suggested that craters might cast shadows similar to trees, and our idea would not work.
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“So, we decided to look at the replica Moon landing site in northern Arizona where the Apollo astronauts trained for their mission to the Moon.”
Drones were used at different times of the day to confirm whether craters really did cast shadows differently to trees.
The researchers incorporated cutting-edge imaging techniques to confirm whether their theory would work on a large scale.
By using the Polarization and Directionality of Earth’s Reflectance (POLDER) satellite, the researchers were able to see whether the shadows on Earth at different sun angles and times of the day.
Earth has more than three trillion trees
They also reduced the resolution to replicate how our planet would look like as a single pixel to an alien observer as it rotates around the Sun.
Then, the team compared this to related data from red planet Mars, the Moon, Venus and Uranus to see if Earth’s multicellular life was unique.
They learnt areas of Earth where trees were in abundance, such as the Amazon, multicellular life could be distinguished.
When it came to observing Earth in its entirety as a single pixel, distinguishing multicellular life was extremely difficult.
However, the potential for observing shadows could be closer than scientists have ever been before.
Doughty believes the technique remains valid in theory—a future space telescope could rely on the shadows found in a single 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.”