How can they actually figure that out? According to some experts, there are theories that abundant upright photosynthetic multicellular life, a.k.a trees, will form shadows at high sun angles that will make them distinguishable from single cellular life. Researchers can test and have tested this concept using Earth as an exoplanet.
First, the experts planned to test the notion using Unmanned Arial Vehicles (UAVs) at a duplicated Moon landing site close to Flagstaff, Arizona, and show the fact that trees have both a unique reflection signature, which is a red edge, as well as a geometric signature – the shadows at high sun angles – that can differentiate then from replica Moon craters.
The following step involved the measurement of reflectance signatures for Earth at various phase angles using the POLDER, or Polarization and Directionality of Earth’s reflectance satellite directional reflectance ranges, and then mitigate Earth to only one pixel.
More Research is Needed
According to researchers, they had to compare Earth to other planetary bodies, such as Mars, the Moon, Venus, and Uranus, and come up with the best theory regarding Earth’s directional reflectance, which needs to be between powerfully backscattering rocky bodies with no weathering, similar to Mars and the Moon, and cloudy objects with more isotropic scattering, like Venus and Uranus.
The modeling outcome has Earth in parallel with powerfully backscattering Mars, and the empirical results put our planet in line with more isotropic scattering, Venus. This means that both the modeled and empirical results had to have potential flaws.
The team of researchers that carried out this simulation suggested additional phases be added to the tests, that can eventually determine whether this method could actually distinguish upright multicellular life on exoplanets.