The search for life on other planets is fascinating, challenging and enlightening. University of Hawai‘i researchers and their partners are trying to find signs of life in a planetary system only a few light years away from Earth, as reported by UH last week.
A green leaf absorbs almost all red, green and blue light (RGB), but it reflects and transmits infrared light (shown in grey). The reflected infrared light is only weakly polarized due to the reflection of a healthy leaf, but the reflected RGB light is strongly polarized due to biopigments. Measuring the amount of polarized light at different colors reveals the signature of the leaf biopigments. Green sand reflects and polarizes sunlight almost equally in all wavelengths, which distinguishes it from a leaf that is a similar color. Similarly, yellow plants are different from yellow sand, etc. Credit: S. Berdyugina
New technique finds photosynthetic biopigment signatures
The team has measured various biological photosynthetic pigments in the laboratory. They absorb almost all solar light of specific colors in the visible and convert it into chemical bonds to store energy. For example, chlorophyll pigments absorb blue to red light and reflect a small part of green in the visible, as seen in green plants. All infrared light is reflected, and this is employed in agriculture to monitor water content in crops.
The scientists have found that the part of visible light reflected by various plants with vibrant colors oscillates in certain directions, while incident light oscillates in all directions. Thanks to this peculiarity, this reflected light can be detected remotely by using polarizing filters (similar