A new scientific technique developed by a team of University of Hawaii astronomers may help in the search for life in the planetary system closest to ours, and maybe beyond.
Led by Svetlana Berdyugina, a visiting scientist at the UH NASA Astrobiology Institute, the team has found a way to detect life forms through reflected light using polarizing filters — similar to Polaroid sunglasses or 3-D movie goggles — even in the glow of a star millions of times brighter than a planet.
The findings, published in the International Journal of Astrobiology, were presented last week at the International Astronomical Union General Assembly in Honolulu.
Scientists from the University of Hawaii are Jeff Kuhn, David Harrington and John Messersmith. Berdyugina is from the Institute of Physics of the University of Freiburg and the Freiburg Kiepenheuer Institute for Solar Physics.
In their research, the team developed a method of detecting life as we know it in photosynthetic pigments, which offer a unique signature in the light they reflect.
The scientists measured different biological photosynthetic pigments in the laboratory. These biopigments absorb almost all solar light of specific colors in the visible spectrum and convert it into chemical bonds to store energy. Chlorophyll pigments, for example, absorb blue to red light and reflect a small part of green in the visible, as seen in green plants.
The scientists found that the part of visible light reflected by plants oscillates in certain directions, while other light oscillates in all directions. Due to this phenomenon, the reflected light can be seen remotely using polarizing filters, with each biopigment having its own colored mark seen in polarized light.
“Indeed, we can detect colors as we measure really a spectrum of polarized light,” Berdyugina said. “We can distinguish liquid water and (photosynthetic pigments, such as those found in plants). They differ by both color and polarization. For instance, ocean is blue because it reflects the sky and its polarization is almost color-independent. Biopigments have particular color and polarization associated with this color.”
Berdyugina’s team was the first to detect reflected light from an exoplanet — a planet in a different solar system — using polarization in 2008, and they were able to improve the detection in 2011.
“So we are confident (the new technique) works well, and it will help to see photosynthetic life on other planets,” she said.
Given the limitations of existing telescopes, the team has its sights set on discovering life in Alpha Centauri, the planetary system nearest to the sun, the scientist said.
There are three stars in the Alpha Centauri system, the closest being only 4.37 light years from earth.
In 2014, a small planet was discovered around Alpha Centauri B, one of the stars, but it is too hot and too close to its sun to sustain life.
Berdyugina said her team is hoping to find more planets within the habitable zones of the three Alpha Centauri stars, while looking for signals of both atmosphere and surface reflection by biopigments, ocean and more.
“We are ready to detect this kind of life if it exists,” she said. “We will first use telescopes and detectors which are available now and test our luck with Alpha Cen. If there is no life there, we definitely want to go for other systems, and then we will need bigger telescopes.”
There are three extremely large telescopes either under construction or in the development stages right now, including the Thirty Meter Telescope planned for the top of Mauna Kea.