NASA Ames/JPL-Caltech/Tim Pyle via The New York Times

April 24, 2022

Astrobiologists Develop a “Color Catalog” to Identify Alien Life

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The Carl Sagan Institute at Cornell has revolutionized the way researchers think of space and its inhabitants by creating a  method of identifying extraterrestrial life: color cataloging. 

Color cataloging process involves analyzing pigments of microorganisms in extreme environments on Earth and recording the color they reflect when exposed to certain wavelengths of light. The colors — ranging from dark purples to vibrant greens — are cataloged in order to build a reference when analyzing the color reflections of other planet surfaces. 

“[Life] has different shapes, different colors, different organisms, different relationships between organisms, so it varies,” said Lígia Fonseca Coelho, an astrobiologist working with Prof. Lisa Kaltenegger, an astronomer and Director of the Carl Sagan Institute “[Catalogs] are one way…of trying to solve [this variation].”

Coelho and Kaltenegger are currently working on expanding upon a catalog they created which encompasses the colors a variety of microorganisms on Earth reflect, focusing specifically on the frigid microorganisms of the Hudson Bay in Canada. They are doing this by cataloging specific samples of life on Earth from specific types of environments, in order to add their signatures to a database. Kaltenegger explained that this database will act as a forensic toolkit that will help researchers find life in the universe, both inside and outside this solar system.   

According to Kaltegger, the procedure for analyzing microbiota was originally developed in 2015 at the Carl Sagan Institute. Coelho continued to help build upon the method in 2015 by helping to include microorganisms from frozen environments that were originally missing from the catalog. 

Coelho collected over 80 different biota from frozen environments. These are microorganisms that thrive in ice, mirroring some of the conditions seen in space. The microorganisms were then taken to Portugal to be identified, with the most vibrant ones being brought to the Carl Sagan Institute at Cornell. 

Coelho had discovered this vibrancy by accident. After leaving some collected microbiota on her bench, she noticed that they were exponentially more colorful than samples that were hydrated and observed. The moment of forgetfulness led to the monumental discovery that microorganisms displayed more vibrant pigments when exposed to more extreme conditions. From a more universal perspective, this information can be applied to studying possible extraterrestrial life on anything from icy exoplanets to extreme desert planets.

The biopigments that these microbes produce have big benefits. The first is that they are produced in situations of stress, so the colors can be predicted depending on the kind of environment the microorganisms would be inhabiting. The second is that their vibrancy allows them to be easily identifiable in these extraterrestrial environments.

“We are using Earth as our key to find life in the cosmos — it is the only place where we know life exists,” Kaltenegger said. “By using the diversity of life on Earth as our key we can start to search for it on other planets and moons.” 

On Mar. 15, Kaltenegger and Coelho recently published the paper, “Color Catalogue of Life in Ice: Surface Biosignatures on Icy Worlds” in the journal Astrobiology with some of these findings. “[We] asked if there is life that can strive in icy environments on Earth. If it can strive here, maybe it can evolve on frozen planets or icy moons somewhere else too,” Kaltenegger said. “[I]f it leaves a colorful imprint on frozen worlds, then we can spot it with the next generation of telescopes that will search for life in the cosmos.” 

Kaltenegger explained that these colorful frozen microorganisms on Earth are what lead to the conclusion of possibilities of other diverse forms of life evolving in a similar manner.

However, according to Coelho, while Earth is the only reference for what colors living things reflect in different environments, it is not a perfect system. Researchers have acknowledged that the planets explored may not match up exactly with the colors present in the catalog, but it can give them an idea of what to look for. 

Creating this reference has deepened the understanding of the colors that make up Earth, as well as how life on Earth can possibly be related to planets throughout the universe. “We have created the first spectra catalog of life that can survive and strive on frozen environments on Earth,” Kaltenegger said. “[We] have a key to find life on other frozen worlds in the cosmos.”