Was Mars ever a living world? Billions of years ago, before it became a freeze-dried desert, the Red Planet looked much more like Earth, with liquid water and mild temperatures on its surface. Perhaps it also harbored life. But most signs of ancient Martians are now just traces of organic compounds and faint fossil forms hidden in the planet’s rusty rocks.
Scientists today use robots to study this arid landscape, remotely guiding their search for life through a combination of satellite images and ground snapshots from the rovers and landers themselves. Such imagery, however, leaves much to be desired – for all but the closest views, rocks lacking biosignatures versus those teeming with fossilized microorganisms can be nearly indistinguishable. However, in a study recently published in Scientific reportsa team led by researchers from the University of Hawaii has shown a possible shortcut to finding the most promising targets for astrobiological tracking, whether on the Red Planet or on another world elsewhere in the solar system.
The technique is based on a curious fact of biology – terrestrial biology, anyway: in the many kingdoms of life, all kinds of organisms produce pigments, proteins, lipids and other molecules that emit a glow indicator – fluorescence – when excited by certain wavelengths of light. . Using carefully tuned laser pulses on millions of years old fossiliferous rocks from Colorado, Wyoming and Utah’s Green River Formation, researchers have demonstrated that such “biofluorescence” can be a way efficient way to quickly and efficiently flag candidate biological material for more detailed examination. Their prototype instrument, dubbed Compact Color Biofinder, is sensitive enough to detect the presence of biofluorescent materials up to five meters away, even in daylight, and can project the laser pulses over a large target area, allowing vast expanses of territory. quickly investigated.
According to the team members, this unique daytime sensitivity makes the Biofinder, which has been in development for a decade, a particularly attractive option for searching for remnants of ancient life. The capability comes from the instrument’s camera, which captures brief exposures of targets. “When you have a camera that opens for a short time, you don’t see daylight,” says Anupam Misra, a researcher at the University of Hawaii and lead author of the paper.
Another notable strength of the instrument is its – so to speak – agnostic attitude towards life detection. While other labs looking for extraterrestrial life can target the most detailed components of life as it appears on Earth, such as certain DNA sequences common to single-celled organisms that thrive in extreme environments on our planet, the Compact Color Biofinder takes a much more general approach. approach. All he’s looking for are compounds that fluoresce when stimulated by laser pulses. On Earth, all living organisms possess aromatic amino acids, usually as a byproduct of metabolic processes. All aromatic amino acids show fluorescence. Given the ubiquity of fluorescent amino acids in life, the researchers surmised that even if life on other planets does not use the exact amino acids found on Earth, they can still detect it as long as it emits a fluorescence. “If there is life on Mars and it’s not ‘life as we know it,’ then the Biofinder may be the only way to see it,” says co-author study Christopher McKay, an astrobiologist and planetary scientist at NASA’s Ames Research Center.
One of the challenges is that amino acids and biological compounds aren’t the only materials on Earth that emit light when stimulated by lasers. Abiotic minerals also emit their own light, called phosphorescence. It can be confused with biofluorescence, but the team built the Biofinder from the start to distinguish between these two very different phenomena. In general, phosphorescence signals last much longer than their fluorescent counterparts, allowing the Biofinder to distinguish between them.
Although McKay suggests the Biofinder might be the best bet for uncovering ancient remains of unknown lifeforms on Mars, that doesn’t mean the instrument would provide the final say in figuring out what exactly it had filmed. “You can look at a pie, but tasting it gives you a lot more information about it,” he says.
Any samples illuminated by the Biofinder would then have to be “digested” in analytical lab instruments so scientists could better understand what they found, McKay says. But where he finds the general nature of the Biofinder a plus, Patrick Gasda, a researcher at Los Alamos National Laboratory, sees the lack of specifics as the main drawback of the approach. Gasda worked on SuperCam, an instrument aboard the Mars Perseverance rover. SuperCam sifts through the rock and soil of Mars using laser spectroscopy, bathing targets in highly focused beams of laser light to gather more specific information about the underlying chemical composition. “You could see if there’s carbon and nitrogen,” he says. But even spectroscopy is not the same as a real digestive analysis. “You would probably want to take a sample of it” for more direct rather than remote study, he says.
Although he was not involved in the most recent study, Gasda worked on the Biofinder in 2012 while pursuing his doctorate. as a student of Misra at the University of Hawaii. Currently, Gasda is working with Misra on a version of the Biofinder called OrganiCam. Like the Biofinder, OrganiCam uses laser-induced fluorescence imaging to spot signs of life. But it adds a chemical analysis technique called Raman spectroscopy, which uses a laser to determine the molecular composition of the target. Like the Biofinder, the OrganiCam is not yet ready for spaceflight. In addition to having to be miniaturized to fit on a lander, Gasda says, both instruments also require more robust cases and microcircuits to enable them to withstand rocket launches, planet crashes and the deleterious effects of cosmic radiation. .
While the Biofinder can offer revolutionary applications for space exploration one day, it might be of more immediate use right here on Earth for searching for life in extreme – and possibly extremely delicate – environments. As an example, McKay cites caverns filled with giant gypsum crystals buried deep in a mountain range in Mexico. Exotic lifeforms can comfortably exist in crystals, he says, but the only way to check right now would be to open them up and look inside. “Sacrilege!” McKay said. “There must be a better way.” With something like the Biofinder, researchers could instead subject these crystals to less invasive probes.
Whether on Earth, Mars, or an entirely different world, says McKay, “the central idea from my perspective is being able to understand the biology of a target without chipping, drilling, or sampling.”
