From the air, most of Greenland looks completely barren—a vast, frigid, inhospitable expanse of ice where nothing could possibly live. A closer look, however, shows that this isn’t true at all. The surface of the ice of Greenland is peppered with dark holes, ranging from a few inches to a few feet across, harboring self-contained micro-ecosystems that can host life in variety of different flavors, from red and green algae to cyanobacteria and the tiny organisms known as tardigrades and rotifers.
These so-called cryoconite holes are remarkable enough in themselves—but they could also play a crucial role in our search for potential life on, of all places, Mars. To understand why takes a bit of explaining.
Cryoconite itself is a mix of mineral dust, soot, ice algae, bacteria and other microorganisms that blows onto the icecap in Greenland and other frozen parts of the world; it was first described and named by the Finnish Arctic explorer Nils A. Nordenskiöld during his travels to Greenland in 1870. Because it’s dark and absorbs heat from the sun, cryoconite can accelerate the melting of the surface during summer. As the dark particles begin to coalesce, they can literally melt their way into the ice, creating cylindrical shaped holes that melt deeper and deeper as the sun warms their base until they’re too deep for sunlight to reach.
Melting catalyzed by cryoconite can add to Greenland’s contribution to global sea-level rise. For this reason, there has been growing interest within the scientific community in understanding how biological and mineralogical materials absorb and reflect light at different frequencies (that is, different colors), with the ultimate goal of factoring these processes into the models that simulate current estimates and future projections of Greenland’s melting.
Part of this work needs to be done on the ground: the spectral “fingerprints” collected on the surface can in theory be used in conjunction with satellite images to map the spatial and temporal evolution of cryoconite across wide swaths of territory from space. For obvious reasons, the more colors a satellite can collect within the electromagnetic spectrum, the more detailed its maps will be. It’s like the difference between a grainy or blurry photo and a sharp one.
Sensors that collect data in a relatively small number of spectral bands (up to a few tens) are called multispectral, while those collecting hundreds of bands are called hyperspectralsensors. Multispectral data are routinely collected over our planet but cannot properly be used for mapping cryoconite over Greenland, at least not yet. The acquisition and use of hyperspectral data are still crucial. Unfortunately, there is currently no satellite with a hyperspectral sensor orbiting the Earth, and previous space-based hyperspectral sensors were “turned on” only for specific periods and over selected areas.
Hence, despite the fact that we have now abundant and unprecedented measurements from the ground concerning spectral properties, we cannot benefit from them because of the paucity of spaceborne hyperspectral data. This problem has been recognized in the recently released 2018 Earth Science Decadal Survey, the goal of which is to help shape science priorities and guide NASA investments into the next decade.
Collecting spectrally rich data over our home planet is not only going to unveil undiscovered secrets and crucial processes that can tell us how our ice sheets will respond to climate change. It can also offer a tool to decipher the alphabet of life on other planets, like a Rosetta stone that is under our eyes and it is just waiting to be discovered. Contrarily to what happens on Earth, hyperspectral data is very abundant over Mars. The spatial and temporal coverage, as well as the spectrally dense nature of the Mars dataset, offer a unique opportunity to explore potential signs of life, such as cryoconite-analog ecosystems, by merging ground-based data from Earth with space-based data from the Red Planet.
The application of spectral fingerprints of cryoconite collected on Earth (now impossible to be collected on Mars) to the hyperspectral Mars data (not available on Earth) is not a new concept. Nevertheless, the data revolution that has occurred over the past few years offers a unique chance for a paradigmatic shift: today it is indeed possible to download and process huge volumes of data collected around Mars with a click on our laptops.
Moreover, our knowledge of processes on Mars has improved dramatically, allowing scientists to produce high-quality, robust, spectrally dense satellite maps with the same quality as those over the Earth. And lastly, recent improvements of our understanding of the ice sheets and their processes has promoted and catalyzed a collection of datasets focusing on the hyperspectral properties of ice and snow algae, bacteria and other bio-ecological systems that is unprecedented.
Continuing collecting in-situ data of cryoconite systems is, therefore, fundamental not only to studying the impact of biological activity on the potential sea level rise from Greenland but also to investigating the potential existence of life on Mars. By looking at our survival on this planet we also look into our chances to find places that other organisms already call home.
At the same time, we need to be able to study our planet from space as well as we do the Red Planet. Let us remember that looking into the microscopic world of life that strives on the ice of our planet and understanding the impact of anthropogenic activity on the Earth’s climate is not only a duty for ethical, societal and economic reasons but also an area of research that could unveil the mysterious secrets of life.