Life within Ice

A beautiful shot of micro-penitentes on Mt Rainier near Seattle, WA as photographed by Mark Sanderson in 2006 ( CC3.0, license and original file and description here ). What I love about this image is the lack of anything familiar that could indicate the scale of the features - aside from the notes from the photographer. They could be cm across or km! This is a familiar feeling from looking at images that come back from spacecraft that challenge our preconceptions. Today, PhD student Giang reflects on his recently published work trying to understand whether such textures could arise on Mars and if so, how big would they be and in what directions would they be orientated? Such models are needed to help us interpret what we see.

By Giang Nguyen

Perhaps it’s a mental coping mechanism from the summer heat, but I’ve been thinking a lot about ice. The behaviour of water ice across the solar system is studied by many people in the PVL group, and I am no exception. I’ve been looking at how water affects the atmosphere since my undergrad where I studied terrestrial weather systems. Later, the work for my Master’s consisted of surveying the icy conditions of the Martian north polar cap to look for surface-atmosphere interaction. Finally, with my PhD well on its way, I’ve been tasked with studying the atmospheric conditions of possible icy worlds beyond our solar system.

As you might guess, water is somewhat an important volatile for the propagation of life on Earth. Since there isn’t another planetary body within the solar system that is like Earth, it is helpful to look at the most extreme conditions Earth has to offer for clues. From my introductory paragraph, you’re probably thinking that I’m going to talk about Earth’s arctic polar conditions but that won’t be the case. The geography of interest here is actually high-altitude deserts, chiefly the Atacama desert located within South America’s Andes mountains.



The dry environment of alpine regions accompanied with strong constant solar radiation through a thinner atmosphere makes the highland deserts a difficult place for life to thrive. These conditions make the Atacama desert comparable to the Martian surface. Studying life in these harsh conditions may provide insight not just for the possibility of life on Mars but across icy worlds yet to be explored.

Alpine regions in the mid-latitudes host interesting ice structures called penitentes where light reflection within a snow/ice field sublimates the icy surface in a certain pattern. This sublimation pattern creates uniform jagged ice-blades with strong consistency in spacing and direction. A recent study done by researchers at the University of Colorado in Boulder found snow algae in penitentes on Volcán Llullaillaco (https://doi.org/10.1080/15230430.2019.1618115). The red-coloured algae are able to survive in the barren environment of the Andes highlands despite high UV flux. The penitente structure can shelter the algae from solar radiation and temperature fluctuation that would otherwise hamper the algae’s survivability. The sublimation of ice also provides the necessary moisture for these orgnanisms to stay alive.

I’ve studied penitentes extensively where I worked to simulate their formation on Mars (https://doi.org/10.1016/j.pss.2019.05.003). Under the Martian sky, my research showed that penitentes can grow cumulatively year-round from 60o N to the South Pole (Fig. 1) with a spacing of about 25 m. The asymmetry between the north and south hemisphere lies in the fact that dust activity is more prevalent in the south which affects penitente growth through atmospheric scattering. While penitente formation is possible on Mars, no one has been able to find these features on the Martian surface.

Fig 1: Plot shows the favourable penitente growth conditions throughout a year with respect to latitude through a “differential heating factor”. A differential heating factor of above 1 implies penitente growth. The red lines indicate preferred penitente direction with horizontal lines being East-West and vertical lines being North-South.

The polar region of Mars is the best place to look for penitentes because of the availability of water ice. However, due to the low sun elevation in the poles, it is difficult for penitentes to form. Ice in the Martian mid-latitudes generally exists as a thin layer buried underneath the current Martian surface. With recent explorations into this topic, researchers at the U.S Geological Survey have found exposed subsurface ice at various location on Mars (https://doi.org/10.1126/science.aao1619). This, of course, is great for possible Martian penitente growth as the high elevation of low latitude sun creates better conditions for penitentes to form. This, in turn, can expand possible environments for microbial life to survive on Mars.

The prospect of penitentes sheltering microbes from extreme weather conditions is a new and exciting discovery that affects how we might look for life on other planets. With this newly discovered exposed ice in the Martian mid-latitudes, Martian penitente growth is no longer limited to the poles which gives us more places to look for penitentes. Possible penitente fields on Mars could become an oasis for simple organisms or even a place where we might search for biosignatures in an otherwise harsh and barren world. Ultimately, this can extend our search for life beyond Mars where we can direct our curious gaze onto ice-covered planetary bodies that inhabit the great emptiness we call space.