What Are Nieves Penitentes? The Strange Icy Spikes Found In Some Of Earth’s Most Alien Landscapes

If you’re lucky enough to go hiking in South America’s Andes Mountains, you just might spot a strange weather phenomenon known as nieves penitentes (Spanish for “penitent snows”), so named for their resemblance to the pointed headwear of Christianity’s Holy Week penitents.

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It’s the curious result of differential ablation as hollow areas of snow catch the Sun and sublimate into gas, while spiky areas less exposed to the light endure even after the rest of the snow has gone. They’re found at elevations exceeding 4,000 meters (13,123 feet) and can grow anywhere from a few centimeters to over 5 meters (16.4 feet).

Nieves penitentes appear as sharp, spiky protrusions reminiscent of the white hats worn by penitents during penance. Their name may have human origins, but their appearance is entirely otherworldly, transforming landscapes into something you’d expect to see on an alien planet, and with good reason.

At the highest elevations of the Andes, conditions are desert-like with the extremes of aridity, solar radiation, and temperature fluctuations. It’s considered a good analog for studying Mars-like soils on Earth, which it was why it was so intriguing when we found life on penitentes.

In 2018, we learned for the first time that nieves penitentes are an important habitat for snow algae. Using molecular and microscopic approaches, a study found that red patches of penitentes ice contained algae from the genera Chlamydomonas and Chloromonas, and that the surrounding soil hosted more complex bacterial and eukaryotic communities. Big news for Earth, and beyond.

“In this environment penitentes provide both water and shelter from harsh winds, high UV radiation, and thermal fluctuations, creating an oasis in an otherwise extreme landscape,” wrote the authors. “Intriguingly, recent planetary investigations have suggested the existence of penitente-like structures on other planetary bodies of our solar system. Therefore, penitentes and the harsh environment that surrounds them provide a new terrestrial analog for astrobiological studies of life beyond Earth.”

And as for what that life might look like? It's a good question.