penitentes Penitentes in front of the Atacama Large Millimeter/submillimeter Array telescope and the Licancabur volcano in northern Chile. European Southern Observatory/Flickr

If you, like me, are in the northern hemisphere, any kind of snow may seem a bit like a mirage right now.

But the strange formations known as penitentes are wacky enough they may make you question what you're seeing even when you're expecting snow.

Penitentes are spikes of snow that form typically only in high-altitude areas, like Chile's Atacama Desert. They can get as tall as 20 feet in the right conditions. Their name comes from their resemblance to a group of monks who wear spiky hats.

And they've been around for a while. In fact, Charles Darwin wrote about them, saying:

"These frozen masses, during the process of thawing, had in some parts been converted into pinnacles or columns, which, as they were high and close together, made it difficult for the cargo mules to pass."

When they aren't getting in Darwin's way, penitentes have been stumping the scientists who have tried to understand how they form. But there's finally a theory that seems pretty plausible. It replaces a guess that wind shaped the spikes.

penitentes ice formations ESO/Wikimedia Commons

It's easy to think a sheet of freshly fallen snow is flat, but it turns out there are small dips and dimples from the start. These actually concentrate sunlight, heating the snow more quickly. And where penitentes form, it's actually so dry that heat vaporizes snow directly to steam. The process eventually hollows out spaces between the spikes.

According to the latest version of the theory, the distance between spikes in any given area is pretty standardized because it's determined by wind speed. The more wind there is, the more water vapor is carried away, letting more snow be vaporized in its place and creating deeper troughs between spikes.

And penitentes may not be limited to Earth: Scientists think they may also exist on Europa, the icy moon of Jupiter that's currently one of the most likely candidates for housing alien life.

You can watch timelapse footage of penitentes forming and melting here: