Why NASA Scientists are now interested in this U.S. National Park.

Most of us know NASA primarily for their missions in space exploration; most notably their current Mars Exploration Program. This program has continued to be a long-term effort of robotic exploration of the Red Planet. The Mars Perseverance rover has been crawling along the surface of our neighboring planet for years; collecting samples, and data for the larger goal of answering key questions about the potential for life on Mars. The rover mission takes the next step by not only seeking signs of habitable conditions on Mars in the ancient past, but also searching for signs of past microbial life itself.

So, if NASA is so concerned with what’s on Mars, why are their scientists now looking at Wind Cave National Park in South Dakota?

First, let’s descend into Wind Cave for a bit. This Park in South Dakota was the seventh to be established, and the first cave to be designated a national park anywhere in the world. Thank Teddy Roosevelt for that one. It’s a park that is commonly overlooked being in the shadow of the Black Hills and Mount Rushmore. Though the park protects one of the largest and most complex cave systems in the world, and above the surface, Wind Cave protects one of the last remaining prairie habitats in North America. Today, it is one of the best places on the continent to experience the mixed-grass prairie. Bison are a common sight here, grazing and wallowing among prairie dog towns.

Below the prairies, Wind Cave is an intricate maze of 150 miles of labyrinths, making it one of the largest in the world. However, Wind Cave is not like any other cave in the world. It is a true standout. You might expect to find stalagmites and other common save geologic formations, but not in Wind Cave. This cave was formed in a truly unique way.

A warm shallow sea covered the area about 350 million years ago. Fragments of seashells, eventually became limestone. Bodies of gypsum also formed during this time when arid conditions caused seawater to evaporate and the minerals to crystallize.

Naturally acidic freshwater pouring in dissolved the limestone leaving behind the first cave passages.

These ancient seas continued to advance and retreat over the area for the next 240 million years. Water did not flow through the cave like a river. Instead, the water probably sat in the limestone for long periods of time, slowly enlarging small cracks into larger passageways, creating Wind Cave’s complex maze-like pattern.

Today the water level is about 500 feet below the surface at a hidden area known as "the Lakes."

The result of this process didn't create common cave formations. Instead, an incredibly rare geologic formation occurs within Wind Cave. It’s known as boxwork: a kind of crystallization or honeycomb effect on the cave ceilings that’s truly mesmerizing. The features are what’s left after erosion.

Boxwork formations in Wind Cave
Boxwork formations in Wind Cave

Boxwork is so rare, in fact, that 98% of it is found only in Wind Cave. A small percentage is found in the nearby Jewel Cave in South Dakota, and just a small bit in a cave in Ukraine.

The other boxwork formations that we know about don’t occur on Planet Earth.

Indeed the Mars Rover discovered the same boxwork geologic structures on Mars.

Now NASA scientists have been studying Wind Cave’s geology looking for clues and correlations as to how water might have shaped these same structures on Mars. The existence of these formations on Mars, at the very least, suggests that water activity was at one point intermittently stable over a long period of time on Mars. Additionally, the amount of water required to create such large structures must have been enough to create at least part of the elements needed for a habitable environment.

There is still much to be learned about the geology of both Wind Cave and Mars, and this discovery raises more questions than it answers. Perhaps by studying both the boxwork on Earth and Mars, NASA scientists can puzzle together the timeline of both water and possible life on Mars.

Boxwork formations found on Mars
Credit: NASA/University of Arizona/JPL-Caltech.