The hunt for caves on Mars has already begun.

The area is wild, and going there is bound to be expensive. But when humans finally make it to the Red Planet, one of the best options for shelter will be underground caves. These rocky hollows, found in swarms on both Earth and the Moon, are natural defenses against the harsh conditions of Mars.

In a presentation at this month’s Geological Society of America Communications 2022 meeting in Denver, researchers identified nine major cave candidates worthy of future exploration. All of these grottoes appear to extend at least some distance underground, and are close to accessible landing sites for a lightweight rover.

According to Nicole Bardabelias, a geoscientist at the University of Arizona, these structures could provide a respite from the harsh Martian environment. “Anything on the surface can be hit by heavy radiation, a meteorite or a micrometer bomb, and it has really big day-to-night temperature swings,” she says.

To home in on the most desirable real estate on Mars, Ms. Bardabelias and her colleagues consulted the Mars Global Cavern Candidate Catalogue. This summary, based on images collected by instruments aboard the Mars Odyssey spacecraft and the Mars Reconnaissance Orbiter, shows more than 1,000 candidate caves and other features that appear unique on Mars. (Think of it as the first multi-spec service for Mars.)

As any savvy home buyer would sift through the search results of Zillow or StreetEasy, the researchers narrowed down the catalog by applying two criteria. First, they called for a cave-friendly spaceship landing site 60 miles away. Second, they require high-quality images to be available.

Ms. Bardabelias and her colleagues determined that an ideal landing site is below an elevation of 3,300 feet. Such relatively low landings are convenient because they give the spacecraft more time to slow down as they travel through Mars’ thin atmosphere, Ms. Bardabellis said.

“Mars has enough of an atmosphere that you can’t slow it down, but not enough to give you significant amounts of aerobraking,” she said of using the planet’s atmosphere to slow down an incoming spacecraft. “If you don’t have enough space between when you hit the top of the atmosphere and where you need to land, it’s going to be very, very difficult to get the entry, descent and landing sequence right.”

The team requested top-shelf images for each cave candidate. That honor goes to the HiRISE, or High Resolution Imaging Science Experiment, camera on the Mars Reconnaissance Orbiter, unless brokers agree to use NASA’s Mars helicopter to photograph Martian real estate. Ms. Bardabelias is the lead operations engineer for HiRISE, which can detect features on Mars up to 3 feet away but has so far imaged less than 5 percent of the planet’s surface.

There were 139 clear tunnels that met the team’s criteria, and Ms. Bardabelia and her colleagues examined each image by hand. After disregarding non-cave features such as bridge-shaped rock formations, the team analyzed the crater-like features that remained. The researchers found only what appeared to be some distance underground, sampling nine major cave candidates.

These potential tunnels, the largest of which has an opening that could swallow a football field, are all worth a closer look, Ms Bardabellis said. But none of the rovers currently operating on Mars are strong enough to explore these tunnels, so that task falls to spacecraft currently orbiting the Red Planet. Subsequent HiRISE images taken from different angles and under different lighting conditions will reveal new details about these caves, Ms Bardabelia said. You can help the HiRISE team decide what to photograph next by voting for your favorite cave.

A space scientist at the US Geological Survey’s Center for Astrogeological Sciences and the creator of the Mars Global Cave Candidate Catalog said that it is appropriate that we look for caves for shelter as we prepare to explore new worlds. Involved in research. “All this leads us to the dawn of humanity.”

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