The neighborhood is a joker, and settling there is necessarily expensive. But one of the best options for shelter when humans finally arrive on the Red Planet will be underground caves. These rocky hollows, which exist en masse on Earth and the Moon, are natural buffers against the harsh conditions of Mars.
In a presentation this month at the Geological Society of America Connects 2022 meeting in Denver, researchers identified nine prime candidate caves worthy of future exploration. All of these caves appear to extend at least some distance underground, and they are close to landing sites accessible to a light rover.
These structures would provide respite from the harsh Martian environment, said University of Arizona geoscientist Nicole Bardabelias. “Anything on the surface is subject to strong radiation, possible bombardment from meteorites or micrometeorites, and very large temperature variations between day and night,” she said.
To settle in the most sought-after real estate in Mars, Ms. Bardabelias and her colleagues consulted the Mars Global Cave Candidate catalog. This compendium, based on images collected by instruments aboard the Mars Odyssey spacecraft and the Mars Reconnaissance Orbiter, lists more than 1,000 candidate caves and other special features on Mars. (Think of it as the first Martian multiple listing service.)
Just as any savvy homebuyer would filter search results on Zillow or StreetEasy, the searchers narrowed the catalog by imposing two criteria. First, they required a cave to be about 60 miles from a suitable spacecraft landing site. Second, they stipulated that high resolution images be available.
Ms. Bardabelias and her collaborators defined a suitable landing site as one below an elevation of about 3,300 feet. These relatively low spots are favorable landing sites because they give spacecraft more time to slow down as they travel through Mars’ thin atmosphere, Bardabelias said.
“Mars has just enough atmosphere that you can’t ignore it, but not enough to give you a significant amount of aerobraking,” she said, referring to the atmosphere’s use of a planet 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’re supposed to land, it’s going to be very, very difficult for you to do the entry sequence right, to descent and landing.
The team also required that first-order images be available for each candidate cave. Until brokers appropriate NASA’s Mars Helicopter for Martian real estate photography, that honor belongs to HiRISE, or the High Resolution Imaging Science Experiment camera aboard the Mars Reconnaissance Orbiter. Ms Bardabelias is chief operations engineer for HiRISE, which is able to discern features on Mars as small as around 3ft in diameter, but has imaged less than 5% of the planet’s surface to date.
There were 139 apparent caves that met the team’s criteria, and Ms. Bardabelias and her collaborators manually reviewed images of each. After ignoring features such as bridge-like rock formations that were obviously not caves, the team analyzed the remaining pit-like features. The researchers only focused on those that appeared to extend some distance underground, resulting in a sample of nine main candidate caves.
These potential caves, the largest of which has an opening that could swallow up a football pitch, are all worthy of closer examination, Ms Bardabelias said. But none of the rovers currently operating on Mars are close enough to explore any of these caverns, so that task falls, for now, to spacecraft orbiting the Red Planet. HiRISE tracking images taken from different angles and under different lighting conditions will reveal new details about these caves, Bardabelias said. You can help the HiRISE team decide what to photograph next by voting for your favorite cave.
It’s normal that we again seek out caves for shelter as we prepare to explore new worlds, said Glen Cushing, space scientist at the US Geological Survey’s Astrogeology Science Center and creator of the Mars Global Cave Candidate Catalog, not involved in research. “It takes us back to the dawn of humanity.”
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