For more than a decade, NASA’s Curiosity rover has been exploring Mars, analyzing the surface of Gale Crater, where a lake once existed in the early days of Mars. Recent study of both new and old Curiosity images has revealed signs that, long after the lake itself dried up, enough underground water remained in the former lakebed to form the semiprecious gemstone opal
An opal gemstone found on Mars evokes classic science fiction images of grizzled Martian prospectors searching for mother lodes and fending off claim jumpers. While people may one day wear jewelry from Mars, the current excitement isn’t about bling; as Space.com reports, it could be a sign of a substance on Mars that’s even more precious than opal gemstones: water.
The first hints of opal gemstones on Mars, according to Metal Tech News, were detected as early as 2008 by the Mars Reconnaissance Orbiter, but these early detections from space gave no hints of the concentration level of “opal-like minerals” that might be found on Mars.
Observing a Network of Fracture Halos
The Curiosity rover has provided much closer views of a type of feature called a fracture halo: an area of lighter-colored material surrounding fractures in a rock surface. The lighter coloring of the halo is the sheen of opal, essentially the same sheen that makes opal a semiprecious stone.
As fracture halos continued to turn up in the images sent back from Curiosity, it became clear to mission scientists that not only was gemstone discovered on Mars, but these fractures were also widespread on the planet. A search back through the archive of images already taken by Curiosity showed even more.
Says researcher Travis Gabriel, per Interesting Engineering, “Our new analysis of archival data showed striking similarity between all of the fracture halos we’ve observed much later in the mission. Seeing that these fracture networks were so widespread and likely chock-full of opal was incredible.”
Seeing Through Rock With Neutrons
While most of Curiosity’s instruments, like its cameras, were intended for investigation of the immediate surface, it carries one instrument that could be used to “see” down into the subsurface fractures that the halos surround. This instrument, called Dynamic Albedo of Neutrons (DAN), measures the speed of neutrons that are kicked off the surface of Mars by high-energy cosmic rays from space. The DAN readings, according to Live Science, have shown that some of the neutrons detected have been slowed down by interacting with hydrogen atoms — a telltale sign of the presence of water.
Opal gemstones are formed by a solution of silica and water; on Earth, this formation process can take place in hot springs or on the seabed. Today, the open surface of Mars, which is nearly unprotected by its thin atmosphere, is fiercely hostile to life, bombarded by the same radiation that kicks loose the neutrons detected by DAN. This has been the case throughout the “modern” era of Mars, which extends back some 2.9 billion years. But even a slight distance underground — for example, in a rock fracture — conditions would have been far more benign. If enough water remained in the fractures to form opals, even millions of years after the lake above had evaporated, life may also have persisted there.
The Implications of Finding Water on Mars
Opal gemstones, and the water that helped to form them, have breathtaking implications for the ongoing search for life on Mars. Some of the effects will be almost immediate. Even as Curiosity continues exploring Gale Crater, another NASA Mars rover, Perseverance, is currently exploring another crater that was an ancient lakebed: Jezero Crater. Its mission is now being adjusted to look for signs of fracture halos and opals in Jezero Crater.
Looking forward, the widespread presence of opal found on Mars could provide a boon for future missions, in addition to being a research objective. The reason is that, in spite of being a gemstone, opal is technically not quite a “mineral.” It does not have a rigid crystal structure, and with proper processing, some of the water in it can be recovered. According to EarthSky, researchers estimate that a single square meter of fracture halo material, down to a depth of one foot, could contain a gallon and a half of recoverable water.
The polar regions of Mars were already known to be rich in water ice, while Gale Crater is near the Martian equator. If recoverable subsurface water is widely available in equatorial regions of Mars, it could be a boon for astronauts during future long-term missions to Mars. This, in turn, could bring us another step closer to wearing bling from Mars.
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