A boulder opal found in Australia, not Mars. Image: Photography by Mangiwau via Getty Images
NASA’s Curiosity rover has discovered a wealth of opals on Mars that could help resolve the question of whether life has ever existed on the red planet, and provide water for any future human missions to the Martian surface, reports a recent study.Opals are prized as gemstones because they display shimmering colors that often look like iridescent rainbows. These gems form when silicon oxides get sloshed around in wet environments and then harden in fissures between rocks. This process transforms opals into miniature oases that can contain as much as 20 percent liquid water.
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Martian opals have previously been spotted from afar by a NASA orbiter, and they have been identified in Martian meteorites that landed on Earth. Now, a team led by Travis Gabriel, a research scientist for the United States Geological Survey, shows that the Curiosity rover has also encountered light-toned opal deposits on the Martian surface.Gabriel and his colleagues said that these opals were formed in “a vast fluid event in recent Martian geologic history” that may have made Mars habitable for longer than previously assumed, and perhaps even preserved microbial life in the alien gemstones, according to a recent study published in the Journal of Geophysical Research: Planets. The high water content of opals could make them a useful source of hydration for future humans on Mars, especially at the planet’s equator, where water ice is far more scarce than at the poles.The “water-rich subsurface network” that produced the opal deposits “was shielded from modern harsh surface conditions, allowing for a potentially habitable environment on Mars in a more recent era,” Gabriel and his colleagues said in the study. “These light-toned features are also ideal for follow-up investigation or sample return as similar opal-rich deposits on Earth are known to preserve traces of microbial life.”“Additionally, the features themselves contain a considerable amount of readily released water, making them an ideal resource at the otherwise dry Martian equator,” the team added.
Curiosity landed in Gale Crater, an impact basin on Mars, in August 2012, and it has produced a litany of discoveries ever since. The rover has amassed evidence that water likely flowed over Gale Crater billions of years ago, producing conditions that would have been habitable to life. Its successor, NASA’s Perseverance rover, is now also searching an ancient lakebed for signs of this past life on Mars.Gabriel and his colleagues realized that Curiosity has been stumbling over opals for years by studying old observations from the rover with new analytical techniques. The team identified light-colored rocks surrounding geological features known as “fracture halos” at multiple sites on Curiosity’s road trip. Observations from several instruments on the rover, including data obtained from drill cores of the Martian surface, suggest that these halos contain abundant reserves of water-rich opals.“Our new analysis of archival data showed striking similarity between all of the fracture halos we've observed much later in the mission,” Gabriel said in a statement. “Seeing that these fracture networks were so widespread and likely chock-full of opal was incredible.”Scientists know that Mars was much wetter and warmer some 3.7 billion years ago, but the presence of opal deposits at Gale Crater suggests that the planet may have also experienced short-lived floods within the past few hundred millions years. While it’s unlikely that life still persists on the desiccated Martian surface, these brief deluges have helped microbes survive deeper underground, or preserved their microbial remains in opals that are easily accessible from the surface.“Given the widespread fracture networks discovered in Gale Crater, it's reasonable to expect that these potentially habitable subsurface conditions extended to many other regions of Gale Crater as well, and perhaps in other regions of Mars,” Gabriel said in the statement. “These environments would have formed long after the ancient lakes in Gale Crater dried up.”Even if these opals don’t ultimately point to alien life on Mars, they could be an important part of a life support system for humans on Mars. The team estimated that about 1.5 gallons of water could be harvested from a one-meter-long halo, enabling astronauts to quench their thirst with the help of extraterrestrial opals. In this way, the recent study may open a window into the Martian past, when microbes may have flourished in bygone lakes and reservoirs, while also paving the way toward human exploration of the red planet in the future.