A terrestrial opal from Australia.
A research team using new methods to analyze data from NASA’s Curiosity, a rover operating on Mars since 2012, was able to independently verify that fracture halos contained opal, on Earth a gemstone formed by the alteration of silicon-dioxide by water.
The study finds that the vast subsurface fracture networks would have provided conditions that were potentially more habitable than those on the surface.
In 2012, NASA sent the Curiosity rover to Mars to explore Gale Crater, a large impact basin with a massive, layered mountain in the middle. As Curiosity has traversed along the Mars surface, researchers have discovered light-toned rocks surrounding fractures that criss-cross certain parts of the Martian landscape, sometimes extending out far into the horizon of rover imagery. Recent work finds that these widespread halo networks served as one of the last, if not the last, water-rich environments in a modern era of Gale Crater. This water-rich environment in the subsurface would have also provided more habitable conditions when conditions on the surface were likely much more harsh.
Selfie of Curiosity rover with Martian rocks in the background.
As part of a new study published in the Journal of Geophysical Research: Planets, led by former Arizona State University NewSpace Postdoctoral Fellow Travis Gabriel, now a research physicist for the U.S. government, archival data from several instruments were examined and showed considerable anomalies near light-toned rocks earlier in the traverse. By happenstance, Curiosity rover drove right over one of these fracture halos many years ago, long before Gabriel and ASU graduate student and co-author Sean Czarnecki joined the rover team.
Looking at the old images, they saw a huge expanse of fracture halos extending far into the distance. By applying new methods for analyzing instrument data, the research team found something curious. These halos not only looked like halos found much later in the mission, in completely different rock units, but were similar in their composition: a whole lot of silica and water.
“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. “Seeing that these fracture networks were so widespread and likely chock-full of opal was incredible.”
Observing drill cores taken at the Buckskin and Greenhorn drill sites many years into the mission, scientists confirmed that these light-toned rocks were very unique compared to anything the team had seen before.
In addition to looking back through archival data, Gabriel and his team went searching for opportunities to study these light-toned rocks again. Once they arrived at the Lubango drill site, a bright-toned fracture halo, Gabriel led a dedicated measurement campaign using the rover’s instruments, confirming the opal-rich composition.
Opal-rich halos as seen crosscutting the bedrock extend into the subsurface of Mars.
The discovery of opal is noteworthy as it can form in scenarios where silica is in solution with water, a similar process to dissolving sugar or salt in water. If there is too much salt, or conditions change, it begins to settle at the bottom. On Earth, silica falls out of solution in places like lake and ocean bottoms and can form in hot springs and geysers, somewhat similar to the environments at Yellowstone National Park.
Since scientists expect that this opal in Gale Crater was formed in a modern Mars era, these subsurface networks of fractures could have been far more habitable than the harsh modern-day conditions at 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. “These environments would have formed long after the ancient lakes in Gale Crater dried up.”
The significance of finding opal on Mars will have advantages for future astronauts, and exploration efforts could take advantage of these widespread water resources. Opal itself is made up of predominantly two components: silica and water – with a water content ranging from 3 to 21 percent by weight – with minor amounts of impurities such as iron. This means that if you grind it down and apply heat, the opal releases its water. In a previous study, Gabriel and other Curiosity rover scientists demonstrated this exact process. Combined with growing evidence from satellite data that shows the presence of opal elsewhere on Mars, these resilient materials may be a great resource for future exploration activities elsewhere on Mars.
Material provided by the Arizona State University.
