A research team using new methods to analyze data from NASA’s Curiosity rover, operating on Mars since 2012, has been able to independently verify that the rupture halo contains opal, a gemstone formed on Earth by the conversion of silicon dioxide by water.
The study showed that extensive networks of subsurface fractures would provide potentially more habitable conditions 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 its center. As Curiosity traversed the Martian surface, researchers discovered bright rocks surrounding cracks that cut through parts of the Martian landscape, sometimes extending far into the horizon of the rover’s images. Recent work has shown that these vast halo networks served as one of the last, if not the last, water-rich environments in the modern era of Gale Crater. This water-rich subsurface environment would also provide more habitable conditions when surface conditions were likely to be much harsher.
As part of a new study published in the journal Journal of Geophysical Research: Planets, led by Travis Gabriel, a former Arizona State University NewSpace postdoctoral fellow and now a research physicist for the US government, examined archival data from several instruments and found significant anomalies near the bright rocks at the start of the traverse. Coincidentally, the Curiosity rover passed right over one of the broken halos many years ago, long before Gabriel and ASU graduate student and co-author Sean Czarnecki joined the rovers team.
Looking at old photos, they saw a vast expanse of crack halos stretching far into the distance. Using new methods to analyze instrument data, the research team discovered something interesting. These halos not only looked like halos found much later in the mission, in completely different rock units, but had a similar composition: a whole lot of silica and water.
“Our new analysis of archival data showed a striking similarity between all the crack halos we observed much later in the mission,” said Gabriel. “Seeing these fracture networks were so widespread and possibly filled with opal was amazing.”
Observing drill cores taken from the Buckskin and Greenhorn drilling sites many years after the mission began, the scientists confirmed that these bright rocks were very unique compared to anything the team had seen before.
In addition to reviewing archival data, Gabriel and his team began looking for ways to re-examine these bright rocks. When they arrived at the Lubango drilling site, a bright fissure halo, Gabriel conducted a dedicated measurement campaign with the rover’s instruments, confirming the iridescent-rich composition.
The discovery of opal is notable because it can form in scenarios where silica is in solution with water, a process similar to dissolving sugar or salt in water. If there is too much salt or conditions change, it starts to settle to the bottom. On Earth, silica falls out of solution in places such as lake and ocean bottoms and can form in hot springs and geysers, somewhat similar to environments in Yellowstone National Park.
As scientists expect this opal in Gale Crater to have formed during the modern age of Mars, these subsurface fracture networks may have been much more habitable than the harsh modern conditions on the surface.
“Given the extensive fracture networks discovered in Gale Crater, it is reasonable to expect that these potentially habitable subsurface conditions have also extended to many other regions of Gale Crater and possibly other regions of Mars,” said Gabriel. “These environments formed long after the ancient lakes in Gale Crater dried up.”
The importance of finding opal on Mars will benefit future astronauts, and exploration efforts could take advantage of these vast water resources. Opal itself is mainly composed of two components: silica and water – with a water content ranging from 3 to 21 percent by weight – with small amounts of impurities such as iron. This means that if you grind it and apply heat, the opal will release its water. In a previous study, Gabriel and other Curiosity rover scientists demonstrated exactly this process. Combined with the growing evidence from satellite data that indicates the presence of opal elsewhere on Mars, these resilient materials could be an excellent resource for future exploration efforts elsewhere on Mars.
Material provided by Arizona State University.