NASA's Curiosity rover finds water halos filled with opal on Mars

Subsurface fractures may have offered more habitable conditions than the surface, with access to water and radiation protection.
Nergis Firtina
Light-toned fracture halos as seen crosscutting the bedrock extend into the subsurface.
Light-toned fracture halos as seen crosscutting the bedrock extend into the subsurface.

Malin Space Science Systems/NASA/JPL-Caltech 

Led by Arizona State University, a research team was able to independently confirm that fracture halos included water-rich opal, potentially acting as a crucial resource for human exploration, by analyzing data from NASA's Curiosity rover and its neutron spectrometer Dynamic Albedo of Neutrons, or DAN, on Mars.

As reported by Arizona State University, the extensive subterranean fracture networks would have created environments that may have been more habitable than those on the surface in terms of water content and radiation shielding, according to the study.

In order to investigate Gale Crater, a sizable impact basin with a gigantic, stratified mountain in the center, NASA deployed the Curiosity rover to Mars in 2012. Researchers have found light-toned rocks surrounding fractures that crisscross some areas of the martian terrain and occasionally reach far into the horizon of rover imagery as Curiosity has traveled over the surface of Mars.

According to recent research, Gale Crater's extensive halo networks were one of the water-rich habitats. When circumstances on the surface were probably much harsher, this water-rich ecosystem in the subsurface would have also afforded better habitable conditions.

The study's archival data from many devices were analyzed by Postdoctoral Fellow Travis Gabriel, who is now a research physicist for the US government, and revealed significant anomalies near light-toned rocks earlier in the traverse.

“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.”

The nature of the light-colored rocks that surround the ground-breaking cracks, or "fracture halos," in Gale Crater was investigated by Gabriel and his team of scientists.

It was formed in a modern Mars era

These underground networks of fractures may have been much more hospitable than the hard surface conditions of modern Mars, which is what scientists believe opal in Gale Crater developed in.

“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 aim of the study

Together with other volatiles like carbon dioxide, the poles of Mars contain a significant amount of water ice. By contrast, the equator of Mars lacks water now and does not appear to have abundant water ice resources close to the surface. The study suggests that water-rich opal may be lining many landscapes across regions of Mars where scientists otherwise don't expect water.

Despite the aridity of the current environment, the opal in Gale Crater maintains water. These durable minerals may be a significant resource for future exploration endeavors elsewhere on Mars if opal elsewhere on Mars also maintains water to the same degree as the opal in Gale Crater, which is supported by rising evidence from satellite data.

The study was published in the Journal of Geophysical Research on December 19.

Study abstract:

We analyze spatially pervasive, light-toned “halos” associated with fractures in a sedimentary unit (Stimson) of Gale crater, Mars, and report a similar network of halos discovered in a separate geologic group (Bradbury). Through a dedicated active neutron measurement campaign, we provide independent confirmation of the water-rich nature of these features. Together with mineralogical and geochemical data, these features are consistent with abundant hydrated amorphous silica (opal-A). We suggest that the mineral and amorphous assemblages are indicative of formation under low-temperature and predominantly low-pH conditions (passive silica enrichment) with a minor contribution of silica (active silica enrichment) from adjacent units. We show that there is significant amorphous silica in the array of sedimentary rocks in the Gale crater, allowing them to play a role in an active silica enrichment phase of halo formation. We suggest that the involved alteration event was short-lived and our finding of vast halo networks in a distant, older unit implies a more vast network of hydrologic subsurface conduits than previously known. This relatively recent subsurface hydrologic system was present long after the transition from a warm and wet to a cold and dry Martian environment, extending the habitability conditions on Mars to an epoch that is generally considered not favorable for life on the surface. Finally, our bulk H quantification of these features, which ranges from ∼3–6 wt% H2O-equivalent-H, suggests that the amorphous material in halos hosts ample supplies of readily released water, making them a considerable resource at the otherwise dry Martian equator.