One of the major unknowns to be addressed by future Mars missions is the Martian interior. Understanding its structure is critical because it will help us understand the formation of the atmosphere, the fate of life on Mars, and, ultimately, planetary evolution, including Earth’s evolution.
According to a new study, the original crust of Mars is more complex and evolved than previously thought. Researchers discovered that the Martian crust contains higher concentrations of the chemical element silicon, implying that Mars’ original surface was similar to Earth’s first crust.
Mars’ early crust may be more complex than previously thought, and it may even be similar to the crust of our own planet. The surface of Mars is uniformly basaltic, the result of billions of years of volcanism and flowing lava on the surface that cooled. Because Mars’ crustal history was thought to be relatively simple because it did not undergo large-scale surface remodeling like the shifting of continents on Earth.
Researchers discovered locations in Mars’ southern hemisphere with higher concentrations of silicon, a chemical element, than would be expected in a purely basaltic setting, according to a new study.
There is more silica in the composition that makes the rocks not basalt, but what we call more evolved in composition. That tells us how the crust formed on Mars is definitely more complex than what we knew. So, it’s more about understanding that process, and especially what it means for how Earth’s crust first formed.
Valerie Payré
“There is more silica in the composition that makes the rocks not basalt, but what we call more evolved in composition,” says Valerie Payré, assistant professor in the Department of Earth and Environmental Sciences at the University of Iowa and the study’s corresponding author. “That tells us how the crust formed on Mars is definitely more complex than what we knew. So, it’s more about understanding that process, and especially what it means for how Earth’s crust first formed.”
Mars, according to scientists, formed about 4.5 billion years ago. The exact origin of the Red Planet is unknown, but there are theories. One theory holds that Mars formed as a result of a massive collision of rocks in space, which resulted in an entirely liquefied state, also known as a magma ocean. According to the theory, the magma ocean gradually cooled, resulting in a crust, similar to a layer of skin, that is uniquely basaltic.
Another theory is that the magma ocean was not all-encompassing and that parts of Mars’ first crust had a different origin, with silica concentrations different from basaltic.
Payré and her colleagues examined data from the Mars Reconnaissance Orbiter for the planet’s southern hemisphere, which previous research indicated was the oldest. The researchers discovered nine feldspar-rich locations, such as craters and fractures in the terrain, which are associated with silicic lava flows rather than basaltic lava flows.
“This was the first hint,” Payré explains. “We investigated the silica concentrations there because the terrains are feldspar-rich.”
Feldspar had been found previously in other regions on Mars, but further analysis showed the chemical composition in those areas was more basaltic. That did not deter the researchers, who turned to another instrument, called THEMIS, which can detect silica concentrations through infrared wavelength reflections from the Martian surface. With data from THEMIS, the team determined the terrain at their chosen locations was more silicic than basaltic.
Meteorites such as Erg Chech 002, discovered in the Sahara and dating roughly to the birth of the solar system, show similar silicic and other mineral compositions to the nine locations on Mars, lending credence to their findings. The crust was also dated to about 4.2 billion years, making it the oldest crust discovered on Mars to date. Payré admits to being surprised by the discovery.
“There have been rovers on the surface that have observed rocks that were more silicic than basaltic,” she says. “So, there were ideas that the crust could be more silicic. But we never knew, and we still don’t know, how the early crust was formed, or how old it is, so it’s kind of a mystery still.”
While Mars’ crustal origin is unknown, Earth’s crustal history is even more obscure, as any remnants of our planet’s original crust have been long erased due to billions of years of continental plate shifting. Nonetheless, the discovery could shed light on Earth’s origins.
“We don’t know the origins of our planet’s crust; we don’t even know when life first appeared,” Payré says. “Many people believe the two are related. Understanding what the crust was like a long time ago could thus help us understand the evolution of our planet as a whole.”
