Determining the history of Mars, and how it formed and evolved over time, has been the goal of all orbiter missions for decades to the Red Planet.
Analyzing data from several Mars missions, a team of researchers led by Steve Raff of Arizona State University’s School of Earth and Space Exploration has determined that the mysterious olive-coloured bedrock in Mars’ Josef Crater, and in and around Jezero Crater, may be a type of rock called ignimbrite. Igneous and sedimentary rocks formed as a result of massive volcanic eruptions.
If this theory, published Tuesday in the journal Icarus, is correct, it could lead to a better understanding of olivine-rich bedrock elsewhere on Mars, and may also point to a pattern of volcanism more common in Mars’ early history.
Stephen Ruff of Arizona State University’s School of Earth and Space Exploration says: “There are a lot of ideas about the origin of the olive-rich bedrock that cover large parts of an area called (Nili Fosai), which includes Jezero crater. This has been an ongoing debate for nearly 20 years. Primary rocks rich in olive and carbonate are also found in Joseph crater, which was explored 16 years ago by NASA’s Spirit rover.”
Both sites contain the highest abundance of olivine so far identified on Mars, and similarities in composition and morphology of widely separated olivine-rich rocks had not previously been investigated, and now they appear to have formed in a similar manner.
Olivine is a common silicate mineral that comes from magma generated in the mantle of Mars (this same process occurs on Earth as well), so some kind of volcanic process is a plausible explanation for the origin of the olivine-rich rocks on Mars, but scenarios have been proposed ranging from lava flows to the impact of Giant shovels olivine from the mantle.
Raff and the research team aimed to test a leading hypothesis involving ash deposited gently from volcanic plumes, but their observations revealed a more violent history.
In particular, Raff examined the mosaic of images from the Mars Spirit microscope imaging device (which resembles the lens of a geologist’s hand) and noticed rocks with an unusual texture.
Raff consulted an online library of pictures of rocks on Earth and came across some igneous rocks with a texture remarkably similar to that of a mosaic from Mars.
“It was a wonderful moment,” Raff says. “I was seeing the same kind of texture in the Josef crater rock as in a very specific type of igneous rock found here on Earth.”
The images were of a type of rock called ignimbrite, which is essentially igneous and sedimentary at the same time. Ignambrite is formed as a result of lava flows of ash, pumice and blocks from the largest known volcanic eruptions on Earth.