Scientists discover new rock type on Mars

An international team of scientists has identified a completely new type of rock on the Red Planet and, for the first time ever, discovered the mineral garnet in a Martian sample.  

The breakthrough offers a rare glimpse into Mars's ancient past and could help researchers piece together the planet's 4.5-billion-year geological history. 

The discovery was made by an international research team including James Darling, Professor of Earth and Planetary Science, from the University of Portsmouth’s School of the Environment and Life Sciences. 

On Earth, garnet - a dark-red gem popular with Ancient Egyptians, Romans and the Victorian elite alike - is January’s birthstone.  It is a cornerstone mineral in geology, providing a powerful record of the tectonic forces, ore-forming processes, and fluid-rock interactions that shape Earth’s crust and mantle. 

The discovery on Mars, offers a new geological time capsule, preserving clues about the temperatures, pressures and processes that shaped the planet billions of years ago. 

Professor Darling said: “The findings add a striking new dimension to our understanding of the geology of Mars and open an exciting new window into the evolution of our planetary neighbour.” 

The research was led by Tanya Kizovski, Assistant Professor of Earth Sciences, from Brock University in Canada. 

She said: “This discovery is going to expand our knowledge of the geologic processes that are possible on this planet. This new garnet-bearing rock type could give us clues to how Mars has changed throughout its history and new insights into the ancient environments that could have formed the garnet and related minerals.” 

Kizovski and colleagues at the Royal Ontario Museum (ROM) came to know of the garnet’s presence while analysing a fragment of a Martian meteorite known as NWA 8171 within the ROM’s collections. 

Kizovski sought to identify the fragment’s minerals and chemical composition. 

“This little section of the meteorite looked really interesting, and the chemistry was a bit odd,” she said. “At first, we assumed it was a mineral called pyroxene, which is very common, but then we decided to take a second look.”

Using the University of Portsmouth Electron Microscopy and Microanalysis Unit and the ROM’s specialised laser equipment, the team - which also includes researchers from the Universita di Trieste in Italy and the Open University in the UK - were surprised to discover garnet, a mineral that had not been identified on Mars until now.  

The team analysed the fragment’s chemistry and minerology and speculated on the garnet’s origin. 

Professor Kizovski said: “Garnet is a classic example of a mineral often found in metamorphic rocks on Earth. The process of metamorphism transforms igneous or sedimentary rocks into a new form through exposure to extreme heat, high pressure or hot fluids.  

“On Mars, the heat and pressure needed to produce garnet through metamorphism could have come from the impact of a meteorite hitting the surface of Mars, magma rising up into the Martian crust or both.” 

Kizovski is quick to caution that the research doesn’t definitively indicate whether the garnet-bearing rock formed on Mars or was delivered to the Red Planet and incorporated into its surface in a meteorite landing, leaving the possibility for an “extra-Martian” origin. 

Scientists need to now study the garnet’s isotopic signatures to verify if it was originally produced on Mars or on another planetary body.  

“Measuring oxygen isotopes from the garnet-bearing rock type itself would help to confirm if it is Martian in origin or from an exotic meteorite impactor,” Kizovski said. “Isotopes are a collection of atoms with equal numbers of protons and electrons, but different numbers of neutrons.” 

However, that process would entail destroying some of the sample, “which was avoided thus far due to its rarity, as it may be the only garnet-bearing Martian rock we have for study,” she added. 

ROM curator Kim Tait and Research Assistant Jessica Tomacic, together with Professor Darling, are continuing to study the sample. “With their work and more comparisons to rover and orbital data, I’m hopeful that we will be able to learn more about the origin and history of garnet on Mars,” Kizovski said. 

The team’s study Expanding Mars’ lithologic diversity: discovery of a garnet-bearing clast in NWA 8171, was published Tuesday, June 16 in Geochemical Perspectives Letters. 

This research project is funded in part by the Government of Canada’s Natural Sciences and Engineering Research Council (NSERC) and the Killam Trusts Dorothy Killam fellowship, as well as Science and Technology Facilities Council (STFC) funding at Portsmouth.