NASA has released a striking image of a flat piece on the surface of Mars’ Jezero Crater with a mushroom-shaped rock protruding from it. The ‘mushroom’ measures between 1 and 2 cm high and less than 1 cm wide. The rock was in an area the rover explored in 2022 called Hogwallow Flats. Many aspects distinguish that rock from the rest examined at Jezero: it was very fine-grained compared to others, contained a higher proportion of sulfate salts, and had interesting rock characteristics.
The ‘mushroom’ is actually a geological feature known as concretion. Concretions are solid masses within a rock that form as water flows through sediment, dissolving minerals and reprecipitating them into a more compact configuration. Concretions are usually harder than the surrounding rock, making them less vulnerable to erosion and weathering.
On Earth, concretions come in a wide variety of shapes (from spherical to irregular) and sizes (from 1 mm to 2.2 meters) and first appear in the terrestrial rock record more than 3 billion years ago.
“We don’t know when the ‘mushroom’ concretion first formed at Hogwallow Flats, but as wind carved through the surface of Mars over billions of years, it eroded the softer bedrock around this hard concretion.” , explains Hemani Kalucha, a doctoral student at Caltech who participated in the ‘fungus’ research. Now all that remains of the surrounding bedrock is a very thin rock needle connecting the concretion to the flat rock below.
Near this interesting feature, the team also saw large disc-shaped concretions, small, spherical concretions, and pointed concretions. The space exploration vehicle removed a sample from Hogwallow Flats called ‘Bearwallow’ that may contain a concretion, so if the samples are returned to Earth we can learn even more about Martian concretions and how they formed.
