LONDON (Natural History Museum) -- Thousands of mounds and hills in Mars’ barren northern plains are full of clay minerals, providing evidence that the rocks here were once soaked with water, a new study reveals. 
These mounds are all that is left of a landscape, roughly the size of the UK, that has been almost entirely eroded away.
A researcher at London’s Natural History Museum, Dr. Joe McNeil, with collaborators at The Open University, used high-resolution images and compositional data captured by orbiters to understand the geology of the mounds. The findings are published in the journal Nature Geoscience.
The team discovered that the mounds, which are up to half a kilometer tall, are the remnants of ancient highlands which retreated by hundreds of kilometers after erosion wore away the terrain billions of years ago. These actions played a key role in shaping the Martian landscape which divides the planet’s low-lying northern hemisphere from its higher southern hemisphere.
The mounds are made of layered deposits containing clay minerals, formed through water interacting with rock over millions of years. These clay layers are sandwiched between older, non-clay layers below and younger, non-clay layers above, marking distinct geological events in Mars’ history.
Dr. McNeil said, “These mounds are incredibly exciting because they preserve the complete history of water in this region within accessible, continuous rocky outcrops. They are a prime location for future missions aimed at uncovering whether Mars ever had an ocean and whether life could have existed there.”
The study also reveals that the mounds are geologically linked to the nearby plains of Oxia Planum, which the European Space Agency’s Rosalind Franklin rover is set to launch in 2028 looking for signs of past and present life. By piecing together Mars’ ancient past, scientists are uncovering the story of a planet that may have once been capable of supporting life.
“Mars is a model for what the early Earth might have looked like, as its lack of plate tectonics means that much of its ancient geology is still in place,” Joe continues. “As more missions visit the red planet, the more we’ll be able to dig into our own planet’s history to work out how life began.”
As part of the NHM’s mission to transform the science of natural history, our research is focused on providing solutions from and for nature. This study is part of our Planetary Origins and Evolution research theme which explores the origins and systems underpinning the evolution of the Earth, its moon and planetary systems.