Water will be one of the most important resources for human explorers on Mars. They’ll need it for drinking, propellant, breathing, and more. It makes sense to land near a spot where there’s water ice close to the surface.
NASA has released a new map of Mars’s northern hemisphere showing all the places where subsurface water ice has been detected, some of which are surprisingly close to the equator, as well as surprisingly close to the surface. This map could decide the first human landing site.
It is a scientific certainty that Mars was once a much different place, with a denser atmosphere, warmer temperatures, and where water once flowed. Evidence of this past is preserved in countless surface features, ranging from river channels and alluvial deposits to lakebeds. However, roughly 4 billion years ago, the planet began to change into what we see today, an extremely cold and desiccated environment. Between all that, it is possible Mars experienced glacial and interglacial periods, which is evidenced by images like the one taken by the NASA Mars Reconnaissance Orbiter (MRO) shown above.
Olympus Mons, located at the northwest edge of the Tharsis Montes region on Mars, was appropriately named. Based on readings obtained by the Mars Orbiter Laser Altimeter (MOLA), an instrument aboard NASA’s Mars Global Surveyor (MGS), this mountain is the tallest in the Solar System, standing 21.9 km (13.6 mi) tall – about two and a half times the height of Mount Everest (8.85 km; 5.5 mi). According to current estimates, this extinct shield volcano formed during Mars’ Hesperian Period (ca. 3.7 to 3 billion years ago), which was characterized by widespread volcanic activity and catastrophic flooding.
This coincides with a period when Mars had a denser atmosphere, a warmer environment, and flowing water on its surface. This included a global ocean that spanned much of the northern hemisphere, known today as the Northern Lowlands, encompassing Olympus Mons. According to a recent study led by researchers from the Centre National de Recherches Scientifique (CNRS), features found on the slopes of Olympus Mons indicate that it could have been a massive volcanic island where volcanic eruptions flowed into the ocean, similar to ones found on Earth.
In a first for Martian water science, NASA’s Perseverance rover has discovered geological evidence of a large, fast-moving river in Mars’ ancient past. The high-energy river once emptied into Jezero crater, which the rover has been exploring since early 2021, and is a totally different water system than anything seen previously on the red planet.
The surface of Mars is a pretty desolate place at first glance. The soil is many times as dry as the driest desert on planet Earth, the temperatures swing from one extreme to the other, and the air is incredibly thin and toxic. And yet, there’s ample evidence that the planet was once much warmer and wetter, with lots of flowing and standing water on its surface. Over time, as Mars’ atmosphere was slowly stripped away, much of this water was lost to space, and what remains is largely concentrated around the poles as glacial ice and permafrost.
For years, space agencies have been sending robotic landers, rovers, orbiters, and aerial vehicles to Mars to learn more about when this transition took and how long it took. According to China’s Tianwen-1 mission, which includes the Zhurong rover, there may have been liquid water on the Martian surface later than previously thought. According to new research from the Chinese Academy of Sciences (CAS), the Zhurong rover observed salt-rich dunes in the Utopia Planitia region that showed cracks and crusts, indicating the possible presence of water as recently as a few hundred thousand years ago.
This week, NASA’s Curiosity rover stumbled across the best evidence yet that liquid water once covered much of Mars in the planet’s distant past: undulating rippled rock formations – now frozen in time – that were sculpted by the waves of an ancient shallow lake. But perhaps the biggest surprise is that they were discovered in an area that researchers expected to be dry.
Today, Mars is colloquially known as the “Red Planet” on a count of how its dry, dusty landscape is rich in iron oxide (aka. “rust”). In addition, the atmosphere is extremely thin and cold, and no water can exist on the surface in any form other than ice. But as the Martian landscape and other lines of evidence attest, Mars was once a very different place, with a warmer, denser atmosphere and flowing water on its surface. For years, scientists have attempted to determine how long natural bodies existed on Mars and whether or not they were intermittent or persistent.
Another important question is how much water Mars once had and whether or not this was enough to support life. According to a new study by an international team of planetary scientists, Mars may have had enough water 4.5 billion years ago to cover it in a global ocean up to 300 meters (almost 1,000 feet) deep. Along with organic molecules and other elements distributed throughout the Solar System by asteroids and comets at this time, they argue, these conditions indicate that Mars may have been the first planet in the Solar System to support life.
The Curiosity rover has now reached its primary target on Mount Sharp on Mars, the mountain in the middle of Gale Crater the rover has been climbing since 2014. This target is not the summit, but a region over 600 meters (2,000 feet) up the mountain that planetary geologists have long anticipated reaching.
Known as the “sulfate-bearing unit,” the region is a boundary between the rocks that saw a lot of water in their history and those that didn’t; a possible shoreline, if you will. That boundary is already providing insights into Mars’ transition from a wet planet to dry, filling in a key gap in the understanding of the planet’s history.
When planning crewed missions to Mars, the key phrase is “follow the water.” When astronauts set down on the Red Planet in the next decade, they will need access to water to meet their basic needs. Following the water is also crucial to our ongoing exploration of Mars and learning more about its past. While all of the water on the Martian surface exists as ice today (the majority locked away in the polar ice caps), it is now known that rivers, lakes, and an ocean covered much of the planet billions of years ago.
Determining where this water went is essential to learning how Mars underwent its historic transformation to become the dry and cold place it is today. Close to twenty years ago, the ESA’s Mars Express orbiter made a huge discovery when it detected what appeared to be a massive deposit of water ice beneath the southern polar region. However, recent findings by a team of researchers from Cornell University indicate that the radar reflections from the South Pole Layered Deposit (SPLD) may be the result of geological layering.
Mars exploration has been ongoing for decades at this point, and some regions of the planet have become more interesting than others. Of particular interest is a basin known as Utopia Planitia. It was the site of the Viking-2 landing, one of the first-ever successful missions to Mars. From data collected during that mission, scientists developed a theory that the crater that formed Utopia might have been the site of an ancient ocean. New results from China’s Zhurong rover point to an even more exciting past – repeated flooding.