Water is ubiquitous on Earth – about 70% of Earth’s surface is covered by the stuff. Water is in the air, on the surface and inside rocks. Geologic evidence suggests water has been stable on Earth since about 4.3 billion years ago.

The history of water on early Mars is less certain. Determining when water first appeared, where and for how long, are all burning questions that drive Mars exploration. If Mars was once habitable, some amount of water was required.

We studied the mineral zircon in a meteorite from Mars and found evidence that water was present when the zircon crystal formed 4.45 billion years ago. Our results, published in the journal Science Advances today, may represent the oldest evidence for water on Mars.

A wet red planet

Water has long been recognised to have played an important role in early Martian history. To place our results in a broader context, let’s first consider what “early Mars” means in terms of the Martian geological timescale, and then consider the different ways to look for water on Mars.

Like Earth, Mars formed about 4.5 billion years ago. The history of Mars has four geological periods. These are the Amazonian (from today back to 3 billion years), the Hesperian (3 billion to 3.7 billion years ago), the Noachian (3.7 billion to 4.1 billion years ago) and the Pre-Noachian (4.1 billion to about 4.5 billion years ago).

Evidence for water on Mars was first reported in the 1970s when NASA’s Mariner 9 spacecraft captured images of river valleys on the Martian surface. Later orbital missions, including Mars Global Surveyor and Mars Express, detected the widespread presence of hydrated clay minerals on the surface. These would have needed water.

The Martian river valleys and clay minerals are mainly found in Noachian terrains, which cover about 45% of Mars. In addition, orbiters also found large flood channels – called outflow channels – in Hesperian terrains. These suggest the short-lived presence of water on the surface, perhaps from groundwater release.

Most reports of water on Mars are in materials or terrains older than 3 billion years. More recent than that, there isn’t much evidence for stable liquid water on Mars.

But what about during the Pre-Noachian? When did water first show up on Mars?

A window to Pre-Noachian Mars

There are three ways to hunt for water on Mars. The first is using observations of the surface made by orbiting spacecraft. The second is using ground-based observations such as those taken by Mars rovers.

The third way is to study Martian meteorites that have landed on Earth, which is what we did.

In fact, the only Pre-Noachian material we have available to study directly is found in meteorites from Mars. A small number of all meteorites that have landed on Earth have come from our neighbouring planet.

An even smaller subset of those meteorites, believed to have been ejected from Mars during a single asteroid impact, contain Pre-Noachian material.

The “poster child” of this group is an extraordinary rock called NWA7034, or Black Beauty.

Black Beauty is a famous Martian meteorite made up of broken-up surface material, or regolith. In addition to rock fragments, it contains zircons that formed from 4.48 billion to 4.43 billion years ago. These are the oldest pieces of Mars known.

While studying trace elements in one of these ancient zircons we found evidence of hydrothermal processes – meaning they were exposed to hot water when they formed in the distant past.

Trace elements, water and a connection to ore deposits

The zircon we studied is 4.45 billion years old. Within it, iron, aluminium and sodium are preserved in abundance patterns like concentric layers, similar to an onion.

This pattern, called oscillatory zoning, indicates that incorporation of these elements into the zircon occurred during its igneous history, in magma.

The problem is that iron, aluminium and sodium aren’t normally found in crystalline igneous zircon – so how did these elements end up in the Martian zircon?

The answer is hot water.

In Earth rocks, finding zircon with growth zoning patterns for elements like iron, aluminium and sodium is rare. One of the only places where it has been described is from Olympic Dam in South Australia, a giant copper, uranium and gold deposit.

The metals in places like Olympic Dam were concentrated by hydrothermal (hot water) systems moving through rocks during magmatism.

Hydrothermal systems form anywhere that hot water, heated by volcanic plumbing systems, moves through rocks. Spectacular geysers at places like Yellowstone National Park in the United States form when hydrothermal water erupts at Earth’s surface.

Finding a hydrothermal Martian zircon raises the intriguing possibility of ore deposits forming on early Mars.

Previous studies have proposed a wet Pre-Noachian Mars. Unusual oxygen isotope ratios in a 4.43 billion-year-old Martian zircon were previously interpreted as evidence for an early hydrosphere. It has even been suggested that Mars may have had an early global ocean 4.45 billion years ago.

The big picture from our study is that magmatic hydrothermal systems were active during the early formation of Mars’ crust 4.45 billion years ago.

It’s not clear whether this means surface water was stable at this time, but we think it’s possible. What is clear is that the crust of Mars, like Earth, had water shortly after it formed – a necessary ingredient for habitability.

This article is republished from The Conversation under a Creative Commons license. Read the original article here.

This image provided by NASA shows the InSight Mars lander in a selfie photo composite on April 24, 2022, the 1,211th Martian day, or sol, of the mission.
| Photo Credit: AP

An immense reservoir of liquid water may reside deep under the surface of Mars within fractured igneous rocks, holding enough to fill an ocean that would cover the entire surface of Earth’s planetary neighbor.

That is the conclusion of scientists based on seismic data obtained by NASA’s robotic InSight lander during a mission that helped decipher the interior of Mars. The water, located about 7.2 to 12.4 miles (11.5 to 20 km) below the Martian surface, potentially offers conditions favorable to sustain microbial life, either in the past or now, the researchers said.

“At these depths, the crust is warm enough for water to exist as a liquid. At more shallow depths, the water would be frozen as ice,” said planetary scientist Vashan Wright of the University of California, San Diego’s Scripps Institution of Oceanography, lead author of the study published on Monday in the journal Proceedings of the National Academy of Sciences.

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“On Earth, we find microbial life deep underground where rocks are saturated with water and there is an energy source,” added planetary scientist and study co-author Michael Manga of the University of California, Berkeley.

The InSight lander touched down in 2018 to study the deep interior of Mars, gathering data on the planet’s various layers, from its liquid metal core to its mantle and its crust. The InSight mission ended in 2022.

“InSight was able to measure the speed of seismic waves and how they change with depth. The speed of seismic waves depends on what the rock is made of, where it has cracks and what fills the cracks,” Mr. Wright said. “We combined the measured seismic wave speed, gravity measurements and rock physics models. The rock physics models are the same as the ones we use to measure properties of aquifers on Earth or map oil and gas resources underground.”

The data indicated the presence of this reservoir of liquid water within fractured igneous rocks – formed in the cooling and solidification of magma or lava – in the Martian crust, the planet’s outermost layer.

“A mid-crust whose rocks are cracked and filled with liquid water best explains both seismic and gravity data,” Mr. Wright said. “The water exists within fractures. If the InSight location is representative and you extract all the water from the fractures in the mid-crust, we estimate that the water would fill a 1-2 km deep (0.6-1.2 miles) ocean on Mars globally.”

The Martian surface is cold and desolate today but once was warm and wet. That changed more than 3 billion years ago. The study suggests that much of the water that had been on the Martian surface did not escape into space, but rather filtered down into the crust.

“Early Mars had liquid water on its surface in rivers, lakes and possibly oceans. The crust on Mars could also have been full of water from very early in its history, too,” Mr. Manga said. “On Earth, groundwater underground infiltrated from the surface, and we expect this to be similar to the history of water on Mars. This must have occurred during a time when the upper crust was warmer than it is today.”

Water would be a vital resource if humankind ever is to place astronauts on the Martian surface or establish some sort of long-term settlement. Mars harbors water in the form of ice at its polar regions and in its subsurface. But the depth of the apparent underground liquid water would make it difficult to access.

“Drilling to these depths is very challenging. Looking for places where geological activity expels this water, possibly the tectonically active Cerberus Fossae (a region in the northern hemisphere of Mars), is an alternative to looking for deep liquids,” Mr. Manga said, though he noted that concerns about protecting the Martian environment would need to be addressed.