Water on Mars has been escaping for at least a billion years. Find out how NASA’s MAVEN spacecraft has shed new light on why this happens.
I remember the excitement in the summer of 1975. I was in high school, and Viking 1 had landed on the surface of Mars.
We eagerly waited in front of our television sets to see the first Martian images ever transmitted to Earth. We’d seen the moon, but this was our first glimpse of a planet from its surface.
It wasn’t so different from the moon–rocky and desolate. Then, once NASA had corrected the colour, we were all impressed by how much redder the barren surface was. It also differed from the moon with its signs of erosion from wind and water, although we didn’t see any water on Mars.
Another Dry, Dead, Lifeless World
It was another dry, dead, lifeless world. That was a letdown for those of us hoping to see signs of life, yet it was still fascinating. That fall, the Viking 2 lander sent home other engrossing, bleak vistas.
Twenty years later, in 1997, two other spacecraft re-ignited interest in Mars. The Mars Global Surveyor mapped the entire planet’s entire surface from orbit while studying the Martian atmosphere and its interior.
The Mars Pathfinder delivered another captivating, barren 360˚ landscape with its famous Twin Peaks to our computer screens. The Worldwide Web was just catching on at the time.
There Was Once Plenty of Liquid Water on Mars
Pathfinder included a rover named Sojourner. Together, they found that the red planet used to be much warmer and that there was once plenty of liquid water on Mars.
NASA continued searching for liquid surface water in 2004 with the two Mars Exploration Rovers Spirit and Opportunity. They found evidence that our nearest neighbour was once flush with water even though it now looks like the badlands of Arizona.
For the last six years, the Mars Atmosphere and Volatile Evolution (MAVEN) orbiter has delved deeper into the Martian climate. Last week, the journal Science published a paper by University of Arizona graduate student Shane Stone that uses data from the MAVEN spacecraft.
“Mars Somehow Lost the Majority of Its Atmosphere”
Stone explains, “We know that billions of years ago, there was liquid water on the surface of Mars. There must have been a thicker atmosphere, so we know that Mars somehow lost the majority of its atmosphere to space. “
Maven’s orbit ducks down into the Martian atmosphere to an altitude of roughly 60 kilometres (100 miles) every 4 1/2 hours. It uses its Neutral Gas and Ion Mass Spectrometer (NGIMS) to measure how many water ions it can find inside the upper atmosphere.
Reviewing this data, the researchers found that when Mars moves closest to the Sun, the planet warms up, causing surface ice to rise into the atmosphere. Once it reaches the upper atmosphere, it escapes into space.
Winds Whipping Up the Dust Globally
This happens once every Martian year (687 Earth days). Mars also has yearly local dust storms and a roughly 10-year cycle of winds whipping up the dust globally.
These disturbances also warm the planet, evaporating more surface ice into the atmosphere. The massive dust storms are intense.
Blasts can drive 20 times more water into the upper atmosphere. A 45-day storm on Mars releases as much water into space as the planet typically loses in a year.
Processes Gradually Reduce the Volume of Water on Mars
All of these processes gradually reduce the volume of water on Mars. Traditionally, scientists had thought that when the ice evaporated into the Martian atmosphere, the Sun eliminated it in a slow, steady process.
If this standard explanation was correct, MAVEN wouldn’t find much water at its high altitude, but it did. “This is important because we didn’t expect to see any water in the upper atmosphere of Mars at all,” Stone explained.
This new study upends conventional views about the water on Mars. “The loss of its atmosphere and water to space is a major reason Mars is cold and dry compared to warm and wet Earth,” Stone said. “This new data from MAVEN reveals one process by which this loss is still occurring today,”
Lost the Equivalent of an Ocean 17 Inches Deep
The investigators believe that this process has removed the water from Mars for at least a billion years. When they did the math, they found that the planet has lost the equivalent of an ocean 17 inches deep as a result.
Stone went on to say, “If we took water and spread it evenly over the entire surface of Mars, that ocean of water lost to space due to the new process we describe would be over 17 inches deep. An additional 6.7 inches would be lost due solely to the effects of global dust storms.”
A billion years is as far back as the scientists can calculate at this point. They’re not sure how long the process has been going on or what other conditions may have affected the water on Mars before that.
Earth is a Gem Within Our Solar System
Earth is a gem within our Solar System. As we’ve written before, Earth’s abundance of water is both a boon and a mystery.
Understanding how abundant water is on exoplanets is essential to our quest for life on other worlds. These discoveries on Mars take us a step closer to satisfying our curiosity about how life begins and whether we’re alone in the universe.
The team plans to find ways to look further back in time and learn more about primordial Martian water processes. They believe there’s more to the story.
“Nail Down the Impact of this Process”
“Before the process we describe began to operate, there must have been a significant amount of atmospheric escape to space already,” Stone said. “We still need to nail down the impact of this process and when it began to operate.”
We always have more to learn if we dare to know.
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Abundance of Water: Where Did It All Come From?