New research suggests that the incredible tilt of Mars’ axis of rotation over the past 20 million years may have driered the planet. The findings may help solve the mystery of how Mars, which once contained lakes, rivers and perhaps oceans, lost water.
The dry, dusty desert covers most of the surface of Mars today. Astronomers believe that the majority of the planet’s scarce water reserves are frozen in fine-grained surface taints with ice on the surface, confined to the polar regions.
However, the red planet is not always so dry. The gully, lake beds and valleys, photographed by early NASA missions like the Viking Project, suggest that the planet’s surface has been regularly flooded with billions of gallons of liquid water since the birth of Mars. In fact, planetary scientists have calculated that the volume of water carving these geological features corresponds to a thickness of at least 300 feet (100 meters) across the planet’s surface.
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One hypothesis of where the water went is that many of them “boiled.” In a joint email to Live Science, Gabriella Gilli and Francisco González-Galindo, astronomers at the Astrophysics Institute in Spain, first and second authors of new research, respectively, explained the process.
Water vapor in the Mars atmosphere – kicked high by a powerful sandstorm – would have been split into atomic hydrogen and oxygen due to the powerful ultraviolet rays of the sun. Some of this lightweight atmospheric hydrogen would have had enough energy to escape into space.
“If we consider that in the end hydrogen in Mars’ atmosphere is born from water, the escape of hydrogen atoms involves the loss of water molecules,” said Gili and Gonzalez Galindo.
Related: Mars Rover captures first close-up photo of the giant “SpiderWebs” on Red Planet
NASA’s ongoing measurements from Mars’ atmosphere and volatile emission missions suggest that around 100 trillion hydrogen atoms currently leave the Mars atmosphere per second. However, using current escape rates, Mercury has lost over 4 billion years is, at best, only a quarter of the amount calculated to have sculpted various geological features. In other words, most of Mars’ historic water losses cannot be explained by this mechanism alone.
To resolve this contradiction, the authors of the new study proposed a different idea. This means that Mars lost much more water when its axis of rotation was very tilted in the past. Today, Mars’ tilt, or diagonal, is 25.2 degrees compared to the orbital plane around the Sun, similar to Earth’s 23.5 degrees. However, the slope of the red planet has not remained stable for the past millions of years.
“The main reason is that Mars, contrary to Earth, does not have a huge moon (the moon) that plays a major role in stabilizing planetary orbital fluctuations,” Gili and Gonzalez Galindo said. As a result, Mars is spinning violently between a massive 66 degrees, ranging from 0 to 66 degrees, on an average of 35 degrees.
Researchers assumed that Mars tilted further, and that Arctic received more sunlight. Daniel Law, a postdoctoral researcher at the University of Michigan who was not involved in the study, agreed with the reasoning, saying, “During the increase in Mars’ axial tilt, Earth’s temperature actually increased, and some of the water ice told Live Science via email. [across the planet] Sublimates into water vapor. ”
To test their hypotheses, the authors of the new study have been transformed into a computational simulation called the Mars Planetary Climate Model. The team changed the planet’s tilt to virtually 30 and 35 degrees, tracking the amount of hydrogen lost in Mars year. They also used real data to assess the impact of sandstorms.
Analysis revealed that such storms increase hydrogen loss by up to 50% depending on the strength of the storm. However, the actual eye-openings came with oblique results. At a 35° slope, an average of 19 hydrogen atoms (compared to current values) escaped from the Mars atmosphere per second. This corresponds to the annual loss of Mars of billions of hydrogen atoms compared to today’s hydrogen loss. Gilli and González-Galindo pointed out that this would be converted to Mars, the equivalent of a 260-foot (80 m) global water layer over its lifespan.
Findings published in Nature Astronomy on May 21 showed that changes in the Earth’s tilt significantly increased the amount of hydrogen, or the loss of water.
“Atmosphere thermal escape suggests that it played a greater role than thought in drying out the planet,” Gili and Gonzalez Galindo said. However, they said factors such as the planet’s dust composition could have also influenced water loss, unlike current values.
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