Canyons on Mars may have formed when the Red Planet tilted sharply on its side, triggering dramatic shifts in climate that sent water flowing down slopes to form valleys, a new study finds.
Scientists first discovered canyons on Mars in 2000. They look a lot like channels that form on Earth in the Dry Valleys of Antarctica, which were carved out by water from melting glaciers. As such, the Martian valleys indicated that water once flowed on Mars, and may still flow at times.
“It looks a lot like Earth, but it’s on Mars, so how could it have formed there?” The study’s lead author James Dixon, a planetary scientist at Caltech in Pasadena, told Space.com. “It was a big puzzle that many scientists worked on.”
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The problem with possible canyons on Mars is that these valleys are often found at altitudes where no liquid water would be expected given the current Martian climate. The air on the Red Planet at present is too cold and thin for liquid water to last long, and it is even cooler and thinner at higher elevations than it is at lower elevations, just as it is on Earth.
Previous research has suggested that these gullies may have a different source — carbon dioxide frost that sublimated, or turned directly into steam, when Mars experienced warm spells, causing rocks and debris to slide down slopes. However, much is still unknown about this scenario, as it does not occur in nature on Earth.
Another possibility is that these grooves formed in the past, when the Martian climate was more suitable for the small amounts of liquid water on Mars’ surface. This may explain the height of the canyons – meltwater from glaciers could flow down slopes, excavating channels.
To see if liquid water could exist on Mars, scientists examined how its axial tilt, or skew, changed over time and the potential effects of this tilt. The greater the inclination of a planet’s poles relative to its orbit around the sun, the greater the variation in the amount of sunlight received by different parts of that world throughout the year.
Earth’s axial tilt of 23.5 degrees results from its seasons. Mars’ tilt is currently about 25 degrees, but it has varied between 15 and 35 degrees over hundreds of thousands of years, which could result in more dramatic changes in climate.
The researchers studied how higher declination times on Mars would lead to sharper fluctuations between winter and summer, and possibly climates more favorable to liquid water. They developed a global 3D model of the Martian climate to see what would happen at an inclination of 35 degrees.
Scientists found that at the Martian sites where the gullies are now located, the sublimation of carbon dioxide ice would make the Martian atmosphere significantly denser. In addition, surface temperatures are likely to have exceeded the melting point of water ice. It is likely that these conditions have occurred repeatedly over the past millions of years, with the last being about 630,000 years ago.
In addition, these canyon areas currently have a lot of water ice near the surface, and likely have had a lot more over the past million years. The researchers suggest that during times of high axial tilt, much of this ice may have melted to form gullies at higher elevations where they are now seen.
Altogether, the scientists argue that a combination of melting ice, rising carbon dioxide, and high eccentricity could help explain the pattern of gullies seen on Mars.
“One important implication is that we can now predict that when Mars’ orbit tilts again, it should be able to generate meltwater in these gullet locations,” Dixon said.
Since life exists on Earth almost anywhere there is water, future research may want to focus on these canyons on Mars to see if life existed on the Red Planet, and perhaps still lives there.
“If you’re looking for a still life, these sites would be good targets,” Dixon said.
Scientists explain in detail their findings June 30 in Science.
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