Planets

Did Asteroid Impacts Incubate Mars' Ancient Oceans?

A bombardment of asteroids on a once-icy ancient Mars may have created vast oceans of liquid water, which persisted for 200 million years.

Last year, NASA researchers looked at water in the Red Planet's atmosphere and compared it to water trapped in ancient meteorites from Mars. The research suggested that roughly 87 percent of the water escaped to space. But there's ample evidence out there that Mars was once soaked in water. For example: All three rovers that landed on the surface have found evidence of it in various forms - minerals formed in water, or ancient streambeds.

If an ocean did exist, it would be where the rovers are - in the northern plains, since it is low-lying ground. But how did that water get there in the first place?

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An emerging hypothesis suggests that a few billion years ago, much of Mars was covered in water ice (similar to the poles of today). The ice likely came from asteroids depositing it on to the surface. Then came an event known as the Late Heavy Bombardment, where asteroid debris pummeled the inner solar system roughly four billion years ago. The asteroids could have melted the Martian ice and created an ocean for as long as 200 million years.

The research comes from Timothy Parker, a research scientist at NASA's Jet Propulsion Laboratory, who has researched the possibility of a past ocean on Mars since the 1980s. That's when the Viking missions were beaming back black-and-white images of Mars at what today would be considered extremely low resolution. Even then, Parker told Discovery News, he could see what he described as "wave-refracted shorelines" in the northern plains of Mars, shorelines that appeared similar to what is on Earth.

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As better, more high-resolution data arrived in the 1990s and beyond, Parker noticed something odd. The supposed Martian ocean interiors are lower than the shorelines. This is opposite to what happened on Earth, when isostatic rebound (the ground rising up after large icebergs melt) made the interiors higher than the shorelines. What accounted for the mystery?

The Opportunity rover (pictured in January 2016) may be examining an area that was covered in ocean a few billion years ago, new research suggests. | NASA/JPL-Caltech

The new work on Mars focuses on Meridiani Planum, the region in which the Opportunity rover has been driving since 2003. Researchers have seen a lot of material associated with evaporation there - primarily sulfate (salt) deposits. From Earth observations (such as in the Bahamas), Parker says that to get that kind of deposition, you need to have a very shallow ocean just a few meters deep. This leads to concentrated water evaporation over a broad, shallow area, leaving behind expansive sulfate deposits.

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Parker suggests that Mars did not natively have an ocean - it was too far from the sun and its atmosphere, even back then, was quite thin. Instead, he suggests that Mars was an ice-covered planet. The sulfates came from meteorites that hit the surface and temporarily melted the ice, forming a shallow pool of water.

"Once the Late Heavy Bombardment ceased, the ocean regressed and froze over," Parker said. That would explain the shorelines staying depressed, because the resulting ice didn't evaporate rapidly as what was seen on Earth after ice ages; instead, it slowly sublimated into the Martian atmosphere.

He also pointed out that such an ocean would have been covered in debris and ice. At the shorelines, it would create channels that look like they were carved by thick lava (an alternate explanation for possibly water-carved channels on Mars).

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Artist's impression of Comet Siding Spring making a close pass by Mars in October 2014. Mars has been hit by countless asteroids and comets in its history. | NASA's Goddard Space Flight Center Conceptual Image Lab

Parker believes that Opportunity is driving on an ocean lakebed because of the number of large polygonal cracks it has encountered (implying massive evaporation). Also, some parts of Endeavour Crater (its current roving grounds) have damage, scour marks and the like that suggest ice being pushed around in vast quantities by water and hitting the shoreline. But his hypothesis is not universally accepted by the team, he added.

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Another explanation for a liquid ocean could be the planet gradually outgassing volatiles through volcanism, but this depends on factors such as how thick the atmosphere was on Mars and how much sunlight the sun had to warm the planet. The general consensus was the young sun only had 70 percent the strength of the current one, so Parker said he isn't sure this alternate hypothesis is viable.

Parker presented his research at the Lunar and Planetary Science Conference in Texas in March. He said his goal is to get some discussion from the community, and to begin correlating the work with results from other missions such as NASA's orbital MAVEN (Mars Atmosphere and Volatile Evolution) mission, which is investigating the mysteries of Mars' thin atmosphere.

Artist’s impression of a primitive ocean on Mars, which one set of researchers suggested had more water than the Arctic Ocean on Earth. (Most of that water was later lost to space.) NASA/GSFC

Long-distance-moving pebbles and mountains growing out of lake deposits -- this was the Mars of several billion years ago, showing extensive evidence of

liquid

water shaping the landscape. While hard to imagine when looking at images of the dust-swept Martian landscape of today, NASA's Curiosity rover has gathered a lot of information showing how the rocks were shaped and formed by liquid water. Here are some of its key findings.

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Image: This self-portrait of NASA's Curiosity Mars rover shows the vehicle at the "Big Sky" site, where its drill recently collected the mission's fifth taste of Mount Sharp.

Pebbles like this on Mars were long-distance travelers,

perhaps moving as far as 30 miles on Mars

. The research team that came up with this figure based their work both on how the stones were shaped -- they had a model predicting how the stones change as they scrape against other objects -- and erosion tests from observations in the lab, Puerto Rico and New Mexico.

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Image: Curiosity's images of rounded pebbles show evidence that they were shaped and carried by water on ancient Mars -- imagine rocks being carried by babbling streams and rivers flowing down the slopes of Gale Crater and you wouldn't be far wrong.

This picture of the "Kimberley" formation shows strata (rock layers) that are lower near the base of Mount Sharp, the informal name that NASA gives to Aeolis Mons. This shows how the

water flowed into a probable lake

about 3.3 billion to 3.8 billion years ago, before the mountain formed. While the skies look blue in this image, don't be fooled; engineers color-adjusted the image so that it looks similar to colors on Earth. This assists geologists with making comparisons between our planet and the Red Planet.

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These veins are the leftovers of fluids that brought minerals with them. These minerals fell into the cracks of a rock that was already broken apart and

changed the chemistry of the rock itself

. The veins are so resistant to erosion that they today stand prominently on Mars, up to 6 centimeters (2.5 inches) high around the bedrock, which was softer and eroded over the eons.

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Mount Sharp

grew through river deposits

, according to data obtained from the Curiosity rover -- indicating that water could have persisted on the Red Planet for a long time. NASA describes these pictured rocks as typical of what you would find under river deposits; it uses words such as "thick-laminated" and "evenly-stratified". Geologists looking at this formation, on the edge of "Hidden Valley", are believed to show the remains of sediments that fell on to a lake floor nearby where a flowing river brought in water. The colors have been corrected to look approximately like what you would see on Earth, for better comparisons.

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Within weeks of landing in August 2012, Curiosity stumbled upon a major find: a dry riverbed, showing that water flowed not far from where the rover landed in Gale Crater. Several sites showed evidence of this water,

including "Hottah."

From looking at how big the stones were and seeing that they were rounded, the scientists estimated that the water moved at about three feet per second, somewhere between ankle and hip deep.

MORE: Curiosity's Mars Crater was Once a Vast Lake