Planets

Boiling Water May Be Cause of Martian Streaks

The results of Earth-bound lab experiments appear to back up the theory that dark lines on Martian slopes are created by water.

The results of Earth-bound lab experiments appear to back up the theory that dark lines on Martian slopes are created by water - though in an otherworldly manner, scientists said Monday.

A team from France, Britain and the United States constructed models and simulated Mars conditions to follow up on a 2015 study which proffered "the strongest evidence yet" for liquid water - a prerequisite for life - on the Red Planet.

That finding had left many scientists scratching their heads as the low pressure of Mars' atmosphere means that water does not survive long in liquid form. It either boils or freezes.

The Mysteries Behind The Dunes Of Mars: Photos

Identifying water on the Red Planet is complicated by our limited understanding of natural processes under conditions so different to those on Earth.

In September last year, a team reported in the journal Nature Geoscience that curious lines running down slopes on the Martian surface in "summer" may be streaks of super-salty brine.

They said they had found evidence in the lines of "hydrated" salt minerals, which require water for their creation.

When Liquid Water Gushes On Mars: Photos

The lines, up to a few hundred meters in length and typically under five meters (16 feet) wide, appear on slopes during warm seasons, lengthen, then fade as they cool.

"Under certain circumstances, liquid water has been found on Mars," NASA concluded at the time.

For the latest study, also published in Nature Geoscience, researchers took to the lab to try and explain how water could have made the lines.

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The team, led by Marion Masse of the University of Nantes in France, included several of the authors of last year's headline-making study.

They placed a block of ice on a 30-degree plastic slope covered with loose fine-grained sand, and allowed it to melt in a chamber in which Martian pressure and summer temperature was recreated.

They repeated the experiment under Earth conditions to compare the processes.

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Under Martian pressure, they found, melting ice produced a liquid which boiled vigorously as it flowed downslope and filtered into the sand.

The evaporating water vapor blasted grains upward, creating ridges which collapse onto themselves when they become too steep, forming channels.

"The morphologies produced on the sandy slopes in these experiments are remarkably similar to the streaks observed on Mars," Wouter Marra of the geosciences faculty of the University of Utrecht in the Netherlands commented on the study.

"This process in which unstable boiling water causes grains to hop and trigger slope failures may underlie some of the active landforms observed on the Martian surface."

How does the wind blow on Mars? It sounds like a simple question, but scientists are still learning a lot about how that happens. With few meteorological stations on the surface, one of the best

indicators is observing sand dunes from orbit

-- vast formations that march across the Martian surface, sometimes as much as several feet per year. In recent months,

Curiosity has been maneuvering

for an unprecedented close-up look at these dunes to see, in great detail, how the grains of sand shift. Scientists are trying to figure out mysteries such as why ripples appear larger on some Martian dunes than Earth ones, and why they're of a different texture. Read on to explore some of the most recent findings and past observations of Mars' mysterious dunes.

PHOTOS: Curiosity Plays in Sandy Martian Dunes

Image: This observation was imaged by Curiosity's front Hazard Avoidance Camera (Hazcam) on Sol 1184 (Dec. 5) as it carried out a closeup investigation of dunes on the slopes of Mount Sharp.

This is one of the first images ever of a rover next to a large dune on Mars. Previously, NASA Mars Exploration Rovers Spirit and Opportunity were by much smaller ripples. NASA is trying to learn more about how dunes, which are distinguished by steep flanks like the one pictured here, move about on Mars. The challenge is modelling Martian winds and sands, which are obviously not as well-known as what is found on Earth. Curiosity is on the lookout for evidence of sand slides,

which happened relatively recently in this picture

-- a season ago in Martian terms.

MORE: The Weird Wind-Rippled Surface of Mars

Image: Panoramic image of the Curiosity rover next to "Namib Dune" on Dec. 18, 2015.

In 2009, the Spirit rover was exploring Gusev Crater -- filled with fluffy regolith -- when it became mired in a sand trap nicknamed "Troy." While not technically a dune, scientific investigations of the region before Spirit got stuck and eventually died showed what sand can hide underneath. In this case, the rover was sitting atop a sulfate deposit, associated with a hydrothermal (steam) vent. The rover's demise showed how difficult it is to predict the composition of sand in even flat regions on Mars.

MORE: Mapping Mars' Ripples Unveils Dune Mysteries

Image: The Spirit rover captured the region where it got stuck, nicknamed "Troy", in April 2009.

For the last few years, Opportunity has been exploring Endeavour crater on Mars.

This picture was taken while the rover was en route

, in April 2010. The dunes pictured here are relatively modest -- just 20 centimeters (8 inches) tall. The brighter spot in the foreground is a rock outcrop. Opportunity's controllers changed its route to Endeavour after discovering sand ripples (larger than the ones pictured here) that could have posed a threat to the rover.

MORE: Mind-Blowing Beauty of Mars' Dunes

Image: Ripples in Endeavour crater as seen by the Opportunity rover in April 2010.

In 2014, the Mars Reconnaissance Orbiter's powerful camera, HiRISE, captured dunes in the extremely active area of Nili Patera. The dunes have been tracked moving an average of 1.7 meters (5.5 feet) in less than four Earth months, according to

a Geophysical Research Letters journal article

. What's even more astonishing is just how big these dunes are: up to 50 meters (164 feet) high. You can see more

incredible HiRISE pictures of Martian dunes in a previous Discovery News article.

MORE: The Psychedelic Landscape of Mars

Image: Nili Patera, a very active dune field on Mars, caught by the HiRISE camera on the Mars Reconnaissance Orbiter.

Once again, this image shows the amazing extent of dunes on Mars. This image is of the formations in Bunge Crater, taken by NASA Mars Odyssey's thermal emission imaging system in 2006, covering a region about 14 kilometers (9 miles) wide. The dunes are moving towards the left of the picture in this perspective. Scientists are doing their best to understand these processes by using computer models and comparing these dunes with ones on Earth.

PHOTOS: The Weirdest Craters on Mars

Image: Bunge Crater dunes -- described as "fans and ribbons" of dunes by NASA -- take on the appearance of a rough skin on the surface of Mars. Picture taken by Mars Odyssey in January 2006.

This ESA Mars Express picture shows dunes towering in Rabe Crater as high as 200 meters (656 feet) high, nearly twice the height of the Empire State Building. They're mostly made up of basalt (volcanic rock) and have complex geology, according to the European Space Agency: "Its flat floor has a number of smaller craters and large sunken pits within it. The bulk of the dune material sits atop the flat remnant of the original crater floor, but then some of it spills dramatically down into the pits below."

MORE: Sand Dunes Could Reveal Weather on Alien Worlds

Image: Ripples of dunes inside a crater are visible in this 3-D view based on Mars Express data on Rabe Crater. Images to construct this view were taken in 2005 and 2014.