Weird Mars Streaks Could be Liquid Water Stains

Dark seasonal streaks on slopes near the Martian equator may be a sign of flowing salt water on Mars, liquid runoff that melts and evaporates during the planet's warmer months, scientists say.

NASA's Mars Reconnaissance Orbiter spotted the dark streaks on Mars as they formed and grew in the planet's late spring and summer seasons, when the Martian equatorial region receives the most sunlight. The streaks then faded the next season as cooler temperatures prevailed.

PHOTOS: Hebes Chasma: Mars Express Stares into Martian Abyss

These seasonally occurring flows - known as Recurring Slope Lineae - were previously seen on Martian slopes at mid-latitudes, but the MRO spacecraft has now detected them near the equator of the Red Planet. While there have been no direct detections of liquid water, the new findings hint at a surprisingly active water cycle on Mars today, said study leader Alfred McEwen, a professor of planetary geology at the University of Arizona in Tucson. [Photos: The Search for Water on Mars]

"Now we've found them in equatorial regions," McEwen told SPACE.com. "This is more surprising, given peoples' expectations that the equatorial region was completely dry. It suggests there may be much more water in the near-surface crust than we imagined before."

Flowing Water On Mars?

The dark, narrow lines were observed on long, steep slopes in Valles Marineris, an extensive series of canyons located along the equator of Mars. In some cases, the fingerlike streaks stretched nearly 3,700 feet (1,130 meters).

NEWS: Mars Rover Finds Ancient Life-Supporting Lakebed

The discovery is detailed in the Dec. 10 edition of the journal Nature Geoscience and will be discussed today at the annual American Geophysical Union meeting in San Francisco.

Researchers are still puzzling over the likely cause of these tantalizing streaks, but McEwen said they could be produced by the melting and subsequent evaporation of frozen salty water trapped deep in the planet's crust.

But, much is still unknown about whether the streaks are actually caused by liquid water, and if so, where the water is coming from. So far, researchers say the best explanation is that the liquid is a salty, or briny, solution. Salty water can stay liquid at colder temperatures, which means brines could conceivably flow on the frigid surface of Mars.

PHOTOS: Mars Through Curiosity's Powerful MAHLI Camera

"Water should be rapidly evaporating, so it's difficult to explain long flows unless it's sufficiently salty water," McEwen said.

Also, Mars has a very dry atmosphere, which makes it unlikely that freshwater flows on the surface of the planet, said Vincent Chevrier, a planetary scientist at the University of Arkansas in Fayetteville, who was not involved with the new study.

"Water has a tendency to evaporate very quickly when it's exposed at the surface," he told SPACE.com.

Chasing Streaks on Mars Last year, Chevrier led a team of researchers who investigated the seasonal flows found on Martian slopes at mid-latitudes. The scientists modeled the behaviors of different brine mixtures to see if any could exhibit similar characteristics to what had been observed on Mars.

Chevrier and his colleagues found that calcium chloride did not immediately evaporate, and left behind some liquid that could create the types of streaks seen on the Red Planet.

Others have attempted to explain the seasonal markings with "non-liquid" solutions, such as wind patterns, but so far none have seemed plausible, McEwen said.

PHOTOS: Alien Robots That Left Their Mark on Mars

"So far, there aren't any good dry hypotheses," he said. "There are some possibilities, and we keep them open as working hypotheses, but no one has been able to come up with a detailed model that makes sense."

While scientists have long viewed present-day Mars as a dry and dusty world, evidence abounds that water once flowed across much of the planet billions of years ago. Frozen water has been detected near the planet's surface at middle-to-high latitudes, but so far, no definitive evidence of liquid water has been found.

The new findings raise intriguing questions about the possibility of liquid water on present-day Mars, which has ties to the ongoing search for life on the Red Planet.

"It's certainly very surprising to me that this is happening on Mars today," McEwen said. "If it is water, that really changes our thinking of the planet's water cycle and habitability."

NEWS: Mars Probe to Study How Planet Lost Its Water

On Earth, life teems wherever liquid water is found, which means a wetter Mars could have tantalizing prospects for hosting extraterrestrial life.

"Earth is loaded with liquid water -it's a liquid water paradise," Chevrier said. "I'm not saying this means life is possible on Mars, but this is a good small step."

Follow Denise Chow on Twitter @denisechow. Follow us @Spacedotcom, Facebook or Google+. Originally published on SPACE.com.

[*]The Search for Life on Mars (A Photo Timeline) [*]7 Biggest Mysteries of Mars [*]Mars Myths & Misconceptions: Quiz

Copyright 2013 SPACE.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

A portion of the Coprates Chasma showing dark streaks on generally north-facing slopes in northern summer and southern winter. Coprates Chasma is a huge canyon that forms part of the Valles Marineris system

The Martian surface is peppered with impact craters of all shapes, sizes and ages. However, many of the craters are just plain weird.

But just how 'weird' is weird?

Curious, Discovery News asked the High-Resolution Imaging Science Experiment (HiRISE) team which craters they considered to be the strangest. HiRISE is the most advanced camera to be put into Mars orbit. It is attached to NASA's Mars Reconnaissance Orbiter (MRO) and currently snapping features on the Red Planet's surface -- it has seen a ton of strange objects (sadly, it hasn't found a top secret military base yet, despite what you may have heard to the contrary). So, let's take a tour of some of the weirdest craters Mars has on offer...

Special thanks to Ari Espinoza of the HiRISE team for helping to compile this list (originally published Dec. 30, 2011. Updated May 7, 2013)

Crater, Horst and Graben: Is that a piece of modern art? Actually, it's an impact crater that has been bent and twisted by tectonic processes. Along the fault line that crosses this crater, blocks of rock are forced upward (called "horst") and downward (called "graben"). This is interesting to planetary scientists as it shows that tectonic activity was occurring after the crater was formed.

Rolling Stones Logo? If you squint and use a little imagination, you may see the Rolling Stones' logo. Well, that's what the HiRISE team told us anyway. (I'm still squinting...) In reality, it's an impact crater on a sloping surface. Presumably, the "tongue" of material is slipping down the slope.

Bulls-Eye Impact? Did a small meteorite have the incredible fortune to slam into the center of a larger impact crater? Probably not.

This is one of several examples of "terraced" craters where alternating layers of hard and soft material in the surface layers of the Martian surface have been hit by a single meteorite. The result is a concentric nesting of ridges inside the same crater. Pretty!

What the...? What's the weirdest kind of impact crater? The kind that may not be an impact crater at all (but looks like one). On the slopes of Pavonis Mons, one of Mars' shield volcanoes, this crater has a hole in the middle. The hole is a "skylight," or the collapsed roof of a subterranean lava tube. The loose material above the collapsed roof appears to have slumped into the skylight, creating a crater lookalike. But what caused the roof of the lava tube to collapse? Could a meteorite be to blame? No idea, but HiRISE will be taking some more photos of this little oddity to find out.

Two-for-One Crater Special: What could be worse than a meteorite hitting you? Two meteorites hitting you... at the same time! Yes, that's exactly what happened here. It seems highly likely that one object tumbled through the Martian atmosphere and split in two. In doing so, the two halves impacted in the same location. As can be seen from this example, both halves were likely the same size, producing a rather satisfying imprint.

Another Double-Whammy: Looks like double-impacts are becoming a trend! This time, in addition to the two co-joined impact craters, HiRISE has picked out the rays that are produced when space rocks slam into the Martian surface.

Hit Me Baby Three More Times? It may seem hard to believe, but Mars also has triple-impact craters! It stands to reason that after countless impacts, you might get the occasional meteorite that splits into three when blasting through the atmosphere. So here you have it, a triple-impact crater.

A Triple Ricochet Crater: Another three (likely simultaneous) impacts, only this time their craters are elongated. This suggests the meteorites hit the surface at an oblique angle.

A Simple Blemish: In an apparently featureless plain in the north polar region, a single, small crater appears as the only blemish. Looking closely, the crater seems to be filled with ice.

Bubbly Landscape: This cluster of impact craters in the northern plains of Utopia Planitia contain strange uplift features likely caused by ground ice upheaval.

Crater of Mud: The strange concentric rings inside this crater near the Martian volcano Elysium Mons are thought to be the ancient remnants of a mud flow. Therefore, it is believed this crater wasn't caused by an impact from space, but by material flowing away from under the surface. The crater was then formed as the material above slumped.

Cracked Cookie Crater? There's an odd pair of craters in Hrad Vallis that the HiRISE website describe as a "pair of odd craters." Why so... odd? Well, to me, the larger crater looks like a cracked cookie, probably crevasses and faults carved across its diameter.

The Crater with a Robot Visitor: What makes this crater weird? Well, it's not the crater, it's the little man-made robot that's parked on the crater's western rim that makes this scene weirdly awesome. It's even weirder to think that a robot in Mars orbit has taken a photo of another robot on the Martian surface a couple of hundred miles below. Robots looking out for robots on alien worlds...

This is of course NASA's tenacious Mars Exploration Rover Opportunity that keeps exploring the Martian surface since exceeding its primary mission duration of 3 months back in 2004. Opportunity now has company on the Martian surface -- on Aug. 5, 2012, the nuclear-powered Curiosity landed inside Gale Crater to look for clues behind the habitability of the red planet.

In March 2013, HiRISE spotted a series of non-impact craters in Acidalia Planitia. These may not be impact craters, but they are unlike any other crater discovered on Mars to date! So the process behind their formation will remain a mystery... for now.