We often picture Mars as a dead, barren, endlessly rolling landscape of red sand and rocks. But there's a lot more going on down at the Martian surface than most of us Earthworms would imagine.
In orbit around Mars since 2006, NASA's Mars Reconnaissance Orbiter (MRO) has spent nearly a decade using its half-meter wide telescopic lens, coined the High Resolution Imaging Science Experiment (HiRISE), to capture some very impressive images of the Martian surface.
Over the years, HiRISE has captured detailed images of a geologically diverse landscape, a mix of ancient features as well as ones that are newly formed, and a host of Martian oddities. From melting ice caps to powerful wind storms, here are seven strange and distinctively Earth-like features detected on the surface of Mars (and no, none of them are faces).
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This isn't a photo-shopped picture of blue sand dunes somewhere on Earth, it's an image of the surface of Mars captured in infrared by HiRISE. These particular dunes have formed in an area on Mars that can reach temperatures as low as minus 100 degrees Celsius, and only rarely reach temperatures above freezing.
But these low temperatures aren't the cause of their blue color. Because infrared cameras capture light in the blue end of the color spectrum, the red sands of Mars aren't accurately represented in this image. Infrared is used to make detailed measurements of surface temperatures at various points around the Martian surface.
By comparing images of the same series of dunes taken over a period of years, scientists have concluded that the Martian winds move these sand dunes at a global average of about 1 meter per Martian year—which is equivalent to 687 Earth-days—with some moving at speeds much quicker than that.
Complex geological features aren't restricted to the surface of Earth, with sand dunes being the most commonly observed feature on Mars. The distribution and appearance of specific dunes provides clues as to wind and weather patterns in localized areas, allowing scientists to better map the weather system of Mars and make more accurate predictions about the type of terrain any given area.
By combining infrared temperature data with extrapolated weather conditions based on the appearance of sand dunes, scientists are able to create highly detailed weather maps across the Martian surface. Eventually, this study could aid in the planning of future rover missions (in order to prevent wear-and-tear on rover equipment) and eventual manned missions to Mars.
A fresh Martian impact crater measuring 30 meters in diameter, the blast generated at impact scorched the area and left dark streaks across the surrounding terrain. Because the impact blew away most of the surrounding red dust, this enhanced-color infrared image makes the crater appear especially blue against a neutral-colored Martian landscape.
The fact that Martian winds haven't yet blown enough sand in to re-cover the area suggests that this crater is relatively new. As HiRISE continues to survey the Martian surface year after year, before-and-after images show fresh craters appearing on the surface—approximately 200 new craters measuring at least 3.9 meters in diameter appear every year on Mars.
From 2006 to 2008, this crater was home base for NASA's Opportunity rover. Taken five days after Opportunity arrived at the rim of the crater, the rover can be seen as a small spec in the above image (at the 10 O'clock position; mouse-over the image to show its location). A higher resolution version of the above image with Opportunity more clearly visible can be seen here.
Opportunity spent its time examining exposed rock layers in the 750 meter-wide, 75 meter-deep crater. By combining data obtained by HiRISE, scientists were able to determine that Victoria crater had originally been approximately 600 meters wide by 125 meters deep. This means that, over a long time period, Martian winds steadily eroded the crater walls and filled the crater in with about 50 meters worth of sediment, which suggests the crater has been around for quite some time.
This image of Mars' Southern polar carbon dioxide ice cap shows an area of the red planet that remains covered in ice year-round. At higher latitudes, carbon dioxide ice forms across the Martian surface during Winter (as Mars moves further from the sun) and melts with the approach of Spring. But in some areas of the Southern polar region, ice persists throughout the year.
Reminiscent of a cluster of ice bergs trapped in a frozen sea, the elevated regions are composed of carbon dioxide ice (known as 'dry ice' here on Earth) that is several meters thick. The lowered regions are thought to form when the carbon dioxide rapidly changes from solid to gas during the warmer months, leaving some elevated pockets of ice behind.
Since HiRISE is able to observe the expansion and contraction of ice in the polar regions year-over-year, scientists are in the process of trying to determine whether Mars' climate is changing. Similarly to how we use satellites to measure the amount of ice present in our North and South poles on Earth, HiRISE is attempting to determine whether ice on the Martian poles has been steadily growing or declining over time.
Whereas Mars' Southern pole is primarily covered in carbon-dioxide ice, the North pole of Mars is more reminiscent of Earth—covered in a bright white layer of water ice year-round.
This image shows the Northern pole, a region consisting of an endless number of small mounds of ice about one meter tall and 20 meters wide. This landscape stretches for hundreds of kilometers in every direction with no change in appearance, just a repeating pattern across the entire North pole. Scientists haven't been able to explain how these types of patterns can be so uniform over such long distances on Mars.
Occurring in the Athabasca region, which contains many of the youngest lava flows on Mars, this circular feature is nearly 2 kilometers across and appears to have been formed by underground volcanic processes.
Although Mars' core is known to be at least partially molten, its smaller size and larger distance from the Sun than Earth means that its core is much cooler. Its cooler core means that Mars' volcanic activity should have ground to a halt a long time ago, yet features such as this still litter the Martian landscape and confound the scientists who study them.
Near the base of Olympus Mons, the largest volcano in the solar system (it protrudes 22 kilometers above the Martian surface, but is no longer active), is this ancient lava channel. Although it's been filled in with many years with Martian sand and dust, the channel once ran underground at various points as a continuous lava tube before popping back out onto the surface.
Due to the slower process of erosion on the Martian surface, features such as this can persist for much longer on Mars than they do on Earth. Whereas the ever-changing surface of Earth tends to quickly erase its geologic history, these ancient and well-preserved features of Mars can provide clues as to what the Martian surface may have looked like in the very distant past.
Over the many years of continuous, close-up observations of the Martian surface, scientists have consistently found evidence for the past, or even present, existence of liquid water on the surface of Mars. Gullies such as these, measuring from 1 to 10 meters wide, can be found in abundance at various locations around the red planet.
Despite years of observation and rover exploration, scientists are still unable to account for how or when these gullies could have formed. Because Mars' gravity is so low and its atmosphere so thin, the sparse atmospheric pressure remaining on the surface is such that any liquid water should evaporate just as though it were in the vacuum of space.
And yet, features that look to have been formed by flowing liquid can be found nearly everywhere on Mars.
These gullies have formed on the northern wall of an unnamed crater, and water is again implicated in their formation—perhaps through the melting of snow or ground ice. Most Martian gullies appear to have been formed quite recently, since impact craters are rarely seen on them.
Although there are various compelling theories to explain for the formation of Martian gullies, if the liquid water hypothesis turns out to be correct, then the recency of their formation would suggest that liquid water has existed on Mars in the very recent past, and is therefore likely to exist at present.
Most scientists presume that, if any water does remain on Mars, it's locked deep below the surface where it remains insulated from the vacuum of space.
These repeating geometric patterns are thought to have formed as a result of cyclic thermal contraction recurring year-over-year, as growing and shrinking ice features cause cracks to form in permanently frozen ground. These sorts of polygonal shapes are common in the Northern lowlands of Mars, and are useful in helping scientists identify areas in which frozen sub-surface water could be present.
Although these geometric shapes tend to indicate the past or present existence of ground ice, sometimes the Martian surface tells a more complicated story. In this case, rather than being an indicator for the presence of sub-surface ice or water, the geometric pattern imaged above is actually formed by wind-swept sand dunes intersecting with one another as they slowly inch across the barren landscape.
These dark lines swirling across the surface of Mars aren't formed by giant underground worms, they're most likely tracks left behind by dust devils—whirlwinds that can reach over a kilometer in height. As these whirlwinds lift the reddish dust off of the Martian surface, they expose a darker layer of soil below.
Although made of the same material, sand on the surface of Mars appears red because the iron particles in the sand have been oxidized from exposure to solar rays, whereas the material that's typically buried deeper below the surface hasn't yet been exposed long enough to change color.
This area pictured above was imaged about two Martian years prior (nearly four Earth years) and also contained dust devil tracks. However, those tracks were completely different than the ones visible above. This suggests that, at some point in the past couple of years, strong winds had erased the old tracks and newly formed whirlwinds had come through to produce new tracks.
However, these dark streaks having been formed by dust devils is just one of many theories. Other ideas implicate liquid water in their formation, or perhaps even the growth of Martian organisms on the surface.
This image shows a dust devil that's about 30 meters wide at it base, extending to a height of 800 meters. The winds of Mars are at their strongest while Mars is closet to the sun, meaning dust devil activity typically decreases as Mars moves further away in its orbit. This image was taken while Mars was furthest from the sun and Martian winds were at their mildest, showing that dust devils regularly form in the off-season as well.
Perhaps the strangest aspect of the Martian surface is how similar many of its features are to Earth's surface. Separated by millions of kilometers of space and perhaps a billion years of planetary evolution, a glimpse at Mars is in many ways a glimpse at the future of Earth.
Because Mars is both smaller and further from the sun than Earth, it cooled much faster. While Earth was still a molten ball of rock spewing out seas of lava onto its surface, Mars would've been just cooling down enough to resemble the primordial Earth from which life first formed. Evidence suggests that Mars may have supported an ocean of liquid water up to 500 million years before one existed on Earth.
Recent estimates suggest that Mars had enough water 4.3 billion years ago to cover its entire surface up to 143 meters deep. And since all evidence points to Earth's first ocean having formed about 3.8 billion years ago, Mars would've had a significant head-start in terms of habitability for organic life forms.
The catch-22 is that the swift cooling which jump-started the formation of oceans on Mars also led to their downfall. The leading hypothesis is that, as Mars' molten core gradually cooled, Mars' magnetic field weakened significantly and volcanoes stopped spewing gasses out into the Martian atmosphere. Without a magnetic field to counteract the powerful solar winds, Mars' atmosphere slowly seeped into outer space. Without volcanic out-gassing to replenish this loss of atmosphere, atmospheric pressure flatlined and water evaporated until little or nothing remained.
In contrast, Venus is closer to the sun and its molten core more active, spewing volcanic gasses for billions of years and creating a thick, toxic, scorching atmosphere that's violently inhospitable to life as we know it and instantly boils liquid water into vapor.
Mars is smaller and its core significantly cooler, its gravity is too weak to sustain an atmosphere, and it has no way to replenish what's been lost to outer space. This has resulted in a thin, nearly non-existent atmosphere that doesn't allow water to exist on its surface.
We're in a convenient spot—not too hot, not too cold, just the right size. We don't know if Mars or any other world in the solar system can support any kind of life. But we do know that Mars once resembled Earth much more than it resembles itself today, and it's important to find out exactly how and why things changed, and what effect, if any, these changes had on any Martian life (if it ever existed at all).