Tag Archives: slope streaks

Martian impacts and streaks

Slope-streaked crater on Mars
Click for full image.

In the most recent image download from the high resolution camera on Mars Reconnaissance Orbiter (MRO), there was the cool image to the right, reduced and cropped to post here, of a crater that appeared to have hundreds and hundreds of slope streaks along its inner slopes.

Slope streaks are quite mysterious. They are found in the equatorial regions as dark (though sometimes light) streaks on steep slopes, appearing throughout the year and slowly fading over time. They also appear to be a geological phenomenon unique to Mars. Nothing on Earth or any other planet appears to correspond.

As such, their nature and cause remains unknown, though there are a bunch of theories, with the most popular being that these are a kind of dust avalanche. They are always found in connection with dust-covered terrain, but they also make no significant topological change to the surface, other than brightness.

The slope streaks in this crater are especially intriguing, because of the number of streaks. In digging further into the MRO archive I found a number of images of this crater and its surrounding terrain. It appears that sometime before 2012 there was a relatively recent impact close to the exterior of the eastern rim of this crater. The image below, taken in 2014 by MRO, shows this impact as the large dark splotch, with the new crater indicated by the arrow..
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Mars’ mysterious slope streaks become even more mysterious

Bright slope streaks in Arabia Terra
Click for full image.

Mars is an alien planet. This fact needs to be restated over and over, because we humans have an uncontrolled and unconscious tendency to view the things we find on Mars and assume they are caused by and resemble phenomenon we see all the time here on Earth.

Not. Mars has a very different climate, a significantly weaker gravitational field (about one third of Earth’s), and a geological and environmental make-up very alien from Earth’s. While many phenomenon there might have parallels on Earth, it is very dangerous to assume they are the same, because more often than not, they are exceedingly dissimilar and mysterious.

The image on the right is another example of this, reduced and cropped to post here. It is of some slope streaks in the Arabia Terra region on Mars, the largest most extensive region in the transition zone between the northern lowland plains and the southern highlands. I found it in my review of the August 30th release of new images from the high resolution camera on Mars Reconnaissance Orbiter.

As I already noted in my previous article about the mysterious slope streaks of Mars:

The bottom line, as noted in one paper, “The processes that form slope streaks remain obscure. No proposed mechanism readily accounts for all of their observed characteristics and peculiarities.”

Mars is strange. Mars is alien. Mars epitomizes the universe in all its glory.

The image above only reinforces this conclusion.
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The mysterious slope streaks of Mars

Massive flow on Mars
A typical Martian slope streak.

The uncertainty of science: In the past decade or so scientists have documented in detail a number of features on the Martian surface that evolve or change over time. From the constantly changing poles to the tracks of dust devils to landslides to the appearance of seasonal frost, we have learned that Mars is far from a dead world. Things are happening there, and while they are not happening as quickly or with as much energy as found on Earth, geological changes are still occurring with regular frequency, and in ways that we do not yet understand.

Of the known changing features on Mars, two are especially puzzling. These are the two types of changing streaks on the slopes of Martian cliffs, dubbed recurring slope lineae (referred as RSLs by scientists) and slope streaks.

Lineae are seasonal, first appearing during the Martian summer to grow hundreds of feet long, and then to fade away with the arrival of winter. Their seasonal nature and appearance with the coming of warm temperatures suggests that water plays a part in their initiation, either from a seep of briny water or an avalanche of dust. Or a combination of both. The data however does not entirely fit these theories, and in fact is downright contradictory. Some studies (such as this one and this one) say that the seasonal lineae are caused by water. Other studies (such as this one and this one) say little or no water is involved in their seasonal formation.

The answer remains elusive, and might only be answered, if at all, when Curiosity takes a close look at two lineae in the coming years.

Slope streaks however are the focus of this post, as they are even more puzzling, and appear to possibly represent a phenomenon entirely unique to Mars. I became especially motivated to write about these mysterious ever newly appearing features when, in reviewing the May image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO), I found four different uncaptioned images of slope streaks, all titled “Slope Stream Monitoring.” From this title it was clear that the MRO team was re-imaging each location to see if any change had occurred since an earlier image was taken. A quick look in the MRO archive found identical photographs for all four slope streak locations, taken from 2008 to 2012, and in all four cases, new streaks had appeared while older streaks had faded. You can see a side-by-side comparison of all four images below the fold.
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