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..
Click for full image.
The small arrows near the bottom left indicate matching features on the center-right of the image above, to show the relative location of this impact to all the slope streaks.
Most of the photographs of this impact are labeled as monitoring the recent impact, not the slope streaks. It appears that the goal of these images is to see if there is some relationship between the impact and the slope streaks. Since one cause of streaks is thought to be a rockfall at the top that triggers the streak, it might be that the impact triggered almost all of these streaks, at one time, with later sporadic rockfalls (due to the relative instability of the recently shaken surface) causing later streaks.
When I asked Misha Kreslavsky of the University of California in Santa Cruz to look at this new image, he was able to spot two new streaks, one very tiny, with the second larger streak indicated by black arrow on the left center of the first image above. He also noted that, “it looks like many streaks here are formed during ‘streak showers,’ short active periods separated by long periods of low formation rate.” This speculation on his part confirms the possibility that the majority of these streaks occurred at one time, when the impact hit.
At the same time, he added, “I don’t think that all those abundant slope streaks had been triggered by this impact: They have different shades of gray, probably they are of different age. But the impact could indeed triggered a bunch of streaks.”
Click for full image.
A wider lower resolution image of the entire crater, taken in 2012 by the context camera on MRO and cropped to post here on the right, provides further support for the impact cause. Note how most of the streaks are on the crater’s eastern interior, nearest the impact.
I imagine this scenario. When the bolide smashed down, the tremors and small secondary impacts that are documented in all directions around the crater, immediately caused a streak shower, mostly on the nearest slopes of the crater.
That the streaks only occurred on the inside of the crater also illustrates once again their unusual nature. They occurred in the dusty areas inside the crater, not on its outside rim where there is not as much dust.
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