HiRISE Updates Week of 2017 Feb 06

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HiRISE Updates Week of 2017 Feb 06

Postby bystander » Sun Feb 12, 2017 3:44 pm

Author wrote:
A Recent Cluster of Impacts (ESP_047768_1995) (HiClip)

The dark spots in this enhanced-color infrared image are the recent impact craters that occurred in the Tharsis region between 2008 and 2014. These impact craters were first discovered by the Mars Context Camera (or CTX, also onboard the Mars Reconnaissance Orbiter) as a cluster of dark spots. The meteoroid that formed these craters must have broken up upon atmospheric entry and fragmented into two larger masses along with several smaller fragments, spawning at least twenty or so smaller impact craters.

The dark halos around the resulting impact craters are a combination of the light-toned dust being cleared from the impact event and the deposition of the underlying dark toned materials as crater ejecta. The distribution and the pattern of the rayed ejecta suggests that the meteoroid most-likely struck from the south (which is up in the cutout).

HiRISE frequently monitors new impact craters similar to this one; however, this is the first image of this particular impact taken by HiRISE, thanks to a request by the CTX team. Subsequent images will likely follow to monitor if there are any changes to the site from wind-blown activity or dust-deposition over time.

Ayanna Jones and James Wray wrote:
A Nine Kilometer Impact Crater and Its Central Peak (ESP_048173_1930) (HiClip)

This image reveals an impact crater, nine kilometers in diameter, with a central peak. Impact craters of various sizes and ages can be found across the Martian surface. Each impact crater on Mars possesses a unique origin and composition, which makes the HiRISE team very interested in sampling as many of them as possible!

Like the impact of a droplet into fluid, once an impact has occurred on the surface of Mars, an ejecta curtain forms immediately after, contributing to the raised rim visible at the top of the crater’s walls. After the formation of the initial crater, if it is large enough, then a central peak appears as the surface rebounds. These central peaks can expose rocks that were previously deeply buried beneath the Martian surface.

The blue and red colors in this enhanced-contrast image reflect the effects of post-impact sedimentation and weathering over time.

James Wray wrote:
Unlocking an Impact Crater's Clues (ESP_048456_1640) (HiClip)

Mars is a dynamic planet. HiRISE has witnessed many surface changes over the past ten years, including hundreds of new craters formed by ongoing impacts. Most of these impacts are likely caused by asteroids that have strayed into collision courses with Mars. The planet’s much thinner atmosphere compared to Earth makes small asteroids less likely to burn up prior to hitting the Martian surface.

This new crater, which formed explosively at the point of impact, has a diameter of roughly 8 meters (about 25 feet), but its surrounding blast zone and ejecta extend over a kilometer (about one mile) beyond the crater itself. The materials exposed nearest the crater have distinctive yellowish and lighter grey appearances, while more distant ejected materials range from dark brown to bright bluish in an enhanced-color view. These varied materials may have originated from different layers penetrated by the impact.

This new impact was discovered using the lower-resolution Context Camera (CTX), also on board Mars Reconnaissance Orbiter. An older CTX image of this region from May 2012 shows a uniformly dust-covered surface, while a newer CTX image from September 2016 reveals the crater’s dark blast zone. New craters on Mars are easiest to locate in such dust-coated terrains, where they provide opportunistic “road cuts” that allow scientists to see beneath the dust blanket and determine the underlying rock compositions and textures.

This particular crater formed about 300 kilometers (roughly 200 miles) east of the Spirit rover’s final resting spot in Gusev Crater.

Kirby Runyon wrote:
A Dragonfly-Shaped Crater (ESP_048462_1585) (HiClip)

The broader scene for this image is the fluidized ejecta from Bakhuysen Crater to the southwest, but there’s something very interesting going on here on a much smaller scale.

A small impact crater, about 25 meters in diameter, with a gouged-out trench extends to the south. The ejecta (rocky material ejected from the crater) mostly extends to the east and west of the crater. This “butterfly” ejecta is very common for craters formed at low impact angles. Taken together, these observations suggest that the crater-forming impactor came in at a low angle from the north, hit the ground and ejected material to the sides.

The top of the impactor may have sheared off (“decapitating” the impactor) and continued downrange, forming the trench. We can’t prove that’s what happened, but this explanation is consistent with the observations. Regardless of how it formed, it’s quite an interesting-looking “dragonfly” crater!

This is a stereo pair with ESP_048528_1585.

Credit: NASA/JPL-Caltech/University of Arizona

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