Megabreccia in the Central Uplift of Stokes Crater
Megabreccia in the Central Uplift of Stokes Crater
ESP_017257_2360  Science Theme: Geologic Contacts/Stratigraphy
Stokes is a large, approximately 60 kilometer diameter (38 mile) impact crater located in the northern lowland plains of Mars.

Craters this large invariably have a central structural uplift, which form mountain peaks in or near the center of the crater. The northern plains are largely covered by lavas and sediments, but craters such as Stokes allow us to observe the otherwise buried bedrock, exposed within its central uplift.

The first cutout shows a wide variety of colors and textures in a jumbled, fragmental pattern, i.e. “megabreccia.” In the stereo anaglyph we can see that many of the fragmental blocks stick out, indicating that they are more resistant to erosion than the the surrounding finer-grained material between the blocks. There is also an abundance of dark sand dunes and other smaller wind-driven bedforms on top of the area of exposed bedrock.

Megabreccia, consisting of very large fragments of pre-existing bedrock, is created by energetic processes, but especially by impact events on Mars. Although megabreccia deposits can coat central uplifts, it may not have been the Stokes impact that made this megabreccia.

The formation of a crater’s central uplift does not commonly break up and jumble the deep bedrock. So if these megabreccias are exposures of the deep bedrock brought up to the surface by the central uplift, and are not merely deposits draped on the central uplift, then it is most likely that these megabreccias were created by much larger and older basin-forming impacts that now lie buried beneath the surface.

With the aid of high-resolution images, and especially the 3D anaglyphs, we hope to decipher whether the materials observed in the central uplift were formed by the host crater or prior to the formation of that crater. Either way, crater central uplifts can provide windows into the deepest and oldest geologic history of Mars. For example, if there was a very ancient ocean in the Northern lowlands, these rocks could include deposits from that ocean.

This pair of images (also see ESP_016980_2360) was targeted to acquire stereo coverage of the eastern slopes of the central uplift (see PSP_09332_2360 for an adjacent area).

Written by: Alfred McEwen  (5 May 2010)

This is a stereo pair with ESP_016980_2360.
Acquisition date
02 April 2010

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
310.9 km (193.2 miles)

Original image scale range
31.7 cm/pixel (with 1 x 1 binning) so objects ~95 cm across are resolved

Map projected scale
25 cm/pixel and North is up

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Phase angle

Solar incidence angle
46°, with the Sun about 44° above the horizon

Solar longitude
72.0°, Northern Spring

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North azimuth:  96°
Sub-solar azimuth:  339.2°
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NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA’s Science Mission Directorate, Washington. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.