Distinctive Rayed Impact Crater in Meridiani Planum
This "fresh" (very well-preserved) impact crater has created a radial pattern of dark rays. The image was suggested to address the question of why the rays are dark.
Is the crater so fresh and recent that there hasn't been time for bright dust to settle on the rays? That doesn't seem likely, as we can see windblown deposits inside the crater, which requires at least thousands of years to form after the impact event. Also, fresh craters with dark ejecta are common in Meridiani, and they can't all be extremely recent.
Did the crater eject a subsurface layer of dark material? Maybe, but all of the bedrock exposures in the surrounding region are relatively bright. The surface layer is darker than the bedrock because dark materials like hematite concretions ("blueberries" found by Opportunity rover) are resistant to wind erosion and get left as a lag deposit. At HiRISE scale the rays are seen to be a thin deposit, perhaps less than 1 meter thick.
Distinctive Rayed Impact Crater in Meridiani Planum
This "fresh" (very well-preserved) impact crater has created a radial pattern of dark rays. The image was suggested to address the question of why the rays are dark.
Is the crater so fresh and recent that there hasn't been time for bright dust to settle on the rays? That doesn't seem likely, as we can see windblown deposits inside the crater, which requires at least thousands of years to form after the impact event. Also, fresh craters with dark ejecta are common in Meridiani, and they can't all be extremely recent.
Did the crater eject a subsurface layer of dark material? Maybe, but all of the bedrock exposures in the surrounding region are relatively bright. The surface layer is darker than the bedrock because dark materials like hematite concretions ("blueberries" found by Opportunity rover) are resistant to wind erosion and get left as a lag deposit. At HiRISE scale the rays are seen to be a thin deposit, perhaps less than 1 meter thick.