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First Super Close-Up Pictures of Mars
Alien54 writes "The most powerful camera ever to orbit Mars will get its first close look at the Red Planet on Friday. The High-Resolution Imaging Science Experiment (HiRISE) camera flying aboard NASA's Mars Reconnaissance Orbiter (MRO) will relay its first low-altitude images to scientists at The University of Arizona beginning September 29. User-friendly web tools will be available to both the science community and the public to view/analyze HiRISE images and to submit observation requests. Processed images will be released soon after acquisition to allow everyone to share in the scientific discovery process. By combining very high resolution and signal-to-noise ratio with a large swath width, it is possible to for images to be collected on scales down to 1 meter."
The reason is that a complete hood will cause glare/lens flare from the light reflected off of the inside of the sides of the hood exposed to the sun.
Setup your lamp and tennis ball. Now point a camera with a full hood at the tennis ball. Notice that parts of the inside of your hood will be illuminated by the lamp. This will cause major light pollution for a highly sensitive camera.
Actually, while the Earth's atmosphere does prevent the formation of the smallest craters, the main reason Earth has far fewer craters than Mars is that the Earth's surface is, on average, much much younger than Mars' surface. Most cratering occured very early in the existence of the solar system, and on Earth erosion and continental drift mean that practically nowhere on Earth can we find a surface that is as old as the early cratering periods. Even the oldest rocks on Earth (in locations such as Canada, South-Africa & Australia) may be old, but they were not always at the surface.
On Mars, there never was any real "rebuilding" of the surface at the scale of what happened on Earth (except for some volcanism, wind erosion and water erosion). This means Mars retains almost all the ancient craters which on Earth have long disappeared.
Now, besides that, Mars' atmosphere is only about 1% of Earth's, and as such, is also much less capable of slowing down meteoroids, so on Mars, craters can form which are considerably smaller than the smallest that can form on Earth, because meteoroids small enough to burn up in Earth's atmosphere would still reach the surface at orbital velocities on Mars.
So, basically, plate-tectonics, erosion and a bigger atmospheric shield are all reasons why Earth has far fewer craters than Mars.