Craters on Mars
Image courtesy National Aeronautic and Space Administration (fair use policy)
This historic image, transmitted to Earth by Mariner 4 in the early afternoon of 15 July 1965, proved beyond doubt that Mars has impact craters like those of the Moon. With that, we had to conclude that Earth, too, is a cratered planet, with all that implied:
- Because Earth has very few craters preserved at the present day, while the other planets have many, Earth must erase its wounds. Very soon after Mariner 4, the theory of plate tectonics arose to explain how Earth's surface renews itself. And despite the rarity of craters on Earth, cosmic impacts are still a present danger.
- Conversely, the Moon and Mars must be tectonically dead. A few years later, Mercury was seen to be heavily cratered too. Today we know that nearly all of the solid bodies in the solar system are heavily cratered. The few exceptions—Io, Europa, and Venus—are teaching us some of the un-Earthlike ways that planetary bodies can be active.
This is a portion of Mariner 4 image 7-04-07b. It and the other Mariner 4 images are archived by NASA.
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