According to the passage, astronomers believe which of the following about the "chunks of debris"? A. They may have destroyed a global magnetic field that once existed on Mars. B. They affected Mars more substantially than other planet in the inner solar system. C. Some of them contained a higher concentration of metallic particles than did rocks on Mars. D. Some of them caused craters that exist in the Terra Sirenum region of Mars. E. Few of them were large enough to cause impacts that would beat rocks to 600 degrees Celsius.