Crater Curiosity
Craters form when an object hits the surface of a planet or other body. The impact creates a round impression surrounded by material, called ejecta, that gets blasted out of the crater. Scientists study ejecta because it contains clues about what’s below a planet’s surface. When an object hits Mars at an angle under 20 degrees, the crater is less circular and the ejecta settles in a butterfly shape. Some areas around the crater contain no blast material. Finding craters that formed this way can help scientists understand how meteor impacts change the surface of a planet. To do this, they measure a crater’s circularity ratio. If the ratio is less than 0.925, it suggests that an object impacted at an angle under 20 degrees and created a butterfly ejecta pattern.
Using the circularity ratio formula, 4πA /p2, determine which of the following craters would have the butterfly ejecta pattern.
Aveiro crater (shown in the front of the above illustration)
- A (area) = 67 km2
- P (perimeter) = 30 km
Unnamed crater (shown in the back of the above illustration)
- A (area) = 32 km2
- P (perimeter) = 21 km
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