Butterfly Crater Challenge

The Challenge
Butterfly craters are the most intriguing types of craters on Mars. You’re invited to find more butterfly craters on the HiRISE website or NASA’s website.

Background
Craters form when an object hits the surface of Mars. Mars has been struck by objects coming from the asteroid belt and beyond with all kinds of velocities; thus, Mars has the greatest variety of impact craters in the solar system. A classical round crater is normally less than 8 km wide. When fresh, these craters are small, have smooth bowl-shaped profiles with low, upraised rims, and are surrounded by a sheet of debris, also known as ejecta, blasted out of the crater by the force of impact. The following image is a classical bowl-shaped crater.

Classical Crater


The bowl-shaped crater in the above image is located at (38.684°N, 316.123°E) has a 4 km diameter and apears realtively fresh. It’s a well-formed bowl-shaped classical crater. This type of crater is representative of relative small craters in the solar system with a nearly circular, raised rim and steep, smoothly sloping walls.

Most impacts make a classical round crater because explosions expand in all directions equally. However, when an object hits Mars at an angle under 20 degrees, the crater is less circular. Low-angle impacts produce craters with an oval outline and the ejecta settles in a butterfly shape. Some areas around the crater contain no blast material. Occasionally, there is a smaller crater in line with the oval one and the wings. Elliptical craters with butterfly ejecta patterns make up roughly 5 percent of all craters on Mars. Similar craters are also seen the same abundance on our Moon and Venus. Scientists use a crater’s circularity ratio formula, 4 π A/P2, to determine which of the craters would have the butterfly ejecta pattern. 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. The following image is a butterfly crater.

Butterfly Crater


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