The high velocities characteristic of objects striking a planet's surface result in impact craters that are circular even if the impact angle is not vertical. A crater's ejecta blanket often provides the only clue that an impactor came in at a lower angle. Elongated craters, such as this 33 × 20 km crater located near the base of the volcano Ceraunius Tholus, are produced by impacts at angles of less than about 15° from the surface. The crater appears very young, but floor deposits at the channel terminus suggest that a volcanic eruption occurred after (and perhaps was initiated by) the impact event. This crater is one possible source of the SNC meteorites.
Crater at 25.19° N, 97.45° W; Viking Orbiter frame 516A24