page_title: Mars
section_title: Impact topography
hierarchical_section_title: Mars / Physical characteristics / Geography and naming of surface features / Impact topography
caption_attribution_description: English: This pair of images taken one day apart by the Mars Color Imager (MARCI) weather camera on NASA's Mars Reconnaissance Orbiter reveals when an asteroid impact made the scar seen in the right-hand image. The left image was taken during Martian afternoon on March 27, 2012; the right one on the afternoon of March 28, 2012. The dark area in the "after" image is about 5 miles (8 kilometers) wide. Observations with other cameras on Mars Reconnaissance Orbiter and with cameras on other Mars orbiters have located about 400 fresh impact craters on Mars that have been confirmed with before-and-after images. None except this one have created scars detected in images from MARCI, which is a wide-angle camera used for monitoring Martian weather. Owing to the daily pace of MARCI global coverage, this is the first impact event for which the timing has been constrained within the length of a single Martian day (about 24.7 hours). Subsequent images from two telescopic cameras on Mars Reconnaissance Orbiter revealed craters within this impact scar that had not been present in January 2012. The largest of these craters -- 159 feet (48.5 meters) wide -- is the biggest fresh impact crater ever clearly confirmed anywhere with before-and-after images. These two MARCI images are centered at 3.34 degrees north latitude, 219.38 degrees east longitude. MARCI is one of six instruments on NASA's Mars Reconnaissance Orbiter. The camera was built and is operated by Malin Space Science Systems, San Diego. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington.
context_page_description: Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being only larger than Mercury. In English, Mars carries the name of the Roman god of war and is often referred to as the "Red Planet". The latter refers to the effect of the iron oxide prevalent on Mars's surface, which gives it a reddish appearance distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, with surface features reminiscent of the impact craters of the Moon and the valleys, deserts and polar ice caps of Earth.
  The days and seasons are comparable to those of Earth, because the rotational period as well as the tilt of the rotational axis relative to the ecliptic plane are similar. Mars is the site of Olympus Mons, the largest volcano and highest known mountain on any planet in the Solar System and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons, Phobos and Deimos, which are small and irregularly shaped.
context_section_description: The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. Research in 2008 has presented evidence regarding a theory proposed in 1980 postulating that, four billion years ago, the northern hemisphere of Mars was struck by an object one-tenth to two-thirds the size of Earth's Moon. If validated, this would make the northern hemisphere of Mars the site of an impact crater 10,600 by 8,500 kilometres (6,600 by 5,300 mi) in size, or roughly the area of Europe, Asia, and Australia combined, surpassing the South Pole–Aitken basin as the largest impact crater in the Solar System.
  Mars is scarred by a number of impact craters: a total of 43,000 craters with a diameter of 5 kilometres (3.1 mi) or greater have been found. The largest confirmed of these is the Hellas impact basin, a light albedo feature clearly visible from Earth. Due to the smaller mass of Mars, the probability of an object colliding with the planet is about half that of Earth. Mars is located closer to the asteroid belt, so it has an increased chance of being struck by materials from that source. Mars is more likely to be struck by short-period comets, i.e., those that lie within the orbit of Jupiter. In spite of this, there are far fewer craters on Mars compared with the Moon, because the atmosphere of Mars provides protection against small meteors and surface modifying processes have erased some craters.
  Martian craters can have a morphology that suggests the ground became wet after the meteor impacted.
caption: Fresh asteroid impact on Mars at 3°20′N 219°23′E﻿ / ﻿3.34°N 219.38°E﻿ / 3.34; 219.38. These before and after images of the same site were taken on the Martian afternoons of 27 and 28 March 2012 respectively (MRO).[158]
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