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Zunil (crater)
Encyclopedia
Zunil is an impact crater
near the Cerberus Fossae
on Mars
, with a diameter of 10.4 km (6.5 mi). It is named after a town
in Guatemala
. Visible in images from the Viking 1
and Viking 2
Mars orbiters in the 1970s, Zunil was subsequently imaged at higher resolution for the first time by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in 2000.
A ray system associated with the Zunil impact, visible in infrared images from the Mars Odyssey Thermal Emission Spectrometer (THEMIS) was later detailed by McEwen et al. (2003); prior to this, large craters with ray systems had not been seen on Mars.
The debris from a recent landslide was first spotted on the south-east wall of the crater by the Mars Global Surveyor Mars Orbiter Camera (MOC) in 2003, and was subsequently imaged at higher resolution by the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE
) in December 2006.
The impact created a ray system
, visible in the infrared
, that extends up to 1600 km from the crater and produced hundreds of millions of secondary crater
s with diameters ranging from 10 m to 100 m. Very few of these secondary craters lie within 80 km of Zunil. Around 80% of the craters in Athabasca Valles
are Zunil secondaries. If similar impacts also produced comparable amounts of secondaries, this calls into question the accuracy of crater counting
as a dating technique for geologically young Martian surface features.
A simulation of the Zunil impact ejected on the order of ten billion rock fragments greater than 10 centimeters in diameter, the total ejecta comprising 30 km3. These formed about a billion secondary craters 10 m in size up to 3500 km away from the primary impact. It is possible that some of these fragments from the impact made it to Earth to become shergottites, a form of Martian meteorite.
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
near the Cerberus Fossae
Cerberus Fossae
The Cerberus Fossae are a series of semi-parallel fissures on Mars formed by faults which pulled the crust apart in the Cerberus region . Ripples seen at the bottom of the fault are sand blown by the wind ....
on Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
, with a diameter of 10.4 km (6.5 mi). It is named after a town
Zunil
Zunil is a municipality in the Quetzaltenango department of Guatemala with a surface area of . Zunil is located from the city of Quetzaltenango, on the bank of the Salamá River. Zunil has an altitude of approximately above mean sea level. The population is about 14,000 people, 100% indigenous...
in Guatemala
Guatemala
Guatemala is a country in Central America bordered by Mexico to the north and west, the Pacific Ocean to the southwest, Belize to the northeast, the Caribbean to the east, and Honduras and El Salvador to the southeast...
. Visible in images from the Viking 1
Viking 1
Viking 1 was the first of two spacecraft sent to Mars as part of NASA's Viking program. It was the first spacecraft to successfully land on Mars and perform its mission, and until May 19, 2010 held the record for the second longest Mars surface mission of 6 years and 116 days .- Mission :Following...
and Viking 2
Viking 2
The Viking 2 mission was part of the American Viking program to Mars, and consisted of an orbiter and a lander essentially identical to that of the Viking 1 mission. The Viking 2 lander operated on the surface for 1,281 Mars days and was turned off on 11 April 1980 when its batteries failed...
Mars orbiters in the 1970s, Zunil was subsequently imaged at higher resolution for the first time by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in 2000.
A ray system associated with the Zunil impact, visible in infrared images from the Mars Odyssey Thermal Emission Spectrometer (THEMIS) was later detailed by McEwen et al. (2003); prior to this, large craters with ray systems had not been seen on Mars.
The debris from a recent landslide was first spotted on the south-east wall of the crater by the Mars Global Surveyor Mars Orbiter Camera (MOC) in 2003, and was subsequently imaged at higher resolution by the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE
HiRISE
High Resolution Imaging Science Experiment is a camera on board the Mars Reconnaissance Orbiter. The 65 kg , $40 million instrument was built under the direction of the University of Arizona's Lunar and Planetary Laboratory by Ball Aerospace & Technologies Corp....
) in December 2006.
Formation
The impact which formed Zunil occurred no more than a few million years ago and hence the crater is in a relatively pristine form. It was probably not produced in a high velocity impact, such as from a comet. If the interpretation that Zunil is the source of the basaltic shergottite meteorites is correct, then the crater formed in basalt deposited 165–177 million years ago.The impact created a ray system
Ray system
A ray system comprises radial streaks of fine ejecta thrown out during the formation of an impact crater, looking a bit like many thin spokes coming from the hub of a wheel. The rays can extend for lengths up to several times the diameter of their originating crater, and are often accompanied by...
, visible in the infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
, that extends up to 1600 km from the crater and produced hundreds of millions of secondary crater
Secondary crater
Secondary craters are impact craters formed by the ejecta that was thrown out of a larger crater. They sometimes form radial crater chains.-External links:*...
s with diameters ranging from 10 m to 100 m. Very few of these secondary craters lie within 80 km of Zunil. Around 80% of the craters in Athabasca Valles
Athabasca Valles
Athabasca Valles is an outflow channel on Mars, cut into its surface by catastrophic flooding. It is one of the youngest known of these structures, probably forming only in the geologically recent past of Mars. The flood produced distinctive "teardrop" landforms similar to those found in the...
are Zunil secondaries. If similar impacts also produced comparable amounts of secondaries, this calls into question the accuracy of crater counting
Crater counting
Crater counting is a method for estimating the age of a planet's surface. The method is based upon the assumptions that a new surface forms with zero impact craters, and that impact craters accumulate at some constant rate...
as a dating technique for geologically young Martian surface features.
A simulation of the Zunil impact ejected on the order of ten billion rock fragments greater than 10 centimeters in diameter, the total ejecta comprising 30 km3. These formed about a billion secondary craters 10 m in size up to 3500 km away from the primary impact. It is possible that some of these fragments from the impact made it to Earth to become shergottites, a form of Martian meteorite.
See also