Zunil is an

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...

near the

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. They are 1235 km across and centered at 11.28 °N and 166.37 °E. Their northernmost latitude is 16.16 ...

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

, with a diameter of . It is named after the town of

Zunil Zunil () is a town and municipality in the Quetzaltenango department of Guatemala with a surface area of .Elysium quadrangle The Elysium quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Elysium quadrangle is also referred to as MC-15 (Mars Chart-15). The name Elysium r ...

. Visible in images from the

Viking 1 ''Viking 1'' was the first of two spacecraft, along with ''Viking 2'', each consisting of an orbiter and a lander, sent to Mars as part of NASA's Viking program. The lander touched down on Mars on July 20, 1976, the first successful Mars land ...

and

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. ''Viking 2'' was operational on Mars for sols ( days; '). The ''Vik ...

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 The Thermal Emission Spectrometer (TES) is an instrument on board Mars Global Surveyor. TES collects two types of data, hyperspectral thermal infrared data from 6 to 50 micrometres (μm) and bolometric visible-NIR (0.3 to 2.9 μm) measurements. TE ...

(THEMIS) was later detailed by McEwen et al. (2003); before 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 High Resolution Imaging Science Experiment is a camera on board the ''Mars Reconnaissance Orbiter'' which has been orbiting and studying Mars since 2006. The 65 kg (143 lb), US$40 million instrument was built under the direction o ...

) 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. Wikizunil

The impact created a

ray system A ray system comprises radial streaks of fine '' ejecta'' thrown out during the formation of an impact crater, looking somewhat like many thin spokes coming from the hub of a wheel. The rays may extend for lengths up to several times the diameter ...

, visible in the

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

, that extends up to from the crater and produced hundreds of millions of

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. In addition, secondary craters are often seen as clusters or rays surrounding primary craters. The study of ...

s with diameters ranging from . Very few of these secondary craters lie within of Zunil. Around 80% of the craters in

Athabasca Valles The Athabasca Valles are a late Amazonian-period outflow channel system in the central Elysium Planitia region of Mars, located to the south of the Elysium Rise. They are part of a network of outflow channels in this region that are understood ...

are Zunil secondaries. If similar impacts also produced comparable amounts of secondaries, this calls into question the accuracy of

crater counting Crater counting is a method for estimating the age of a planet's surface based upon the assumptions that when a piece of planetary surface is new, then it has no impact craters; impact craters accumulate after that at a rate that is assumed known. ...

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 in diameter, the total ejecta comprising . These formed about a billion secondary craters 10 m in size up to 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 A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, and traversed interplanetary space before landing on Earth as a meteorite. , 277 meteorites had been classified as Martian, less than half a percen ...

. Research published in the journal ''Icarus'' has found pits in Zunil Crater that are caused by hot ejecta falling on ground containing ice. The pits are formed by heat forming steam that rushes out from groups of pits simultaneously, thereby blowing away from the pit ejecta.Tornabene, L. et al. 2012. "Widespread crater-related pitted materials on Mars. Further evidence for the role of target volatiles during the impact process". ''Icarus''. 220: 348-368.

References

External links

Themis page about Zunil

{{Portal bar, Solar System Impact craters on Mars Elysium quadrangle Extraterrestrial landslides

Formation

See also

References

External links