Zunil (crater)

Zunil
Planet Mars
Region Athabasca Valles
Diameter 10.4 km
Eponym Zunil

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.[1]

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.[2]

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,[3] and was subsequently imaged at higher resolution by the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) in December 2006.[4]

Contents

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.[5]

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 craters 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.[5][6]

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.[5]

See also

References

  1. ^ "MOC narrow-angle image M21-00859—Crater traverse at 7.8 N 193.8 W". Malin Space Science Systems. http://www.msss.com/moc_gallery/m19_m23/images/M21/M2100859.html. Retrieved 2001-10-08. 
  2. ^ McEwen et al. (2003). "Discovery of a large rayed crater on Mars: Implications for recent volcanic and fluvial activity and the origin of Martian meteorites". Lunar and Planetary Science Conference. http://www.lpi.usra.edu/meetings/lpsc2003/pdf/2040.pdf. 
  3. ^ "MOC narrow-angle image R08-02140—Zunil Crater and its ejecta". Malin Space Science Systems. http://www.msss.com/moc_gallery/r03_r09/images/R08/R0802140.html. Retrieved 2004-04-20. 
  4. ^ "Recent Landslide in Zunil Crater (PSP_001764_1880)". University of Arizona. http://hirise.lpl.arizona.edu/PSP_001764_1880. Retrieved 2008-06-28. 
  5. ^ a b c McEwen, A.S. et al. (2005). "The rayed crater Zunil and interpretations of small impact craters on Mars". Icarus 176 (2): 351–381. Bibcode 2005Icar..176..351M. doi:10.1016/j.icarus.2005.02.009. http://www.mars.asu.edu/christensen/classdocs/mcewen_zunil_Icarus_2005.pdf. Retrieved 2006-09-08. 
  6. ^ Kerr, R (2006). "Who can Read the Martian Clock?". Science 312 (5777): 1132–1133. doi:10.1126/science.312.5777.1132. PMID 16728612. 

External links