Mariner (crater)

Mariner Crater

Mariner 4 discovery image
Planet	Mars
Coordinates	35°06′S 164°30′W / 35.1°S 164.5°W / -35.1; -164.5Coordinates: 35°06′S 164°30′W / 35.1°S 164.5°W / -35.1; -164.5
Diameter	170 km

Jack N. James (center), JPL's Mariner 4 Project Manager, with a group in the White House presenting the spacecraft's famous picture Number 11 of Mars to US President Lyndon B. Johnson (center right) in July 1965. This was the discovery image of Mariner crater, and is named for the Mariner 4 spacecraft.^[1]

Mariner Crater is a crater on Mars with a diameter of 170 km. it is located in the Phaethontis quadrangle at 35.1° south latitude and 164.5° west longitude. It was named for Mariner IV spacecraft.^[2] In fact it is probably the best image that was taken with the Mariner IV spacecraft. Images of this crater are shown from the Mariner 4 and Mars Reconnaissance missions. One can compare the resolutions from the Mariner IV camera, CTX, and HiRISE.

Gullies

The Phaethontis quadrangle is the location of many gullies that may be due to recent flowing water. Some are found in Mariner (Martian crater).^[3][4] Gullies occur on steep slopes, especially craters. Gullies are believed to be relatively young because they have few, if any craters, and they lie on top of sand dunes which are young. Usually, each gully has an alcove, channel, and apron. Although many ideas have been put forward to explain them, the most popular involve liquid water either coming from an aquifer or left over from old glaciers.^[5]

There is evidence for both theories. Most of the gully alcove heads occur at the same level, just as one would expect of an aquifer. Various measurements and calculations show that liquid water could exist in an aquifer at the usual depths where the gullies begin.^[6] One variation of this model is that rising hot magma could have melted ice in the ground and caused water to flow in aquifers. Aquifers are layer that allow water to flow. They may consist of porous sandstone. This layer would be perched on top of another layer that prevents water from going down (in geological terms it would be called impermeable). The only direction the trapped water can flow is horizontally. The water could then flow out onto the surface when it reaches a break, like a crater wall. Aquifers are quite common on Earth. A good example is "Weeping Rock" in Zion National Park Utah.^[7]

On the other hand, much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust. This ice-rich mantle, a few yards thick, smooths the land, but in places it has a bumpy texture, resembling the surface of a basketball. Under certain conditions the ice could melt and flow down the slopes to create gullies. Because there are few craters on this mantle, the mantle is relatively young. An excellent view of this mantle is shown below in the picture of the Ptolemaeus Crater Rim, as seen by HiRISE.

Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water comes back to ground at lower latitudes as deposits of frost or snow mixed generously with dust. The atmosphere of Mars contains a great deal of fine dust particles. Water vapor will condense on the particles, then fall down to the ground due to the additional weight of the water coating. When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulating the remaining ice.^[8]

As soon as gullies were discovered,^[9] researchers began to image many gullies over and over, looking for possible changes. By 2006, some changes were found.^[10] Later, with further analysis it was determined that the changes could have occurred by dry granular flows rather than being driven by flowing water.^[11][12][13] With continued observations many more changes were found in Gasa Crater and others.^[14] With more repeated observations, more and more changes have been found; since the changes occur in the winter and spring, experts are tending to believe that gullies were formed from dry ice. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon-dioxide frost and temperatures that would not have allowed for liquid water. When dry ice frost changes to a gas, it may lubricate dry material to flow especially on steep slopes.^[15][16][17] In some years frost, perhaps as thick as 1 meter,

• 
  This topographic map shows volcanic peaks in white because of their great height. Near the equator, a line of three volcanoes points south to Phaethontis and three large craters-the area where there are many gullies. Click on the image for a good view.
• 
  Map of Phaethontis quadrangle. Click on to enlarge and see some crater names.
• 
  Mariner Crater, as seen by Mariner 4. This is probably the best picture that our first spacecraft to fly by Mars took. Image located in Phaethontis quadrangle.
• 
  Section of Mariner Crater that was imaged by the Mariner 4 space craft. The crater on the floor of the much larger Mariner Crater is the smaller of the two craters on the floor. Straight troughs in the south are visible in this image and in the Mariner photo. This image was taken with CTX camera (on Mars Reconnaissance Orbiter).
• 
  Enlargement of troughs from previous image of Mariner Crater. Possible gullies are visible on north wall. This image was taken with CTX camera (on Mars Reconnaissance Orbiter).
• 
  Gullies on the wall of a crater on the floor of Mariner Crater. Some of these gullies were also imaged with HiRISE. Note: this is an enlargement of a previous CTX image.
• 
  Crater wall inside Mariner Crater, as seen by HiRISE.

See also

• Planetary nomenclature
• Impact crater
• List of craters on Mars
• Mariner 4
• Exploration of Mars
• Space exploration
• Space probe
• Martian Gullies

References

External links

• HRSC 2476 crop