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The Phaethontis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Phaethontis quadrangle is also referred to as MC-24 (Mars Chart-24).^[1]

The Phaethontis quadrangle lies between 30° and 65 ° south latitude and 120° and 180 ° west longitude on Mars. This latitude range is where numerous gullies have been discovered. Around a group of large craters is Mariner Crater, first observed by the Mariner IV spacecraft in the summer of 1965. It was named after that spacecraft.^[2] Russia's Mars 3 probe landed in the Phaethontis quadrangle at 44.9° S and 160.1° W in December 1971. It landed at a speed of 75km per hour, but survived to radio back 20 seconds of signal, then it went dead. Its message just appeared as a blank screen.^[3]

Gullies

The Phaethontis quadrangle is the location of many gullies that may be due to recent flowing water. Some are found in the Gorgonum Chaos^[4] and in many craters near the large craters Copernicus and Newton (Martian crater).^[5][6] 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. ^[7]

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. ^[8] 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 porus sandstone. This layer would be perched on top of another layer that prevents water from going down (in gelogical terms it would be called impermeable). The only direction the trapped water can flow is hoizontally. The water could then flow out onto the surface when the aquifer reaches a break, like a crater wall. Aquifers are quite common on Earth. A good example is "Weeping Rock" in Zion National Park Utah.^[9]

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, smoothes 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.

The ice-rich mantle may be the result of climate changes. 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.^[10]

Gorgonum Chaos as seen by Mars Reconnaisance Orbiter HiRISE. Image about 4 km wide.	Group of gullies on north wall of crater that lies west of the crater Newton (41.3047 degrees south latitude, 192.89 east longitide)	Crater wall inside Mariner Crater showing a large group of gullies, as seen by HiRISE.	Gullies. Notice how channels curve around obstacles.
Gullies with branches.	Group of deep gullies, as seen by HiRISE.

Magnetic Stripes and Plate Tectonics

The Mars Global Surveyor (MGS) discovered magnetic stripes in the crust of Mars, especially in the Phaethontis and Eridania quadrangles. The magnetometer on MGS discovered 100 km wide stripes of magnetized crust running roughly parallel for up to 2000 km. These stripes alternate in polarity with the north magnetic pole of one pointing up from the surface and the north magnetic pole of the next pointing down. When similar stripes were discovered on Earth in the 1960s, they were taken as evidence of plate tectonics. However, there are some differences, between the magnetic stripes on Earth and those on Mars. The Martian stripes are wider, much more strongly magnetized, and do not appear to spread out from a middle crustal spreading zone. Because the area containing the magnetic stripes is about 4 billion years old, it is believed that the global magnetic field probably lasted for only the first few hundred million years of Mars' life, when the temperature of the molten iron in the planet's core might have been high enough to mix it into a magnetic dynamo . Younger rock does not show any stripes.

When molten rock containing magnetic material, such as hematite (Fe2O3), cools and solidifies in the presence of a magnetic field, it becomes magnetized and takes on the polarity of the background field. This magnetism is lost only if the rock is subsequently heated above a particular temperature (the Curie point which is 770°C for iron). The magnetism left in rocks is a record of the magnetic field when the rock solidified. ^[11]

Chloride Deposits

Using date from Mars Global Surveyor, Mars Odyssey and the Mars Reconnaissance Orbiter, scientists have found widespread deposits of chloride minerals. A picture below shows some deposits within the Phaethontis quadrangle. Evidence suggests that the deposits were formed from the evaporation of mineral enriched waters. The research suggests that lakes may have been scattered over large areas of the Maritan surface. Usually chlorides are the last minerals to come out of solution. Carbonates, sulfates, and silica should precipitate out ahead of them. Sulfates and silica have been found by the Mars Rovers on the surface. Places with chloride minerals may have once held various life forms. Furthermore, such areas should preserve traces of ancient life.^[12]

Evidence of water from chloride deposits in Phaethontis. Picture from HiRISE.

Gallery

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.	Mariner Crater, as seen by Mariner 4. This is probably the best picture that our first spacecraft to fly by Mars took.	Map of Phaethontis quadrangle. Click on to enlarge and see some crater names.	Close up image of Phaethontis surface taken with Mars Global Surveyor. Holes are thought to be caused by buried ice turning into a gas.
Ptolemaeus Crater Rim, as seen by HiRISE. Click on image to see excellent view of mantle deposit.	Tader Valles, as seen by THEMIS. Smooth material in channels may be a mantle in the form of dirty snow .	Pickering Crater lava flow, as seen by HiRISE. Click on image to see details at edge of flow.	Icaria Fossae Graben, as seen by HiRISE. Click on image for a better view of Dust Devil Tracks.
Sirenum Fossae Layers, as seen by HiRISE. Scale bar is 500 meters long.	Atlantis Chaos, as seen by HiRISE. Click on image to see mantle covering and possible gullies. The two images are different parts of the original image. They have different scales.

See also

• Climate of Mars
• Water on Mars

References