 Topographic map of Arcadia Planitia | |
| Feature type | Plains |
|---|---|
| Coordinates | 47°12′N184°18′E / 47.2°N 184.3°E /47.2; 184.3 |
Arcadia Planitia is a smooth plain with fresh lava flows and Amazonian volcanic flows onMars. It was named byGiovanni Schiaparelli in 1882 after theArcadia region of ancientGreece. It dates from theAmazonian period's arcadia formation'slava flows and smallcinder cones. It includes a more recently developed large region ofaeolian materials derived fromperiglacial processes.
It is located northwest of theTharsis region in the northern lowlands, spanning roughly the region 33.9–64.2° North and 165.9–210.4° East, straddling partly in theCebrenia quadrangle (MC-07), and partly in theDiacria one (MC-02), and centered at47°12′N184°18′E / 47.2°N 184.3°E /47.2; 184.3.[1] Arcadia marks a transition from the thinly cratered terrain to its north and the very old cratered terrain to the south.On its east it runs into theAlba Mons volcanoes.Its elevation relative to thegeodetic datum varies between 0 and -3 km.[2]
Many low-lying areas of Arcadia are marked by grooves and sub-parallel ridges. These features indicate glaciation and appear similar to those on Earth, where the freezing and thawing of water located between ground layers contributes to the slow flow of near-surface materials. This supports the proposition that ground ice exists in the near-surface of Arcadia Planitia, and therefore this location is an area of interest for potential exploration missions.[3]
Large impacts often create swarms of small secondary craters from the debris that is blasted out as a consequence of the impact. Studies of a type of secondary craters, called expanded craters, have given us insights into places where abundant ice may be present in the ground.[4] Expanded craters have lost their rims, which may be because any rim that was once present has collapsed into the crater during expansion or lost its ice if composed of ice.
Excess ice (ice in addition to what is in the pores of the ground) is widespread throughout the Martian mid-latitudes, especially in Arcadia Planitia. In this region are many expanded secondary craters that probably form from impacts that destabilize a subsurface layer of excess ice, which subsequently sublimates. Withsublimation, the ice changes directly from a solid to gaseous form. In the impact, the excess ice is broken up, resulting in an increase in surface area. Ice will sublimate much more if there is more surface area. After the ice disappears into the atmosphere, dry soil material will collapse and cause the crater diameter to become larger.[5] Places on Mars that display expanded craters may indicate where future colonists can find water ice.
Martian gullies are small, incised networks of narrow channels and their associated downslopesediment deposits, found on the planet ofMars. They are named for their resemblance to terrestrialgullies. First discovered on images fromMars Global Surveyor, they occur on steep slopes, especially on the walls of craters. Usually, each gully has adendriticalcove at its head, afan-shapedapron at its base, and a single thread of incisedchannel linking the two, giving the whole gully an hourglass shape.[6] They are believed to be relatively young because they have few, if any craters. A subclass of gullies is also found cut into the faces of sand dunes which themselves considered to be quite young. On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers believed that the processes carving the gullies involve liquid water. However, this remains a topic of active research. The pictures below show gullies in Arcadia Planitia.
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