 Topographic map of Acidalia Planitia | |
| Feature type | Plains |
|---|---|
| Coordinates | 49°46′N339°16′E / 49.76°N 339.26°E /49.76; 339.26 |
| Diameter | 3362.97 km |
Acidalia Planitia is aplain onMars, between theTharsis volcanic province andArabia Terra to the north ofValles Marineris, centered at49°48′N339°18′E / 49.8°N 339.3°E /49.8; 339.3.[1] Most of this region is found in theMare Acidalium quadrangle, but a small part is in theIsmenius Lacus quadrangle. The plain contains the famousCydonia region at the contact with the heavily cratered highland terrain.
The plain is named after a correspondingalbedo feature on a map byGiovanni Schiaparelli, which was in turn named after the mythologicalfountain of Acidalia.Some places in Acidalia Planitia show cones, which some researchers have suggested are mud volcanoes. The scientific community is divided over whether an ancientocean existed on the plain and other parts of the northern lowlands.[2]
There are several hypotheses regarding the geological history of Acidalia Planitia based on evidence from satellite data.
Acidalia Planitia was once covered by ancient crust. Its surface eroded into knobs of iron/magnesiumphyllosilicates during theAmazonian.[3] Sediments filled the empty plain, leaving the phyllosilicate knobs as protrusions through the surface. The spatial density of these knobs is consistent with the ancient crust that was once above Acidalia Planitia.[3]
Hydrated silica materials surround the phyllosilicate knobs and the sides of rocky slopes. Rather than covering the entire surface, these features are localized.[3] This indicates that the plain was once home to springs and steam vents not extensive bodies of water such as oceans orglaciers.[3]
Utopia Planitia is a similar plain at the same latitude as Acidalia Planitia.[4] Etched flows in its terrain suggest that mud flowed into Utopia Planitia creating a large reservoir of water and mud in the deepest part of the basin, about 1000 km across. This may have been the remnants of a more extensive ocean that covered all of the northern lowlands including Acidalia Planitia.[5] TheVastitas Borealis Formation (VBF) stretched across both Utopia and Acidalia Planitiae and delineated the threshold for an ancient ocean. The two segments of the VBF at Utopia and Acidalia have congruent ages, reliefs, crater frequencies,albedos, thermal properties, andsuperpositions of geological features. This suggests that the Acidalia Planitia may have once been covered by a large Martian ocean.[5]
Craters on Acidalia Planitia are asymmetrical.Mars Orbital Laser Altimeter (MOLA) data revealed that the slopes of the pole-facing crater walls are shallower than the equator-facing slopes.[6] Other studies show the opposite asymmetry to be true. The two theories indicate either biased glacial deposition during the Amazonian era or long-term creep of hundreds of meters of ice-richregolith beneath the surface, respectively.[6]
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.[7] 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 are 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.
Cone-shaped features with higher albedo than surrounding rocks litter the surface of Acidalia Planitia. The most similar terrestrial feature to these formations aremud volcanoes.[8] On Mars, mud volcanoes have an average diameter of ~1 km and a relief of 10 to 180 meters. Their higher albedo is a result of more crystallineiron oxides than the rest of Acidalia Planitia.[8] Mud volcanoes erupt sediments from deep beneath the surface and change the rising rocks very minimally. These rocks are used to analyze organic matter as mud volcanoes also create subterranean conduits for ancient ground water that may have hostedmicrobiota.[8]
In the 2011 novelThe Martian by Andy Weir, andits 2015 film adaptation, Acidalia Planitia is the landing site of the Ares III mission, where the protagonist is stranded following a dust storm.[9]
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