Features on Mars are grouped by their aerological(geological) category or type. These groupings are based on the general physical appearance of the feature in question. However, just because two or more features look alike does not mean that they originated and evolved via the same geologic/aerologic processes. For example, is a large hole in the ground the result of a large impact or volcanic activity or the result of sapping? For a number of features, these questions will remain unanswered until we obtain much more detailed information about the features in question.
The Classification of Martian Features
The following table lists each feature type along with a brief description of what that type category represents.
- Albedo Feature
- These are features we observe because of variations in the amount of sunlight reflected by the martian surface. A surface that reflected all the light hitting it would have an albedo of 1.0 while a surface that absorbed all light hitting it would have an albedo of 0.0. Therefore the dark features on Mars have a lower albedo than the bright features.
- A linear string of craters, perhaps produced by a train of impactors, much like Shoemaker-Levy 9 did to Jupiter. Alternatively, the chain of crater-like features could be volcanic in origin and represent the collapse of subsurface lava tubes.
- A crater-like, irregularly shaped depression or hollow. These are not thought to be of impact origin.
- An area of jumbled or hummocky terrain that is thought to have been created as a result of groundwater sapping.
- A large canyon or a depression/trough with steep sides.
- A smallish hill or knob. A group is referred to as colles, the plural form of collis.
- A circular depression created by an impacting body.
Craters can be subdivided as being (from small to large) simple, complex, central peak basin, peak ring basin, and multi-ring basin.
Mars is unique in that is has craters with ejecta deposits that have a unique "flowing" appearance. It is believed that the presence of groundwater or ice is responsible for these features.
- An elongated prominence, ie. a longer than wide area of high ground.
The Earth analogue would be a ridge. This term was originally used by the Romans to indicate a mountain ridge.
- Only one example of this type of feature is found on Mars - Galaxias Fluctus. The term was originally used to describe a feature on Io that looks like a flow. The latin meaning is a wave or billow. Here it is used to describe a flow-like feature.
- One or more linear depressions most likely the result of faulting. These depressions are long and narrow and resemble a ditch or trench.
The Earth analogue is most likely a graben. On Mars, fossa often occur in groups. A group of fossa are referred to as fossae, the plural of fossa.
- Used to describe those features that appear to be the result of a landslide. The latin meaning for labes is a "falling in" or "sinking in."
- An area of intersecting liner depressions/canyons/valleys. The classic example is Noctis Labyrinthus.
- An elevated area with a flat top and steep sides (think of a cake). The Earth analog would be the mesas of the US southwest.
- A large isolated mountain, as opposed to Montes (a chain of mountains). On Mars, most are of volcanic origin.
- A complex crater, or an irregularly shaped one, with low relief that has scalloped edges and radiating channel-like features. Most are thought to be volcanic in origin.
- A plain whose area is at a lower altitude than the surrounding regions.
- A reasonably smooth, flat, relatively uncratered area of ground that is higher than the surrounding region and that is bordered by steep sides.
The Earth analogue would be a plateau.
- A cliff or scarp that is straight/linear rather than sinuous.
- A cliff or scarp that is irregular or lobate in appearance.
- A feature that has the appearance of a furrow, ditch, or wrinkle. These often occur in groups.
- An extended areal region or land mass. It is used in reference to the older, cratered highlands.
- An isolated, dome-shaped small mountain or hill. These are thought to be of volcanic origin. The plural form is tholi.
- An area of dunes that are very wave-like in appearance. The plural form is undae.
- Vallis is a sinuous valley most of which are probably of fluvial origin.
- A very large lowland plain. The only feature in the Solar System to which this description has been attached is Vastitas Borealis.
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