Inplanetary nomenclature, achasma/ˈkæzmə/ (plural:chasmata/ˈkæzmətə/) is a deep, elongated, steep-sideddepression.[1] As of 2020, theIAU has named 122 such features in the Solar System, onVenus (63),Mars (25), Saturn's satellitesMimas (6),Tethys (2),Dione (8) andRhea (5), Uranus's satellitesAriel (7),Titania (2) andOberon (1) and Pluto's satelliteCharon (3). An example isEos Chasma onMars.
Below are images of some of the major chasmata of Mars. The map shows their relative locations.
Parts of the floor of Candor Chasma contains layered deposits that have been termed interior layered deposits (ILD's). These layers may have formed when the whole area was a giant lake. Some places on Mars contain hydratedsulfate deposits. Sulfate formation involves the presence of water. TheEuropean Space Agency'sMars Express found evidence of perhapsepsomite andkieserite. Scientists want to visit these areas with robotic rovers.[2]
Images of rocks in the canyon walls almost always show layers. Some layers appear tougher than others. In the image below ofGanges Chasma Layers, as seen byHiRISE, one can see that the upper, light-toned deposits are eroding much faster than the lower darker layers. Some cliffs on Mars show a few darker layers standing out and often breaking into large pieces; these are thought to be hard volcanic rock instead of soft ash deposits. An example of hard layers is shown below in the picture of layers in the canyon wall in Coprates, as seen byMars Global Surveyor. Because of its closeness to the Tharsis volcanic region, the rock layers may be made of layer after layer oflava flows, probably mixed with deposits of volcanic ash that fell out of the air following big eruptions. It is likely the rock strata in the walls preserve a long geological history of Mars.[3] Dark layers may be due to dark lava flows. The dark volcanic rockbasalt is common on Mars. However, light-toned deposits may have resulted from rivers, lakes, volcanic ash, or wind blown deposits of sand or dust.[4] TheMars Rovers found light-toned rocks to containsulfates. Probably having been formed in water, sulfate deposits are of great interest to scientists because they may contain traces of ancient life.[5]
Hebes Chasma, a large enclosed valley, may have once held water. Hydrated minerals have been found there. It is thought that large-scale underground springs of groundwater at different times burst to the surface to form deposits called Light Toned Deposits (LTD's). Some suggest present or fossilized life forms may be found there because the deposits are relatively young.[6]
