Evidence of water on Mars found by Mars Reconnaissance Orbiter

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Springs in Vernal Crater, as seen by HIRISE. These springs may be good places to look for evidence of past life because hot springs can preserve evidence of life forms for a long time. Location is Oxia Palus quadrangle.

The Mars Reconnaissance Orbiter's HiRISE instrument has taken many images that strongly suggest that Mars has had a rich history of water-related processes. A major discovery was finding evidence of hot springs. These may have contained life and may now contain well-preserved fossils of life.

Evidence from images[edit]

Research, in the January 2010 issue of Icarus, described strong evidence for sustained precipitation in the area around Valles Marineris.[1][2] The types of minerals there are associated with water. Also, the high density of small branching channels indicates a great deal of precipitation because they are similar to stream channels on the Earth.

Some places on Mars show inverted relief. In these locations, a stream bed appears as a raised feature, instead of a depression. The inverted former stream channels may be caused by the deposition of large rocks or due to cementation of loose materials. In either case erosion would erode the surrounding land and consequently leave the old channel as a raised ridge because the ridge will be more resistant to erosion. Images below, taken with HiRISE show sinuous ridges that are old channels that have become inverted.[3]

In an article published in January 2010, a large group of scientists endorsed the idea of searching for life in Miyamoto Crater because of inverted stream channels and minerals that indicated the past presence of water.[2][4]

Using data from Mars Global Surveyor, Mars Odyssey and the Mars Reconnaissance Orbiter, scientists have found widespread deposits of chloride minerals. Usually chlorides are the last minerals to come out of solution. A picture below shows some deposits within the Phaethontis quadrangle. Evidence suggests that the deposits were formed from the evaporation of mineral-enriched waters. Lakes may have been scattered over large areas of the Martian surface. Carbonates, sulfates, and silica should precipitate out ahead of them. Sulfates and silica have been discovered by the Mars Rovers. Places with chloride minerals may have once held various life forms. Furthermore, such areas should preserve traces of ancient life.[5]

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

Rocks on Mars have been found to frequently occur as layers, called strata, in many different places. Columbus Crater is one of many craters that contain layers.[6] Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers.[7] Many places on Mars show rocks arranged in layers. Scientists are happy about finding layers on Mars since layers may have formed under large bodies of water. Sometimes the layers display different colors. Light-toned rocks on Mars have been associated with hydrated minerals like sulfates. The Mars Rover Opportunity examined such layers close-up with several instruments. Some layers are probably made up of fine particles because they seem to break up into fine dust. In contrast, other layers break up into large boulders so they are probably much harder. Basalt, a volcanic rock, is thought to form layers composed of boulders. Basalt has been identified all over Mars. Instruments on orbiting spacecraft have detected clay (also called phyllosilicates) in some layers.[8][9] Scientists are excited about finding hydrated minerals such as sulfates and clays on Mars because they are usually formed in the presence of water.[10] Places that contain clays and/or other hydrated minerals would be good places to look for evidence of life.[11]

Below are a few of the many examples of layers that have been studied with HiRISE.

Much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust.[12] This ice-rich mantle, a few yards thick, smoothes the land. But in places it displays a bumpy texture, resembling the surface of a basketball. Because there are few craters on this mantle, the mantle is relatively young. The images below, all taken with HiRISE, show a variety of views of this smooth mantle.


Gullies[edit]

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 returns to the 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.[13] Water vapor condenses on the particles, then they 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 insulates the remaining ice.[14]

HiRISE has carried out many observations of gullies that are assumed to have been caused by recent flows of liquid water. Many gullies are imaged over and over to see if any changes occur. Some repeat observations of gullies have displayed changes that some scientists argue were caused by liquid water over the period of just a few years.[15] Others say the flows were merely dry flows.[16] These were first discovered by the Mars Global Surveyor.

Alternate theories for the creation of surface gullies and channels include wind erosion,[17] liquid carbon dioxide,[18] and liquid methane.[19]

Below are some of the many hundreds of gullies that have been studied with HiRISE.

Of interest from the days of the Viking Orbiters are piles of material surrounding cliffs. These deposits of rock debris are called lobate debris aprons (LDAs). These features have a convex topography and a gentle slope from cliffs or escarpments; this suggests flow away from the steep source cliff. In addition, lobate debris aprons can show surface lineations just as rock glaciers on the Earth.[20] Recently[when?], research with the Shallow Radar on the Mars Reconnaissance Orbiter has provided strong evidence that the LDAs in Hellas Planitia and in mid northern latitudes are glaciers that are covered with a thin layer of rocks. Radar from the Mars Reconnaissance Orbiter gave a strong reflection from the top and base of LDAs, meaning that pure water ice made up the bulk of the formation (between the two reflections).[21][22] Based on the experiments of the Phoenix lander and the studies of the Mars Odyssey from orbit, frozen water is now known to exist at just under the surface of Mars in the far north and south (high latitudes). The discovery of water ice in LDAs demonstrates that water is found at even lower latitudes. Future colonists on Mars will be able to tap into these ice deposits, instead of having to travel to much higher latitudes. Another major advantage of LDAs over other sources of Martian water is that they can easily detected and mapped from orbit. Lobate debris aprons are shown below from the Phlegra Montes, which are at latitude of 38.2 degrees north. The Phoenix lander set down at about 68 degrees north latitude, so the discovery of water ice in LDAs greatly expands the range of easily available on Mars.[23] It is far easier to land a spaceship near the equator of Mars, so the closer water is available to the equator the better it will be for future colonists.

Below are examples of lobate debris aprons that were studied with HiRISE.

Bright part is water ice that has been exposed by impact. The ice was identified using CRISM on the MRO. Location is Cebrenia quadrangle.

Research, reported in the journal Science in September 2009,[24] demonstrated that some new craters on Mars show exposed, pure, water ice. After a time, the ice disappears, evaporating into the atmosphere. The ice is only a few feet deep. The ice was confirmed with the Compact Imaging Spectrometer (CRISM) on board the Mars Reconnaissance Orbiter (MRO). The ice was found in five locations. Three of the locations are in the Cebrenia quadrangle. These locations are 55.57° N, 150.62° E; 43.28° N, 176.9° E; and 45° N, 164.5° E. Two others are in the Diacria quadrangle: 46.7° N, 176.8° E and 46.33° N, 176.9° E.[25][26][27] This discovery proves that future colonists on Mars will be able to obtain water from a wide variety of locations. The ice can be dug up, melted, then taken apart to provide fresh oxygen and hydrogen for rocket fuel. Hydrogen is the powerful fuel used by the space shuttle main engines.

Columnar jointing[edit]

Columnar jointing in basalt, Marte Vallis

In 2009, HiRISE discovered columnar jointing in rocks on Mars.[28] Such jointing is accepted as having involved water. To make the parallel cracks of columnar jointing, more cooling is necessary, and water is the most logical choice. Scientists calculate that the water was present intermittently for a few months to a few years.[29]

Light-toned layered deposits[edit]

HiRISE has sent back many images of large surface areas that are termed "light-toned layered deposits." These 30–80 meter thick deposits are believed to have been formed from the action of water. They contain evidence of stream channel systems.[30] Furthermore, chemical data from the Compact Reconnaissance Imaging Spectrometer orbiting the planet have shown water related mineral forms: opal (hydrated silica) and iron sulfates.[31] These can be formed from the action of low temperature acid solutions reacting with basaltic rocks. These features of light-toned layered deposits strongly suggest that there was long lasting precipitation and surface runoff during the Hesperian epoch of Martian history.[1][32]

References[edit]

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