Planum Australe (
Latin
Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
: "the southern plain") is the southern polar plain on
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
. It extends southward of roughly 75°S and is centered at . The geology of this region was to be explored by the failed
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeedin ...
mission
Mars Polar Lander
The Mars Polar Lander, also known as the Mars Surveyor '98 Lander, was a 290-kilogram robotic spacecraft lander launched by NASA on January 3, 1999, to study the soil and climate of Planum Australe, a region near the south pole on Mars. It form ...
, which lost contact on entry into the
Martian atmosphere.
In July 2018, scientists reported the discovery, based on
MARSIS radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
studies, of a
subglacial lake on Mars, below the
southern polar ice cap, and extending sideways about , the first known stable body of water on the planet.
Ice cap
Planum Australe is partially covered by a permanent
polar ice cap
A polar ice cap or polar cap is a high-latitude region of a planet, dwarf planet, or natural satellite that is covered in ice.
There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, no ...
composed of frozen
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
and
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
about 3 km thick. A seasonal ice cap forms on top of the permanent one during the Martian winter, extending from 60°S southwards. It is, at the height of winter, approximately 1 meter thick. It is possible that the area of this ice cap may be shrinking due to localized
climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
. Claims of more planetwide
global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
based on imagery, however, ignore temperature data and global datasets. Spacecraft and microwave data indicate global average temperature is, at most, stable, and possibly cooling.
In 1966, Leighton and Murray proposed that the Martian polar caps provided a store of CO
2 much larger than the atmospheric reservoir. However it is now thought that both polar caps are made mostly of water ice. Both poles have a thin seasonal covering of CO
2, while in addition the southern pole has a permanent residual CO
2 cap, about 8 to 10 metres thick, that lies on top of the water ice. Perhaps the key argument that the bulk of the ice is water is that CO
2 ice isn't mechanically strong enough to make a 3 km thick ice cap stable over long periods of time. Recent evidence from
SHARAD ice penetrating radar has revealed a massive subsurface CO
2 ice deposit approximately equal to 80% of the current atmosphere, or 4-5 mbar, stored in Planum Australe.
Data from
ESA's
Mars Express
''Mars Express'' is a space exploration mission being conducted by the European Space Agency (ESA). The ''Mars Express'' mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally ref ...
indicates that there are three main parts to the ice cap. The most reflective part of the ice cap is approximately 85%
dry ice
Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and sublimates directly from the solid state to the gas state. It is used primarily ...
and 15% water ice. The second part, where the ice cap forms steep slopes at the boundary with the surrounding plain, is almost exclusively water ice. Finally, the ice cap is surrounded by
permafrost
Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface ...
fields that extend for tens of kilometres north away from the scarps.
The centre of the permanent ice cap is not located at 90°S but rather approximately 150 kilometres north of the geographical south pole. The presence of two massive
impact basins
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...
in the western hemisphere -
Hellas Planitia and
Argyre Planitia - creates an immobile
area of low pressure
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...
over the permanent ice cap. The resulting weather patterns produce fluffy white
snow
Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.
It consists of frozen crystalline water throughou ...
which has a high
albedo
Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refle ...
. This is in contrast to the
black ice
Black ice, sometimes called clear ice, is a thin coating of glaze ice on a surface, especially on streets. The ice itself is not black, but visually transparent, allowing the often black road below to be seen through it. The typically low level ...
that forms in the eastern part of the polar region, which receives little snow.
Features
There are two distinct subregions in Planum Australe -
Australe Lingula and
Promethei Lingula. It is dissected by canyons
Promethei Chasma,
Ultimum Chasma,
Chasma Australe
In planetary nomenclature, a chasma (''plural'': chasmata ) is a deep, elongated, steep-sided depression. As of 2020, the IAU has named 122 such features in the Solar System, on Venus (63), Mars (25), Saturn's satellites Mimas (6), Tethys (2), ...
and
Australe Sulci. It is theorised that these canyons were created by
katabatic wind. The largest crater in Planum Australe is
McMurdo Crater.
Geysers on Mars
The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight.
Then, sublimed CO
2 (and probably water) increase pressure in their interior, producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.
This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars. The
Mars Geyser Hopper
The Mars Geyser Hopper (MGH) is a NASA design reference mission for a Discovery-class spacecraft concept that would investigate the springtime carbon dioxide Martian geysers found in regions around the south pole of Mars.
The power technology t ...
lander is a concept mission that would investigate the geysers of Mars.
Saltwater lakes
In September 2020, scientists confirmed the existence of several large
saltwater lakes under the
ice in the south polar region of the planet
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
. According to one of the researchers, “We identified the same body of water
s suggested earlier in a preliminary initial detection but we also found three other bodies of water around the main one ... It’s a complex system.”
See also
*
Climate of Mars
*
List of plains on Mars
This is a list of plains on Mars. Such features are named after the nearest classical albedo feature in compliance with the International Astronomical Union's rules of planetary nomenclature. Plains may be named denoted "planitia" or "planum", dep ...
*
Martian polar ice caps
The planet Mars has two permanent polar ice caps. During a pole's winter, it lies in continuous darkness, chilling the surface and causing the deposition of 25–30% of the atmosphere into slabs of CO2 ice (dry ice). When the poles are again e ...
*
Planum Boreum
Planum Boreum (Latin: "the northern plain") is the northern polar plain on Mars. It extends northward from roughly 80°N and is centered at . Surrounding the high polar plain is a flat and featureless lowland plain called Vastitas Borealis which ...
, the northern polar plain
References
External links
Accumulation and erosion of south polar layered deposits in the Promethei Lingula region, Planum Australe, Mars Planum Australe on Google Mars
Stratigraphy and Topography of McMurdo Crater area, Planum Australe, MarsUSGS map of Planum Australe
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Plains on Mars
Polar regions of Mars
Mare Australe quadrangle