Similar to Earth, Mars features an axial tilt that determines its seasons, known as its obliquity and can change over hundreds of millions of years.
As Mars’ obliquity shifts, sunlight disappears from certain parts of its surface while remaining bright in others, which causes ice to vanish in polar regions and humidity to increase elsewhere on its planet.
The Tharsis dome
Tharsis dome on Mars is an expansive volcanic province containing three of its most massive volcanoes: Olympus Mons, Arsia Mons and Pavonis Mons. These mountains form an east-west line spanning roughly the central portion of its map; their respective volcanic cores lie on an elongated rise measuring some 5,000 km wide by 12 kilometres thick – quite an enormous area for a planet half as big as Earth!
Volcanic activity in Mars’ Tharsis region during its formative years led to an obvious bulge and altered its spin axis reorientation – just as life could be emerging on its surface. Scientists have used simulations to demonstrate this effect can explain many features of Martian topography such as river networks.
As magma cooled, it compacted the lithosphere. This led to tear faults connecting rifts with basal compression zones. While Earth uses plate tectonics for such processes, Mars’ thick lithosphere cannot sink down into its mantle like this – instead differentials between hot and cold regions in its mantle drive large-scale circulation that forms features like Valles Marineris.
Radial faults could also have produced the unique shape of Tharsis dome. Its unique form may have helped tamp down any sudden increases in height, as well as leading to valley formation which is common on Mars.
At first, scientists were baffled by the Tharsis dome’s location of dry riverbeds that flow into Chryse Planitia from Chrysis Dome. Now however, researchers from Universite Paris-Sud’s Laboratoire de Meteorologie Dynamique believe these riverbeds may have arisen because of its new spin axis orientation and that is likely why their position was changed so dramatically.
The tilt of Mars Odyssey’s spin axis plays a critical role in controlling water vapor flow and surface accumulation of ice, as well as melting depth range. Scientists simulated its structure under Tharsis dome using data from SEIS instrument on Mars Odyssey, taking note of depleted shergottite phase diagram and extrapolated its melting range based on layer thicknesses.
The axial tilt
Similar to Earth, Mars spins on an axis tilted at an obliquity angle of 25 degrees from its orbital plane. This tilt is known as its obliquity and it causes seasonal variation on Mars. But unlike Earth, unlike Mars has no major moon to keep its obliquity stable and two small ones don’t provide sufficient counterweight against Jupiter’s powerful gravitational pull; therefore its obliquity wiggles on timescales from thousands to millions of years.
Obliquity of Mars is crucial, as it determines how much water can be stored in its polar regions and how much sunlight reaches its equator. For example, when Mars is farthest from the Sun and has low obliquity, the polar regions become unexpectedly warm as most surface ice slowly sublimates away into air (sublimates). Any new surface ice formation must begin from cold-water vapor or it will quickly melt away.
As the obliquity increases and temperatures at the poles become cooler, a new cycle begins. Once polar ice forms again, surface vapor will begin to freeze into crystallized sheets of ice; as it does so it radiates less heat while absorbing more of the Sun’s rays.
As the climate of Mars becomes similar to our own, polar ice sheets will gradually begin growing again, while water locked up at the poles will move to form mountain glaciers on its way towards Earth-like climate zones and form mountain glaciers there.
Mars may have undergone similar processes in its past, though it’s hard to be certain due to its fragile surface topography. Scientists do have some insights though – they know the polar surface was once covered in rivers and shallow seas; studying riverbed shapes gives an idea of what happened on its surface at that time.
Scientists can gain further insights into the ancient topography of Mars by studying its modern-day north and south poles – also known as pole stars – which today point toward Polaris. Due to the planet’s obliquity, however, its northern pole has gradually shifted toward either Deneb or one of its Summer Triangle stars like Vega or Altair over time.
The equator
The equatorial plane, often referred to as one of five main circles of latitude (also called great circles), circumnavigates a planet like Earth and marks the point at which Sun rays perpendicularly strike its surface during spring and fall equinoxes, when day and night have equal duration. Furthermore, this point marks where rotation axis meets plane of orbit to form what is known as the equatorial plane (one of five great circles).
Mars takes two times longer to orbit the Sun than Earth, leading to drastic differences in insolation across its surface. This explains why southern summers are so hot and dry while northern winters remain bitter cold – another contributing factor being planet tilt.
As with Earth, Mars features an axial tilt of roughly 25 degrees that causes its seasons. But unlike on Earth, Mars’ tilt is unstable; it wobbles roughly once every 120,000 years according to University of Hawaii’s Astrobiology Institute and this fluctuation alters how much sunlight reaches Mars’ surface.
Current estimates put Mars’ obliquity (tilt of its axis relative to its plane of orbit) at about 24.4 degrees, similar to Earth. This may reflect Moon’s gravitational pull as well. But in early Solar System times, its tilt may have been much greater.
Astronomers from University of California, Los Angeles conducted research into the chemical composition of Mars rocks to understand its changing climate over time. They observed a layered surface similar to tree rings on Mars that suggests its climate may have shifted over time. Furthermore, authors examined layers of rock covering polar ice caps which had eroded away and slumped over time, hinting that they once provided much warmer and wetter climate conditions than now exist.
Mars’ obliquity has undergone considerable fluctuations over the course of our Solar System’s history, reaching values higher than 25 degrees at times in its past. If this is indeed the case, this could help explain why large reservoirs of water ice were discovered at mid-latitudes rather than only at its poles.
The northern plains
The northern plains are an expansive region formed of alluvial deposits brought to Earth by rivers like Indus, Ganges and Brahmaputra and their tributaries, and home to numerous lakes including one of the largest freshwater bodies on Earth known as Great Rann of Kutch. Not only are they an invaluable source of fresh water but they are also home to fossil-rich soil that has made the northern plains an important site for research on Mars – specifically searching for evidence of life on that red planet.
Mars experiences climate changes over time due to both its tilted axis and longer orbit around the Sun than Earth does, leading to different seasons, with southern summers being shorter and warmer than northern winters.
Astronomers now understand that Earth’s present lopsidedness is caused by its past tilt being much greater, which led to vast underground reservoirs of ice formed throughout its mid latitudes as opposed to just at its poles.
Mars currently exhibits an obliquity (tilt relative to its orbital plane) of approximately 25 degrees; not too dissimilar from Earth’s 23 degree tilt. This angle causes its seasons and polar ice caps.
Few tens of millions of years ago, Mars was at roughly 60 degrees of obliquity – joining Uranus and Pluto as one of only three planets that lay “sideways”.
At one point in time, Mars’ polar ice caps were considerably larger than they are now and its air pressure much higher; liquid water could form and flow freely on their surfaces. When the obliquity cycle reversed and their size began to diminish, air pressure dropped as water in the ice sublimated back into vapor form before refreezeing, causing its volume to shrink while liquid water sublimated out, leading to less accumulation on surfaces while sublimation also took place and sublimated back out causing further shrinkage of polar ice caps while its liquid water eventually sublimated out before refreeze caused further diminution as sublimation caused water sublimate back into vapour before refreeze again causing further shrinkage whilst increasing surface area with less space available for liquid water accumulation on surfaces before.
Scientists have observed this process time after time on Mars, leading to its distinctive seasonal changes. Scientists have monitored this cyclical climate change using evidence found from rocks and soil samples collected on its surface; in particular they studied rock layers at Becquerel Crater which have evidence of sedimentary rocks laid down over 100,000 years, suggesting climate fluctuations triggered by changes to its orbital obliquity cycle were involved in their formation.