Tharsis
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| Tharsis | |
|---|---|
| Name | Tharsis |
| Type | volcanic plateau |
| Location | Mars |
| Coordinates | ~0°N, 265°E |
| Diameter | ~4000 km |
| Discoverer | International telescopic observations; mapped by Mariner 9 |
| Notable features | Olympus Mons, Ascraeus Mons, Pavonis Mons, Arsia Mons, Noctis Labyrinthus |
Tharsis is a vast volcanic plateau on Mars that dominates the planet's western hemisphere, hosting the largest shield volcanoes in the Solar System and a complex array of tectonic and volcanic constructs. The province has been central to studies by missions such as Mariner 9, Viking program, Mars Global Surveyor, and Mars Reconnaissance Orbiter, and figures in hypotheses linking internal dynamics to surface habitability and climate evolution. Tharsis influences global topography, atmospheric circulation, and the distribution of fluvial and aeolian landforms across Valles Marineris and the adjacent southern highlands.
Geography and geology
The plateau spans roughly from the equator to mid-northern latitudes, bounded by provinces and basins like Amazonis Planitia, Utopia Planitia, and Isidis Planitia and overlooking canyons such as Valles Marineris and plains including Chryse Planitia. Surface materials include extensive lava flows, ash deposits, and layered sediments studied by orbiters like Mars Odyssey and landers such as Viking 1. Tharsis sits atop a crustal thickness anomaly identified by gravity and altimetry data from Mars Global Surveyor and Mars Express, and its rim and flanks show erosional and depositional interactions with channels feeding into basins like Hellas Planitia and Arsia Chasma. Regional stratigraphy preserves episodic emplacement of basaltic shields, flood basalts, and pyroclastic units comparable in context to provinces on Moon and Earth such as the Deccan Traps and Iceland.
Volcanism and major volcanoes
The Tharsis rise hosts the giants Olympus Mons and the Tharsis Montes trio: Ascraeus Mons, Pavonis Mons, and Arsia Mons, along with complex edifices like Elysium Mons at the province margin and a chain of paterae including Ulysses Patera. These volcanoes record long-lived effusive activity dominated by low-viscosity basaltic lavas analogous to eruptions observed at Hawaii and Iceland, interspersed with explosive phases inferred from pyroclastic deposits mapped by Mars Reconnaissance Orbiter and spectral signatures detected by Mars Odyssey. Caldera complexes and flank vents indicate magma supply variations studied through gravity inversions from Mars Global Surveyor and seismic constraints retrieved indirectly by models inspired by data from missions such as InSight. Comparative planetology links Tharsis volcanism to processes documented at Mount Etna and in the Sierra Nevada (U.S.) volcanic province.
Tectonics and structural features
Tharsis drives a network of radial and concentric faults, grabens, and wrinkle ridges manifested in systems like Valles Marineris and the radial fossae that extend across the western hemisphere. Rift and extensional features include the Claritas Fossae and Noctis Labyrinthus complex, while compressional tectonics produced wrinkle ridges in regions such as Tempe Terra and Tithonium Chasma. Global stress models constrained by topography from Mars Orbiter Laser Altimeter predict lithospheric flexure and regional uplift comparable to scenarios used to explain foreland basins on Venus and uplifted domes on Earth like the Colorado Plateau. Fault mapping from Mars Reconnaissance Orbiter imagery reveals interactions between intrusion-driven dike swarms and surface volcanism similar to patterns observed in the Afro-Arabian rift.
Formation and geologic history
Tharsis formation spans the Noachian through Amazonian, with early episodes of crustal reworking and large-scale magmatism during the Hesperian interpreted from crater counts and stratigraphic relations observed by Viking program and Mars Global Surveyor. The rise likely originated from long-lived mantle upwelling, possibly a plume or multiple plumes, with geochemical implications probed by martian meteorites such as SNC meteorites and isotopic studies referencing data comparable to Apollo program lunar samples. Successive construction of the Tharsis Montes and Olympus Mons, intercalated with fluvial episodes recorded in valley networks observed near Margaritifer Terra and Nirgal Vallis, suggests episodic surface environments influenced by volcanic outgassing and transient climates posited by climate modelers using inputs from Mars Climate Orbiter era studies. Late-stage activity produced smaller shields, lava plains, and collapse features contemporaneous with sedimentary deposits in basins like Meridiani Planum.
Climate and atmospheric interactions
Tharsis' topographic prominence alters atmospheric circulation, affecting Hadley cell behavior and dust storm initiation monitored by Mars Global Surveyor and Mars Reconnaissance Orbiter. Outgassing of volatiles during Tharsis volcanism likely injected substantial amounts of water vapor, carbon dioxide, and sulfur species into the Mars atmosphere, scenarios explored in climate models by researchers referencing Paleoclimatology analogs and greenhouse forcing comparable to hypotheses for Venus early atmospheres. The plateau's elevation influences pressure and temperature gradients that control ice stability at mid-latitudes studied by instruments aboard Mars Odyssey and Mars Express, and its role in slope winds and katabatic flows has been documented during global dust events tracked by the Mars Color Imager.
Exploration and observations
Tharsis has been a primary target for orbital mapping by missions including Mariner 9, Viking program, Mars Global Surveyor, Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, and imaging by HiRISE. Surface-focused missions such as Viking 1 approached Tharsis-adjacent plains, while future mission concepts and rover proposals consider sampling Tharsis basalts to constrain martian mantle chemistry and volcanic chronology in the tradition of sample-return planning by Mars Sample Return advocates. Remote sensing datasets from instruments like MOLA, THEMIS, CRISM, and SHARAD have enabled high-resolution stratigraphic, mineralogical, and subsurface analyses, advancing interpretations of magmatic history, potential hydrothermal alteration near calderas, and the province's influence on planetary evolution.