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| Hesperian epoch | |
|---|---|
| Name | Hesperian epoch |
| Period | Hesperian |
| Caption | Representative Hesperian-aged lava plains and valley networks |
| Start | ~3.7 billion years ago |
| End | ~3.0 billion years ago |
| Predecessor | Noachian epoch |
| Successor | Amazonian epoch |
| Planet | Mars |
Hesperian epoch The Hesperian epoch is a formal chronostratigraphic interval on Mars defined by widespread volcanic, tectonic, and fluvial modification of the surface between the older Noachian epoch and younger Amazonian epoch. It is characterized by the emplacement of extensive lava plains, the formation of large outflow channels and valley networks, and global changes in surface and atmospheric processes recorded in crater densities, stratigraphic contacts, and mineral assemblages observed by spacecraft and instruments. Interpretations of Hesperian events draw on data from missions such as Mariner 9, Viking, Mars Global Surveyor, Mars Odyssey, Mars Reconnaissance Orbiter, and Mars Science Laboratory.
The Hesperian epoch is conventionally defined as beginning around 3.7 billion years ago with the decline of heavy bombardment tied to the end of the Late Heavy Bombardment hypotheses and ending near 3.0–2.9 billion years ago before the onset of Amazonian processes. Chronology relies on crater-counting techniques calibrated against lunar absolute ages established by studies of samples from Apollo program missions and radiometric constraints from Martian meteorites such as the Shergottite group. International stratigraphic committees for planetary geology use landscape unit boundaries—transitional contacts between Noachian highland terrains and Amazonian surfaces—to delineate the Hesperian in regional and global maps produced by teams at institutions like the United States Geological Survey.
Hesperian terrains are typified by intercalated plains of low crater density, tectonic features including rift zones and fault-bounded basins, and reworked highland surfaces modified by erosion and deposition. These terrains often display mineralogical signatures of alteration minerals such as sulfates and altered mafic phases identified by instruments aboard Mars Express and MAVEN. Regional examples include the Tharsis volcanic province, the Valles Marineris system margin deposits, and the adjacent equatorial plains where Hesperian-aged wrinkle ridges and lobate flows are abundant. Geologic mapping frameworks developed by teams at NASA Jet Propulsion Laboratory and the Lunar and Planetary Institute correlate stratigraphic markers across mapsets to distinguish Hesperian units from Noachian cratered highlands and Amazonian mantling deposits.
The Hesperian marks extensive volcanic resurfacing manifested as vast low-viscosity lava plains and construction of volcanic constructs on scales comparable to terrestrial flood basalts. Prominent volcanic centers active during or initiating in the Hesperian include portions of Tharsis Montes, Elysium Mons, and the broad shield fields of Arabia Terra margins. Lava plains display morphological features such as flow fronts, tube-fed channels, and wrinkle ridges captured in imagery from HiRISE and CTX cameras aboard Mars Reconnaissance Orbiter. Volcanism during this epoch is linked to regional tectonics like the formation of the Valles Marineris graben system and to mantle processes inferred from gravity and topography studies conducted by teams using data from Mars Global Surveyor and MOLA altimetry.
Hesperian landscapes preserve evidence for transient but high-energy aqueous activity including formation of large outflow channels (e.g., Kasei Valles, Ares Vallis) and valley networks carved by runoff and possibly catastrophic floods. Sedimentary deposits interpreted as fluvio-lacustrine terraces, deltaic constructs, and layered sulfates indicate episodic surface water stability and the alteration of rocks in oxidizing conditions detected by instruments on Opportunity (rover), Spirit (rover), and Curiosity (rover). Proposed climate scenarios range from warm and wet transient episodes driven by volcanic outgassing and impact heating to cold and icy conditions with localized melting, discussed in publications from research groups at Caltech, Brown University, and the Smithsonian Institution.
Hesperian stratigraphic units include the widespread ridged plains, smooth plateau basalts, layered sulfate-bearing strata, and extensive alluvial and fluvial deposits mapped in regional schemes such as the global geological map produced by USGS authors. Key rock units correlated with the Hesperian include Hesperian ridged plains (hrp) and volcanic plains (hv), layered deposits in chaotic terrains, and large sedimentary fans adjacent to outflow channels. Mineralogic mapping from the CRISM spectrometer and thermal inertia measurements from THEMIS provide compositional constraints linking these units to basaltic volcanism, pervasive alteration to sulfates, and emplacement of poorly consolidated sediments.
Debates persist over the onset, duration, and intensity of Hesperian processes: whether the epoch represents a geologically brief but intense period of global change or a protracted transition involving waning volcanism and intermittent aqueous activity. Contrasting interpretations arise from crater chronology uncertainties, differences in regional stratigraphic correlations, and alternative climate models advanced by researchers at University of Arizona and Imperial College London. Disagreements extend to the relative timing of sulfate deposition versus volcanic resurfacing, the role of groundwater sapping versus surface runoff in valley formation, and the contribution of large impacts versus endogenic processes in driving transient warming episodes.
Evidence for Hesperian processes derives from orbital imaging, spectroscopy, and landed investigations. Early reconnaissance by Mariner 9 and the Viking program established the basic dichotomy of old highlands and younger plains later refined by Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter. In situ data from landed assets—Viking 1, Viking 2, Pathfinder, Spirit (rover), Opportunity (rover), and Curiosity (rover)—have characterized sedimentary textures, sulfate-rich strata, and basaltic compositions interpreted as Hesperian-age materials. Ongoing and future missions such as ExoMars Trace Gas Orbiter and sample-return initiatives led by NASA and European Space Agency aim to refine absolute ages and unambiguously tie returned samples to Hesperian rock units for radiometric dating.
Category:Mars epochs