Periods Of High Obliquity Research Articles

Geomorphological study of the gullies in Penticton crater, Mars: Classification and origin

Penticton crater, a southern hemisphere mid-latitude crater on Mars is covered with features that are typical examples of the martian gullies that resemble the terrestrial gullies on Earth. We studied the gullies present in Penticton crater, classified them and interpreted their formation mechanism using a remote sensing approach. A wide variety of gullies including the classic gullies, channel gullies, alcove-apron features, linear gullies and a distinct light toned gully were detected in the crater. With its diverse classes of gullies and absence of a preferential orientation trend between pole-facing and equator-facing slopes, Penticton crater serves as an ideal location for observing present-day gully activity and studying the mechanism of modern gully formation. The geomorphological study points out prominent glacial features like lobate debris apron (LDA), lineated valley fill (LVF), and concentric crater fill (CCF) in the region. Extensive morphologic evidence suggests previous existence of latitude dependent mantle (LDM) on the pole-facing crater walls. The morphometric analysis using parameters like length, orientation, alcove and apron width of the gullies for all the four martian seasons suggest that the gullies are currently not active. The age estimated using crater size frequency distribution indicated that the study area is 5.5 ± 0.7 Ma, which falls in the range of the high obliquity period of Mars. We propose a rare scenario where there are multiple gully forming mechanisms acting on the same crater. Our results implies that the gullies on the pole-facing slopes are formed on LDM due to destabilization triggered by the sublimation during the recent shift in martian obliquity. However, morphometric parameters including the apex slopes gives the impression that the gullies on the steeper equator-facing slope were most likely formed by the sliding of dry granular sand.

The habitability conditions of possible Mars landing sites for life exploration

A major focus of Mars exploration is the search for life. Since the Viking landers in the 1970's, no mission has searched for evidence of modern life. Future landed missions with this objective will require a landing site that optimizes the potential for current or geologically-recent habitable conditions. While the definition of habitability is broad, we concentrate on two conditions for habitability of temperature and water activity. In addition, we consider the access to subsurface ice (e.g., via a lander drill) as a major requirement. To examine potential landing sites, we utilize a standard model of temperature and ground-ice stability to explore a range of latitudes for the past 2.5 Myrs of orbitally induced climate change. We find that in the current epoch, habitable conditions do not occur within the ice-rich permafrost, where stable ice is limited to poleward of ∼47°N. Habitable conditions defined as favorable to metabolic activity in Earth-like potential Mars organisms did occur seasonally during periods of high obliquity >33°, when ground ice would have been more ubiquitous. The most recent occurrence was about 510 kyrs ago when temperatures and water activities seasonally exceeded the threshold for metabolic activity of −40 °C and 0.6, respectively. Periods such as these last 10s of kyrs at each occurrence. At no time or location do habitability conditions favor propagation (cell replication above −18 °C) in Earth-like Mars organisms. We present a model of subsurface stratigraphy based on the occurrence of ground ice, the age of the ice, and history of habitable conditions. From this stratigraphy we find that all latitudes offer some potential for life exploration. However, middle-latitude sites (47°N to 61°N) offer access to 100-kyr-old ice that experienced past habitable conditions, while high-latitudes sites (>61°N) offer this plus access to “ancient ice” > > 1 Myrs old. Access to, and comparison between, multiple stratigraphic layers with differing ages and histories will maximize the science results of a life exploration mission. These latitude limits may vary slightly with surface conditions of slope and soil properties.

An Analysis of Glacial and Fluvial Morphologies within Impact Craters in the Equatorial Region in Arabia Terra, Mars

Arabia Terra is an ancient and large terrain which is located north of the Martian equator. Due to its ancient nature, it is heavily cratered, and these craters hold evidence of geologic processes during Mars’ history. During periods of high obliquity (>35°) it has been suggested that polar ice migration can occur at the lower latitudes. By investigating the impact craters within a localized area in the equatorial region of Arabia Terra, it can be determined how far this migration once occurred. This study aimed to investigate craters ≥1 km in diameter within the 0°N–10°N, 340°E–350°E area of Arabia Terra and determine the frequency of glacial and fluvial morphologies within this region. We divided the search area into two sections, 0°N–5°N, 340°E–350°E and 5°N–10°N, 340°E–350°E, to help identify any latitudinal variations between the glacial and fluvial morphologies.

Gullies on Mars could have formed by melting of water ice during periods of high obliquity.

Gullies on Mars resemble water-carved channels on Earth, but they are mostly at elevations where liquid water is not expected under current climate conditions. It has been suggested that sublimation of carbon dioxide ice alone could have formed Martian gullies. We used a general circulation model to show that the highest-elevation Martian gullies coincide with the boundary of terrain that experienced pressures above the triple point of water when Mars' rotational axis tilt reached 35°. Those conditions have occurred repeatedly over the past several million years, most recently ~630,000 years ago. Surface water ice, if present at these locations, could have melted when temperatures rose >273 kelvin. We propose a dual gully formation scenario that is driven by melting of water ice followed by carbon dioxide ice sublimation.

Data and software for Dickson et al. (Gullies on Mars formed by melting of water ice during periods of high obliquity)

Data and software for Dickson et al. (Gullies on Mars formed by melting of water ice during periods of high obliquity)

Data and software for Dickson et al. (Gullies on Mars formed by melting of water ice during periods of high obliquity)

Data and software for Dickson et al. (Gullies on Mars formed by melting of water ice during periods of high obliquity)

Data and software for Dickson et al. (Gullies on Mars formed by melting of water ice during periods of high obliquity)

Data and software for Dickson et al. (Gullies on Mars formed by melting of water ice during periods of high obliquity)

Data and software for Dickson et al. (Gullies on Mars formed by melting of water ice during periods of high obliquity)

Data and software for Dickson et al. (Gullies on Mars formed by melting of water ice during periods of high obliquity)

Stratigraphy and Volumes of the Units Within the Massive Carbon Dioxide Ice Deposits of Mars

AbstractThe south polar layered deposits of Mars contain a massive CO2 ice reservoir formed during periods of low planetary obliquity and partial atmospheric collapse. Within the reservoir are bounding layers (BLs) that are believed to consist entirely of water ice and modify CO2 ice stability during periods of higher obliquity and insolation. Here we use three‐dimensional data from the Shallow Radar instrument to extend and update past mapping efforts of the reservoir in order to evaluate its internal structure and mass distribution. By mapping the entirety of each BL as two distinct reflectors, we provide individual volumetric calculations of the multiple CO2 units for the first time (146, 1,472, and 5,493 km3) and discover a new, smaller unit (12 km3). Our volumetric measurements provide critical parameters to understanding past climatic states and climatological modeling, including the magnitude of atmospheric collapse and rebound over three separate events. We also provide updated thickness and areal extent measurements of BL1 (31 ± 5 m, 1,001 km2), BL2 (32 ± 9 m, 5,415 km2) and BL2+3 (42 ± 12 m, 4,232 km2), with maximum thickness of ∼80 m. By mapping the entirety of the BLs, we find novel radar observations, attainable only in 3D, which support previous interpretations that both BL are composed of water ice. Our novel measurements will support climatological studies of Mars’ atmosphere in the past 500 kyr.

Evidence for widespread glaciation in Arcadia Planitia, Mars

Viscous flow features, including lobate debris aprons and lineated valley fill, are common ice-related features found across the mid-latitudes of Mars. These features are commonly found along the dichotomy boundary and around massifs where snow and ice can accumulate and flow to topographic lows during periods of higher obliquity. We have identified and mapped glacial-related features reminiscent of lineated valley fill and lobate debris aprons in the lower mid-latitudes of Arcadia Planitia based on morphology, albedo, thermal infrared reflectance, thermal inertia, and subsurface radar reflections. Three sinuous features show surface morphologies and supporting spectral properties indicative of massive buried ice, including distinct boundaries, arcuate and linear banding, deep radar reflections, dielectric constants similar to water-ice, expanded secondary craters, and proximity to lobate debris aprons. We interpret the sinuous and lobate features of Arcadia Planitia to be buried debris-covered glaciers formed during higher obliquity periods in Mars' recent past. These sinuous features appear to be channelized ice that once flowed but currently reside in a flat-lying region. Although their origin is unclear, we consider an interpretation analogous to stagnated terrestrial ice streams due to a lack of obvious topographic dependence. The abundant evidence of widespread near-surface ice in a flat-lying lower mid-latitude region of Mars makes Arcadia Planitia a potentially favorable site for future missions due to the high potential for in situ resource utilization.

Ice-rich landforms of the southern mid-latitudes of Mars: A case study in Nereidum Montes

Mapping of Viscous Flow Features (VFFs), a general grouping of ice-rich flow features that includes Lobate Debris Aprons (LDA), Concentric Crater Fill (CCF), Lineated Valley Flow (LVF), small lobate flows (i.e., glacier-like flows, or GLFs), and arcuate ridges, in the southern hemisphere of Mars shows a dense concentration in Nereidum Montes, along the northern rim of Argyre basin. Further mapping within a subregion in northwest Nereidum Montes (45.3°–48.5° S, 307°–312° E) shows a large number of well-preserved VFFs and ice-rich mantling deposits. Processed SHARAD data across a VFF within the region indicates that it is composed of nearly pure water ice.Model ages obtained from crater counts and their associated size-frequency distributions (SFDs) on both ice-rich mantling deposits and small lobate VFFs suggest that the deposits stabilized several to tens of Ma ago in the Late Amazonian Epoch, and that small lobate VFFs likely formed due to the mobilization of mantling deposits. SFD for a larger VFF shows a model age of 100 s of Ma, consistent with ages for LDAs in eastern Hellas. Deposition of ice in Nereidum Montes that led to the formation of VFFs likely occurred during periods of high obliquity in the Late Amazonian.Our results show that VFFs have more complete and diverse preservation states in Nereidum Montes than similar features in other regions on Mars. This region contains uniquely well-preserved mantling deposits above arcuate ridges and beyond the margins of lobate VFFs and gully aprons. This key observation ties arcuate ridges to the flow of mantling deposits, part of a continuum model for mid-latitude ice-rich landforms.

Opposite response modes of NADW dynamics to obliquity forcing during the late Paleogene

Although the responses of North Atlantic Deep Water (NADW) is deeply connected to orbital rhythms, those under different tectonic and atmospheric boundary conditions remain unknown. Here, we report suborbitally resolved benthic foraminiferal stable isotope data from J-anomaly Ridge in the North Atlantic from ca. 26.4–26.0 Ma. Our results indicate that the formation of NADW during that time interval was increased during the obliquity-paced interglacial periods, similar to in the Plio-Pleistocene. During the late Oligocene, the interglacial poleward shifts of the stronger westerlies in the southern hemisphere, which occurred due to the higher thermal contrasts near the upper limit of the troposphere, reinforced the Antarctic Circumpolar Current (ACC) and, in turn, the Atlantic meridional overturning circulation (AMOC). However, such a response mode in deep ocean circulation did not occur during the middle Eocene because of different tectonic boundary conditions and the immature states of the ACC. Instead, the middle Eocene interglacial conditions weakened the formation of the proto-type NADW due to less heat loss rate in high-latitude regions of the North Atlantic during high obliquity periods. Our findings highlight the different responses of deep ocean circulation to orbital forcing and show that climate feedbacks can be largely sensitive to boundary conditions.

Cold-based glaciation of Pavonis Mons, Mars: evidence for moraine deposition during glacial advance

The three large volcanoes in the Tharsis region of Mars: Arsia, Pavonis, and Ascraeus Montes all have fan-shaped deposits (FSDs) on their northern or western flanks consisting of a combination of parallel ridges, knobby/hummocky terrain, and a smooth, viscous flow-like unit. The FSDs are hypothesized to have formed in the Amazonian during a period of high spin-axis obliquity which redistributed polar ice to the equatorial Tharsis region resulting in thick (> 2 km), flowing ice deposits. Based on previous ice flow simulations and crater surveys, the ridges are interpreted to be recessional drop moraines formed as debris on the ice sheet surface was transported to the ice margin—forming a long ridge sequence over an extended (∼100 Myr) period of ice sheet retreat. We test this hypothesis using a high-resolution, thermomechanical ice sheet model assuming a lower ice loss rate (~ 0.5 mm/year) than prior work based on new experimental results of ice sublimation below a protective debris layer. Our ice flow simulation results, when combined with topographic observations from a long sequence of ridges located interior of the Pavonis FSD, show that the ridged units were more likely deposited during one or more periods of glacial advance (instead of retreat) when repetitive pulses (approx. 120 kyr periodicity) of ice accumulation during high obliquity produced kinematic waves which advected a large volume of surface debris to the ice margin. If ridge deposition does occur during glacial advance, it could explain the cyclic pattern of ridge spacing and would link the dominant, 120 kyr periodicity in obliquity to the time interval between adjacent ridges. By measuring the spacing between these ridges and applying this timescale, we constrain the velocity of glacial margin to be between 0.2 and 4 cm/Earth year—in close agreement with the numerical simulation. This re-interpretation of the FSD ridged unit suggests that the timescale of FSD formation (and perhaps the duration of the Amazonian high obliquity period) was shorter than previously reported.

Mars in ice ages for ∼25% of post-Noachian geologic history

Mars is currently a hyperarid, hypothermal desert planet, whose surface inventory of water is primarily confined to the north and south polar ice caps. Previous studies have shown that Mars has undergone massive shifts in its spin-axis obliquity (present-day is 25.2°) due to secular spin orbit resonances. During periods of higher obliquity, water-ice from the polar caps is mobilized to the mid-latitudes (∼35° obliquity) and even the equator (≥45° obliquity), where it is deposited as snow and accumulates over time to form thick regional surface ice sheets. Abundant evidence exists today for the remnants of these ice ages in the form of debris-covered glaciers and ice deposits, but due to the chaotic nature of orbital simulations beyond ∼20 Ma, it has remained unclear to what temporal extent Mars has experienced such ice ages. Recent developments have suggested that impact events which formed in martian surface ice deposits exhibit a distinctive double-layered ejecta morphology. In tandem with cratering statistics, this observation offers the potential to better our understanding of the history of ice ages on Mars. This work explores the timing of ice age events by evaluating the size-frequency distribution of craters forming in surface ice. Using Hartmann isochron model ages, this work shows that Mars has experienced mid-latitude ice ages for up to a cumulative ∼680 Myr out of the past 3.6 Ga, and experienced equatorial ice ages for up to a cumulative ∼250 Myr within the same time period. The results of this study indicate that Mars has experienced mid-latitude/equatorial ice age states for up to approximately 25% of its post-Noachian geologic history, emphasizing that much of the geologic history of Mars is dominated by the presence of widespread non-polar surface ice sheets.

Geomorphological analysis of gullies on the central peak of Lyot Crater, Mars

Abstract The central peak region of Lyot Crater provides an intriguing case study of Martian gully formation on local topographic highs. To better understand how these gullies formed, we carried out a detailed morphological analysis using a HiRISE stereo image pair and a digital terrain model. Gully lengths range from c. 2.2 to 4.3 km, with maximum depths from 17 to 54 m. Alcove slopes range from c. 20 to 22°, channel slopes range from 12 to 16° and apron slopes range from 10 to 14°. In general, these slopes are much lower than both the angle of repose ( c. 33°) required to initiate dry flows and the apex slope required to keep these flows from depositing (>21°) under Mars gravity. We find that the observed gully morphology and spatial associations are consistent with an origin by liquid flow. Apron volumes are c. 10–40% of the gully volume, which we suggest indicates significant volatile loss (water and/or CO 2 ) in the slope materials in which they formed because apron volumes emplaced by dry gravitational flows would equal or exceed the gully volumes due to their lower packing density. These observations, coupled with the gullies’ unique micro-environmental setting, lead us to favour a fluvial origin. In addition, we find that the gullies formed almost exclusively on the western slope region, which suggests a possible orographic component. Potential water sources may have been supplied locally in the recent geological past by dry winds blowing across an ice-covered lake situated in a low elevation area just west of the central peak or more globally during periods of higher obliquity. In either case, the integration of morphometric and morphological investigations suggests that these gullies probably formed by surface runoff and through-flow from snow- or icepack melting on the central peak of Lyot Crater.

Mars: Formation and fate of a frozen Hesperian ocean

Late Hesperian-aged, circum-Tharsis floods interpreted to have formed by catastrophic release of groundwater cut large channels and debouched significant quantities of water into the northern lowlands of Mars. The floods are thought by many to have formed an ocean of significant volume and depth, encircled by contacts that have been interpreted as shorelines. Models of catastrophic groundwater release require a thick and continuous cryosphere with mean annual temperatures well below freezing much like those today. In this environment, the bodies of liquid formed by individual outflow events would have been very short lived, undergoing rapid freezing. We investigate the case where floods repeatedly flowed into the northern lowlands under climatic conditions that resemble those of the present day; the water from each flood froze in a geologically short period of time to form an ice layer. Successive ice layers accumulated to form an ocean-sized body of ice that filled the basin up to the -3650 contour, thereby enclosing a 110 m global equivalent layer (GEL) of water. Subsequent to the filling of the basin the ice slowly sublimated into the atmosphere to be lost to space or to accumulate in various surface and near-surface cold traps, such as the polar layered deposits. Where is this excess water today? The presence of the thick global cryosphere meant that only minor amounts of water were lost from the surface back into the global groundwater system. Approximately 20-30 m GEL of water is estimated to be at or near the surface today and exchanging with the atmosphere on geologic time scales (this includes the polar layered deposits and deposits elsewhere at depths less than approximately 80 m). Below the exchangeable reservoir is a non-exchangeable reservoir of unknown capacity. Present day loss rates to space fall far short of those needed to eliminate the mid-Hesperian ice ocean and those needed to cause the observed doubling of the D/H of the exchangeable reservoir since the mid-Hesperian. The discrepancy implies earlier loss rates must have been higher. Assuming a linear increase in loss rates because of the higher early EUV output of the Sun, we estimate that for a present inventory of 30 m GEL, 42 m GEL remains to be accounted for. Possibilities include greater dependence of losses of EUV than assumed, and enhanced losses during periods of high obliquity. In addition, large volumes of ice may be present near the surface at high latitudes outside the polar layered deposits as indicated by recent discoveries of ice layers in cliffs.

Exposed subsurface ice sheets in the Martian mid-latitudes.

Thick deposits cover broad regions of the Martian mid-latitudes with a smooth mantle; erosion in these regions creates scarps that expose the internal structure of the mantle. We investigated eight of these locations and found that they expose deposits of water ice that can be >100 meters thick, extending downward from depths as shallow as 1 to 2 meters below the surface. The scarps are actively retreating because of sublimation of the exposed water ice. The ice deposits likely originated as snowfall during Mars' high-obliquity periods and have now compacted into massive, fractured, and layered ice. We expect the vertical structure of Martian ice-rich deposits to preserve a record of ice deposition and past climate.

The formation of gullies on Mars today

Abstract A decade of high-resolution monitoring has revealed extensive activity in fresh Martian gullies. Flows within the gullies are diverse: they can be relatively light, neutral or dark, colourful or bland, and range from superficial deposits to 10 m-scale topographic changes. We observed erosion and transport of material within gullies, new terraces, freshly eroded channel segments, migrating sinuous curves, channel abandonment, and lobate deposits. We also observed early stages of gully initiation, demonstrating that these processes are not merely modifying pre-existing landforms. The timing of activity closely correlates with the presence of seasonal CO 2 frost, so the current changes must be part of ongoing gully formation that is driven largely by its presence. We suggest that the cumulative effect of many flows erodes alcoves and channels, and builds lobate aprons, with no involvement of liquid water. Instead, flows may be fluidized by sublimation of entrained CO 2 ice or other mechanisms. The frequent activity is likely to have erased any features dating from high-obliquity periods, so fresh gully geomorphology at middle and high latitudes is not evidence for past liquid water. CO 2 ice-driven processes may have been important throughout Martian geological history and their deposits could exist in the rock record, perhaps resembling debris-flow sediments.

Testing landslide and atmospheric‐effects models for the formation of double‐layered ejecta craters on Mars

AbstractDouble‐layered ejecta (DLE) craters are distinctive among the variety of crater morphologies observed on Mars, but the mechanism by which they form remains under debate. We assess two ejecta emplacement mechanisms: (1) atmospheric effects from ejecta curtain‐induced vortices or a base surge and (2) ballistic emplacement followed by a landslide of ejecta assisted by either surface‐ or pore‐ice. We conduct a morphological analysis of the ejecta facies for three DLE craters which impacted into irregular pre‐existing topography. We find that the unique topographic environments affected the formation of grooves and the inner facies, and thus appear to be inconsistent with an atmospheric‐effects origin but are supportive of the landslide hypothesis. We distinguish between the two landslide models (lubrication by either surface‐ or pore‐ice) by assessing relationships between DLE crater ejecta and morphologic features indicative of buried ice deposits, including sublimation pits, ring‐mold craters, expanded secondary craters, and excess ejecta craters. The association of DLE craters with these features suggests that surface ice was present at the time of the impacts that formed the DLE craters. We also compare the Froude numbers of DLE crater ejecta to landslides, and find that the ejecta of DLE craters are kinematically and frictionally similar to terrestrial landslides that overran glaciers. This suggests that the grooves on DLE craters may plausibly form through the same shear/splitting mechanism as the landslides. In summary, our analysis supports the hypothesis that DLE craters form through meteoroid impacts into decameters‐thick surface ice deposits (emplaced during periods of higher obliquity) followed by ejecta sliding on the ice.

火星表面の永久凍土と周氷河作用

Following the development of high-resolution imaging, digital elevation models, thermal and hydrological data, and onsite ground information during the early period of the 21st century, the periglacial geomorphology of the Martian surface advanced rapidly. Images can even resolute meter-scale landforms, enabling identification of most periglacial features and analysis of their global distributions and detailed morphologies. This review focuses on progress in research covering permafrost distribution, patterned ground, possible heave and subsidence features, lobate debris forms, and slope-lineated features during the last decade. Most of the Martian high-latitude surface is underlain by ice-rich ground called the latitude-dependent mantle (LDM), which favors permafrost-related features possibly developed under warm-humid conditions during past high-obliquity periods or partially s,till active under the present cold-dry conditions. Thermal contraction cracking is likely to prevail in the LDM, resulting in high-centered, flat-top polygons, possibly underlain by sublimation-type wedges or sand wedges that prevail at high latitudes. The surface patterns change into subdued or peak-top polygons toward the mid-latitudes, probably reflecting long-term sublimation of the LDM. Some researchers attribute stone circles to sorting due to freeze-thaw, but the features are much larger than candidates on the Earth. Small isolated domes with concentric cracks or craters at the top may include pingos, which also prevail at high- to mid-latitudes. Asymmetrical scalloped depressions may result from sublimation or thawing of the LDM, but there is a debate between pole-ward and equator-ward slope retreats. Lobate debris aprons may originate from creep of ice-rock mixtures or debris-covered glaciers, but the distinction between the two origins is unclear, as in the long-lasting debate on terrestrial candidates. Some thin, smaller debris lobes at high latitudes resemble stone-banked solifluction lobes on the Earth, which may indicate the occurrence of seasonal freeze-thaw cycles in the recent past. Time-series images indicate active slope features, including gullies, slope streaks, and recurrent slope lineaes that develop below cliffs. These active features may originate from outflows of brine that thaws far below the melting point of water ice.