Geology topics

Donna Viola

Publications and source records attributed to Donna Viola.

7 recordsLinked to original sources

USGS2023

A large new crater exposes the limits of water ice on Mars

Water ice in the Martian mid-latitudes has advanced and retreated in response to variations in the planet's orbit, obliquity, and climate. A 150 m-diameter new impact crater near 35°N provides the lowest-latitude impact exposure of subsurface ice on Mars. This is the largest known ice-exposing crater and provides key constraints on Martian climate history. This crater indicates a regional, relatively pure ice deposit that is unstable and has nearly vanished. In the past, this deposit may have been tens of meters thick and extended equatorward of 35°N. We infer that it is overlain by pore ice emplaced during temporary stable intervals, due to recent climate variability. The marginal survival of ice here suggests that it is near the edge of shallow ice that regularly exchanges with the atmosphere.

Geophysical Research Letters↗

USGS2023

Toward consistent change detection across irregular remote sensing time series observations

The use of remote sensing in time series analysis enables wall-to-wall monitoring of the land surface and is critical for assessing and understanding land cover and land use change and for understanding the Earth system as a whole. However, variability in remote sensing observation frequency through time and across space presents challenges for producing consistent change detection results throughout the available satellite record using approaches such as the Continuous Change Detection and Classification (CCDC) change detection methodology. Here we investigate new modifications to this methodology with the goal of improving accuracy and consistency in results and increasing flexibility for operational usage and future development. The modified method (Band-First Probability, or CCD-BFP) change detection procedure works by calculating a test for each band through time before summarizing between bands. We evaluate the CCD-BFP method compared to an existing implementation of CCDC using a variety of approaches, including a validation dataset of human-interpreted locations, comparison with data from fire events, use of simulated remote sensing data, and qualitative inspection of areas of interest. We find CCD-BFP improves consistency across time and space compared to the existing implementation of CCDC, with more similarity in rates of change across Landsat swath boundaries and before and after the launch of Landsat 7. Also, we find that CCD-BFP detects more of the change events in the validation dataset while reducing the overall number of change detections, indicating that it is able to more accurately capture the most notable land surface change events.

Remote Sensing of Environment↗

USGS2021

Widespread exposures of extensive clean shallow ice in the mid-latitudes of Mars

Although ice in the Martian midlatitudes is typically covered by a layer of dust or regolith, it is exposed in some locations by fresh impact craters or in erosional scarps. In both cases, the exposed ice is massive or excess ice with a low lithic content. We find that erosional scarps occur between 50° and 61° north and south latitude and that they are concentrated in and near Milankovič crater in the northern hemisphere and southeast of the Hellas basin in the southern hemisphere. These may represent locations of particularly thick or clean bodies of ice. Pits created by retreat of the scarps represent sublimation-thermokarst landforms that evolve in a manner distinct from other ice-loss landforms on Mars. New impact craters reveal that clean subsurface ice is widespread at middle- and high-latitudes in both hemispheres at depths less than 1 m. Both the depth to ice and the ice content appear to exhibit significant variability over tens to hundreds of meters. The lowest-latitude exposed ice is near 39°N and is at the edge of a region where impact exposures between 40° and 50°N are common, consistent with other indications of a high ice content. This lowest-latitude ice may be currently unstable and subliming. Impact craters on lineated valley fill excavate ice blocks that may represent the top of debris-covered glacial ice. Together, these landforms indicate widespread, clean subsurface ice at middle-latitudes on Mars. The distribution and properties of this ice could provide information about past climate conditions.

Journal of Geophysical Research: Planets↗

USGS2020

Sparse subsurface radar reflectors in Hellas Planitia, Mars

Geomorphological features potentially related to subsurface ice, such as scalloped depressions, expanded craters, pedestal craters, and banded terrain, are present in and around Hellas Planitia, Mars. We present a radar survey of the region using the Shallow Radar (SHARAD) instrument on board the Mars Reconnaissance Orbiter (MRO) to identify candidate subsurface reflectors that may be due to the presence of potentially ice-rich deposits. We found that the majority of radar returns are likely from off-nadir surface topography (“clutter”), arising from the rough topography of the region. There is no widespread radar return from any subsurface interfaces. However, we identify a group of six reflectors adjacent to each other on a plateau in Malea Patera in which we have higher confidence. Landforms associated with a likely ice-rich mantle are associated with the plateau, but the thickness of this mantle does not correspond to the expected depth of the reflectors. However, layers beneath the mantle and marginal pitting at the edge of the plateau are similar to those associated with pedestal craters, which may be ice rich and are a similar thickness to the expected depth of the reflectors. Malea Patera has been interpreted to be a volcanic caldera, so the reflectors may be associated with a volcanic deposit within the plateau, although the evidence for this is inconclusive. Because this radar detection is localized and its origin ambiguous, we cannot use it to make conclusions about the thickness of subsurface deposits in the Hellas region as a whole. The lack of widespread radar reflectors in this region, as compared to the northern mid-latitudes where extensive radar reflections have been mapped, may be due in part to higher surface roughness, which creates radar clutter that may obscure subsurface reflectors. However on the southern rim of the basin and south of the basin, the lack of reflectors may indicate that the possible ice-rich deposits observed geomorphologically in this region are too thin to be resolved by SHARAD, are dielectrically similar to the underlying unit, or have a gradual vertical transition in ice content that is not reflective for the radar. This would imply that recent climate processes may have favored widespread, thick ice deposition or preservation in the northern hemisphere as compared to the southern hemisphere.

Icarus↗

USGS2018

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.

Science↗

USGS2015

Expanded secondary craters in the Arcadia Planitia region, Mars: evidence for tens of Myr-old shallow subsurface ice

A range of observations indicates widespread subsurface ice throughout the mid and high latitudes of Mars in the form of both pore-filling and excess ice. It is generally thought that this ice was recently emplaced and is not older than a hundred thousand to a few millions of years old based on ice stability and orbital-induced climate change. We analyze the distribution of subsurface ice in Arcadia Planitia, located in the northern mid latitudes, by mapping thermokarstically expanded secondary craters, providing additional evidence for extensive excess ice down to fairly low latitudes (less than 40°N). We further infer the minimum age of this subsurface ice based on the ages of the four primary craters that are thought to be the source of a large portion of these secondaries, which yields estimates on the order of tens of millions of years old – much more ancient than anticipated. This estimated ancient age suggests that ice can be preserved in the shallow subsurface for long periods of time, at least in some parts of Arcadia Planitia where expanded secondary craters are especially abundant. We estimate the amount of ice lost to sublimation during crater expansion based on measurements of expanded secondary craters in HiRISE Digital Terrain Models. The loss is equivalent to a volume of ice between &sim;140 and 360 km 3 , which would correspond to a global layer of 1–2.5 mm thick. We further argue that much more ice (at least 6000 km 3 ) is likely preserved beneath the un-cratered regions of Arcadia Planitia since significant loss of this excess ice would have caused extensive terrain dissection and the removal of the expanded secondary craters. Both the loss of ice due to secondary crater expansion and the presence of this ice today have implications for the martian climate.

Icarus↗

USGS2014

A new analysis of Mars "Special Regions": findings of the Second MEPAG Special Regions Science Analysis Group (SR-SAG2)

A committee of the Mars Exploration Program Analysis Group (MEPAG) has reviewed and updated the description of Special Regions on Mars as places where terrestrial organisms might replicate (per the COSPAR Planetary Protection Policy). This review and update was conducted by an international team (SR-SAG2) drawn from both the biological science and Mars exploration communities, focused on understanding when and where Special Regions could occur. The study applied recently available data about martian environments and about terrestrial organisms, building on a previous analysis of Mars Special Regions (2006) undertaken by a similar team. Since then, a new body of highly relevant information has been generated from the Mars Reconnaissance Orbiter (launched in 2005) and Phoenix (2007) and data from Mars Express and the twin Mars Exploration Rovers (all 2003). Results have also been gleaned from the Mars Science Laboratory (launched in 2011). In addition to Mars data, there is a considerable body of new data regarding the known environmental limits to life on Earth—including the potential for terrestrial microbial life to survive and replicate under martian environmental conditions. The SR-SAG2 analysis has included an examination of new Mars models relevant to natural environmental variation in water activity and temperature; a review and reconsideration of the current parameters used to define Special Regions; and updated maps and descriptions of the martian environments recommended for treatment as "Uncertain" or "Special" as natural features or those potentially formed by the influence of future landed spacecraft. Significant changes in our knowledge of the capabilities of terrestrial organisms and the existence of possibly habitable martian environments have led to a new appreciation of where Mars Special Regions may be identified and protected. The SR-SAG also considered the impact of Special Regions on potential future human missions to Mars, both as locations of potential resources and as places that should not be inadvertently contaminated by human activity.

Astrobiology↗