103 research outputs found
The Penetration of Solar Radiation into Carbon Dioxide Ice
Icy surfaces behave differently to rocky or regolithâcovered surfaces in response to irradiation. A key factor is the ability of visible light to penetrate partially into the subsurface. This results in the SolidâState Greenhouse Effect (SSGE), as ices can be transparent or translucent to visible and shorter wavelengths, whilst opaque in the infrared. This can lead to significant differences in shallow subâsurface temperature profiles when compared to rocky surfaces. Of particular significance for modelling the SSGE is the eâfolding scale, otherwise known as the absorption scale length, or penetration depth, of the ice. Whilst there have been measurements for water ice and snow, pure and with mixtures, to date there have been no such measurements published for carbon dioxide ice. After an extensive series of measurements we are able to constrain the eâfolding scale of CO2 ice for the cumulative wavelength range 300 nm to 1100 nm, which is a vital parameter in heat transfer models for the Martian surface, enabling us to better understand surfaceâatmosphere interactions at Marsâ polar caps
Planet Four: Terrains - Discovery of Araneiforms Outside of the South Polar Layered Deposits
We present the results of a systematic mapping of seasonally sculpted
terrains on the South Polar region of Mars with the Planet Four: Terrains (P4T)
online citizen science project. P4T enlists members of the general public to
visually identify features in the publicly released Mars Reconnaissance Orbiter
CTX images. In particular, P4T volunteers are asked to identify: 1) araneiforms
(including features with a central pit and radiating channels known as
'spiders'); 2) erosional depressions, troughs, mesas, ridges, and
quasi-circular pits characteristic of the South Polar Residual Cap (SPRC) which
we collectively refer to as 'Swiss cheese terrain', and 3) craters. In this
work we present the distributions of our high confidence classic spider
araneiforms and Swiss cheese terrain identifications. We find no locations
within our high confidence spider sample that also have confident Swiss cheese
terrain identifications. Previously spiders were reported as being confined to
the South Polar Layered Deposits (SPLD). Our work has provided the first
identification of spiders at locations outside of the SPLD, confirmed with high
resolution HiRISE imaging. We find araneiforms on the Amazonian and Hesperian
polar units and the Early Noachian highland units, with 75% of the identified
araneiform locations in our high confidence sample residing on the SPLD. With
our current coverage, we cannot confirm whether these are the only geologic
units conducive to araneiform formation on the Martian South Polar region. Our
results are consistent with the current CO2 jet formation scenario with the
process exploiting weaknesses in the surface below the seasonal CO2 ice sheet
to carve araneiform channels into the regolith over many seasons. These new
regions serve as additional probes of the conditions required for channel
creation in the CO2 jet process. (Abridged)Comment: accepted to Icarus - Supplemental data files are available at
https://www.zooniverse.org/projects/mschwamb/planet-four-terrains/about/results
- Icarus print version available at
http://www.sciencedirect.com/science/article/pii/S001910351730055
Planet Four: A Neural Networkâs search for polar spring-time fans on Mars
Dark deposits visible from orbit appear in the Martian south polar region during the springtime. These are thought to form from explosive jets of carbon dioxide gas breaking through the thawing seasonal ice cap, carrying dust and dirt which is then deposited onto the ice as dark âblotchesâ, or blown by the surface winds into streaks or âfansâ. We investigate machine learning (ML) methods for automatically identifying these seasonal features in High Resolution Imaging Science Experiment (HiRISE) satellite imagery. We designed deep Convolutional Neural Networks (CNNs) that were trained and tested using the catalog generated by Planet Four, an online citizen science project mapping the south polar seasonal deposits. We validated the CNNs by comparing their results with those of ISODATA (Iterative Self-Organizing Data Analysis Technique) clustering and as expected, the CNNs were significantly better at predicting the results found by Planet Four, in both the area of predicted seasonal deposits and in delineating their boundaries. We found neither the CNNs or ISODATA were suited to predicting the source point and directions of seasonal fans, which is a strength of the citizen science approach. The CNNs showed good agreement with Planet Four in cross-validation metrics and detected some seasonal deposits in the HiRISE images missed in the Planet Four catalog; the total area of seasonal deposits predicted by the CNNs was 27% larger than that of the Planet Four catalog, but this aspect varied considerably on a per-image basis
Martian Araneiforms: A Review
Araneiforms are enigmatic dendritic negative topography features native to Mars. Found across a variety of substrates and exhibiting a range of scales, morphologies, and activity level, they are hypothesized to form via insolation-induced basal sublimation of seasonal CO2 ice. With no direct Earth analog, araneiforms are an example of how our understanding of extant surface features can evolve through a multipronged approach using high resolution change-detection imaging, conceptual and numerical modeling, and analog laboratory work. This review offers a primer on the current state of knowledge of Martian araneiforms. We outline the development of their driving conceptual hypothesis and the various methodologies used to study their formation. We furthermore present open questions and identify future laboratory and modeling work and mission objectives that may address these questions. Finally, this review highlights how the study of araneiforms may be used as a proxy for local conditions and perhaps even past seasonal dynamics on Mars. We also reflect on the lessons learnt from studying them and opportunities for comparative planetology that can be harnessed in understanding unusual features on icy worlds that have no Earth analog
Seasonal southern circum-polar spots and araneiforms observed with the colour and stereo surface imaging system (CaSSIS)
The southern polar area of Mars is home to various seasonal activity commonly explained by the Kieffer model.
During southern spring, the ice covering the polar area sublimates and leaves distinct features (spiders, spots,
fans) observable from orbit. The Colour and Stereo Surface Imaging System (CaSSIS) onboard the ExoMars Trace
Gas Orbiter (TGO), provides high-resolution multi-filter images of the Martian surface offering high sensitivity to
colour contrasts. Its stereo capability is pivotal for momentary processes and offers a unique perspective for
studying surface sublimation processes and their relation to atmospheric features. For the first time, we identify
clouds well correlated with surface features (araneiforms and spots at southern circum-polar latitudes) hence
motivating a new campaign to refine these observations over time periods where CO2 sublimation processes
occur. We focus here on the structure of spot deposits and their evolution through time. We identify and describe
seven structures: dark spot, bright-haloed spot, ringed spot, inverted spot, dark-haloed spot, banded spot, and
bright spot. By morphological and spectral analyses, we hypothesize a new chronology of events that characterise
the origin, formation and evolution of these features
First results on Martian carbon monoxide from Herschel/HIFI observations
We report on the initial analysis of Herschel/HIFI carbon monoxide (CO)
observations of the Martian atmosphere performed between 11 and 16 April 2010.
We selected the (7-6) rotational transitions of the isotopes ^{13}CO at 771 GHz
and C^{18}O at 768 GHz in order to retrieve the mean vertical profile of
temperature and the mean volume mixing ratio of carbon monoxide. The derived
temperature profile agrees within less than 5 K with general circulation model
(GCM) predictions up to an altitude of 45 km, however, show about 12-15 K lower
values at 60 km. The CO mixing ratio was determined as 980 \pm 150 ppm, in
agreement with the 900 ppm derived from Herschel/SPIRE observations in November
2009.Comment: Accepted for publication in Astronomy and Astrophysics (special issue
on HIFI first results); minor changes to match published versio
Planet Four: Probing springtime winds on Mars by mapping the southern polar CO2 jet deposits
The springtime sublimation process of Marsâ southern seasonal polar CO2 ice cap features dark fan-shaped de- posits appearing on the top of the thawing ice sheet. The fan material likely originates from the surface below the ice sheet, brought up via CO2 jets breaking through the seasonal ice cap. Once the dust and dirt is released into the atmosphere, the material may be blown by the surface winds into the dark streaks visible from orbit. The location, size and direction of these fans record a number of parameters important to quantifying seasonal winds and sublimation activity, the most important agent of geological change extant on Mars. We present results of a systematic mapping of these south polar seasonal fans with the Planet Four online citizen science project. Planet Four enlists the general public to map the shapes, directions, and sizes of the seasonal fans visible in orbital images. Over 80,000 volunteers have contributed to the Planet Four project, reviewing 221 images, from Mars Reconnaissance Orbiterâs HiRISE (High Resolution Imaging Science Experiment) camera, taken in southern spring during Mars Years 29 and 30. We provide an overview of Planet Four and detail the processes of combining multiple volunteer assessments together to generate a high delity catalog of ⌠400000 south polar seasonal fans. We present the results from analyzing the wind directions at several locations monitored by HiRISE over two Mars years, providing new insights into polar surface winds
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