Shallow Radar (SHARAD), pedestal craters, and the lost Martian layers: Initial assessments

Daniel Cahn Nunes, Suzanne E. Smrekar, Brian Fisher, Jeffrey J. Plaut, John W. Holt, James W. Head, Seth J. Kadish, Roger J. Phillips

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

Since their discovery, Martian pedestal craters have been interpreted as remnants of layers that were once regionally extensive but have since been mostly removed. Pedestals span from subkilometer to hundreds of kilometers, but their thickness is less than ∼500 m. Except for a small equatorial concentration in the Medusae Fossae Formation, the nearly exclusive occurrence of pedestal craters in the middle and high latitudes of Mars has led to the suspicion that the lost units bore a significant fraction of volatiles, such as water ice. Recent morphological characterizations of pedestal deposits have further supported this view. Here we employ radar soundings obtained by the Shallow Radar (SHARAD) to investigate the volumes of a subset of the pedestal population, in concert with high-resolution imagery to assist our interpretations. From the analysis of 97 pedestal craters we find that large pedestals (diameter >30 km) are relatively transparent to radar in their majority, with SHARAD being able to detect the base of the pedestal deposits, and possess an average dielectric permittivity of 4 ± 0.5. In one of the cases of large pedestals in Malea Planum, layering is detected both in SHARAD data and in high-resolution imagery of the pedestal margins. We find that clutter is a major issue in the analysis of radar soundings for smaller pedestals, and tentative detection of the basal reflection occurs in only a few of the cases examined. These detections yield a higher average permittivity of ∼6. The permittivity value derived for the larger pedestals, for which a basal reflection is unambiguous, is higher than that of pure water ice but lower than that of most silicate materials. A mixture of ice and silicates or an ice-free porous silicate matrix can explain a permittivity of ∼4, and radar alone cannot resolve this nonuniqueness. Data from the Compact Reconnaissance Imaging Spectrometer (CRISM) tentatively confirms a mafic component in at least one pedestal in Malea Planum. Interpretation of SHARAD results can support either a mixture of ice and silicates or a porous silicate. The former is compatible with a model where nonpolar ice is periodically deposited in the midlatitudes as a result of obliquity variations. The latter is compatible with ash deposits, at least in where pedestals appear in volcanic centers such as Malea Planum.

Original languageEnglish (US)
Article numberE04006
JournalJournal of Geophysical Research E: Planets
Volume116
Issue number4
DOIs
StatePublished - Apr 27 2011
Externally publishedYes

Fingerprint

radar
craters
crater
Ice
ice
Radar
Silicates
silicates
permittivity
silicate
Temazepam
radar measurement
Permittivity
deposits
imagery
Deposits
Ashes
reconnaissance
temperate regions
high resolution

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

Cite this

Shallow Radar (SHARAD), pedestal craters, and the lost Martian layers : Initial assessments. / Nunes, Daniel Cahn; Smrekar, Suzanne E.; Fisher, Brian; Plaut, Jeffrey J.; Holt, John W.; Head, James W.; Kadish, Seth J.; Phillips, Roger J.

In: Journal of Geophysical Research E: Planets, Vol. 116, No. 4, E04006, 27.04.2011.

Research output: Contribution to journalArticle

Nunes, DC, Smrekar, SE, Fisher, B, Plaut, JJ, Holt, JW, Head, JW, Kadish, SJ & Phillips, RJ 2011, 'Shallow Radar (SHARAD), pedestal craters, and the lost Martian layers: Initial assessments', Journal of Geophysical Research E: Planets, vol. 116, no. 4, E04006. https://doi.org/10.1029/2010JE003690
Nunes, Daniel Cahn ; Smrekar, Suzanne E. ; Fisher, Brian ; Plaut, Jeffrey J. ; Holt, John W. ; Head, James W. ; Kadish, Seth J. ; Phillips, Roger J. / Shallow Radar (SHARAD), pedestal craters, and the lost Martian layers : Initial assessments. In: Journal of Geophysical Research E: Planets. 2011 ; Vol. 116, No. 4.
@article{a59bed83a09347569c8cfe826a430c58,
title = "Shallow Radar (SHARAD), pedestal craters, and the lost Martian layers: Initial assessments",
abstract = "Since their discovery, Martian pedestal craters have been interpreted as remnants of layers that were once regionally extensive but have since been mostly removed. Pedestals span from subkilometer to hundreds of kilometers, but their thickness is less than ∼500 m. Except for a small equatorial concentration in the Medusae Fossae Formation, the nearly exclusive occurrence of pedestal craters in the middle and high latitudes of Mars has led to the suspicion that the lost units bore a significant fraction of volatiles, such as water ice. Recent morphological characterizations of pedestal deposits have further supported this view. Here we employ radar soundings obtained by the Shallow Radar (SHARAD) to investigate the volumes of a subset of the pedestal population, in concert with high-resolution imagery to assist our interpretations. From the analysis of 97 pedestal craters we find that large pedestals (diameter >30 km) are relatively transparent to radar in their majority, with SHARAD being able to detect the base of the pedestal deposits, and possess an average dielectric permittivity of 4 ± 0.5. In one of the cases of large pedestals in Malea Planum, layering is detected both in SHARAD data and in high-resolution imagery of the pedestal margins. We find that clutter is a major issue in the analysis of radar soundings for smaller pedestals, and tentative detection of the basal reflection occurs in only a few of the cases examined. These detections yield a higher average permittivity of ∼6. The permittivity value derived for the larger pedestals, for which a basal reflection is unambiguous, is higher than that of pure water ice but lower than that of most silicate materials. A mixture of ice and silicates or an ice-free porous silicate matrix can explain a permittivity of ∼4, and radar alone cannot resolve this nonuniqueness. Data from the Compact Reconnaissance Imaging Spectrometer (CRISM) tentatively confirms a mafic component in at least one pedestal in Malea Planum. Interpretation of SHARAD results can support either a mixture of ice and silicates or a porous silicate. The former is compatible with a model where nonpolar ice is periodically deposited in the midlatitudes as a result of obliquity variations. The latter is compatible with ash deposits, at least in where pedestals appear in volcanic centers such as Malea Planum.",
author = "Nunes, {Daniel Cahn} and Smrekar, {Suzanne E.} and Brian Fisher and Plaut, {Jeffrey J.} and Holt, {John W.} and Head, {James W.} and Kadish, {Seth J.} and Phillips, {Roger J.}",
year = "2011",
month = "4",
day = "27",
doi = "10.1029/2010JE003690",
language = "English (US)",
volume = "116",
journal = "Journal of Geophysical Research: Atmospheres",
issn = "2169-897X",
number = "4",

}

TY - JOUR

T1 - Shallow Radar (SHARAD), pedestal craters, and the lost Martian layers

T2 - Initial assessments

AU - Nunes, Daniel Cahn

AU - Smrekar, Suzanne E.

AU - Fisher, Brian

AU - Plaut, Jeffrey J.

AU - Holt, John W.

AU - Head, James W.

AU - Kadish, Seth J.

AU - Phillips, Roger J.

PY - 2011/4/27

Y1 - 2011/4/27

N2 - Since their discovery, Martian pedestal craters have been interpreted as remnants of layers that were once regionally extensive but have since been mostly removed. Pedestals span from subkilometer to hundreds of kilometers, but their thickness is less than ∼500 m. Except for a small equatorial concentration in the Medusae Fossae Formation, the nearly exclusive occurrence of pedestal craters in the middle and high latitudes of Mars has led to the suspicion that the lost units bore a significant fraction of volatiles, such as water ice. Recent morphological characterizations of pedestal deposits have further supported this view. Here we employ radar soundings obtained by the Shallow Radar (SHARAD) to investigate the volumes of a subset of the pedestal population, in concert with high-resolution imagery to assist our interpretations. From the analysis of 97 pedestal craters we find that large pedestals (diameter >30 km) are relatively transparent to radar in their majority, with SHARAD being able to detect the base of the pedestal deposits, and possess an average dielectric permittivity of 4 ± 0.5. In one of the cases of large pedestals in Malea Planum, layering is detected both in SHARAD data and in high-resolution imagery of the pedestal margins. We find that clutter is a major issue in the analysis of radar soundings for smaller pedestals, and tentative detection of the basal reflection occurs in only a few of the cases examined. These detections yield a higher average permittivity of ∼6. The permittivity value derived for the larger pedestals, for which a basal reflection is unambiguous, is higher than that of pure water ice but lower than that of most silicate materials. A mixture of ice and silicates or an ice-free porous silicate matrix can explain a permittivity of ∼4, and radar alone cannot resolve this nonuniqueness. Data from the Compact Reconnaissance Imaging Spectrometer (CRISM) tentatively confirms a mafic component in at least one pedestal in Malea Planum. Interpretation of SHARAD results can support either a mixture of ice and silicates or a porous silicate. The former is compatible with a model where nonpolar ice is periodically deposited in the midlatitudes as a result of obliquity variations. The latter is compatible with ash deposits, at least in where pedestals appear in volcanic centers such as Malea Planum.

AB - Since their discovery, Martian pedestal craters have been interpreted as remnants of layers that were once regionally extensive but have since been mostly removed. Pedestals span from subkilometer to hundreds of kilometers, but their thickness is less than ∼500 m. Except for a small equatorial concentration in the Medusae Fossae Formation, the nearly exclusive occurrence of pedestal craters in the middle and high latitudes of Mars has led to the suspicion that the lost units bore a significant fraction of volatiles, such as water ice. Recent morphological characterizations of pedestal deposits have further supported this view. Here we employ radar soundings obtained by the Shallow Radar (SHARAD) to investigate the volumes of a subset of the pedestal population, in concert with high-resolution imagery to assist our interpretations. From the analysis of 97 pedestal craters we find that large pedestals (diameter >30 km) are relatively transparent to radar in their majority, with SHARAD being able to detect the base of the pedestal deposits, and possess an average dielectric permittivity of 4 ± 0.5. In one of the cases of large pedestals in Malea Planum, layering is detected both in SHARAD data and in high-resolution imagery of the pedestal margins. We find that clutter is a major issue in the analysis of radar soundings for smaller pedestals, and tentative detection of the basal reflection occurs in only a few of the cases examined. These detections yield a higher average permittivity of ∼6. The permittivity value derived for the larger pedestals, for which a basal reflection is unambiguous, is higher than that of pure water ice but lower than that of most silicate materials. A mixture of ice and silicates or an ice-free porous silicate matrix can explain a permittivity of ∼4, and radar alone cannot resolve this nonuniqueness. Data from the Compact Reconnaissance Imaging Spectrometer (CRISM) tentatively confirms a mafic component in at least one pedestal in Malea Planum. Interpretation of SHARAD results can support either a mixture of ice and silicates or a porous silicate. The former is compatible with a model where nonpolar ice is periodically deposited in the midlatitudes as a result of obliquity variations. The latter is compatible with ash deposits, at least in where pedestals appear in volcanic centers such as Malea Planum.

UR - http://www.scopus.com/inward/record.url?scp=79955050439&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=79955050439&partnerID=8YFLogxK

U2 - 10.1029/2010JE003690

DO - 10.1029/2010JE003690

M3 - Article

AN - SCOPUS:79955050439

VL - 116

JO - Journal of Geophysical Research: Atmospheres

JF - Journal of Geophysical Research: Atmospheres

SN - 2169-897X

IS - 4

M1 - E04006

ER -