Showing papers by "Carolyn M. Ernst published in 2013"
TL;DR: In this article, the MESSENGER images from the MRS spacecraft show that ~27% of Mercury's surface is covered by smooth plains, the majority of which are interpreted to be volcanic in origin, suggesting high temperatures and high degrees of partial melting in magma source regions persisted through most of the duration of smooth plains formation.
Abstract: [1] Orbital images from the MESSENGER spacecraft show that ~27% of Mercury's surface is covered by smooth plains, the majority (>65%) of which are interpreted to be volcanic in origin. Most smooth plains share the spectral characteristics of Mercury's northern smooth plains, suggesting they also share their magnesian alkali-basalt-like composition. A smaller fraction of smooth plains interpreted to be volcanic in nature have a lower reflectance and shallower spectral slope, suggesting more ultramafic compositions, an inference that implies high temperatures and high degrees of partial melting in magma source regions persisted through most of the duration of smooth plains formation. The knobby and hummocky plains surrounding the Caloris basin, known as Odin-type plains, occupy an additional 2% of Mercury's surface. The morphology of these plains and their color and stratigraphic relationships suggest that they formed as Caloris ejecta, although such an origin is in conflict with a straightforward interpretation of crater size–frequency distributions. If some fraction is volcanic, this added area would substantially increase the abundance of relatively young effusive deposits inferred to have more mafic compositions. Smooth plains are widespread on Mercury, but they are more heavily concentrated in the north and in the hemisphere surrounding Caloris. No simple relationship between plains distribution and crustal thickness or radioactive element distribution is observed. A likely volcanic origin for some older terrain on Mercury suggests that the uneven distribution of smooth plains may indicate differences in the emplacement age of large-scale volcanic deposits rather than differences in crustal formational process.
210 citations
TL;DR: Spacecraft data and a thermal model show that water ice and organic volatiles are present at Mercury’s north pole and correlation of observed reflectance with modeled temperatures indicates that the optically bright regions are consistent with surface water ice, whereas dark regions are consistency with a surface layer of complex organic material that likely overlies buried ice and provides thermal insulation.
Abstract: Measurements of surface reflectance of permanently shadowed areas near Mercury’s north pole reveal regions of anomalously dark and bright deposits at 1064-nanometer wavelength. These reflectance anomalies are concentrated on poleward-facing slopes and are spatially collocated with areas of high radar backscatter postulated to be the result of near-surface water ice. Correlation of observed reflectance with modeled temperatures indicates that the optically bright regions are consistent with surface water ice, whereas dark regions are consistent with a surface layer of complex organic material that likely overlies buried ice and provides thermal insulation. Impacts of comets or volatile-rich asteroids could have provided both dark and bright deposits.
158 citations
TL;DR: In this article, a range of geological settings in which hollows occur is described, including impact structures and low-reflectance material global color unit (GLU) and blue plains, but hollows appear preferentially on equator- or hot-pole-facing slopes.
Abstract: [1] Landforms unique to Mercury, hollows are shallow, flat-floored irregular depressions notable for their relatively high reflectance and characteristic color. Here we document the range of geological settings in which hollows occur. Most are associated with impact structures (simple bowl-shaped craters to multiring basins, and ranging from Kuiperian to Calorian in age). Hollows are found in the low-reflectance material global color unit and in low-reflectance blue plains, but they appear to be absent from high-reflectance red plains. Hollows may occur preferentially on equator- or hot-pole-facing slopes, implying that their formation is linked to solar heating. Evidence suggests that hollows form because of loss of volatile material. We describe hypotheses for the origin of the volatiles and for how such loss proceeds. Intense space weathering and solar heating are likely contributors to the loss of volatiles; contact heating by melts could promote the formation of hollows in some locations. Lunar Ina-type depressions differ from hollows on Mercury in a number of characteristics, so it is unclear if they represent a good analog. We also use MESSENGER multispectral images to characterize a variety of surfaces on Mercury, including hollows, within a framework defined by laboratory spectra for analog minerals and lunar samples. Data from MESSENGER's X-Ray Spectrometer indicate that the planet's surface contains up to 4% sulfur. We conclude that nanophase or microphase sulfide minerals could contribute to the low reflectance of the low-reflectance material relative to average surface material. Hollows may owe their relatively high reflectance to destruction of the darkening agent (sulfides), the presence of alteration minerals, and/or physical differences in particle size, texture, or scattering behavior.
91 citations
TL;DR: In this article, the authors compared optical and S-band radar data for several large (> 20 km diameter) young craters on the Moon and Mercury and found evidence that secondary cratering plays a significant role in the formation of crater rays.
Abstract: [1] Observations of rayed craters at optical and radar wavelengths provide insight into the processes that lead to ray formation and degradation on terrestrial planets. We have compared optical and S-Band radar data for several large (> 20 km diameter), young craters on the Moon and Mercury and find evidence that secondary cratering plays a significant role in the formation of crater rays. Regions where rays appear bright to optical and radar sensors correspond to dense concentrations of secondary craters, and the observed radar enhancement appears to be a result of the deposition of blocky, immature ejecta from the secondary craters and/or the rocky, immature interior walls of the secondary craters. We define a new optical maturity index for Mercury and find that rays in radar and optical images correspond closely, indicating that the rays are rich in centimeter- to decimeter-sized clasts. Rays on the Moon are less prominent at radar wavelengths, suggesting that they are currently composed of smaller clasts, centimeter sized or less. This difference suggests that secondary craters are larger on Mercury and capable of excavating more decimeter-sized clasts. Furthermore, observations of rayed craters provide an opportunity to assign relative ages to the youngest craters on the Moon and Mercury. Although rayed craters on Mercury appear most similar to the youngest craters on the Moon, the apparent ages are more likely influenced by inherent differences in impact velocity, surface gravitational acceleration, and target properties that result in the formation of larger secondary craters on Mercury.
47 citations
TL;DR: In this article, the authors find that radar-bright features near Mercury's north pole are associated with locations persistently shadowed in MESSENGENGER images, which is consistent with the deposits being composed of long-lived water ice, and future thermal modeling of small and low-latitude craters has the potential to further constrain the nature, source and timing of emplacement of the radarbright material.
Abstract: [1] Radar-bright features near Mercury's poles were discovered in Earth-based radar images and proposed to be water ice present in permanently shadowed areas. Images from MESSENGER's one-year primary orbital mission provide the first nearly complete view of Mercury's north polar region, as well as multiple images of the surface under a range of illumination conditions. We find that radar-bright features near Mercury's north pole are associated with locations persistently shadowed in MESSENGER images. Within 10° of the pole, almost all craters larger than 10 km in diameter host radar-bright deposits. There are several craters located near Mercury's north pole with sufficiently large diameters to enable long-lived water ice to be thermally stable at the surface within regions of permanent shadow. Craters located farther south also host radar-bright deposits and show a preference for cold-pole longitudes; thermal models suggest that a thin insulating layer is required to cover these deposits if the radar-bright material consists predominantly of long-lived water ice. Many small (<10 km diameter) and low-latitude (extending southward to 66°N) craters host radar-bright material, and water ice may not be thermally stable in these craters for ~1 Gy, even beneath an insulating layer. The correlation of radar-bright features with persistently shadowed areas is consistent with the deposits being composed of water ice, and future thermal modeling of small and low-latitude craters has the potential to further constrain the nature, source, and timing of emplacement of the radar-bright material.
40 citations
TL;DR: In this article, the authors used the Pantheon fossil graben and wrinkle ridges of Pantheon Fossae to resolve variations in the depth extent of associated faulting in the Caloris basin.
Abstract: [1] The volcanic plains that fill the Caloris basin, the largest recognized impact basin on Mercury, are deformed by many graben and wrinkle ridges, among which the multitude of radial graben of Pantheon Fossae allow us to resolve variations in the depth extent of associated faulting. Displacement profiles and displacement-to-length scaling both indicate that faults near the basin center are confined to a ~ 4-km-thick mechanical layer, whereas faults far from the center penetrate more deeply. The fault scaling also indicates that the graben formed in mechanically strong material, which we identify with dry basalt-like plains. These plains were also affected by changes in long-wavelength topography, including undulations with wavelengths of up to 1300 km and amplitudes of 2.5 to 3 km. Geographic correlation of the depth extent of faulting with topographic variations allows a first-order interpretation of the subsurface structure and mechanical stratigraphy in the basin. Further, crosscutting and superposition relationships among plains, faults, craters, and topography indicate that development of long-wavelength topographic variations followed plains emplacement, faulting, and much of the cratering within the Caloris basin. As several examples of these topographic undulations are also found outside the basin, our results on the scale, structural style, and relative timing of the topographic changes have regional applicability and may be the surface expression of global-scale interior processes on Mercury.
36 citations
TL;DR: In this article, the authors suggest that only thermal contraction can account for the observed pattern of graben, whereas some combination of subsidence and global contraction is the most likely explanation for the central ridges in Rachmaninoff and Mozart.
Abstract: the basin floor, and (3) subsidence following volcanic loading. Our results suggest that only thermal contraction can account for the observed pattern of graben, whereas some combination of subsidence and global contraction is the most likely explanation for the central ridges in Rachmaninoff and Mozart. Thermal contraction models, however, predict the formation of graben in the centermost region of each basin, where no graben are observed. We hypothesize that graben in this region were buried by a thin, late-stage flow of plains material, and images of partially filled graben provide evidence of such late-stage plains emplacement. These results suggest that the smooth plains units in these three basins are volcanic in origin. The thermal contraction models also imply a cooling unit ~1km thick near the basin center, further supporting the view that plains-forming lavas on Mercury were often of sufficiently high volume and low viscosity to pool to substantial thicknesses within basins and craters.
28 citations
01 Mar 2013
TL;DR: Keller et al. as discussed by the authors presented a survey of the results of the International Journal of Astronautic and Geophysical Data (IJGCD) and Planetary Science Institute (PSI).
Abstract: CONTAMINATION EVENT. Mary R. Keller* 1 , Carolyn M. Ernst 1 , Brett W. Denevi 1 , Scott L. Murchie 1 , Nancy L. Chabot 1 , Kris J. Becker 2 , Christopher D. Hash 3 , Deborah L. Domingue 4 , and Raymond E. Sterner II 1 , 1 The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA (*Corresponding author E-mail: Mary.Keller@jhuapl.edu); 2 U. S. Geological Survey Astrogeology Science Center, Flagstaff, AZ 86001, USA; 3 Applied Coherent Technology, Herndon, VA 20170, USA; 4 Planetary Science Institute, Tucson, AZ 85719, USA.
13 citations
01 Mar 2013
TL;DR: In this article, Ernst et al. presented a survey of the major institutions of astronomy, including the National Museum of Astronomy at Columbia University, Palisades, NY 10964, USA, Lamont-Doherty Earth Observatory, Columbia University and the Massachusetts Institute of Technology.
Abstract: vi, Carolyn M. Ernst, Jennifer L. Whitten, James W. Head, Scott L. Murchie, Thomas R. Watters, Paul K. Byrne, David T. Blewett, Sean C. Solomon, and Caleb I. Fassett, The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA, Department of Geological Sciences, Brown University, Providence, RI 02912, USA, Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC 20560, USA, Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA, Department of Astronomy, Mount Holyoke College, South Hadley, MA 01075, USA.
9 citations
01 Mar 2013
TL;DR: Paul K. Byrne, Sean C. Solomon, Francis Nimmo, Thomas R. Watters, Brett W. Denevi, Carolyn M Ernst, Maria E. Banks, Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA, cklimczak@ciw.edu as discussed by the authors
Abstract: Paul K. Byrne, Sean C. Solomon, Francis Nimmo, Thomas R. Watters, Brett W. Denevi, Carolyn M. Ernst, Maria E. Banks, Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA, cklimczak@ciw.edu; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA; 3 Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA; Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC 20560, USA; The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
8 citations
01 Mar 2013
01 Mar 2013
TL;DR: Klima et al. as mentioned in this paper presented a study of the relationship between magnetism and magnetometer properties of the Earth's magnetic field, and found that magnetism can be used to estimate the distance between the Earth and its magnetic field.
Abstract: CRUST. Rachel L. Klima (Rachel.Klima@jhuapl.edu), Noam R. Izenberg, Scott Murchie, Heather M. Meyer, Karen R. Stockstill-Cahill, David T. Blewett, Mario D’Amore, Brett W. Denevi, Carolyn M. Ernst, Jorn Helbert, Timothy McCoy, Ann L. Sprague, Faith Vilas, Shoshana Z. Weider, and Sean C. Solomon. Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA; National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA; Institute for Planetary Research DLR, Berlin, Germany; Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA; Planetary Science Institute, Tucson, AZ 85719, USA; Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA.
01 Dec 2013
TL;DR: In this article, a shape model derived from stereophotoclinometric analysis was used to constrain the mode of pond formation from three existing models, and the locations of 55 pond candidates identified in images registered to the new shape model were updated.
Abstract: NEAR-Shoemaker Multi-Spectral Imager data reveal several hundred “ponds” on 433 Eros: smooth deposits that sharply embay the bounding depressions in which they lie, and whose spectra appear blue relative to that of the surrounding terrain. We investigate the topography of these ponds on Eros using a new shape model derived from stereophotoclinometric analysis, and validated against altimetry from the NEAR Laser Rangefinder, to constrain the mode of pond formation from three existing models. We update the locations of 55 pond candidates identified in images registered to the new shape model. We classify the flatness of these features according to the behavior of the first and second derivatives of the topography. We find that less than half of pond candidates have clearly flat floors. Based on the pond topography, we favor an external origin for the ponds' deposits. We suggest that fine dust may be transported into bounding depressions by electrostatic levitation, but may adhere to slopes, and that seismic shaking may not be sufficient to bring the deposits to an equipotential surface. Disaggregation of a central boulder should result in an obvious break in slope, such a variation is only observed in roughly half the pond candidates.
01 Mar 2013
TL;DR: Carolyn M. Ernst, Brett W. Denevi, Scott L. Murchie, Olivier S. Barnouin, Nancy L. Head, Christian Klimczak, Gregory A. Neumann, Louise M. Prockter, Mark S. Robinson, Sean C. Solomon, and Thomas R. Watters, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA (carolyn.ernst@jhuapl.edu) as discussed by the authors
Abstract: Carolyn M. Ernst, Brett W. Denevi, Scott L. Murchie, Olivier S. Barnouin, Nancy L. Chabot, James W. Head, Christian Klimczak, Gregory A. Neumann, Louise M. Prockter, Mark S. Robinson, Sean C. Solomon, and Thomas R. Watters, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA (carolyn.ernst@jhuapl.edu); Department of Geological Sciences, Brown University, Providence, RI 02912, USA; Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA; Planetary Geodynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA; School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA; Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC 20560, USA.