Surface Roughness and Gravitational Slope Distributions of Vesta and Ceres

Ermakov, A.; Kreslavsky, M. A.; Scully, J. E. C.; Hughson, K.; Park, Ryan

doi:10.1029/2018je005813

Cited by 12 publications

(3 citation statements)

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“…The volcanic cones typically display asymmetric summit craters on the order of tens of meters deep, whereas pingos and the Cerean hills tend to lack these features. The maximum flank slope for the Cerean hills is also similar to that of the terrestrial pingos with a mean well below the anticipated angle of repose (Ermakov et al, 2019). The H:D PDFs of the volcanic cones, though differing in their widths, are largely co-located, implying a characteristic volcanic behavior within our investigated regions, which is consistent with previous investigations (e.g., Wood, 1980).…”

Section: Discussionsupporting

confidence: 89%

Comparative morphometric analysis suggests ice-cored pingo-shaped landforms on the dwarf planet Ceres

Hughson

Schmidt

Lopez

et al. 2022

Geology

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The NASA Dawn mission revealed that the floor of Occator crater on the dwarf planet Ceres (in the main asteroid belt between Mars and Jupiter) is populated with small quasi-conical hills. Many of these features exhibit morphometric properties that are like those of ice-cored periglacial hills called pingos. Alternatively, some of these Cerean hills have also been hypothesized to be cryovolcanic in origin. If these hills are analogous to pingos, they represent ice-rich environments that are attractive targets for future exploration. We report new constraints on the morphologies of the Occator hills that aid in determining their origin. We also directly test how morphologically similar the hills in Occator are to pingos and volcanic cones on Earth using comparative statistical analyses. Using a novel application of kernel density estimation and Markov chain Monte Carlo methods we show that the morphologies of terrestrial pingos and volcanic cones are quantifiably distinct, and that the Cerean hills share significant morphometric similarities with pingos on Earth. Our findings indicate that a statistical treatment of morphometry alone can be a powerful tool for classifying and comparing planetary surface features, and that the majority of the resolved Cerean hills are morphometrically more similar to pingos than to small terrestrial volcanic cones.

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Section: Discussionsupporting

confidence: 89%

Comparative morphometric analysis suggests ice-cored pingo-shaped landforms on the dwarf planet Ceres

Hughson

Schmidt

Lopez

et al. 2022

Geology

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“…The RMS deviation (difference in height between points separated by a constant distance/measuring length) of planetary bodies has also been derived from shape models and laser altimeters at different resolutions (Barnouin-Jha et al 2008;Ermakov et al 2019). The RMS deviation directly relates to the Hurst exponent and the RMS slope can be deduced from the RMS deviation at a given measuring length (Shepard et al 2001).…”

Section: Discussionmentioning

confidence: 99%

Surface roughness of asteroid (162173) Ryugu and comet 67P/Churyumov–Gerasimenko inferred fromin situobservations

Otto

Matz

Schröder

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Alteration processes on asteroid and comet surfaces, such as thermal fracturing, (micrometeorite) impacts or volatile outgassing, are complex mechanisms that form diverse surface morphologies and roughness on various scales. These mechanisms and their interaction may differ on the surfaces of different bodies. Asteroid Ryugu and comet 67P/Churyumov-Gerasimenko, both, have been visited by landers which imaged the surfaces in high spatial resolution. We investigate the surface morphology and roughness of Ryugu and 67P/Churyumov-Gerasimenko based on high resolution in situ images of 0.2 mm and 0.8 mm pixel resolution over an approximately 25 cm and 80 cm wide scene, respectively. To maintain comparability and reproducibility, we introduce a method to extract surface roughness descriptors (fractal dimension, Hurst exponent, joint roughness coefficient, root mean square slope, hemispherical crater density, small scale roughness parameter and Hapke mean slope angle) from in situ planetary images illuminated by LEDs. We validate our method and choose adequate parameters for an analysis of the roughness of the surfaces. We also derive the roughness descriptors from 3-dimensional shape models of Ryugu and orbiter camera images and show that the higher spatially resolved images results in a higher roughness. We find that 67P/Churyumov-Gerasimenko is up to 6% rougher than Ryugu depending on the descriptor used and attribute this difference to the different intrinsic properties of the materials imaged and the erosive processes altering them. On 67P/Churyumov-Gerasimenko sublimation appears to be the main cause for roughness, while on Ryugu micrometeoroid bombardment as well as thermal fatigue and solar weathering may play a significant role in shaping the surface.

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“…Measurements of a body's long wavelength shape, typically expressed in terms of spherical harmonic coefficients of degree l and order m, are useful for at least two additional reasons. First, the topographic roughness spectrum of a body may itself contain information about geophysical parameters of interest, such as elastic thickness (Araki et al, 2009;Conrad et al, 2021;Nimmo et al, 2011), interior rheology (Fu et al, 2017), and surface structure (Ermakov et al, 2019). Second, the ratio of a body's gravity to topography at different values of l-the admittance-captures key information about its structure, and has been employed very successfully around the solar system.…”

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confidence: 99%

Improved Determination of Europa's Long‐Wavelength Topography Using Stellar Occultations

Abrahams

Nimmo

Becker

et al. 2021

Earth and Space Science

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Europa's global shape is only poorly constrained, with our best models inferred from four Galileo limb profiles (Current values are that its axes (a, b, c) are (1562.6 km, 1560.3 km, 1559.5 km) with uncertainties of roughly 0.2 km (uncertainty estimated by comparing the different shape models in Nimmo et al. (2007)), and the topographic variance at degree 180 (the finest scale in our shape model) has an amplitude of about 20 m (Nimmo et al., 2011)) (Nimmo et al., 2007). Obtaining more precise global and regional topography is important if we want to understand Europa's internal structure and the state of its ice shell (e.g., Ojakangas & Stevenson, 1989), and is an objective of the Europa Clipper mission (Pappalardo et al., 2019). The primary instruments for determining Europa's global shape are the radar instrument REASON (Radar for Europa Assessment and Sounding: Ocean to Near-surface) (Blankenship et al., 2018) and the visible imager EIS (Europa Imaging System) (Turtle et al., 2019). The main limitation in fitting global shape is the fact that neither the radar tracks (black dots in Figure 1) nor the EIS limb profiles (gray dots in Figure 1) have complete global coverage, instead having gaps around the poles and longitudes near 90° and 270° as a consequence of Europa Clipper's resonant flyby geometry. Filling in those gaps has the potential to dramatically improve our ability to fit the global shape and its time variation. A similar problem was encountered by the Abstract Europa Clipper will arrive at Jupiter at the end of this decade and will explore Europa through a series of flybys. One of its many goals is to characterize Europa's topography and global shape using the Europa Imaging System and Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) instruments. In addition, Europa Clipper's UV Spectrograph will observe stars pass behind (be occulted by) Europa. The spectrograph has sufficiently precise timing, corresponding to a topographic precision of order meters, that these occultations can also serve as altimetric measurements. Because of gaps in the REASON radar altimeter coverage imposed by the flyby geometries, the addition of ∼100 occultations results in a substantial improvement in the recovery of Europa's long-wavelength shape. Typically, five extra spherical harmonic degrees of topography can be recovered by combining occultations with radar altimetry.Plain Language Summary Understanding Europa's topography is crucial to understand the moon for a variety of reasons. One way to quantify the topography is global shape, where we describe the entire surface at once. For example, Earth's rotation causes it to bulge at the equator, and we can describe that bulge with a single number: Earth is on average about 40 km larger at the equator than at the poles. A body's global shape as a whole can be described in a similar way, with a series of amplitudes of prescribed shapes (like an equatorial bulge) referred to as "spherical harmonics." Understanding global shape is important because the...

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Surface Roughness and Gravitational Slope Distributions of Vesta and Ceres

Cited by 12 publications

References 75 publications

Comparative morphometric analysis suggests ice-cored pingo-shaped landforms on the dwarf planet Ceres

Comparative morphometric analysis suggests ice-cored pingo-shaped landforms on the dwarf planet Ceres

Surface roughness of asteroid (162173) Ryugu and comet 67P/Churyumov–Gerasimenko inferred fromin situobservations

Improved Determination of Europa's Long‐Wavelength Topography Using Stellar Occultations

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