[Show abstract][Hide abstract] ABSTRACT: A novel method has been developed to determine the rotational parameters of Mercury from data acquired by the MESSENGER spacecraft. We exploit the complementarity of laser altimeter tracks taken at different rotational phases and rigid stereo terrain models to determine a Mercury rotational model. In particular, we solve for the orientation of the spin axis, the rotation rate, and the amplitude of the forced libration. In this paper, we verify the proposed method and carry out an extensive simulation of MESSENGER data acquisition with assumed rotational parameters. To assess the uncertainty in the rotational parameters we use mission-typical assumptions for spacecraft attitude and position knowledge as well as for small-scale terrain morphology. We find that the orientation of the spin axis and the libration amplitude can be recovered with an accuracy of few arc seconds from three years of MESSENGER orbital observations. The rotation rate can be determined to within 5 arc seconds per year. The method developed here serves as a framework for the ongoing analysis of data from the MESSENGER spacecraft. The rotational parameters of Mercury hold important constraints on the internal structure and evolution of the planet.
Planetary and Space Science 05/2015; DOI:10.1016/j.pss.2015.05.006 · 1.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Understanding the role of different planetary surface formation processes within our Solar System is one of the fundamental goals of planetary science research. There has been a revolution in planetary surface observations over the last 8 years, especially in 3D imaging of surface shape (down to resolutions of 10cm) and subsequent terrain correction of imagery from orbiting spacecraft. This has led to the ability to be able to overlay different epochs back to the mid-1970s, examine time-varying changes (such as impact craters, RSLs, CO 2 geysers, gullies, boulder movements and a host of ice-related phenomena). Consequently we are seeing a dramatic improvement in our understanding of surface formation processes.
[Show abstract][Hide abstract] ABSTRACT: This review summarizes the use of High Resolution Stereo Camera (HRSC) data as an instrumental tool and its application in the analysis of geological processes and landforms on Mars during the last ten years of operation. High-resolution digital elevations models on a local to regional scale are the unique strength of the HRSC instrument. The analysis of these data products enabled quantifying geological processes such as effusion rates of lava flows, tectonic deformation, discharge of water in channels, formation timescales of deltas, geometry of sedimentary deposits as well as estimating the age of geological units by crater size–frequency distribution measurements. Both the quantification of geological processes and the age determination allow constraining the evolution of Martian geologic activity in space and time. A second major contribution of HRSC is the discovery of episodicity in the intensity of geological processes on Mars. This has been revealed by comparative age dating of volcanic, fluvial, glacial, and lacustrine deposits.
Volcanic processes on Mars have been active over more than 4 Gyr, with peak phases in all three geologic epochs, generally ceasing towards the Amazonian. Fluvial and lacustrine activity phases spread a time span from Noachian until Amazonian times, but detailed studies show that they have been interrupted by multiple and long lasting phases of quiescence. Also glacial activity shows discrete phases of enhanced intensity that may correlate with periods of increased spin-axis obliquity. The episodicity of geological processes like volcanism, erosion, and glaciation on Mars reflects close correlation between surface processes and endogenic activity as well as orbit variations and changing climate condition.
Planetary and Space Science 02/2015; 112. DOI:10.1016/j.pss.2014.11.029 · 1.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: One major reason for exploring Mars is the similarity of surface features to those present on Earth. Among the most important are morphological and mineralogical indicators that liquid water has existed on Mars at various locations over the entire history of the planet, albeit in decreasing abundance with time. Due to the strong evidence for aqueous processes at or near the surface, Mars is the most Earth-like body in the Solar System. The HRSC instrument is designed to simultaneously map the morphology, topography, structure and geologic context of the surface as well as atmospheric phenomena . After 10 years of ESA's Mars Express orbiting the planet its High Resolution Stereo Camera (HRSC) has covered about 90 % of the surface in stereo and color with resolutions up to 10 m/pixel. Digital elevation models of up to 30-50 m grid spacing , generated from all suitable datasets of the stereo coverage, currently cover about 40% of the surface [1,2]. The geomorphological analyses of surface features, observed by the HRSC indicate major surface modifications by endogenic and exogenic processes at all scales. Endogenic landforms (e.g., tectonic rifts, small basaltic shield volcanoes) were found to be very similar to their equivalents on Earth [1,3,4,5,6,7]. Volcanism may have been active up to the very recent past or even to the present, putting important constraints on thermal evolution models [6,7]. The analysis of diverse landforms produced by aqueous processes revealed that surface water activity was likely episodic, but ranged in age from very ancient to very recent [1,8-16]. Particularly important are prominent glacial and periglacial features at several latitudes, including mountain glaciers and a frozen sea [17-21]. The identification of aqueous alteration minerals and their geological context has enabled a better understanding of paleoenvironmental conditions and pedogenetic processes [23-25]. Dark dunes contain volcanic material and are evidence for the very dynamic surface environment, characterized by widespread erosion, transport, and redeposition . References: Jaumann et al., 2007, PSS 55; Gwinner et al., 2010, EPSL 294; Neukum et al., 2004, Nature 432; Neukum et al., EPSL 294; Hauber et al.,
[Show abstract][Hide abstract] ABSTRACT: We report the surface roughness analysis of the lunar highlands for the baseline range 0.15–100 km. We use the Median Differential Slope αm to investigate the scale dependency of the roughness and derive the global αm distribution from SELENE Laser Altimeter and Terrain Camera data. While αm(l) versus baseline l (km) plots vary among different highland types, all highlands commonly show a peak at 3–30 km. The Pre-Nectarian surface shows a relatively large αm(20–30 km). Our analysis is supported by the simulation of synthetic surface cratering models and crater statistics. In our simulation, a peak of αm(30 km) is successfully reproduced. The actual crater density shows good correlation with an empirical roughness indicator. However, a large part of the Nectarian surface shows a peak at 6–9 km baseline. This peak may be caused by secondary craters and ejecta deposit textures from the Nectarian system basins.
[Show abstract][Hide abstract] ABSTRACT: Planetary topography is the result of complex interactions between geological processes, of which faulting is a prominent
component. Surface-rupturing earthquakes cut and move landforms which develop across active faults, producing characteristic
surface displacements across the fault. Geometric models of faults and their associated surface displacements are commonly applied
to reconstruct these offsets to enable interpretation of the observed topography. However, current 2D techniques are limited in their
capability to convey both the three-dimensional kinematics of faulting and the incremental sequence of events required by a given
reconstruction. Here we present a real-time system for interactive retro-deformation of faulted topography to enable reconstruction
of fault displacement within a high-resolution (sub 1m/pixel) 3D terrain visualization. We employ geometry shaders on the GPU to
intersect the surface mesh with fault-segments interactively specified by the user and transform the resulting surface blocks in realtime
according to a kinematic model of fault motion. Our method facilitates a human-in-the-loop approach to reconstruction of fault
displacements by providing instant visual feedback while exploring the parameter space. Thus, scientists can evaluate the validity of
traditional point-to-point reconstructions by visually examining a smooth interpolation of the displacement in 3D. We show the efficacy
of our approach by using it to reconstruct segments of the San Andreas fault, California as well as a graben structure in the Noctis
Labyrinthus region on Mars.
[Show abstract][Hide abstract] ABSTRACT: We present a technique for the direct measurement of planetary physical
librations from orbiting spacecraft. In order to perform this
measurement our approach combines in situ laser altimeter and image data
obtained by onboard instruments. The technique benefits from the
advantages of those individual data sets as well as their
complementarity. Knowledge of the physical libration of a planet or a
moon is important for accurately constraining the geodetic reference
system of the celestial body. These reference systems are used to
produce accurate maps and for mission planning. In special cases, e.g.,
Mercury, it is also possible to determine constraints on the internal
structure and, by extension, the thermal evolution of a planet by
measuring the amplitude of the librations. In this paper we present the
application of our method to physical librations of Mercury. We use
image data and laser profiles obtained by the NASA MESSENGER spacecraft
now in orbit about Mercury.
[Show abstract][Hide abstract] ABSTRACT: Observations from the MErcury Surface, Space ENvironment, GEochemistry,
and Ranging (MESSENGER) spacecraft, after one Earth year in orbit about
Mercury, have provided new insights into the nature of volcanic activity
on the innermost planet and shown that volcanic characteristics on
Mercury differ from those on other terrestrial planetary bodies.
MESSENGER observations reveal no evidence for large shield volcanoes
like those on Earth, Mars, and Venus, and small numbers of low
shield-like constructs, pit craters, and candidate calderas. No evidence
has been discerned for extensive centers of volcanism as seen on Mars
(e.g., Tharsis, Elysium) or Venus (e.g., Beta and Atla Regiones), or
less well-developed ones as seen on the Moon (e.g., Marius and Rumker
Hills). Nor has evidence been seen for any Venus-like coronae or related
annular deformational features displaying associated volcanism. Only one
radial graben structure (Pantheon Fossae), centrally located in the
Caloris basin, has been documented. Observations of Mercury to date
also reveal no evidence for several types of volcanic features (cones,
leveed flows, or widespread sinuous rilles). Instead, we see evidence on
Mercury for extensive flooding of the surface to form regional smooth
plains that appear to be very extensive lava sheet flows, and
intercrater plains (found between large, old impact craters) that may
also have been formed by volcanic eruptions. Smooth volcanic plains
filling the interior of the Caloris basin show generally uniform ages
and spectral characteristics and are up to several kilometers thick.
Exterior plains of volcanic origin have similar to slightly younger
ages. Contiguous plains at northern high latitudes cover ~6% of the
surface of Mercury, have surface ages and spectral properties that show
no resolvable variation, and have no locatable source regions. The
general characteristics of the plains deposits and features on Mercury
strongly suggest that they were emplaced by flood-lava-style eruptions
rather than collections of narrow, leveed flows typical of small
dike-emplacement events and more limited-volume surface eruptions. In
summary, effusive volcanic deposits on Mercury appear to be
characterized predominantly by: (1) deep magma sources of large volume,
(2) little very shallow crustal storage of magma, and (3) high-volume
eruption rates of lava and correspondingly voluminous outpourings that
produced long and wide lava flows that covered extensive areas. These
observations are consistent with theoretical predictions of vertically
extensive and wide dikes penetrating through the lithosphere and crust.
Deposits of pyroclastic origin and associated source depressions are
globally distributed. The dimensions of individual pyroclastic deposits
around vents signal the involvement of substantial amounts of magmatic
volatiles in the eruptions. Observations by the suite of instruments on
the ESA/JAXA BepiColombo spacecraft will markedly improve our knowledge
of volcanism on Mercury.
[Show abstract][Hide abstract] ABSTRACT: We report roughness measurement results at the baseline scale from 0.15
to 100 km, using the digital topography data derived from the SELENE
Laser Altimeter (LALT) and Terrain Camera (TC).