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Geology topics

Brent A. Archinal

Publications and source records attributed to Brent A. Archinal.

At least 19 recordsLinked to original sources
USGS2025

Lunar grid systems, coordinate systems, and map projections for the Artemis missions and lunar surface navigation

Foreward This document contains design specifications of a navigational standard for the Moon, including a Lunar Transverse Mercator system, a Lunar Polar Stereographic system, a Lunar Grid Reference System, and a unique coordinate structure, Artemis Condensed Coordinates, for Artemis mission navigation and lunar surface science. The National Aeronautics and Space Administration (NASA) Artemis campaign seeks to place humans on the Moon for the first time since the Apollo missions. Early Artemis missions are heavily focused on the lunar south pole, which promises to return valuable data on the Moon’s geologic record, amongst other mission objectives. Coordinate systems in use today for the lunar south pole provides crew members on the surface neither an efficient nor intuitive means to communicate their position and orientation. A novel grid coordinate system, the Lunar Grid Reference System, is proposed to address these concerns for use in real-time extravehicular activity operations on the lunar surface. The many stakeholders involved in the Artemis missions will need a common system to communicate position and orientation while astronauts are operating on the lunar surface. To that end, Artemis crew members will need that system to be efficient and intuitive to promote efficient extravehicular activity timelines and reduce confusion. In the context of this document, these characteristics are addressed on the design of lunar coordinate systems: Efficient.—The number of characters required to communicate a location within a desired precision level in both local and global contexts, and how many steps are required for a recipient or sender to interpret a location. Intuitive.—How well the system aligns with human perceptual abilities, and whether the system yields distances that have the same relationship to actual lunar surface distance in all directions from the point where a person is located. Technological systems are currently being investigated to supplement the crew members’ ability to locate and orient themselves and other assets on the lunar surface; however, it is unlikely that those systems will be fully operational for the first few landed missions. Even with future positional aids, crew members will still need an efficient and intuitive means to communicate position and orientation. In addition, if technological systems fail, the crews will require land navigation skills and have maps available, thus providing further motivation for a crew-centric coordinate system. The contents of this U.S. Geological Survey (USGS) document detail a comprehensive framework for standardizing lunar crewed surface navigation within NASA and outlines the protocols, methods, and designs necessary for achieving consistency and interoperability across relevant space mission teams and lunar surface navigators. Key components of this document include designs of map projections, projected coordinate reference systems (Lunar Transverse Mercator and Lunar Polar Stereographic systems), and a grid system (Lunar Grid Reference System and Artemis Condensed Coordinates) for the Moon. The work proposed in this document seeks to accomplish something similar to the National Geospatial-Intelligence Agency (NGA) document SIG 0012 (NGA, 2014a), but for using grid systems for the Moon. This report incorporates initial feedback and input from NASA’s Artemis Geospatial Data Team, NASA’s Flight Operations Directorate, National Geodetic Survey, USGS Astrogeology Science Center, and NGA and is intended to serve as a resource for all involved with the Artemis missions, as well as for engineers designing and operating lunar infrastructure.

Techniques and Methods↗
USGS2023

The cartographic lunar reference frame

We describe how lunar cartographic coordinates are currently determined internationally, based on recommendations of the International Astronomical Union (IAU) Working Group on Cartographic Coordinates and Rotational Elements. Currently, a mean Earth/polar axis (ME) system-based frame and ephemeris (JPL DE 421 ME) is used for that purpose. Recently, there has been some discussion that a lunar principal axis system-based frame should be used instead. We describe how that would be a major change to how lunar data are currently acquired, and how data and mapping products are created and archived, searched for, accessed, and used, and our concerns that such a change would cause significant problems. Existing lunar data, data products, papers, and databases could need to be converted, or substantial confusion could result due to the ∼1 km difference between systems, perhaps resulting in navigation or safety issues. The publication and dissemination of any proposal(s) to change systems is encouraged, as are comments on a comparatively much smaller update to the current ME frame proposed here.

Conference Paper↗
USGS2021

Improving the usability of Galileo and Voyager images of Jupiter’s moon, Europa

NASA's Voyager 1, Voyager 2, and Galileo spacecraft acquired hundreds of images of Jupiter's moon Europa. These images provide the only moderate- to high-resolution views of the moon's surface and are therefore a critical resource for scientific analysis and future mission planning. Unfortunately, uncertain knowledge of the spacecraft's position and pointing during image acquisition resulted in significant errors in the location of the images on the surface. The result is that adjacent images are poorly aligned, with some images displaced by more than 100 km from their correct location. These errors severely degrade the usability of the Voyager and Galileo imaging data sets. To improve the usability of these data sets, we used the U.S. Geological Survey Integrated Software for Imagers and Spectrometers to build a nearly global image tie-point network with more than 50,000 tie points and 135,000 image measurements on 481 Galileo and 221 Voyager images. A global least-squares bundle adjustment of our final Europa tie-point network calculated latitude, longitude, and radius values for each point by minimizing residuals globally, and resulted in root mean square (RMS) uncertainties of 246.6 m, 307.0 m, and 70.5 m in latitude, longitude, and radius, respectively. The total RMS uncertainty was 0.32 pixels. This work enables direct use of nearly the entire Galileo and Voyager image data sets for Europa. We are providing the community with updated NASA Navigation and Ancillary Information Facility Spacecraft, Planet, Instrument, C-matrix (pointing), and Events kernels, mosaics of Galileo images acquired during each observation sequence, and individual processed and projected level 2 images.

Earth and Space Science↗
USGS2020

Coordination of planetary coordinate system recommendations by the IAU Working Group on Cartographic Coordinates and Rotational Elements–2020 status and future

Our goal is to request input from the lunar and planetary community regarding issues of planetary coordinate systems and cartography standards. We begin with an overview of the work of the International Astronomical Union Working Group on Cartographic Coordinates and Rotational Elements. We briefly describe the operations and membership of the Working Group, some of the various uses of the recommendations it makes, our most recent (2018) published report and the recommendations therein, and the outlook for our next such report. We then consider several issues and questions regarding the future of the Working Group and regarding planetary cartography and planetary data spatial infrastructure in general. This includes possible near-term projects, how we and others might collect and consider community input and includes some ideas regarding possible outcomes or future work that will need to be addressed by the Working Group or other organizations.

Conference Paper↗
USGS2020

A global shape model for Saturn's moon Enceladus from a dense photogrammetric control network

A planetary bodys global shape provides both insight into its geologic evolution, and a key element of any Planetary Spatial Data Infrastructure (PSDI). NASAs Cassini mission to Saturn acquired more than 600 moderate- to high-resolution images (< 500 m/pixel) of the small, geologically active moon Enceladus. The moons internal global ocean and intriguing geology mark it as a candidate for future exploration and motivates the development of a PSDI. Recently, Bland et al. (2018) provided two foundational elements of this PSDI: geodetic control and orthoimages. To provide the third foundational data set we generate a new shape model for Enceladus from Cassini images and a dense photogrammetric control network (nearly 1 million tie points) using the United States Geological Surveys Integrated Software for Imagers and Spectrometers (ISIS) and the Ames Stereo Pipeline (ASP). The new shape model is near-global in extent and gridded to 2.2 km/pixel, ~50 times better resolution than previous global models. Our calculated triaxial shape, rotation rate, and pole orientation for Enceladus is consistent with current IAU values to within the error; however, we determined a new prime meridian offset (Wo) of 7.063o. We calculate Enceladus long-wavelength topography by subtracting the best-fit triaxial ellipsoid from our shape model. The result is comparable to previous global models but can resolve topographic features as small as 5-7 km across in certain areas. To evaluate the spatially varying quality of the model we calculate the point density (variable from 5 to more than 50 per pixel), normalized median absolute deviation of the points within each pixel (typically less than 100 m), and the minimum expected vertical precision of each point (ranging from 2 km to 29 m).

Conference Paper↗
USGS2018

A new Enceladus global control network, image mosaic, and updated pointing kernels from Cassini's thirteen-year mission

NASA's Cassini spacecraft spent 13 years exploring the Saturn system, including 23 targeted flybys of the small, geologically active moon Enceladus. These flybys provided a wealth of image data from Cassini's Imaging Science Subsystem. To improve the usability of the Enceladus data set, we created a new, global photogrammetric control network for Enceladus that enabled compilation of a versatile cartographic package to support geologic mapping and other investigations. The network used 586 images in four image filters with a pixel scale generally between 50 and 500 m per pixel and a phase angle less than 120° and consisted of 10,362 tie points and 173,704 individual image measures, averaging nearly 17 measures per tie point. Least squares bundle adjustment resulted in a root‐mean‐square residual of 0.45 pixel, corresponding to root‐mean‐square ground point uncertainties of 66, 51, and 46 m in latitude, longitude, and radius, respectively. Using our geodetic control network, we created new global image mosaics, coregistered flyby mosaics to support geologic mapping, and updated pointing kernels for every image used in the solution. These products, including the updated pointing kernels, are available to the community through NASA's Planetary Data System Imaging Annex. The bundle adjustment solution also yielded independently determined shape information, resulting in radii within the stated uncertainty of International Astronomical Union values. The challenges of the data set, and the technical methodology described here are applicable to bodies imaged during multiple flybys with variable viewing and illumination geometry, including other midsized satellites of Saturn, and the Europa Clipper mission.

Earth and Space Science↗
USGS2018

Revisiting the Apollo photogrammetric mapping system

The integrated photogrammetric mapping system flown on the last three Apollo lunar missions (15, 16, and 17) in 1971 and 1972 incorporated a Metric (mapping) Camera, a high-resolution Panoramic Camera, and a star camera and laser altimeter to provide support data. The U.S. Geological Survey’s Astrogeology Science Center, the Intelligent Robotics Group of the NASA Ames Research Center, and Arizona State University are working together in an ongoing collaboration to achieve the most complete cartographic development of Apollo mapping system data into versatile digital map products. These will enable a variety of scientific/engineering uses of the data including mission planning, geologic mapping, geophysical process modelling, slope dependent correction of spectral data, and change detection. After a brief discussion of the origins of the mapping system, we describe the Metric and Panoramic cameras, processing of the associated image and support data, work to photogrammetrically control the Metric Camera images, and future plans.

Conference Paper↗
USGS2018

Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015

This report continues the practice where the IAU Working Group on Cartographic Coordinates and Rotational Elements revises recommendations regarding those topics for the planets, satellites, minor planets, and comets approximately every three years. The Working Group has now become a “functional working group” of the IAU and its membership is open to anyone interested in participating. We describe the procedure for submitting questions about the recommendations given here or the application of these recommendations for creating a new or updated coordinate system for a given body. Regarding body orientation, the following bodies have been updated: Mercury, based on MESSENGER results; Mars, along with a refined longitude definition; Phobos; Deimos; (1) Ceres; (52) Europa; (243) Ida; (2867) Šteins; Neptune; (134340) Pluto and its satellite Charon; comets 9P/Tempel 1, 19P/Borrelly, 67P/Churyumov-Gerasimenko, and 103P/Hartley 2, noting that such information is valid only between specific epochs. The special challenges related to mapping 67P/Churyumov-Gerasimenko are also discussed. Approximate expressions for the Earth have been removed in order to avoid confusion, and the low precision series expression for the Moon’s orientation has been removed. The previously on-line only recommended orientation model for (4) Vesta is repeated with an explanation of how it was updated. Regarding body shape, text has been included to explain the expected uses of such information, and the relevance of the cited uncertainty information. The size of the Sun has been updated and notation added that the size and the ellipsoidal axes for the Earth and Jupiter have been recommended by an IAU Resolution. The distinction of a reference radius for a body (here, the Moon and Titan) is made between cartographic uses, and for orthoprojection and geophysical uses. The recommended radius for Mercury has been updated based on MESSENGER results. The recommended radius for Titan is returned to its previous value. Size information has been updated for 13 other Saturnian satellites and added for Aegaeon. The sizes of Pluto and Charon have been updated. Size information has been updated for (1) Ceres and given for (16) Psyche and (52) Europa. The size of (25143) Itokawa has been corrected. In addition, the discussion of terminology for the poles (hemispheres) of small bodies has been modified and a discussion on cardinal directions added. Although they continue to be used for planets and their satellites, it is assumed that the planetographic and planetocentric coordinate system definitions do not apply to small bodies. However, planetocentric and planetodetic latitudes and longitudes may be used on such bodies, following the right-hand rule. We repeat our previous recommendations that planning and efforts be made to make controlled cartographic products; newly recommend that common formulations should be used for orientation and size; continue to recommend that a community consensus be developed for the orientation models of Jupiter and Saturn; newly recommend that historical summaries of the coordinate systems for given bodies should be developed, and point out that for planets and satellites planetographic systems have generally been historically preferred over planetocentric systems, and that in cases when planetographic coordinates have been widely used in the past, there is no obvious advantage to switching to the use of planetocentric coordinates. The Working Group also requests community input on the question submitting process, posting of updates to the Working Group website, and on whether recommendations should be made regarding exoplanet coordinate systems.

Celestial Mechanics and Dynamical Astronomy↗
USGS2017

Towards a planetary spatial data infrastructure

Planetary science is the study of planets, moons, irregular bodies such as asteroids and the processes that create and modify them. Like terrestrial sciences, planetary science research is heavily dependent on collecting, processing and archiving large quantities of spatial data to support a range of activities. To address the complexity of storing, discovering, accessing, and utilizing spatial data, the terrestrial research community has developed conceptual Spatial Data Infrastructure (SDI) models and cyberinfrastructures. The needs that these systems seek to address for terrestrial spatial data users are similar to the needs of the planetary science community: spatial data should just work for the non-spatial expert. Here we discuss a path towards a Planetary Spatial Data Infrastructure (PSDI) solution that fulfills this primary need. We first explore the linkage between SDI models and cyberinfrastructures, then describe the gaps in current PSDI concepts, and discuss the overlap between terrestrial SDIs and a new, conceptual PSDI that best serves the needs of the planetary science community.

ISPRS International Journal of Geo-Information↗
USGS2017

Extracting accurate and precise topography from LROC narrow angle camera stereo observations

The Lunar Reconnaissance Orbiter Camera (LROC) includes two identical Narrow Angle Cameras (NAC) that each provide 0.5 to 2.0 m scale images of the lunar surface. Although not designed as a stereo system, LROC can acquire NAC stereo observations over two or more orbits using at least one off-nadir slew. Digital terrain models (DTMs) are generated from sets of stereo images and registered to profiles from the Lunar Orbiter Laser Altimeter (LOLA) to improve absolute accuracy. With current processing methods, DTMs have absolute accuracies better than the uncertainties of the LOLA profiles and relative vertical and horizontal precisions less than the pixel scale of the DTMs (2–5 m). We computed slope statistics from 81 highland and 31 mare DTMs across a range of baselines. For a baseline of 15 m the highland mean slope parameters are: median = 9.1°, mean = 11.0°, standard deviation = 7.0°. For the mare the mean slope parameters are: median = 3.5°, mean = 4.9°, standard deviation = 4.5°. The slope values for the highland terrain are steeper than previously reported, likely due to a bias in targeting of the NAC DTMs toward higher relief features in the highland terrain. Overlapping DTMs of single stereo sets were also combined to form larger area DTM mosaics that enable detailed characterization of large geomorphic features. From one DTM mosaic we mapped a large viscous flow related to the Orientale basin ejecta and estimated its thickness and volume to exceed 300 m and 500 km 3 , respectively. Despite its ∼3.8 billion year age the flow still exhibits unconfined margin slopes above 30°, in some cases exceeding the angle of repose, consistent with deposition of material rich in impact melt. We show that the NAC stereo pairs and derived DTMs represent an invaluable tool for science and exploration purposes. At this date about 2% of the lunar surface is imaged in high-resolution stereo, and continued acquisition of stereo observations will serve to strengthen our knowledge of the Moon and geologic processes that occur across all of the terrestrial planets.

Icarus↗
USGS2015

Image mosaic and topographic map of the moon

Sheet 1: This image mosaic is based on data from the Lunar Reconnaissance Orbiter Wide Angle Camera (WAC; Robinson and others, 2010), an instrument on the National Aeronautics and Space Administration (NASA) Lunar Reconnaissance Orbiter (LRO) spacecraft (Tooley and others, 2010). The equatorial WAC images were orthorectified onto the Global Lunar Digital Terrain Mosaic (GLD100, WAC-derived 100 m/pixel digital elevation model; Scholten and others, 2012 ) while the polar images were orthorectified onto the lunar LOLA polar digital elevation models (Neumann and others, 2010). The Mercator projection is used between latitudes &plusmn;57&deg;, with a central meridian at 0&deg; longitude and latitude equal to the nominal scale at 0&deg;. The Polar Stereographic projection is used for the regions north of the +55&deg; parallel and south of the &ndash;55&deg; parallel, with a central meridian set for both at 0&deg; and a latitude of true scale at +90&deg; and -90&deg;, respectively. All named features greater than 85 km in diameter or length were included unless they were not visible on the map. Some selected well-known features less than 85 km in size were also included. For listed references, please open the full PDF. Sheet 2: This map is based on data from the Lunar Orbiter Laser Altimeter (LOLA; Smith and others, 2010), an instrument on the National Aeronautics and Space Administration (NASA) Lunar Reconnaissance Orbiter (LRO) spacecraft (Tooley and others, 2010). The image used for the base of this map represents more than 6.5 billion measurements gathered between July 2009 and July 2013, adjusted for consistency in the coordinate system described below, and then converted to lunar radii (Mazarico and others, 2012). For the Mercator portion, these measurements were converted into a digital elevation model (DEM) with a resolution of 0.015625 degrees per pixel, or 64 pixels per degree. In projection, the pixels are 473.8 m in size at the equator. For the polar portion, the LOLA elevation points were used to create a DEM at 240 meters per pixel. A shaded relief map was generated from each DEM with a sun angle of 45&deg; from horizontal, and a sun azimuth of 270&deg;, as measured clockwise from north with no vertical exaggeration. The DEM values were then mapped to a global color look-up table, with each color representing a range of 1 km of elevation. For this map sheet, only larger feature names are shown. For references listed above, please open the full PDF.

Scientific Investigations Map↗
USGS2010

Report of the IAU Working Group on cartographic coordinates and rotational elements: 2009

Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars’ satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) Šteins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn.

Celestial Mechanics and Dynamical Astronomy↗
USGS2008

Ultrahigh resolution topographic mapping of Mars with MRO HiRISE stereo images: Meter-scale slopes of candidate Phoenix landing sites

The objectives of this paper are twofold: first, to report our estimates of the meter‐to‐decameter‐scale topography and slopes of candidate landing sites for the Phoenix mission, based on analysis of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images with a typical pixel scale of 3 m and Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) images at 0.3 m pixel −1 and, second, to document in detail the geometric calibration, software, and procedures on which the photogrammetric analysis of HiRISE data is based. A combination of optical design modeling, laboratory observations, star images, and Mars images form the basis for software in the U.S. Geological Survey Integrated Software for Imagers and Spectrometers (ISIS) 3 system that corrects the images for a variety of distortions with single‐pixel or subpixel accuracy. Corrected images are analyzed in the commercial photogrammetric software SOCET SET (® BAE Systems), yielding digital topographic models (DTMs) with a grid spacing of 1 m (3–4 pixels) that require minimal interactive editing. Photoclinometry yields DTMs with single‐pixel grid spacing. Slopes from MOC and HiRISE are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully; only the Mars Exploration Rover (MER) B site in Meridiani Planum is smoother. MOC results at multiple locations have root‐mean‐square (RMS) bidirectional slopes of 0.8–4.5° at baselines of 3–10 m. HiRISE stereopairs (one per final candidate site and one in the former site) yield 1.8–2.8° slopes at 1‐m baseline. Slopes at 1 m from photoclinometry are also in the range 2–3° after correction for image blur. Slopes exceeding the 16° Phoenix safety limit are extremely rare.

Journal of Geophysical Research E: Planets↗
USGS2008

Surface processes recorded by rocks and soils on Meridiani Planum, Mars: Microscopic Imager observations during Opportunity's first three extended missions

The Microscopic Imager (MI) on the Mars Exploration Rover Opportunity has returned images of Mars with higher resolution than any previous camera system, allowing detailed petrographic and sedimentological studies of the rocks and soils at the Meridiani Planum landing site. Designed to simulate a geologist's hand lens, the MI is mounted on Opportunity's instrument arm and can resolve objects 0.1 mm across or larger. This paper provides an overview of MI operations, data calibration, and analysis of MI data returned during the first 900 sols (Mars days) of the Opportunity landed mission. Analyses of Opportunity MI data have helped to resolve major questions about the origin of observed textures and features. These studies support eolian sediment transport, rather than impact surge processes, as the dominant depositional mechanism for Burns formation strata. MI stereo observations of a rock outcrop near the rim of Erebus Crater support the previous interpretation of similar sedimentary structures in Eagle Crater as being formed by surficial flow of liquid water. Well‐sorted spherules dominate ripple surfaces on the Meridiani plains, and the size of spherules between ripples decreases by about 1 mm from north to south along Opportunity's traverse between Endurance and Erebus craters.

Journal of Geophysical Research E: Planets↗
USGS2008

Cartography for lunar exploration: 2008 status and mission plans

The initial spacecraft exploration of the Moon in the 1960s-70s yielded extensive data, primarily in the form of film and television images, which were used to produce a large number of hardcopy maps by conventional techniques. A second era of exploration, beginning in the early 1990s, has produced digital data including global multispectral imagery and altimetry, from which a new generation of digital map products tied to a rapidly evolving global control network has been made. Efforts are also underway to scan the earlier hardcopy maps for online distribution and to digitize the film images so that modern processing techniques can be used to make high-resolution digital terrain models (DTMs) and image mosaics consistent with the current global control. The pace of lunar exploration is accelerating dramatically, with as many as eight new missions already launched or planned for the current decade. These missions, of which the most important for cartography are SMART-1 (Europe), Kaguya/SELENE (Japan), Chang'e-1 (China), Chandrayaan-1 (India), and Lunar Reconnaissance Orbiter (USA), will return a volume of data exceeding that of all previous lunar and planetary missions combined. Framing and scanner camera images, including multispectral and stereo data, hyperspectral images, synthetic aperture radar (SAR) images, and laser altimetry will all be collected, including, in most cases, multiple data sets of each type. Substantial advances in international standardization and cooperation, development of new and more efficient data processing methods, and availability of resources for processing and archiving will all be needed if the next generation of missions are to fulfill their potential for high-precision mapping of the Moon in support of subsequent exploration and scientific investigation.

The International Archives of the Photogrammetry, ↗
USGS2007

Topography and geomorphology of the Huygens landing site on Titan

The Descent Imager/Spectral Radiometer (DISR) aboard the Huygens Probe took several hundred visible-light images with its three cameras on approach to the surface of Titan. Several sets of stereo image pairs were collected during the descent. The digital terrain models constructed from those images show rugged topography, in places approaching the angle of repose, adjacent to flatter darker plains. Brighter regions north of the landing site display two styles of drainage patterns: (1) bright highlands with rough topography and deeply incised branching dendritic drainage networks (up to fourth order) with dark-floored valleys that are suggestive of erosion by methane rainfall and (2) short, stubby low-order drainages that follow linear fault patterns forming canyon-like features suggestive of methane spring-sapping. The topographic data show that the bright highland terrains are extremely rugged; slopes of order of 30° appear common. These systems drain into adjacent relatively flat, dark lowland terrains. A stereo model for part of the dark plains region to the east of the landing site suggests surface scour across this plain flowing from west to east leaving ∼100-m-high bright ridges. Tectonic patterns are evident in (1) controlling the rectilinear, low-order, stubby drainages and (2) the “coastline” at the highland–lowland boundary with numerous straight and angular margins. In addition to flow from the highlands drainages, the lowland area shows evidence for more prolific flow parallel to the highland–lowland boundary leaving bright outliers resembling terrestrial sandbars. This implies major west to east floods across the plains where the probe landed with flow parallel to the highland–lowland boundary; the primary source of these flows is evidently not the dendritic channels in the bright highlands to the north.

Planetary and Space Science↗