Ceres Landing Site Planning - Requirements for DTMs and Current Status

Introduction

The conceptual development of a Ceres Sample Return mission has intensified interest in the detailed topographic characterization of Occator Crater, a 92 km-wide impact crater on dwarf planet Ceres. This geologically young [1,2] crater hosts carbon-rich bright deposits [3,4,5] - Cerealia Facula and Vinalia Faculae - that are surface expressions of cryovolcanic processes linked to a ~40–50 km-deep brine reservoir [6,7]. These deposits contain a unique combination of sodium carbonates, ammonium chloride, and other hydrated salts [3,4,5] that were only recently exposed to the surface [2,3,8] and may preserve a record of past subsurface aqueous activity. Several Ceres landing site assessments [9] and mission concepts [10] have already considered Occator, with particular attention on these bright faculae as scientifically compelling targets. The success of such missions will depend on accurate, high-resolution Digital Terrain Models (DTMs) to enable safe landing, mobility, and efficient surface operations.

Figure 1. Pan-sharpened RGB orthomisaic of Cerealia Facula [2].

Background

To support ongoing and future mission development efforts, we present a new set of high-resolution DTMs of Occator Crater and its interior faculae [11]. These were generated using stereophotogrammetric (SPG) and multi-view shape-from-shading (SfS) techniques applied to Dawn Framing Camera [12] (FC)  data from multiple mission phases. The datasets include global coverage from the High and Low Altitude Mapping Orbit (HAMO, LAMO), as well as extremely high-resolution data from the highly elliptical XMO7 orbit acquired during Dawn’s second extended mission (XM2). This multitemporal, multi-geometry coverage forms the basis for precise terrain modeling at multiple spatial scales.

Methodology

Our initial DTM products were derived using the USGS ISIS and NASA's ASP [13,14], generating terrain models at Ground Sample Distances (GSDs) of up to 17 m. The workflow incorporated radiometric correction, photometric normalization using Hapke parameters tailored to Ceres’ surface [15], manual tie-point generation for improved co-registration, bundle adjustment [16], and a careful exclusion of over-exposed images covering the faculae. 

Results

An important component of our study involved evaluating published DTMs of Occator Crater, including those produced by DLR [17] and JPL [18]. Our comparison demonstrated significant differences in effective resolution, vertical offsets, and absolute elevation, especially in the complex terrains of Cerealia and Vinalia Faculae. These findings underline the need for further investigation into the sources of these discrepancies, particularly with regard to co-registration accuracy, bundle adjustment stability, and the impact of surface albedo variations on photoclinometry. Our improved terrain models, are suitable for detailed analyses of surface slopes and terrain roughness - key parameters in landing site certification and mobility planning. As illustrated in Figures 2 and 3, Cerealia Facula exhibits highly variable slopes, with regions on and near Cerealia Tholus exceeding 30°, as well as rugged, fractured terrains that pose potential hazards. Only few regions of the surface exhibits slopes <10°, which is considered acceptable for many landing systems. Vinalia Faculae shows broader, flatter regions (<10° slope) with lower local slope variation, though terrain roughness remains a factor at decameter scales. These observations suggest that while scientifically attractive, the faculae present both opportunities and challenges for safe landing and sampling.

Figure 2. Overview of the location of the topographic profile across Cerealia Tholus.

Figure 3. Topographic profiles across Cerealia Tholus of currently published and archived DTMs.

Foresight

To overcome the limitations of our current DTM generation process and further improve terrain fidelity, we are actively developing a new, more robust processing pipeline. This updated approach is based on an iterative co-registration strategy that incorporates all available image data during each refinement stage. Rather than producing separate DTMs for each mission phase, our method begins with a coarse SPG model at HAMO GSD and progressively incorporates higher-resolution data in successive co-registration and DTM generation steps. This will help minimize vertical mismatches between datasets and enable consistent resolution enhancement.

In addition, we plan to expand our SPG processing to include images acquired through the Dawn FC’s narrow-band filters. Preliminary tests show that incorporating these images substantially increases 3D-point density, particularly in areas where clear filter coverage is limited.

While the DTMs presented in this study already provide valuable insight into Occator's topography, particularly for scientific interpretation and regional context, they should not be considered final for engineering use in sample return mission planning. Further refinement is underway to resolve discrepancies between independent datasets, improve the vertical coherence across resolution levels, and produce terrain models optimized for operational robustness. These improvements will be essential for deriving high-fidelity hazard maps, supporting precision landing simulations, and developing terrain-relative navigation solutions.
Ultimately, our efforts contribute to building the necessary geospatial infrastructure to support in-situ exploration of Ceres. The topographic products currently in development will provide a consistent, high-resolution foundation. As the planning and definition of a Ceres Sample Return mission continues to advance, our ongoing work will play a central role in providing the detailed surface context required for mission architecture design, risk mitigation, and the successful return of brine-related samples from one of the most intriguing astrobiological targets in the Solar System.

Bibliography

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