In deep analysis of Ikapati Crater on Ceres

We present a comprehensive mineralogical and geological analysis of Ikapati crater and its surrounding terrain on Ceres using a cross-correlated dataset from the Dawn Framing Camera (FC) and the Visible and Infrared Spectrometer (VIR) onboard the DAWN spacecraft¹. Beside standard analysis tools, we use modern AI techniques for our analyses.

Our spectral and geomorphological analysis reveals that Ikapati impacted the rim of a larger ancient crater. The smooth material associated with this older crater structure exhibit systematically reduced phyllosilicate signatures². Spectra from these smooth materials - including Ikapati's floor - show shallower band depths at both 2.73 µm (OH) and 3.06 µm (NH₄⁺) compared to the surrounding background terrain (Fig.1). This depletion is regionally extensive across the ancient crater's floor, suggesting a significant early thermal alteration due to this impact.

However, an early thermal alteration does not agree with previous surface dating of the Ikapati area, as the smooth material was dated younger than the ejecta blanket of Ikapati^3,4. If that hypothesis is confirmed, this could be possibly explained by the fact that 1: Ikapati also altered thermally the area, and 2: the ejecta blanket of Ikapati is really thin, therefore does not erase older impact craters. Thus its age could eventually be overestimated and actually comparable to that of the smooth material bearing terrains. In addition, further processes can also create biases in crater counting, like including features not recognized as pits or secondary impacts, differences of the measured crater diameter due to target property effects⁵, mass wasting, and flows.

Small, bright impact craters pepper substantial areas of the smooth material, especially on the floor of Ikapati and west of Ikapati’s crater rim. These bright deposits showed absorption features at 3.4 µm and 4.0 µm, diagnostic for the presence of sodium carbonate (natron) and calcium-magnesium carbonate (dolomite/calcite). This indicates that locally, beneath the smooth mateial, there seems to be a bright carbonate layer that could have formed by ascended brines that did not reach the surface.

Figure 1: Left: FC false color moaic (R:0.965 µm , G: 0.749 µm , B: 0.738 µm ). Right: NH₄ band depth overlayed on the FC clear filter mosaic.

A distinctive degradation (notch) of the western crater rim, which is surrounded by dark material (DM), suggests that the notch and the associated DM could have originated from a low-velocity impact that conserved some of the projectile material. This impact potentially led to material flows on both sides of the rim, forming melt ponds which then solidified.

Furthermore, cross-correlated analysis also has been employed to identify yellow Bright Material (yBM) units within the Ikapati region. Its spectrum exhibits a distinctive signature: while the 2.73 µm OH band depth remains shallow (0.15-0.25), the 3.06 µm NH₄⁺ absorption is prominent. The decoupling of OH and NH₄⁺ signatures indicates that yBM could be a distinct alteration product where ammonium has been preserved despite OH depletion through thermal processing. Alternatively, ascending ammonium-rich brines may have led later on to a successive increase in ammonium⁶.

The regional depletion of smooth material units suggests widespread alteration or dehydration of the older crater system, while the excavation of carbonates indicates a local salt-rich subsurface layer. If not pretended by late ammonization, this potential preservation of NH₄⁺ in yBM despite OH depletion has implications for the stability of ammoniated phases and the chemical evolution of Ceres' near-surface environment. This multi-unit mineralogical diversity supports models of brine-driven cryovolcanic activity, impact-driven resurfacing, and complex aqueous alteration histories on Ceres.

Aknowledgments

The authors would like to thank the DLR-Agency and the MPS for their financial support for this project.

References

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