Holden Basin - Chaotic Floor Mystery
Located in the ancient Noachia Terra region within the Margaritifer Sinus quadrangle, the Holden Basin lies adjacent to Holden crater, named after the American astronomer Edward Singleton Holden (1846-1914). Today, the crater and the basin are part of the so-called Uzboi-Ladon-Morava-outflow system, also called ULM system.
Before the impact that created the 140 km in diameter Holden crater, the ULM outflow system was a long series of channels and sinks that emerged from the Argyre basin and traversed northward through Uzboi Vallis into Holden Basin, a large, ancient impact structure. From there it leads through Ladon Valles into Ladon basin, another very large ancient impact basin (see dashed lines in global overview map). It continues through Morava Valles towards the sink of the Margaritifer basin. Even Ares Vallis is believed to have been created by the outflows of the ULM system (see global and overview map images). Taken together, the total area drained may have reached up to 9% of the Martian surface. The impact that created Holden crater most likely happened in the Late Noachian, after the main activity of the ULM. The impact and formation of Holden crater interrupted the ULM outflow system, but Uzboi Vallis to the south breached the up to 900 m high crater walls making Holden the terminal basin for Uzboi and Nigral Valles. Although there is no visible outlet valley at Holden, an area of collapse can be spotted at the eastern side of the crater towards Holden Basin. There is no evidence for significant discharge and through-flowing after the impact, but some minor discharge may have happened along the ULM system after Holden crater was formed. Certainly, the floor of Holden basin was filled with large amounts of ejecta material subsequent to the impact forming Holden crater.
The image shows a chaotic terrain located in the deepest parts of the Holden basin. Here, Ladon Valles starts and travels east, out of the lower part of the image (see color-coded terrain image). The very beginning of Ladon Valles can be seen at the eastern (bottom) edge of the image. Water-bearing materials must have been present in the subsurface and melted in a later process forming the chaotic terrain. The left side of the images (south) shows the slope of the eastern plateau at Holden basin. Here, several smaller and relatively fresh-looking valleys showing width of up to 500 m can be spotted, flowing into the basin. However, a continuation towards the deeper parts of the basin is no longer visible. It is not clear what caused the formation of the chaotic terrain.
The complex history of the ULM system, paired with the overprint by impact, makes the region an interesting goal for future investigations. In addition, Ladon Valles and especially Holden crater both contain layered and phyllosilicate-bearing deposits, making them high-ranking targets for the search for ancient life on the red planet.