Description
The nature of the Martian climate during the Noachian-Hesperian transition (~3.7 Ga), and how surface features such as Valley Networks (VNs) and lakes associated with liquid water formed, is debated. There are two end-member theories. The first is that warm and wet conditions persisted on early Mars long enough that liquid water was stable on the surface for extended periods. The second is that Mars was generally cold and dry, and that geological features indicative of flowing water (e.g. VNs) were formed only very sporadically by meltwater from ice sheets during short climate excursions.
Noachis Terra, in Mars’ southern highlands, is a region where ‘warm, wet’ climate models predict high rates of precipitation, but is poorly incised by VNs. We searched instead for Fluvial Sinuous Ridges (FSRs, aka inverted channels) here as they provide alternate evidence to VNs for stable surface water. We used CTX, MOLA, and HiRISE data and recorded location, length and morphological characteristics.
We find FSRs to be common across Noachis Terra, with a cumulative length of more than 15,000 km. These are often isolated segments, but some systems are hundreds of km in length.
The broad distribution of FSRs suggests a broadly distributed source of water. The most likely candidate is precipitation, suggesting a benign surface environment. For FSRs to have formed mature, interconnected systems, up to tens of metres high, these conditions must also have been relatively long-lived. This suggests that ~3.7 Ga, Noachis Terra experienced warm and wet conditions for a geologically relevant period.
