Impact cratering as a cause of climate change, surface alteration, and resurfacing during the early history of Mars

Abstract

Ancient valley networks (VNs) and related open‐ and closed‐basin lakes are testimony to the presence of flowing liquid water on the surface of Mars in the Late Noachian and Early Hesperian. Uncertain, however, has been the mechanism responsible for causing the necessary rainfall and runoff and/or snowfall and subsequent melting. Impact cratering has been proposed (e.g., Segura et al. 2002) as a process for temporarily raising temperatures and inducing conditions that would produce rainfall, snowmelt, runoff, and formation of the VNs and associated lacustrine features. We refer to the collective effects of this process as the ICASE model (impact cratering atmospheric/surface effects). In this contribution, we assess the proposed impact cratering mechanism in order to understand its climatic implications for early Mars: we outline the step‐by‐step events in the cratering process and explore the predictions for atmospheric and surface geological consequences. For large and basin‐scale impacts, rainfall should be globally and homogeneously distributed and characterized by very high temperatures. Rainfall rates are predicted to be high, ~2 m yr−1, similar to rates in tropical rainforests on Earth, and runoff rates are correspondingly very high. These predicted characteristics do not seem to be consistent with the observed VNs, which are mainly equatorial and not homogeneous in their distribution. Prior to the Late Noachian, however, we predict that basin‐scale impact effects are very likely to contribute significantly to degradation of crater rims and regional smoothing of terrain, implying vast resurfacing and resetting of crater ages following large crater and basin‐scale impacts. Furthermore, the high temperatures of impact‐induced rainwater and snowmelt and the pervasive penetration of heat into the regolith substrate are predicted to have a significant influence on the mineralogical alteration of the crust and its resulting physical properties. We conclude by describing a case example (Isidis basin) and describe how the ICASE model provides an alternative scenario for the interpretation of the layered phyllosilicates in the Nili Fossae and NE Sytris regions. We outline specific conclusions and recommendations designed to improve the ICASE model and to promote further understanding of its implications for the geological, mineralogical, and climate history of early Mars.

Areally Extensive Surface Bedrock Exposures on Mars: Many Are Clastic Rocks, Not Lavas

“…Like other examples presented in this work, this Noachian-aged unit exhibits higher TI than the Hesperian-aged Syrtis Major lavas that overlie the unit (Figure 2d). We thus suggest that the Nili Fossae olivine-bearing unit is friable compared to Syrtis lavas and argue that this favors pyroclastic, detrital sedimentary, or impact-related origins (e.g., Palumbo & Head, 2017). Unaltered regions are found within 300 km distance and within a few hundred meter elevation from the Syrtis lavas, suggesting that preferential wind activity cannot explain the differences in TI and regolith cover between unaltered olivine bedrock and Syrtis lavas.…”

“…Large, basin-scale impacts (e.g., Isidis, Argyre, and Hellas) could have produced olivine-bearing clastic rocks in the form of suevites, and also potentially as condensates from silicate vapor created during the impact (Toon et al, 2010). Indeed, previous authors have suggested that the Nili Fossae and Isidis olivine-bearing bedrock plains units may represent the silicate condensate (Palumbo & Head, 2017) or impact melt (Mustard et al, 2007) from the Isidis basin impact. Indeed, previous authors have suggested that the Nili Fossae and Isidis olivine-bearing bedrock plains units may represent the silicate condensate (Palumbo & Head, 2017) or impact melt (Mustard et al, 2007) from the Isidis basin impact.…”

“…Proposed origins for this unit include lavas Tornabene et al, 2008), impact melts (Mustard et al, 2007), or silicate condensate from vaporized crust following the Isidis basin impact (Palumbo & Head, 2017). Proposed origins for this unit include lavas Tornabene et al, 2008), impact melts (Mustard et al, 2007), or silicate condensate from vaporized crust following the Isidis basin impact (Palumbo & Head, 2017).…”

“…These silicate condensate materials could range from porous/unconsolidated to strongly welded, depending on the thickness of the deposits and temperature at time of deposition (Palumbo & Head, 2017;Toon et al, 2010). Indeed, previous authors have suggested that the Nili Fossae and Isidis olivine-bearing bedrock plains units may represent the silicate condensate (Palumbo & Head, 2017) or impact melt (Mustard et al, 2007) from the Isidis basin impact. For bedrock plains units elsewhere in the highlands, the formation ages would need to be better constrained in order to support or rule out the role of basin-scale impacts.…”

Impact Degassing of H2 on Early Mars and its Effect on the Climate System

“…For almost 50 years now, various gaseous and cloud greenhouse solutions have been proposed only to be discounted upon closer scrutiny (see Haberle et al, for a detailed discussion). Transient warm episodes driven by impacts (Segura et al, , , ), volcanism (Halevy & Head, ; Schmidt et al, ), seasonal effects (Kite et al, ; Palumbo et al, ), climate limit cycles (Batalha et al, ), or methane‐hydrogen bursts (Chassefière et al, 2016) on an otherwise cold icy planet (Wordsworth et al, ) have been proposed, but these mechanisms have been challenged as well (e.g., Barnhart et al, ; Hoke et al, ; Kerber et al, ; Ramirez, ; Palumbo & Head, ; Steakley et al, ; Turbet, Gillmann, et al, ).…”