Crater population and resurfacing of the Martian north polar layered deposits

Present-day accumulation in the north polar layered deposits (NPLD) is thought to occur via deposition on the north polar residual cap. Understanding current mass balance in relation to current climate would provide insight into the climatic record of the NPLD. To constrain processes and rates of NPLD resurfacing, a search for craters was conducted using images from the Mars Reconnaissance Orbiter Context Camera. One hundred thirty craters have been identified on the NPLD, 95 of which are located within a region defined to represent recent accumulation. High Resolution Imaging Science Experiment images of craters in this region reveal a morphological sequence of crater degradation that provides a qualitative understanding of processes involved in crater removal. A classification system for these craters was developed based on the amount of apparent degradation and infilling and where possible depth/diameter ratios were determined. The temporal and spatial distribution of crater degradation is interpreted to be close to uniform. Through comparison of the size-frequency distribution of these craters with the expected production function, the craters are interpreted to be an equilibrium population with a crater of diameter D meters having a lifetime of ~30.75D^(1.14) years. Accumulation rates within these craters are estimated at 7.2D^(−0.14) mm/yr, which corresponds to values of ~3–4 mm/yr and are much higher than rates thought to apply to the surrounding flat terrain. The current crater population is estimated to have accumulated in the last ~20 kyr or less

Geology and Habitability of Terrestrial Planets

Given the fundamental importance of and universal interest in whether extraterrestrial life has developed or could eventually develop in our solar system and beyond, it is vital that an examination of planetary habitability goes beyond simple assumptions such as, "Where there is water, there is life." This book has resulted from a workshop at the International Space Science Institute (ISSI) in Bern, Switzerland (5-9 September 2005) that brought together planetary geologists, geophysicists, atmospheric scientists, and biologists to discuss the multi-faceted problem of how the habitability of a planet co-evolves with the geology of the surface and interior, the atmosphere, and the magnetosphere. Each of the six chapters has been written by authors with a range of expertise so that each chapter is itself multi-disciplinary, comprehensive, and accessible to scientists in all disciplines. These chapters delve into what life needs to exist and ultimately to thrive, the early environments of the young terrestrial planets, the role of volatiles in habitability, currently habitable (but possibly not inhabited) geologic environments, the connection between a planet's inner workings and the habitability of its surface, and the effects on planetary atmospheres of solar evolution and the presence or absence of a magnetosphere. This book serves as a useful reference for those who plan missions that will hunt for biomarkers (especially on Mars), for biologists and geoscientists who seek a broader view of the story, and for researchers and upper level students interested in an in-depth review of the geologic evolution of terrestrial planets, from their cores to their magnetospheres, and how that evolution shapes the habitability of the planetary surface

Introduction: A Multidisciplinary Approach to Habitability

International audienc