A review of issues and challenges

Determining the ages of young planetary surfaces relies on using populations of small, often sub-km diameter impact craters due to the higher frequency at which they form. Smaller craters however can be less reliable for estimating ages as their size-frequency distribution is more susceptible to alteration with debate as to whether they should be used at all. With the current plethora of meter-scale resolution images acquired of the lunar and Martian surfaces, small craters have been widely used to derive model ages to establish the temporal relation of recent geologic events. In this review paper, we discuss the many factors that make smaller craters particularly challenging to use and should be taken into consideration when crater counts are confined to small crater diameters. Establishing confidence in a model age ultimately requires an understanding of the geologic context of the surface being dated as reliability can vary considerably and limitations of the dating technique should be considered in applying ages to any geologic interpretation

The Science Case for Io Exploration

Io is a priority destination for solar system exploration, as it is the best natural laboratory to study the intertwined processes of tidal heating, extreme volcanism, and atmosphere-magnetosphere interactions. Io exploration is relevant to understanding terrestrial worlds (including the early Earth), ocean worlds, and exoplanets across the cosmos

Recommendations for Addressing Priority Io Science in the Next Decade

Io is a priority destination for solar system exploration. The scope and importance of science questions at Io necessitates a broad portfolio of research and analysis, telescopic observations, and planetary missions - including a dedicated New Frontiers class Io mission

High-Fe, low-Al basalts: evidence of extensive mantle processing on Earth, Moon, Mars, Vesta, Venus, and Io

Ferropicrite basalts – basalts with relatively high-Fe and low-Al contents compared to ‘normal' basalts – are a minor but widespread component of magmatism on Earth. We have investigated how widespread high-Fe, low-Al compositions (similar to ferropicrites) are on other terrestrial planetary bodies and suggest that these basalts formed through similar processes

Fully Controlled 6 Meters per Pixel Equatorial Mosaic of Mars From Mars Reconnaissance Orbiter Context Camera Images, Version 1

Abstract NASA's Mars Reconnaissance Orbiter (MRO) spacecraft has operated around Mars since March 2006. The Context Camera (CTX) aboard MRO has returned >125,000 images of Mars, mostly at 5–6 m per pixel (mpp), providing ≈99% coverage with good‐quality images. Reconstruction of MRO's orbit and camera pointing from ground tracking are offset from the Mars global coordinate system. This work focuses on correcting those data for the more than 50,000 images in the equatorial region of Mars, between ±30° latitude, which comprises 50% of Mars' surface area. Determining and making these corrections in a relative control (image‐to‐image) and absolute or full control (image‐to‐ground reference) greatly improves the utility of the image data. Based on this work, the 95th percentile of tie points were offset from the Mars coordinate system by ≈155 m, corresponding to ≈28 CTX pixels. Controlling the more than 50,000 images was accomplished through an efficient, automated approach with additional manual input and validation, described herein. The mosaic was generated with semi‐manual image order from these controlled data and is provided at both 6 mpp and 100 mpp. The mosaic is available to the community through NASA's Planetary Data System Imaging & Cartography Annex

Testing Models for the Formation of the Equatorial Ridge on Saturn's Moon Iapetus via Crater Counting

Iapetus's equatorial ridge, visible in global views of the moon, is unique in the Solar System. The formation of this feature is likely attributed to a key event in the evolution of Iapetus, and various models have been proposed as the source of the ridge. By surveying imagery from the Cassini and Voyager missions, this study aims to compile a database of the impact crater population on and around Iapetus's equatorial ridge, assess the relative age of the ridge from differences in cratering between on ridge and off ridge, and test the various models of ridge formation. This work presents a database that contains 7748 craters ranging from 0.83 km to 591 km in diameter. The database includes the study area in which the crater is located, the latitude and longitude of the crater, the major and minor axis lengths, and the azimuthal angle of orientation of the major axis. Analysis of crater orientation over the entire study area reveals that there is no preference for long-axis orientation, particularly in the area with the highest resolution. Comparison of the crater size-frequency distributions show that the crater distribution on the ridge appears to be depleted in craters larger than 16 km with an abruptly enhanced crater population less than 16 km in diameter up to saturation. One possible interpretation is that the ridge is a relatively younger surface with an enhanced small impactor population. Finally, the compiled results are used to examine each ridge formation hypothesis. Based on these results, a model of ridge formation via a tidally disrupted sub-satellite appears most consistent with our interpretation of a younger ridge with an enhanced small impactor population