Journal Highlights

How Quickly Is Mercury’s Surface Evolving?

From Research Spotlights—

New measurements of impact craters on Mercury’s smooth plains suggest the topography of the solar system’s innermost planet is changing at twice the rate of landforms on the Moon. 

For the last several billion years, collisions with meteoroids, asteroids, and comets have been the primary process modifying the surfaces of both the Moon and the planet Mercury. Over time, smaller impacts, debris ejected from these impacts, and other processes like thermal expansion and contraction degrade the craters these collisions leave behind and make them shallower. Here Fassett et al. use data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission to quantify the rate at which Mercury’s landscape is evolving and compare the results to the lunar surface. 

Using topographic profiles of Mercury generated by two different techniques—direct laser altimetry measurements and high-resolution stereo images—the researchers acquired depth-to-diameter measurements of 204 similarly sized craters on Mercury’s smooth plains. Surprisingly, the results indicate that Mercury’s bowl-shaped craters are substantially shallower than those on the Moon and hence have been more highly modified, despite the fact that the volcanic plains on both bodies are close to the same age. Additional analyses using models that estimate the rate of landform evolution suggest that crater degradation is occurring twice as fast on Mercury as on the Moon. 

This substantial difference in degradation rates raises a number of puzzling questions with potentially broad implications, including whether different weathering processes are occurring on the two bodies and if the crater population on the oldest terrains on Mercury might be highly modified by its fast rate of landform evolution. The results of this study should motivate more research on the factors that control the evolution of landscapes on these and possibly other airless bodies. 

—Terri Cook, Freelance Writer

Editor’s Highlight—Comparing Craters 

An analysis suggests that craters degrade faster on Mercury than the Moon, raising questions about landscape evolution on different planetary bodies.

Fassett et al. [2017] present a detailed analysis of simple crater topography on Mercury that suggests more rapid landform evolution on Mercury than on the Moon (i.e., crater degradation). The analysis uses depth to diameter measurements of impact craters and state-of-the-art diffusion models to investigate degradation states of these craters. The demonstration that landscape evolution on both bodies occurs at substantially different rates has broad implications. Are the dominant processes at work different on each body? Are individual weathering processes enhanced or subdued on each? How do these differing rates affect crater counting and our understanding of surface ages? Overall, the measurement results and analysis of degradation rates suggest more work is needed to understand why the degradation rate on Mercury is faster, how it scales with crater size, and other factors that may have significant implications for understanding the landscape evolution of these bodies.

—Andrew Dombard, Editor, Geophysical Research Letters


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Featured Special Collection

A Census of Atmospheric Variability from Seconds to Decades 

The atmosphere varies naturally on all length scales from millimeters to thousands of kilometers, and on all time scales from seconds to decades and longer.  This special collection of Geophysical Research Letters synthesizes and summarizes that variability through a phenomenological census.  The collection brings together some of the most influential and definitive papers to have been published in this journal in recent years.  The topics covered include turbulence on time scales of seconds and minutes, gravity waves on time scales of hours, weather systems on time scales of days, atmospheric blocking on time scales of weeks, the Madden–Julian Oscillation on time scales of months, the Quasi-Biennial Oscillation and El Niño–Southern Oscillation on time scales of years, and the North Atlantic, Arctic, Antarctic, Pacific Decadal, and Atlantic Multi-decadal Oscillations on time scales of decades.  The collection is accompanied by a Commentary article, which provides an authoritative, concise, and accessible point of reference for the most important modes of atmospheric variability.

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