AGU: Geophysical Research Letters

 

Editors' Highlight

Martian lowlands are not young

The crust of Mars can be described as ancient southern highlands and lower, thinner, and apparently younger northern lowlands. The origin of this difference, or dichotomy, has been controversial: Some theorize that internal processes (like plate tectonics) were responsible, while others suggest that large meteor impacts caused the northern portion's low elevations. NASA's Mars Orbiter Laser Altimeter has revealed a larger-than-expected population of visible and buried impact basins, or "quasi-circular depressions" (QCDs), on Mars, which provides new constraints on the age of the Martian lowlands. Frey (2006) mapped and counted these depressions to determine the total population of craters (both visible and buried) and thereby obtain a more complete record of crater retention for a given area. His investigations showed that the Martian lowlands have a crater density similar to areas of the southern highlands known to be of Early Noachian age, more than 4 billion years old, with large lowland basins possibly older. This suggests that the lowland crust formed and became low no later than 500 million years after Mars formed, which better limits the likely process of origin.

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