Probing Planets from Orbit: Lessons from Mars, Opportunities for Earth
When
Where
Dr. Jack Holt
Research Professor
Institute for Geophysics
University of Texas at Austin
We learn about our planet’s history by examining the geologic record. One could argue that the most continuous, high-fidelity records of the recent past on both Earth and Mars are contained within their polar ice sheets. As we seek to better understand the history of polar ice and major glaciers on Earth, we are often limited by our sparse knowledge of their internal structure and three-dimensional stratigraphy. On Earth, ice cores are insufficient because they only sample discrete locations and don’t address the dynamics of the ice sheet as a whole. Measurements of surface elevation and velocity are critical for quantifying current change, but do not give us the context of longer-term change or elucidate the role of basal processes.
Radar sounding provides a means to access the subsurface across an entire ice sheet. Airborne and surface radar campaigns on Earth over the past 45 years have resulted in many insights, yet there are still large unexplored regions and the variety of radars employed in these challenging campaigns has resulted in a disparate mix of resolution, quality, and positional uncertainties. This hampers modeling efforts that need consistent boundary conditions through time.
Ironically, we have more complete and uniform radar sounding coverage of the polar caps of Mars than we do for Antarctica or Greenland. In just the first five years of the Mars Reconnaissance Orbiter mission we solved some 40-year-old mysteries by having this new view of polar cap stratigraphy and structure to complement imagery and morphology. Although Earth presents challenges to orbital radar sounding, a similar view of our major ice sheets could be achievable. It would enable a new generation of modeling efforts and provide context and direction for field studies where higher resolution or different techniques are needed, rather than conducting the logistically challenging, first-order reconnaissance surveys that continue today.
As on Mars where non-polar regions have also been successfully sounded with radar, it is also quite possible that we could sound arid, lower-latitude regions on Earth. Relative to ice sheets, this is a high-risk, high-payoff scenario but if, for example, aquifers could be mapped from orbit in desert environments, it would represent a significant advance. This is promising based on preliminary investigations, and could be further developed with targeted airborne experiments.