The Once & Future Moon
Smithsonian Air & Space Blogs
Last week, the Science Team of the Mini-RF imaging radar experiment aboard the Lunar Reconnaissance Orbiter (LRO) mission, met in Flagstaff, Arizona. We were there to conduct field studies of some interesting lunar analogs that occur in this area. Scientists study the planets through a variety of means, including images, remote-sensing, and sample return. One technique involves studying the processes and deposits of the Earth as a guide or analog to understanding similar features on the Moon and other bodies. Analogs have been studied since the beginning of the space program and have been essential to unraveling the complex histories of rocky objects in the Solar System.
The team gathered early Wednesday morning north of Flagstaff. Our field guides pictured the three areas we would spend the day visiting, along with geologically similar features found on the Moon. Our technique used airborne radar images of our targets: The SP cone and lava flow, Sunset Crater National Monument and Meteor Crater. Each site offers specific features that one can observe and walk across, using it as a guide toward understanding the same processes that have shaped our Moon. Our field trip illuminated the radar data in a “real world” environment, assisting us as we continue to explore and map with our instrument now orbiting the Moon.
The SP cone and flow is one of the most remarkable volcanic features in the region, with a beautifully symmetrical cinder cone and an extremely rough, blocky lava flow (Fig. 1; for full resolution versions of the surface pictures, click here: a, b, c). As viewed from the ground, the lava flow is blocky and extremely rough at the scale of the L-band radar wavelength (about 25 cm, or almost a foot). Steep flow fronts of blocky lava lie directly upon a smooth plateau of flat-lying sedimentary rocks. These remarkable flow fronts can be up to 50 m high (over 150 feet) and their rubbly, rugged fronts provide a spectacular contrast to the featureless plain upon which they rest. In the radar image, the lava flow is extremely bright, indicating high radar returns and its circular polarization ratio (CPR), one measure of its surface roughness at wavelength scales, is very high.
Many of the geological features seen in radar images of the Earth are also seen in the radar images from the Moon. As we continue to map the Moon with the Mini-RF radar, the sometimes puzzling relations seen in the lunar data are understood better by comparison with Earth analogs. Our entire team acquired valuable insight into how the Moon works and what the surface is like from our day in the field. For a geologist, there is simply no substitute for directly observed field data to fully comprehend the complex history and processes of the Moon.
Equally interesting and important will be the insight and knowledge gained when we sample the Moon in more detail. The Moon has been described as a “dead planet” because compared to the Earth, which has rapid, dynamic processes of erosion, the Moon remains unchanged for millions of years. However, for its ability to retain the ancient historical record of the Earth-Moon system, advantage goes to the Moon. The multi-billion year records of impact and solar wind embedded in the lunar surface awaits our recovery, and will tell us about both the past and possible future of our home planet.