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Patricia Wood Dickerson ¹, William R. Muehlberger ², and Paul W. Bauer ³

1. Geologist, Lockheed Martin, NASA-Johnson Space Center, Houston, TX 77058
2. Dept. of Geological Sciences, University of Texas at Austin, Austin, TX 78712
3. New Mexico Bureau of Mines & Mineral Resources, Socorro, NM 87801

Presented at Space 2000, The 7th International Conference and Exposition on Engineering, Construction, Operations, and Business in Space, co-located with Robotics 2000, The 4th International Conference and Exposition/Demonstration on Robotics for Challenging Situations and Environments, February 27 to March 2, 2000 at the Albuquerque Hilton Hotel, Albuquerque, New Mexico, USA.

Abstract

Astronaut teams acquired roughly 16 km of gravity data in the course of a planetary exploration simulation conducted in the vicinity of Taos, New Mexico. The gravimetric survey was the first phase of a geophysical assessment of the ground-water resources around Taos, an area of rapid population growth, and it was executed to help delineate buried structures that significantly influence ground-water flow and accumulation in the valley. Participants in the investigation learned a technique with direct relevance for lunar and planetary exploration and took a substantive step toward building an exploration culture within and beyond NASA.

Introduction

Successful human missions to the planets and the Moon arise from a vigorous exploration culture on Earth; long before launch, explorers will require the commitment, support, and understanding of their coworkers. To start building that culture and to begin instruction in geophysical methods appropriate for planetary exploration, a field geophysical exercise was launched.

For human exploration of the solar system, instruments must meet criteria of low mass, volume and power demand, of safe operation, and of ruggedness and reliability (Meyer et al., 1995; Hoffman, 1997; Budden, 1999). Tools will be selected for addressing fundamental scientific questions as well as for identifying resources — particularly water — and evaluating their distribution.

Geologic Setting

The Taos area of northern New Mexico, where W. R. Muehlberger has trained astronauts in geological exploration from the Apollo missions forward, was the site selected. New Mexico Bureau of Mines researchers have been defining the water resources of the Taos valley, where the population is rapidly increasing (Figure 1). They had just completed geological mapping and evaluation of water-well data and were ready to begin geophysical work. Investigations to that point had indicated that faults that lay buried beneath the valley alluvium might be influencing or controlling ground-water movement (Bauer, Johnson and Kelson, 1999).

Figure 1. (left, click to zoom) Photograph of the field-training region taken from Mir: Taos, New Mexico (T) is at the foot of Sangre de Cristo range. The Jemez Mts. volcanic complex is left of center. Albuquerque (A) and the adjacent Sandia Mts. are at lower left. (NASA photograph NM 23-714-553)

For the past 25 million years or so, the crust of the Earth has been stretched in this region and a chain of valleys — the Rio Grande rift — now extends from northern Colorado southward into Mexico. Taos occupies the southeastern corner of the San Luis rift valley; the town is in a topographic and structural embayment in the southern Sangre de Cristo range, where three major fault zones intersect (Figure 2). Those faults have moved repeatedly throughout geologic time, some beginning more than a billion years ago — for example, the Picuris-Pecos fault system.

As the valley floor has been dropped down along those structures, streams have carried sediments from the adjacent highlands and deposited them along the Sangre de Cristo range front and beyond. Fault blocks of varying elevation have influenced the courses of streams and have helped to determine where gravels, sands and clays were deposited (ground water commonly accumulates in the coarser grained, more porous sediments). Such faults have influenced not only the deposition of sediments that might become aquifers but also ground-water movement. In some places fractured bedrock serves as a conduit for ground water whereas in others, rock that has been broken down to clay is a barrier to flow.

Method

In the Taos valley, large faults that control ground-water distribution in the subsurface lie buried beneath sediments shed from the Sangre de Cristo range; geophysical methods provide a means to see through that sedimentary cover. The known geology and hydrology (Johnson, 1999) of the site and the probable magnitude of the buried faults suggested that a gravity survey, a technique attempted on the Moon, would provide needed data on the large buried structures. The contrast in density between bedrock (ancient metamorphic rock and massive limestone) versus unconsolidated valley sediment would permit definition of faults that juxtapose the two. Gravity surveying is passive — that is, no energy must be put into the ground in order to acquire data; thus, the method was well suited to a populated setting. The small portable instruments permitted walking traverses — ideal, in view of the congested spring and summer tourist traffic in Taos.

Each field crew was briefed on the geologic setting, on the scientific objectives, and on gravimetric surveying. Then, in the field, the stations where gravity readings would be taken were located by means of laser rangefinder, newly flown aerial photographs, and detailed topographic maps. Field station locations and gravity-meter readings were radioed to "Mars base" and the data were processed in real time by geophysics graduate students from New Mexico Institute of Technology (Figure 3). The next morning, each crew viewed the profile that they had acquired, participated in its interpretation, saw the data entered on the Bureau map, and helped select the location for the next traverse.

Results

Fidelity of the exploration simulation depended upon the application of space-proven instruments to solve a real scientific problem (Figure 4). Not only did data from this gravity survey delineate buried faults that had been suspected on the basis of surface mapping, but a previously unsuspected fault with thousands of feet of displacement was also discovered. Those and other structures that were located geophysically directly influence ground-water movement in the valley, and the survey provided important new data for the project.

As soon as the ~16 km of precise and accurate gravity data acquired by the group had been processed, they were incorporated into ground-water investigations for Taos, an area that is currently the focus of intense scientific study due to serious concerns about ground water resources. This survey provided real data for addressing a pressing societal problem — it was not "make-work". The data will be a component of a subsurface geologic/hydrogeologic model of the basin. This will help provide the framework for estimates of ground water storage and recharge, which will then provide planners and politicians with hard numbers for water-resource management.

The data will be published, with acknowledgment of the astronauts' contributions, in a scientific report by the New Mexico Bureau of Mines, as well as in their science news publication. The Bureau is providing materials to each astronaut for use in presentations to schools and to the public at large. Newspaper science writers in the region observed and reported on the exercise. Articles are being written for NASA internal news publications, for a popular science magazine, and for geological/geophysical research news publications.

Figure 2. (left, click to zoom) Hans Schlegel and Clay Anderson, coached by Tony Lupo (New Mexico Institute of Technology), take a gravity reading at a station northeast of Ranchos de Taos.

Figure 3. (right, click to zoom) John Young, lunar field explorer (with gravity meter), and James Reilly, geologist astronaut (right), assess the relevance of the simulation. W. R. Muehlberger (center) instructs as D. L. Ross, Leo Eyharts, and Lee Archambault (left to right) observe.

Summary

Thirty-one members of the 1998 astronaut candidate class are now experienced in collecting gravity data to define buried faults in the context of a ground-water investigation. All readily mastered the technique and recognized the potential of the method for planetary exploration — particularly of Mars, where windblown sand mantles highly varied terrain. The discovery of magnetic stripes on Mars, perhaps analogous to those that record seafloor rifting on Earth, raises the possibility that gravity surveys might reveal significant buried martian structures.

One or more of these individuals may step on Mars or Earth's Moon, but most will help direct those missions from Earth. They will know at least one investigative technique, they will have helped plan a geophysical traverse, and they will have a sense of the time required for scientifically rigorous planetary exploration. Future geological and geophysical training will build upon this experience and address varied scientific objectives, as candidate sites for lunar and martian exploration are selected. In sum, we believe that the goals for this initial geophysical exploration simulation — to begin building an exploration culture within and beyond NASA and to introduce field methods for planetary exploration — were met and surpassed.

References

1. Bauer, P. W., Johnson, P. S., and Kelson, K. I., 1999, Geology and hydrogeology of the southern Taos valley, Taos County, New Mexico: Socorro, New Mexico Bureau of Geology and Mineral Resources, Final Technical Report to New Mexico Office of the State Engineer, 56 pages, 4 plates.
2. Budden, N. A., editor, 1999, Mars field geology, biology and paleontology workshop: Summary and recommendations: Houston, Lunar and Planetary Institute, Contribution 968, 80 pages.
3. Hoffman, S. J., and Kaplan, D., editors, 1997, The reference mission of the NASA Mars Exploration Study Team: NASA Special Publication 6107.
4. Johnson, P., 1999, Availability and variability of surface-water resources in Taos County, New Mexico — An assessment for regional planning: Socorro, New Mexico Bureau of Geology and Mineral Resources, New Mexico Geology, volume 21, number 1, pages 1 - 9.
5. Meyer, C., Treiman, A. H., and Kostiuk, T., 1995, Planetary surface instruments workshop: Houston, Lunar and Planetary Institute, LPI Technical Report 95-05.

KEYWORDS

alluvium
astronaut training
faults
geophysical exploration
gravity survey
lunar exploration
Mars exploration
Taos, New Mexico
water resources

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