Magnetotelluric Subsurface Sounder, 15-R8043

Printer Friendly Version

Principal Investigators
Robert Grimm
David Stillman
Kerry Neal
Michael Vincent

Inclusive Dates:  03/01/09 – 07/01/10

Background - Electromagnetic (EM) sounding of planetary interiors reveals key indicators of structure and geological evolution, but is not widely recognized because there has been no simple approach applicable to a variety of space missions. Magnetotellurics (MT) — used for the past half-century on Earth — can provide that broad applicability. MT determines the frequency-dependent ground impedance (and hence internal structure) from measurements of the electric and magnetic fields naturally arising from lightning, the ionosphere, the magnetosphere and in space, from the solar wind.

Approach - This project seeks to develop the theory and instrumentation for a prototype planetary MT sounder, with a focus on instruments suitable for upcoming flight opportunities — a landed system for the Moon or Mars and an aerial system for Venus, Mars or Titan. There are three main elements to the project. First, theoretical modeling will determine science goals and performance requirements for future missions. Second, instrument designs will be produced. Third, EM measurements will demonstrate the capability to perform relevant non-ground-contacting electric-field measurements and the ability to process the data to recover the useful (inductive) part of the EM fields.

Accomplishments - EM fields were modeled that are vertically incident from space and fields from lightning that are transmitted horizontally between the ground-ionosphere waveguide. The former was determined to be unsuitable for aerial measurements at altitudes comparable to or greater than an EM skin depth, but the latter can be used at any altitude. This was a major breakthrough that resulted in a new proposal to NASA to perform high-altitude EM surveying on Earth and an invitation to participate in an ESA proposal for a Venus balloon. The project team measured EM fields from an 8-ft diameter balloon to altitudes up to 70 ft, extracted the inductive signal, and showed that the inferred ground properties were consistent with theory. The team developed a novel electrode configuration that can be incorporated into a balloon hull to take advantage of the large surface area and, using the same modeling techniques, designed an electrode layout suitable for use in a geophysical "bird" for airborne surveys on Earth. Project researchers showed quantitatively that an existing patent for aerial MT is physically incapable of meeting its claims. The team developed a design for a landed MT system that is being proposed for two lunar-lander missions. The results of this project enable a range of future Earth and planetary magnetotelluric surveying.

2010 Program Home