PRELIMINARY RESULTS FROM A SURVEY OF CANDIDATE PERMAFROST AND PERIGLACIAL FEATURES ON MARS

The Haughton meteorite impact structure, located on Devon Island, Nunavut is one of the most Mars-like places on Earth. The Haughton crater is cold (average temperature –17°C), dry, rocky, dusty, and windy. As part of the effort at NASA SETI Institute Haughton Mars Project (HMP), the University of Calgary Applied Geophysics Group conducted geophysical surveys, both ground-penetrating radar (GPR) and highresolution seismic, in the summer of 2002. Objectives of the geophysical work were to image the permafrost layer as well as assess deeper geologic horizons. GPR data were acquired using Sensors & Software NOGGIN 250 MHz system and PulseEKKO devices with 50 and 100 MHz antennae. These surveys imaged depths from about 0.5m to 3 m and indicate layering and permafrost events. High-resolution seismic results, recorded with a Geometrics 60-channel recording system and accompanying 28 Hz omni-directional geophones, also show the permafrost layer. Shallow excavations, seismic refractions, and GPR reflections at the site all proved useful and indicate that the permafrost layer is at a depth of about 60cm. We also tested geophysical operations in prototype spacesuits and found the suits to be manageable although cumbersome. We plan on returning to the Haughton crater in the summer of 2003 for further geophysical surveying and system testing. Introduction The Haughton meteorite impact structure on Devon Island, Nunavut in the high Canadian Arctic is one of the most Mars-like places on Earth. The Haughton structure, at 75°22’N longitude and 89°41’W latitude, is a 23 Ma old impact crater about 20 km in diameter [1], [2]. Host rocks of the structure are of Ordovician and Silurian age, mostly of the Allen Bay formation [3]. The impact has left a very impressive scar on the landscape as seen from an airborne radar image. The northwest region of the outer middle rim hosts the base camp for the Haughton Mars Project [4], [5], [6], [7]. Geophysical surveying can be difficult, even in the summer on Devon Island, due to the high winds of the polar area (up to 70 km/hr during this field survey), low summer temperatures (-5°C to +5°C), sleet, rain, snow even though this is characterized as a desert [8], and significant ultraviolet radiation [9]. The site chosen for the GPR and seismic surveys was located near the base camp in the “Von Braun Valley” (VBV). We conducted another series of surveys several kilometres away at the “Gemini Hills”, but only the VBV surveys will be discussed here. We dug several test pits near the base camp to investigate the composition of the near surface. We found a tancoloured, saturated silt with small clasts down to depths of about 45 – 65 cm. We then encountered solid and uniform permafrost with the appearance of frozen silt. Seismic and GPR surveys We used a Geometrics Strata View 60-channel seismic recorder with 28Hz omni-geophones (planted in vertical and horizontal configurations). One of the seismic micro-spreads is shown in Figure 1. A small sledgehammer was employed as a source striking a base plate in either a vertical or horizontal direction. FIG. 1 Photograph the 3-C micro-seismic line in the “Von Braun Valley” at the HMP base camp. We conducted a number of surveys using a variety of source-receiver combinations. That is, vertical source strikes and vertical receivers, horizontal hammer blows and transverse receivers, etc. A data example for a vertical hammer strike with horizontal, inline receivers (the P-S configuration) is shown in Figure 2. We are still analysing the seismic data, but have determined very low preliminary P and S velocities in the near-surface silts (260m/s and 168m/s, respectively) with very high velocities in the permafrost (Pwave velocity = 3100m/s, S-wave velocity = 2060m/s). Third Mars Polar Science Conference (2003) 8115.pdf