Surface Magnetization of Terra Meridiani, Mars Renee French Earth 438 Winter 2014 Opportunity looking out on Santa Maria Crater, sol 2466 (~7 years)

Motivation Terra Meridiani has been proposed as a site of past seafloor spreading due to magnetic offsets in the MGS Magnetometer data at 400 km altitude (Connerney et al., 2005) – If this data is continued to the surface, are the magnetic offsets still observed? – Can magnetic offsets, and thus transform faults, be tied to other geologic features (i.e., offset craters, regional differences in geology)? – What other mechanisms can produce the observed magnetization? – Any other data to suggest that Terra Meridiani was once an active plate boundary? – Can data from MER Opportunity provide any ground truth for this hypothesis?

Location Image credit: NASA

Geologic Investigation Image Credit: NASA/JPL/ASU Squyres and Knoll (2005) Trough x-strat Image 3cm wide Hematite spherules Squyres et al. (2006)

Burns Formation Facies McLennan et al. (2005) Data best supports eolian environment with a fluctuating groundwater table

From Acuña et al. (1999): Measured vertical component of the magnetic field (no altitude correction). Includes aerobraking data. Solid line is the boundary between the northern lowlands and southern highlands. Martian Magnetization

From Connerney et al. (2005): Measured radial (vertical) component of the magnetic field at 400km altitude

Past Seafloor Spreading? Map of the magnetic field at 400 km altitude (Connerney et al., 2005). Dashed lines represent transform faults, letters refer to impact basin names. Map of the magnetic field as a function of latitude (Connerney et al., 2005). Green and orange represent profiles taken to the west and east of the central meridian, respectively.

Methods 2D Fourier Transform Downward continuation; k>25 filtered out Inverse Fourier Transform Geologic units from Scott and Tanaka (1986), Greeley and Guest (1987).

Results: Raw Data

Accuracy Test Aerobraking: Max: 278 Min: -268 DC’ed: Max: 437 Min: -247

Surface Magnetization

Impact influence? Basins are from Schultz et al. (1982) and Schultz and Frey (1990) Basins: 1-Chryse 2- Ladon 3- Aram Chaos 4- overlapped by Newcomb 5- overlapped by Schiaparelli 6- Cassini

Tectonic influence? “Great faults” from Connerney et al. (2005)

Topography 20N, 20E 20S, 340E

Geology Subdued crater unit Etched unitCratered unit Dissected unit Ridged Plains material Chaotic material Older Channel material Hilly unit Mottled Smooth Plains unit Ridged unit Crater materials Smooth unit Undivided material Cratered unit Hilly unit Crater materials Ridged Plains material Smooth unit Scott and Tanaka (1986), Greeley and Guest (1987) All units are interpreted as some type of igneous rock 20S, 340E 20N, 20E

Discussion Downward continued field agrees well with low altitude data. Offsets observed by Connerney et al. (2005) at altitude are also observed at the surface – No other geophysical signature of faults Possible influence from multi-ring basins – May not be a source of magnetization, but rather weaken the intensity Magnetic mineralogy constrained by Opportunity – Will use when considering source models Geologic history from Burns formation does not match a seafloor spreading environment – However, this outcrop is only 7 m thick

Image Credit: Voyage to the Planets, BBC