Title: Modeling
of major martian magnetic anomalies: Further evidence for polar
reorientations during the Noachian
Source: ICARUS
177 (1): 144-173 SEP 2005
Document Type: Article
Language: English
Abstract: Maps
of the vector components of the Mars crustal magnetic field are
constructed at the mapping altitude (360 to 410 km) using a selected
set of data obtained with the Mars Global Surveyor magnetometer during
2780 orbits of the planet in 1999. Forward modeling calculations are
then applied to six relatively strong and isolated, dominantly dipolar,
magnetic anomalies for the primary purpose of estimating bulk
directions of magnetization. Assuming that the magnetizing field was a
(dipolar) core dynamo field centered in the planet, paleomagnetic pole
positions are calculated for the six primary source bodies together
with that for a seventh anomaly analyzed earlier. In agreement with
several previous studies, it is found that six of the seven pole
positions are clustered in what is now the northern lowlands in a
region centered northwest of Olympus Mons (mean pole position: 34
degrees +/- 10 degrees N, 202 degrees +/- 58 degrees E). Assuming that
the dynamo dipole moment vector was approximately parallel to the
rotation axis, the modeling results therefore suggest a major
reorientation of Mars relative to its rotation axis after magnetization
was acquired. Such a reorientation may have been stimulated by internal
mass redistributions associated with the formation of the northern
lowlands and Tharsis, for example. A comparison of the mean paleo
(magnetic) equator to the global distribution of crustal fields shows
that magnetic anomalies tend to occur at low paleolatitudes. The same
appears to be true for the Noachian-aged valley networks, which exhibit
a broad spatial correlation with the magnetic anomalies. A possible
interpretation is that the formation of magnetic anomalies and the
valley networks was favored in the tropics where melting of water ice
and snow was a stronger source of both surface valley erosion and
groundwater recharge during the earliest history of the planet. This
would be consistent with models in which hydrothermal alteration of
crustal rocks played a role in producing the unusually strong martian
magnetic anomalies. (c) 2005 Elsevier Inc. All rights reserved.
Author Keywords: Mars,
magnetic fields; Mars, interior; Mars, surface
KeyWords Plus: EARLY
MARS; FIELD; CRUST; CONSTRAINTS; VOLATILE; BODIES
Addresses: Hood
LL (reprint author), Univ Arizona, Lunar & Planetary Lab, 1629 E
Univ Blvd, Tucson, AZ 85721 USA
Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA
SW Res Inst, Boulder, CO 80309 USA
Publisher: ACADEMIC
PRESS INC ELSEVIER SCIENCE, 525 B ST, STE 1900, SAN DIEGO, CA
92101-4495 USA
Subject Category: ASTRONOMY
& ASTROPHYSICS
IDS Number: 958XL
ISSN: 0019-1035