摘要
We examine the crustal magnetization of Terra Meridiani and Terra Sirenum, the region representing the strongest magnetization in the Southern Hemisphere, by downward continuing mapping level data (400 km altitude) from the Mars Global Surveyor (MGS) Magnetometer and Electron Reflectometer (MAG/ER). We find that the surface magnetization in both regions can be fit with a small number of sources, with the positive sources stronger than negative ones in both regions. The ratio of the strongest positive to strongest negative source for the regions matches within 2%. For both regions, the locations of strong sources are positioned at the outer rings of ancient impact features. We employ two approaches of source depth estimation. One method employs downward continuation of positive and negative sources from mapping level into the subsurface to extrapolate the depth to magnetization. With this approach, source depths generally range from 80 ±20 km in Terra Meridiani and 65 ±25 km in Terra Sirenum. A graphical approach uses the contour map of surface magnetization to estimate depths ranging from 125 km for thick sources in Terra Meridiani and from 82 km for thick sources in Terra Sirenum. These depths require a low (≤∼20 mW/m2) Martian heat flux to permit magnetite, hematite, and/or pyrrhotite (although limited) as carriers through 100 km or more. The upcoming InSight mission will provide invaluable seismic constraints on both crustal and core structure, in addition to the first Martian heat flow measurements that will constrain magnetization.
We examine the crustal magnetization of Terra Meridiani and Terra Sirenum, the region representing the strongest magnetization in the Southern Hemisphere, by downward continuing mapping level data (400 km altitude) from the Mars Global Surveyor (MGS) Magnetometer and Electron Reflectometer (MAG/ER). We find that the surface magnetization in both regions can be fit with a small number of sources, with the positive sources stronger than negative ones in both regions. The ratio of the strongest positive to strongest negative source for the regions matches within 2%. For both regions, the locations of strong sources are positioned at the outer rings of ancient impact features. We employ two approaches of source depth estimation. One method employs downward continuation of positive and negative sources from mapping level into the subsurface to extrapolate the depth to magnetization. With this approach, source depths generally range from 80 ±20 km in Terra Meridiani and 65 ±25 km in Terra Sirenum. A graphical approach uses the contour map of surface magnetization to estimate depths ranging from 125 km for thick sources in Terra Meridiani and from 82 km for thick sources in Terra Sirenum. These depths require a low (≤∼20 mW/m2) Martian heat flux to permit magnetite, hematite, and/or pyrrhotite (although limited) as carriers through 100 km or more. The upcoming InSight mission will provide invaluable seismic constraints on both crustal and core structure, in addition to the first Martian heat flow measurements that will constrain magnetization.
