James J. Frawley

Geometric properties of Martian impact craters: Preliminary results from the Mars Orbiter Laser Altimeter

The Mars Orbiter Laser Altimeter (MOLA) acquired high spatial and vertical resolution topographic data for 18 tracks across the northern hemisphere of Mars during the Fall of 1997. It sampled 98 minimally degraded impact craters between the latitudes of 80°N and 12°S The best fitting depth (d) versus diameter (D) power-law relationship for these craters is: d = 0.14 D0.90 for simple varieties, and d = 0.25 D0.49 for complex structures. The simple-to-complex transition diameter is 8 km (+/−0.5 km). The cross-sectional “shape” of the crater cavities was determined by fitting a power-function to each profile. Variation in the exponent (n) suggest the craters flatten with increasing diameter and impact energy. The ejecta thickness is skewed suggesting that use of existing empirical expressions for the expected radial decay of ejecta thickness is inappropriate for Mars in most cases.

Vertical roughness of Mars from the Mars Orbiter Laser Altimeter

The vertical roughness of the martian surface at ∼250 m spatial scales has been determined in two global latitude bands: an equatorial and a high northern band acquired from 18 tracks of data by the Mars Orbiter Laser Altimeter (MOLA) during the Fall of 1997. The distribution of RMS vertical roughness, as derived from MOLA pulse widths, for the equatorial band is non-gaussian, with an overall mean of 2.8 m RMS, but with secondary populations at 1.5 m and 2–6 m RMS. The higher latitude northern plains of Mars are almost uniformly ∼1 m RMS in their vertical roughness characteristics, suggesting that they are smoother than virtually any terrestrial deserts. We suggest that dust mantling has muted the local topography of Mars, rendering it as smooth as 1–2 m RMS. Heavily cratered uplands near the martian equator are noticeably rougher, indicating more rugged and less-mantled local topography.

Comparing Magsat, Ørsted and CHAMP crustal Magnetic Anomaly Data over the Kursk Magnetic Anomaly, Russia

Prior to the launch of Magsat, it was not obvious that a satellite altitude magnetometer mission would record crustal magnetic fields, despite the POGO and COSMOS-49 results. Subsequent studies, however, soon revealed that Magsat was able to map crustal magnetic anomalies. One of these investigations was centered on the Kursk Magnetic Anomaly (KMA) of Russia. Not only did this earlier Magsat study of the KMA record its magnetic signature at satellite altitude but also it was revealed that the anomaly displayed a significant component of remanent magnetization. With the subsequent launch of the higher altitude Orsted satellite a comparison between the KMA and these newer magnetic anomaly data was made. It was determined that Orsted could indeed record the crustal magnetic field and with a greater signal/noise ratio than Magsat since at a higher altitude the spacecraft was further from the ionosphere. It is not surprising, therefore, that after the successful launch of CHAMP we continued our initial study of the crustal anomaly field over the KMA with these newer magnetic observations. The KMA appears to be well represented in these CHAMP data as well.