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We have used Cassini stereo images to study the topography of Iapetus' leading side. A terrain model derived at resolutions of 4–8 km reveals that Iapetus has substantial topography with heights in the range of −10 km to +13 km, much more than observed on the other middle-sized satellites of Saturn so far. Most of the topography is older than 4 Ga [Neukum, G., Wagner, R., Denk, T., Porco, C.C., 2005...
The Lunar Prospector Electron Reflectometer has obtained the first global map of lunar crustal magnetic fields, revealing that the effects of basin-forming impacts dominate the large-scale distribution of remanent magnetic fields on the Moon. The weakest surface magnetic fields (<0.2 nT) are found within two of the largest and most recent impact basins, Orientale and Imbrium. Conversely, the largest...
We apply improved kinetic modeling of electron transport in the martian thermosphere to fit pitch angle distributions measured by the Mars Global Surveyor (MGS) Magnetometer/Electron Reflectometer (MAG/ER), together with appropriate filtering, binning, averaging and error correction techniques, to create the most reliable ER global map to date of crustal magnetic field magnitude at 185 km altitude,...
We simulate the production and orbital evolution of escaping ejecta due to cometary impacts on Io. The model includes the four Galilean satellites, Amalthea, Thebe, Jupiter's gravitational moments, Saturn and the Sun. Five scenarios are examined: an impact at the apex, the sub-jovian point, the anti-jovian point, the antapex, and at the south pole of Io. We estimate that on average a cometary impact...
We address impact cratering on Io and Europa, with the emphasis on the origin of small craters on Europa as secondary to the primary impacts of comets on Io, Europa, and Ganymede. In passing we also address the origin of secondary craters generated by Zunil, a well-studied impact crater on Mars that is a plausible analog to impact craters on Io. At nominal impact rates, and taking volcanic resurfacing...
Impact basin formation ages give insight into the early evolution of a planet. The martian basins Hellas, Isidis and Argyre provide an important time-marker for the cessation of the magnetic dynamo and the crustal thickness distribution, both established before 4 Ga ago. No martian surfaces are older than 4.15 Ga based on crater count statistics, and all are younger than the oldest lunar ones. I show...
Valley networks, concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity, have been cited as indicators that the climate of Mars differed significantly in the past from the present hyperarid cold desert conditions. Some researchers suggest that the change in climate was abrupt, while others favor a much more gradual transition. Thus, the precise timing of valley...
A model has been developed for the chemical composition of early-time condensates forming during planetary impacts at velocities sufficient for complete evaporation of the impactor (∼22 kms−1). Hydrodynamics is approximated as hemispheric expansion of a chondritic impactor described with the help of a new semi-analytic equation of state. The gas phase is a mixture of a large number of molecular and...
We estimate the impact flux and cratering rate as a function of latitude on the terrestrial planets using a model distribution of planet crossing asteroids and comets [Bottke, W.F., Morbidelli, A., Jedicke, R., Petit, J.-M., Levison, H.F., Michel, P., Metcalfe, T.S., 2002. Icarus 156, 399–433]. After determining the planetary impact probabilities as a function of the relative encounter velocity and...
This paper presents an updated stratigraphical and compositional study of the exposed maria within the Imbrium basin on the Moon. Clementine multispectral data were employed to derive TiO 2 and FeO wt% abundance estimates of potentially distinct basaltic flows. Additionally, NASA Lunar Orbiter images were used to estimate flow ages using crater count statistics. Mare Imbrium shows evidence...
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