DPS Meeting, Madison, October 1998
Session 48P. Venus
Contributed Poster Session, Thursday, October 15, 1998, 5:00-6:30pm, Hall of Ideas

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[48P.05] Numerical simulations of large impacts in thick atmospheres

K. Zahnle (NASA Ames), D. Korycansky (UCSC)

We present numerical simulations of asteroids and comets striking the atmosphere of Venus. We consider a wide variety of objects, both comets and asteroids, ranging in size from 1 to 4 km diameter, striking at impact angles ranging from the vertical to 60 degrees, at velocities from 20 to 90 km/s, in a variety of shapes (including some lumpy spheroidal things), and in 2 and 3 dimensions. Our purpose is to determine the permeability of atmospheres to impacting bodies; i.e., to define the sheltering sky. We find that details of the destruction, deceleration, and dispersal of impactors depend sensitively on initial conditions, but that the ensemble of models produces a relatively robust distribution of atmospheric permeabilities that is asymptotically insensitive to numerical resolution.

The approximately 940 impact craters on Venus provide an excellent dataset against which to test our model. We compute model crater diameters using Schmidt-Housen gravity-scaling, using mass and momentum fluxes passing a fiducial altitude (e.g., the surface) computed from the numerical results. The absolute cratering efficiency (i.e., the crater diameter) is obtained as a function atmospheric permeability. The more permeable the atmosphere, the larger the crater must be for a given impactor. Thus by determining the atmospheric permeability and using the crater distribution observed on Venus, we obtain an independent calibration of Schmidt-Housen scaling at the scale of 20 km craters.

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