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MIT Planetary Science's Comet-Jupiter Impact Simulations

July Collision of Jupiter and Comet
Will Make Waves

Big waves are in store for Jupiter this July. Planetary astronomers have known since the spring of 1993 that fragments of a comet will hit Jupiter this summer. Comet Shoemaker-Levy 9 broke into at least 21 pieces during its last close encounter with the planet in July 1992. The pieces will hit Jupiter at the end of their current two-year orbit around the planet, in July 1994. They will enter the atmosphere travelling at 60 km/sec, decelerating and vaporizing completely in seconds. The average impact energy from each 1-km-diameter comet fragment is equivalent to the simultaneous explosion of about a quarter millon moderately large (1 megaton) hydrogen bombs.

Researchers Joseph Harrington, Raymond LeBeau, Kari Backes, and Prof. Timothy Dowling, all of the Department of Earth, Atmospheric, and Planetary Sciences at MIT, have conducted computer simulations of the collisions' effect on Jupiter's weather. The simulations show waves travelling outward from the impact sites and propagating around the planet in the days following each impact. The waves are surface waves, large motions of the atmosphere that are analogous to the ripples that spread from dropping a pebble in a pond. The temperature deviation inside of a typical wave can be as much as 0.1-1 degree Celsius, which may be visible from Earth in the best telescopic views.

The speed at which these waves travel depends on their depth in the atmosphere and on stability parameters that are only poorly known. Harrington, Dowling, and Dr. Heidi Hammel, also of MIT, will observe the impact and its aftermath with the Hubble Space Telescope and the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. They hope to measure the wave speeds and thus determine the atmospheric parameters more accurately. Better-known parameters will in turn improve our understanding of planetary weather systems.

a: b:

These images are from a simulation of Jupiter's atmosphere one day (a) and two days (b) after the impact of a comet fragment. A set of surface waves propagates outward from the impact site. Height variations relative to a smooth sphere correspond to changes in pressure; the height scale is exaggerated to show the waves. Color tags material initially at the same latitude. Familiar storm features such as the Great Red Spot have not had time to develop in this simulation.

When running the movie, keep your cursor in the viewer window if you have colormap problems when viewing it. The model runs for a period of time prior to any perturbation to allow realistic atmospheric features (such as the row of vortices in the southern hemisphere) to develop. In this simulation, impact occurs on day 193.

Joseph Harrington
MIT Room 54-326
77 Massachusetts Avenue
Cambridge, MA 02139
jh@mit.edu

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