At 2:16 PM 2/19/5, Robin van Spaandonk wrote: >In reply to Horace Heffner's message of Thu, 17 Feb 2005 22:39:35 -0900: >Hi, >[snip] >>That is true. A three body interaction close to Iapidus could produce a >>lower energy collision. The third body might carry away much of the >>momentum, as viewed from Iapidus' inertial frame, or the momentum and >>energy of objects moving in opposed directions could be spent in a head-on >>collision close to Iapidus, spraying it with debris. >[snip] >Another possibility is that part of two approaching bodies is composed of >water ice, which as they collide converts to steam that expands, providing >a cushioning buffer between them, slowing their approach, and carrying >away some of the kinetic energy of the collision, such that when the rocky >bodies collide, the impact is insufficient to melt, or shatter them.
Yes, that works too. In the case of a close to Iapetus collision of two other bodies, the two initially colliding bodies would have the full gravitational potential of the 3 body interaction converted to heat. Suppose, ignoring for a minute the mass of the evaporated ice, the two approaching bodies might have mass about 1/4 of Iapetus, or about 4.7x10^20 kg. The initial iapetus would have a mass of 9.4x10^20 kg, instead of the final mass of 1.88x10^21 kg. Assume the collision happens at an altitude roughly equal to Iapetus' final radius of 730 km. The collision velocity of the two initial impactors will be conservatively: V = (2 G M/(R))^0.5 V = (2 G (4.7x10^20 kg)/(730 km))^0.5 V = 293 m/s So the energy E converted to heat is: E = 2 * .5 m*V^2 = (4.7x10^20 kg)(293 m/s)^2 = 4x10^25 J Thus the heat per gram H is: H = E/m = (4x10^25 J)/(4.7x10^20 kg) = 8.6 J/g which is not a lot of heat to dissipate, so this could simply result in increased temperature, or as you noted, be dissipated by ice. Even 4 times that number will not produce much incremental temperature. Iapetus is so small one has to wonder how eneough energy is developed to smush two bodies together to make it one spherical body. Looks like the three body theory is not even necessary, unless I have a computation error. Iapetus is not very dense, or very big. See: <http://www.star.ucl.ac.uk/~idh/solar/eng/iapetus> Regards, Horace Heffner
