Physicist Rob Sheldon writes to respond to the claim that Jupiter does not shield Earth:
Kevin Grazier, PhD, at the NASA Jet Propulsion Laboratory in Pasadena, describes the study in which he simulated the evolution of tens of thousands of particles in the gaps between the jovian planets for up to 100 million years. Based on the results, Dr. Grazier concludes that the widely reported shield role attributed to Jupiter is incorrect. More.
While I have the greatest respect for people who run tens of Newtonian mechanics simulations of 10,000 bodies for 100 million years, the models only give results that were programmed into the simulation. If, for example, tomorrow someone were to find that the magnetized solar wind could impart a tangential drag to charged planetesimals, then all of those simulations would be worthless.
Accordingly, we should be very careful to qualify the results of a simulation which a brief exploration of a small corner of phase space. It is as if I should declare it impossible to drive to work because my keys were not on the hook by the door. Contrast this conclusion with the observation that my son had wrapped the car around telephone pole on the street. The first is an inference, the second a certainty.
We (and I speak for all scientists), have gotten so lazy that we confer upon our models the same certainty as observation. We call our computer runs “data”, even when our computer models are doing forward-modelling, Monte-Carlo integration of infinite-dimensional subspaces.
I am not simply arguing for modesty and good manners, but against the distortion of the education of a generation of young scientists who take these pronouncements as equally valid as astronomical statistics on binary stars. I taught high school astronomy from a leading college Astronomy textbook and was astonished how as we went from planetary to stellar to cosmology, the degree of speculation and wrong-headed models grew exponentially. I have nothing against speculation–I have been accused of practicing it too enthusiastically–but we should be very careful to label it as such.
See also: Paper: Jupiter doesn’t shield Earth, comets kickstarted life. Researcher: Jupiter teams with Saturn to kick a significant fraction of the particles into the inner Solar System, beneficial for the development of life.
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