Olbers's Planetary Explosion Hypothesis: Genesis and Early Nineteenth-Century Interpretations

Abstract

(ProQuest: ... denotes formulae omitted.)1. IntroductionThe origin of the asteroids has been a subject of controversy ever since they were discovered in the early nineteenth century. The first suggestion as to how they might have originated - as the result of a catastrophic collision or explosion - was widely regarded as a tenable hypothesis by many in the scientific community. Even though he did not develop the idea on his own, Wilhelm Olbers accepted the concept and gave it life. This paper looks at how the idea developed in its early stages, and the ways it was both accepted and rejected by a range of different thinkers in the first half of the nineteenth century.2. GenesisThe first asteroid, Ceres, was discovered by Giuseppe Piazzi on 1 January 1 80 1 . On 28 March 1802 Wilhelm Olbers discovered the second, Pallas.' One of the first persons he notified was his close friend Ferdinand von Ende, who worked as a senior appellate official in the duchy of Brunswick Luneberg. Ende was an amateur astronomer, and was one of the twenty-four observers selected in 1800 to be a member of the 'Celestial Police', that loosely-knit organization formed by Baron Franz von Zach to search for the 'missing planet' between Mars and Jupiter.Less than ten days after the discovery of Pallas, Ende wrote to Olbers:Since your Pallas or Olbers, as de la Lande will certainly call it, will finish its revolution faster than Ceres it was possible for someone searching for Ceres to find it, and mistake it for Ceres. What conflicts originated between the new and old elements! What confusion did not originate from this, what conclusions of a totally perturbed orbit were not drawn - to cut a long story short: only experience or the accidental discovery of the true Ceres made it possible to escape out of this labyrinth. Thus, your discovery is extremely important at this point, so that, as both planets will probably hide in the rays of the Sun, they are not mistaken for each other when they reappear. - Furthermore now we can easily explain some of Mars's irregularities, whose orbit they must considerably perturb etc. And it is also remarkable that there where we expected one planet, we find two very small ones and if we can trust the observations made hitherto, they are still developing [planets]. - One almost wishes to say: once those two small planets had formed a bigger one; at least a comet shock is not more unlikely than throwing a comet against the Sun and the planets splinter off. Maybe, if de la Place's hypothesis of a contraction of the Sun's atmosphere is correct, a comet could be seized at exactly that moment which consequently would, as your Pallas does, complete its revolution on a very inclined orbit. - But these are only dreams that belong in the bedroom and not good society.2As this insightful letter makes clear, it was Ende who was the first to suggest in correspondence that Ceres and Pallas had once formed a larger planet later destroyed by a cometary collision. Olbers took the idea and propounded his own hypothesis, but he never credited Ende for planting in his mind the idea of a catastrophic origin for the small planets.3. Olbers Seeks the Opinion of Gauss and HerschelJust two weeks after reading Ende's letter, Olbers proposed very nearly the same concept to Carl Gauss:There is something unusual about the position of Pallas's orbit. In particular, the very close approach of the paths of Ceres and Pallas at some point gives rise to much thought. How? If Ceres and Pallas were fragments of a former larger planet that had been destroyed by colliding with a comet? It's still too early to indulge in such dreams; but a collision with a comet isn't totally impossible. A number of years ago I found the following solution to what was initially a seemingly difficult problem using probability theory. If I knew nothing more about a comet other than that it approaches the Sun closer than a planet, and the mean distance of the planet from the Sun is R, then the probability that it approaches the Sun before or after its passage through perihelion is as a. …