lew@ihuxr.UUCP (Lew Mammel, Jr.) (05/02/84)
After a lot of looking around, I found a formula for the particle flux distribution of micrometeorites in earth orbit. It is in SPACE GEOLOGY by Elbert A. King. A formula is given for the cumulative particle flux, in particles/m2/day, as a function of minimum mass: F = 10^-9.4 * (m^.306 + .00685)^-4.38 King refers to this as the mass-flux distribution in the text, but the figure which actually contains the formula clearly identifies it as a particle flux. This is the form in which the data is taken by detectors which count anything over a certain "size" (by some definition), so I think particle flux is right. To derive the mass flux, I differentiated the formula and integrated m * dF/dm. I used Simpson's rule on a log scale. Details on request. I broke the integral into ranges so I could see which particles contribute the major portion of the mass. Here is the result: log10(mass) mass-flux 0 1.76385e-09 -1 3.65056e-09 -2 7.14909e-09 -3 1.25962e-08 -4 1.83131e-08 -5 1.93162e-08 -6 1.27093e-08 -7 4.63724e-09 -8 9.17624e-10 -9 1.07672e-10 -10 8.71082e-12 The entry labeled "0" includes particles of mass <1 gram but >.1 gram, and so on. The flux is in grams/m2/day. The contribution of particles of mass less than 10^-7 grams is small. The total flux is 8.1e-08 grams/m2/day. The total particle flux is about 1/m2/day, so the effective mass of an average particle is 8e-8, near the cutoff of mass contribution, as would be expected. Since the earth has a cross section of about 1e14 m2, the mass accumlation per day should be 8e6 grams, or about 3000 metric tons per year. This is way down from the several millions per year estimated by Pettersson in his infamous SciAm article that the creationists cite. They also cite some early satellite data. I think these data points are shown in the figure from which I obtained the above formula. It shows several points labeled "Explorer VIII" which are way above the curve by four orders of magnitude. The caption states that "No acoustic detector data have been used in the construction of the curve" but I don't know if this refers to the Explorer VIII data or not. The data on the curve is labeled "Penetration sensors", and one point is from "Gemini windows". For those interested, the following article is cited: Kerridge, J. F. (1970) Micrometeorite environment at the earth's orbit: Nature, vol. 228, p. 616-619. I haven't gotten a hold of this yet, but I'm working on it. Lew Mammel, Jr. ihnp4!ihuxr!lew