2

5) Interplanetary dust grains have been collected by aircraft (from the upper atmosphere) and spacecraft and returned to Earth for study. Some of these grains turn out to be actual interstellar dust grains traveling through the Solar System. These grains show a porous structure and have a mean density of ~2 grnfcm3. (For reference, rocks have a density of ~3 gmfcm3 and water has a density of l gm/cm3.) Assume that all ISM grains have a radius of 1 micron, a density of 2 gnu/cm}, that 1% of the total ISM mass is in the form of grains. Also, assume the same disk dimensions as above in problem 4. :1. Compute the mass density of solid phase matter in the Galactic disk in Mg per pc3. 1). Compute the mass density of solid phase matter in the Galactic disk in gm per cm3. c. Compute the number density of grains in the Galactic disk in grains per km3. 1:]. Compute the mean separation between grains in km