25. Orbits of photographic meteors

Abstract

New photographic observations of meteors in the brightness range −5 > Mp > −18 (?) and with a median value of M = −8·5 have yielded orbits with a precision of better than 1° in the angular elements and of about 0·05 in e and 1/a. A comparison of 100 of these fireball orbits with Super-Schmidt orbits shows: (1)A class of orbits, comprising about 25% of the faint meteors, of long period, is almost completely absent among the fireballs.(2)Small perihelion distances (q < 0·2 AU) are not found. A maximum at q ~ 0·7 AU, which also appears in the Super-Schmidt orbits of short period, corresponds to the perihelion distances of all but two of the Apollo objects.(3)The distribution of aphelia shows a marked decrease at Jupiter when compared to a similar distribution of small, faint meteor orbits. With the existing material, we cannot determine whether this represents an important evolutionary distinction between meteoroids of different mass or is simply the result of an inappropriate choice of the division between ‘large’ and ‘small’ orbits in the faint meteor data.Provisional values of the bulk density of 28 of the fireballs as determined from the photometric mass and the observed mass-area ratio indicate that these meteoroids do not differ significantly from those observed with the Super-Schmidt cameras. Evidence of gross fragmentation of these large objects at high elevation and evidence of small or negligible terminal masses suggest that the material is friable. There is no certain evidence that any appreciable fraction of fireballs is produced by high-density, cohesive material.If the above analysis is correct, we should expect an occasional (1 year−1 106 km−2?) meteorite fall of discoverable size originating from a low-density meteoroid.