The interplanetary and near-Jupiter meteoroid environments

Abstract

The meteoroid penetration detectors on the Pioneer 10 splicecraft recorded 67 meteoroid penetrations through the 25-•tm stainless steel test material while the spacecraft was between 1.0 and 5.1 AU. Ten of these penetrations occurred during the encounter with Jupiter.• The cumulative spatial density of meteorolds with masses greater than 2 X 10 -9 g his been calculated from these data for interplanetary space and for the near-Jupiter space. The spatial density is found to be essentially constant in interplanetary space between I and 5 AU, approximately l0 -9 m -a, and 1-2 orders of magnitude greater near Jupiter. There was no increase in the spatial density of meteorolds in the asteroid belt and hence no evidence that there is a significant asteroidal component of 2 X l0 -9 g meteorolds. It is uncertain whether the meteoroids detected near Jupiter were in orbit about Jupiter or were gravitationally focused toward the planet from solar orbits. Prior to thePioneer 10 mission, no measurements had been made of the concentration of meteoroids in interplanetary space beyond 1.6 A U or near Jupiter. It was generally believed that the meteoroid population had two components, a cometary component and an asteroidal component. Southworth [1967] estimated the distribution of cometary meteoroids:in the solar system from the orbits of approximately 13,000 radar meteors. This result was largely dependent on extrapolation because only meteoroids that cross 1 AU can be observed as radar meteors. He concluded that the spatial density decreased monotonically outward from the sun, varying as R-•'5-R -•"ø between the orbits of earth and Jupiter. More recently, Southworth and Sekanina [1973] estimated the distribution of meteoroids in the solar system from the orbits of approximately 20,000 radar meteors observed in 1969.Southworth and Sekanina reached the new and surprising conclusion from these data that the spatial density was at a minimum at 0.7 AU and at a maximum in the asteroid belt, between 2 and 3 A U. They were uncertain about the fraction of the sample that was cometary in origin and the fraction that was asteroidal. The mass distribution of small asteroidal meteoroids was estimated by Kessler [ 1970] based on the mass distribution of the large observed asteroids and the intensity of the counterglow.Kessler concluded that the spatial density of asteroidal meteoroids is a maximum at 2.5 AU having a value of 3 x l0 -9 m -8 for 2 x 10 -• g meteoroids. This is a factor of 4.4 greater than the spatial density that he calculated for 2 X 10 -9g meteoroids at 1 AU. Calculations by Whipple [1971] placed the likely upper limit on the spatial density of asteroidal meteoroids at the order of 5-10 times that near the earth's orbit. The concentration of meteoroids in interplanetary spacebetween 1.0 and 5.1 AU and near Jupiter has now been measured with the pressurized cell penetratioh detectors on Pioneer 10. These detectors have a sensitivity of approximately 2 X 10 -* g. Meteoro M detectors of the pressurized cell type have been used p...

New information recovered from the Pioneer 11 meteoroid experiment data

“…In this section, we reproduce a part of the instrument description from (Humes et al 1974;Humes 1980) sufficient to construct our model. For more details see the papers and references therein.…”

2.1.1 In-Situ Records of Interplanetary Dust Particles - Methods and Results

“…Some of the techniques listed are not used any more. Some other detectors, however, which have first been used more than 10 years ago are still in use today and are gaining important new results: the pressurized cells on the Pioneer 10/11 mission (Humes et al, 1974). The use of Kassel (1973) and by Rauser (1974).…”

Evidence for Ice Meteoroids Beyond 2 AU

“…The observation of a constant, or increasing, spatial density leads to some interesting conclusions regarding the processes that control the population of P-10 particles between 2 and 5 AU from the sun. We shall explore some of these processes below and shall obtain the result that the P-10 meteoroid data can be best understood if many of the penetrat ing meteoroids are made of ice.At 1 AU, Whipple (1967) derived a lifetime against collisional destruction of particles in the mass range 10~^g to 10~8g of about 4 x 10 5 yr. At heliocentric distances from the sun between 2 and 5 AU, the collision lifetimes should be longer than they are at 1 AU because mutual meteoroid impact velocities will be less and because the spatial density of the ^10~^ g particles is derived by Humes et al (1974) to be somewhat less than at 1 AU. Thus, a collision lifetime of ^10 6 yr is derived for the particles that penetrate the P-10 sensors in the heliocentric range 2 < R < 5 AU.…”

“…At 1 AU, Whipple (1967) derived a lifetime against collisional destruction of particles in the mass range 10~^g to 10~8g of about 4 x 10 5 yr. At heliocentric distances from the sun between 2 and 5 AU, the collision lifetimes should be longer than they are at 1 AU because mutual meteoroid impact velocities will be less and because the spatial density of the ^10~^ g particles is derived by Humes et al (1974) to be somewhat less than at 1 AU. Thus, a collision lifetime of ^10 6 yr is derived for the particles that penetrate the P-10 sensors in the heliocentric range 2 < R < 5 AU.…”

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Humes et al (1974) deduced from the P-10 (Pioneer 10) meteoroid penetration data that the spatial density of 2 x 10~9 g and larger meteoroids was nearly constant (or possibly increasing) with increasing heliocentric distances between 2 and 5 AU from the sun. With an assumed mass density of 0.5 g/cm , P-10 particles (particles whose mass is > 2 x 10 g) would have a particle radius in excess of about 10 ym.

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