Particle erosion mechanisms and mass redistribution in Saturn's rings

A variety of physical processes can erode the surfaces of planetary ring particles. According to current estimates, the most efficient of these over the bulk of Saturn's rings is hypervelocity impact by 100 micron to one centimeter radius meteoroids. The atoms, molecules, and fragments ejected from ring particles by erosion arc across the rings along elliptical orbits to produce a tenuous halo of solid ejecta and an extensive gaseous atmosphere. Continuous exchange of ejecta between different ring regions can lead to net radial transport of mass and angular momentum. The equations governing this ballistic transport process are presented and discussed. Both numerical and analytic studies of idealized ring systems illustrate that ballistic transport can cause significant mass redistribution in the rings, especially near regions of high density contrast, such as the inner edges of the A and B rings. Ejecta exchanges can also alter local particle sizes and compositions and may produce pulverized regoliths at least several centimeters deep. The meteoroid erosion rate is so high that significant global torques and mass loss are possible on times shorter than a solar system life time.     

A high-altitude barium radial injection experiment

On 16 March 1980 a rocket launched from Poker Flat, Alaska, carried a new type of high-explosive barium shaped charge to 571 km, where detonation injected a thin disk of barium vapor with high velocity nearly perpendicular to the magnetic field. The purpose of the experiment, named “King Crab,” was to advance knowledge of the instabilities, waves, and optical and magnetic effects produced. The TV images of the injection are spectacular, revealing three major regimes of expanding material which showed early instabilities in the neutral gas. The most unusual effect of the injection is a peculiar rayed barium-ion structure lying in the injection plane and centered on a 5 km “black hole” surrounding the injection point. Preliminary computer simulations show a similar rayed structure development due to an electrostatic instability.     

Electric Charging and Discharging Processes of Moving Projectiles

Every type of missle is electrically charged during free flight. The physical mechanism, leading to the electric charging and discharging effects, was investigated by measuring the electric field surrounding projectiles while leaving the muzzle region, during free flight, and on impact on targets. The electric charge on projectiles is 10-13 108C. Numerous experimental results were obtained with calibers 4-155 mm and velocities 50-120lm/ s. A physical model about the complex charging effects is derived.     

Passive remote sensing of aerosols from space now and in the future

Aerosols modify scattered solar radiation leaving the atmosphere and this fact will be exploited to determine the aerosol optical depth. The interaction processes between solar radiation and aerosol particles are outlined. A quasi-linear relationship (‘conversion curves’) between the radiance at the satellite, L_sat, and the aerosol optical depth, a_Dλ, is found from both numerical and empirical studies. Because L_sat is not only controlled by a_Dλ, but also by a series of other atmospheric parameters (perturbing quantities), the concept of ‘favourable viewing conditions’ is presented, where the effects of the perturbing quantities are minimal. The paper ends with some lines of thought on a concept for a turbidity satellite.     

How important are changes in body weight for mass perception?

It is often assumed that weight judgements depend primarily on the effort experienced in lifting an object against a 1-G force. Changes in effort and in other weight-cues certainly alter apparent heaviness; but there is a tendency towards mass-constancy when such changes are unrelated to mass. Under water or altered G, both the observer's body and other objects change their effective weight: the change in the former probably provides a cue to the latter. Mass-constancy increases with opportunity for adaptation to the change, leaving a negative aftereffect on return to normal circumstances. The discrimination of weight or mass also deteriorates with sudden changes in arm weight, just as it does with other types of maladaptation and with a reduction in sensory cues. The relative importance of arm weight and other factors has not been precisely measured, but experiments in prolonged spaceflight should help to elucidate the issue.     

The Onset of Long Term Modulation in the Heliosphere in Cycle 23

The combination of Voyager 1 (77.9 AU, 34.4° N) and Voyager 2 (61.2 AU, 24.5° S) at moderate heliolatitudes in the distant heliosphere and Ulysses with its unique latitudinal surveys in the inner heliosphere along with IMP 8 and other satellites at 1 AU constitutes a network of observatories that are ideally suited to study cosmic rays over the solar minimum of cycle 22 and the onset of solar activity and the long term cosmic ray modulation of cycle 23. Through 2000.7 there have been three well-defined step decreases in the cosmic ray intensity at 1 AU with the cumulative effect being in good agreement with the net decrease in cycle 21 at a comparable time in the solar cycle. Over this period the intensity changes at Ulysses are similar to those at 1 AU. In the distant heliosphere the initial decreases appear to be smaller than those at 1 AU. However the full effects of the interplanetary disturbances producing the most recent and largest step decrease in the inner heliosphere have not yet reached V-2. This revised version was published online in August 2006 with corrections to the Cover Date.     

Representations of solar EUV fluxes for aeronomical applications

The development of significantly improved representations of solar EUV inputs for computer-aided investigations of the terrestrial thermosphere and ionosphere has become attractive particularly for the present solar cycle which has been covered by reasonably complete and continuous EUV observations from the AE-E Satellite. These representations try to satisfy some rather incongruous $\text{requirements of spectral detail}$, regarding (a) the strong wavelength-dependence in the $\text{terrestrial}$ atmospheric cross sections of the various types of EUV photon interactions, (b) the great differences in the relative amplitudes of the various types of variations in the full-disk fluxes of $\text{solar}$ emissions at different wavelengths, and (c) the persisting desire to use only a $\text{small number of daily indices}$ as actual input variables for computational models supposed to cover the entire EUV wavelength range (remembering the great success of empirical thermospheric models using only two indices). These general physical and specific aeronomical demands indeed outline a very difficult task. The present study, based mainly on AE-E satellite observations during 1976–1979, represents an exploratory step, only clarifying some important developmental aspects, without recommending any specific formulations for immediately practicable adoption in aeronomical modelling at this time.     

Direct observation of charge state abundances of energetic He,C, O,and Fe emitted in solar flares

The ionic charge states of helium, carbon, oxygen, and iron have been determined for three solar particle enhancements by an electrostatic deflection analyzer, which is combined with a thin window proportional counter dE/dX vs. E system. The observations are obtained during the periods September 23 to 29, 1978, June 6 to 8, 1979, and September 15 to 26, 1979, with an instrument onboard the ISEE-3 spacecraft. The mean ionic charge states for He, C, and oxygen exhibit a high degree of ionization with values of Q = 2, 6, and 7.2, respectively. The charge state of iron is near 13 charge units. Variations from flare to flare and within the September 23, 1978 flare are small. The most surprising feature of the charge state measurement is the observation of a small (～10%) but finite contribution of singly ionized helium.