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[en] A new theory for galactic arm formation shows the arms to be continually eminating from the galactic nucleus due to a continual influx of cosmic dust. In the neighborhood of the nucleus the problem is treated as a fluid flow and a simple solution is given using conservation of momentum. When rotational dynamics are included the spinning arm system is the result. This solution resolves the problem of the missing mass, accounts for warped disk galaxies and gives a probable source for the gravity waves measured by Weber which eminate from our galactic center. Reversal of arm direction is demonstrated and examples of such reversals are cited. An approximate theoretical estimate of the age of our Sun is found to be in good agreement with radio isotope dating. A general result shows why twin star systems are in such great abundance in a galaxy. It gives a model of galactic evolution which begins with only a single massive nucleus with the collapsing gas clouds forming the arms. (orig.)

[en] Hypervelocity (69 km/s) impact of cometary material with surfaces of the GIOTTO spacecraft will induce a number of spurious and possibly harmful phenomena. The most serious of these is likely to be spacecraft charging that results from impact-produced plasma distributions surrounding GIOTTO. The ESA Plasma Environment Working Group, whose studies are the basis for this report, finds that charging may become significant within approx. 10₅ km of the nucleus where potentials of approx. = +20 V are to be expected. In addition to spacecraft charging, impact produced plasma may interfere with in situ plasma measurements, particularly those of ion plasma analyzers and mass spectrometers

[en] The Dust Coordinate Sensor (DCS) is a dual detector instrument located on the beamline of the 3 MV hypervelocity dust accelerator at the University of Colorado Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT). This instrument non-destructively measures the three-dimensional trajectories of charged, hypervelocity (3–8 km/s), micron-sized dust particles in flight by utilizing the image charge induced on grids of wire electrodes. Where previous peak detection was typically limited to dust particles carrying charges $>\sim 100$ fC, new signal processing techniques developed for DCS allow for effective trajectory measurements on particles carrying charges as small as 6 fC. The new signal processing also effectively eliminates false signal detections completely. The position measurements are matched by timestamp to the charge and velocity for each launched dust particle. Verification of the system was performed with independent impact location measurements on a target placed in the beamline. These measurements agree to within 1 mm² of the predicted locations using DCS trajectories. This study demonstrates the capability of the instrument including new processing methods. Precise trajectory measurement along the beamline enables new options for instrument calibration, scientific experiments, and improvement of the accelerator performance.

[en] Analysis of four small-scale photographs of Comet West taken on 5--8 March 1976 offers evidence of five discrete bursts of dust from the comet's nucleus between 19 and 28 February, i.e., from six days before perihelion to three days after it. The images of the comet on the photographs were computer-enhanced to increase the contrast of the fine structure. The timing of two of the bursts suggests very strongly that they accompanied the two breakup events that gave birth to the companion nuclei D and B. The primary breakup, on 19 February, also coincides with a 2-magnitude surge in the comet's brightness. Some of the other dust bursts might be correlated with less conspicous flare-ups observed in both the visual brightness and the thermal emission of the comet. A distinct intensity discontinuity makes up the trailing boundary of the main body of the dust tail. When the observed position of the discontinuity is corrected for an effect of particle-expulsion velocity, it is found to correspond to dust expelled from the comet exactly at perihelion. It is suggested that because of its timing, the intensity discontinuity could be a product of particle evaporation sharply peaked at perihelion

[en] The isotopic composition of Mg was measured in different phases of a Ca-Al rich inclusion in the Allende meteorite. Large excesses of ²⁶Mg of up to 10% were found. These excesses correlate strictly with the ²⁷Al/²⁴Mg for four coexisting phases with distinctive chemical compositions. Models of in situ decay of ²⁶Al within the solar system and of mixing of interstellar dust grains containing fossil ²⁶Al with normal solar system material are presented. The observed correlation provides definitive evidence for the presence of ²⁶Al in the early solar system. This requires either injection of freshly synthesized nucleosynthetic material into the solar system immediately before condensation and planet formation, or local production within the solar system by intense activity of the early Sun. Planets promptly produced from material with the inferred ²⁶Al/²⁷Al would melt within approx.3 x 10⁵ yr

[en] The present investigation has the objective to provide a summary of the existing evidence on the disappearance of comets and to draw conclusions regarding the physical processes involved in the disappearance. Information concerning the classification of evidence and the causes of apparent disappearance of comets is presented in a table. Attention is given to the dissipating comets, the headless sungrazing comet 1887 I, and the physical behavior of the dissipating comets and the related phenomena. It is found that all comets confined to the planetary region of the solar system decay on astronomically short time scales. However, only some of them appear to perish catastrophically. Some of the observed phenomena could be successfully interpreted. But little insight has been obtained into the character of the processes which the dissipating comets experience. 98 references

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