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Harris, A. W.

Publications and source records attributed to Harris, A. W..

65 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Satellite formation. II

A satellite formation model is extended to include evolution of planetary ring material and elliptic orbital motion. In this model the formation of the moon begins at a later time in the growth of the earth, and a significant fraction of the lunar material is processed through a circumterrestrial debris cloud where volatiles might have been lost. Thus, the chemical differences between the earth and moon are more plausibly accounted for. Satellites of the outer planets probably formed in large numbers throughout the growth of those planets. Because of rapid inward evolution of the orbits of small satellites, the present satellite systems represent only satellites formed in the last few percent of the growths of their primaries. The rings of Saturn and Uranus are most plausibly explained as the debris of satellites disrupted within the Roche limit. Because such a ring would collapse onto the planet in the course of any significant further accretion by the planet, the rings must have formed very near or even after the conclusion of accretion.

Harris, A. W.↗
NASA NTRS1978

Dynamics of planetesimal formation and planetary accretion

The paper reviews the dynamical processes by which condensed matter in the solar nebula accumulates into planets. The basic processes are: (1) gravitational instability; (2) conversion of the radial gradient of orbital motion into random motion between planetesimals; and (3) collisions, which damp the random motion and result in aggregation and/or fragmentation of planetesimals. Each of these processes is defined analytically, and models, based on these results, of planetary growth, axial rotation rates, and formation of satellite systems are formulated.

Harris, A. W.↗
NASA NTRS1977

ALSEP-quasar differential VLBI

A program of ALSEP-quasar very-long-baseline interferometry (VLBI) is being carried out. These observations employ primarily a 'four-antenna' technique whereby simultaneous observations with two antennas at each end of an intercontinental baseline are used to derive the differential interferometric phase between a compact extragalactic radio source (usually a quasar) and a number of ALSEP transmitters on the lunar surface. A continuous ALSEP-quasar differential phase history over a period of a few hours will lead to milliarcsecond angular accuracy in measuring the lunar position against the quasar reference frame if suitable calibration measurements are obtained. Development of this application of the four-antenna technique has been underway for more than a year and is producing high-quality data utilizing Deep Space Network stations. These high-accuracy observations are of value to tie the lunar ephemeris to a nearly inertial extragalactic reference frame, to test gravitational theories, and to measure the earth-moon tidal friction interaction.

Slade, M. A.↗
NASA NTRS1977

An analytical theory of planetary rotation rates

An approximate analytical theory is derived for the rate of rotation acquired by a planet as it grows from the solar nebula. This theory was motivated by a numerical study by Giuli, and yields fair agreement with his results. The periods of planetary rotation obtained are proportional to planetesimal encounter velocity, and appear to suggest lower values of this velocity than are commonly assumed to have existed during planetary formation.

Harris, A. W.↗
NASA NTRS1976

ALSEP: Quasar differential VLBI

A program of Apollo Lunar Surface Experiments Package (ALSEP)-Quasar Very Long Baseline Interferometry (VLBI) is being reported. These observations primarily employ a 4 antenna technique, whereby simultaneous observations with two antennas at each end of an intercontinental baseline are used to derive the differential interferometric phase between a compact extragalactic radio source (usually a quasar) and a number of ALSEP transmitters on the lunar surface. A continous ALSEP-quasar differential phase history over a few hour period leads to extremely high angular accuracy in measuring the lunar position against the quasar reference frame. This application of the 4 antenna technique has been underway for more than a year and is now producing high quality data utilizing Deep Space Network (DSN) stations in Australia, Spain, and Goldstone, California, as well as the Spaceflight Tracking and Data Network (STDN) Apollo station at Goldstone.

Slade, M. A.↗
NASA NTRS1975

Dynamics of lunar origin and orbital evolution

The considerable differences in bulk composition of the moon and the earth have led most investigators to favor the capture hypothesis of lunar origin. However, upon closer examination all forms of the hypothesis still seem much less plausible dynamically than formation by accretion, i.e., acquisition of the moon in many small pieces rather than as predominantly one body. Models of accretion do suggest that the proto-lunar matter had a significantly different history from the proto-earth matter. A better understanding of collisions is needed to infer the compositional consequences of this history. Recent work on the acceleration of the moon's orbit exacerbates the time scale problem of orbital evolution. However, it now is much clearer that the locus of tidal dissipation is in the oceans and hence that the solution to the time scale problem lies in differing oceanic configurations in the past.

Kaula, W. M.↗
NASA NTRS1975

A co-accretional model of satellite formation

A model of the accumulation process of a satellite about an accreting planet is proposed in order to explain the difference in relative size between the moon and the outer planets' satellites. The parameter that most strongly affects the final mass ratio of the pair in this model is the time at which the secondary embryo is introduced. Thus the difference between terrestrial and outer planet satellite systems is easily understood in terms of the differences in Q (the specific dissipation function of the particles in the circumplanetary cloud) between these planets. The high Q of the outer planets does not allow a satellite embryo to survive a significant portion of the accretion process; therefore only small bodies formed very late in the accumulation of the planet remain as satellites.

Harris, A. W.↗
NASA NTRS1975

Collisional breakup of particles in a planetary ring

Jeffreys (1947) estimated the size of fragments resulting from breakup of a satellite inside the Roche limit, obtaining a result of about 100 km. This result does not allow for the further breakup of the fragments due to collisions among themselves, which should reduce the maximum size to less than about 3 km for rock, or less than about 1 km for ice. This result affects not only Jeffreys' speculations as to the origin of Saturn's rings, but also recent speculations on the origin of the moon by capture and the possible tidal destruction of satellites of Mercury or Venus.

Harris, A. W.↗
NASA NTRS1973

Dynamically plausible hypotheses of lunar origin

The implausibility of the capture hypothesis of lunar origin is pointed out. The reason for this implausibility is the extreme weakness of the only known energy sink for pure capture, tidal friction. A mechanism proposed by Alfven and Arrhenius (1972) is the locking of the moon in synchronization with a longitudinal variation in the earth's gravitational field. It is shown that collision with preexisting satellite matter is the most effective means of capturing a moon.

Kaula, W. M.↗