David Parry Rubincam

NASA, Washington, West Virginia, United States

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Publications (31)103.27 Total impact

  • David Parry Rubincam
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    ABSTRACT: The thermal expansion and contraction of particles orbiting a planet can cause secular orbit evolution. This effect, called here the thermal expansion effect, depends on particles entering and exiting the shadow of the body they orbit. A particle cools off in the shadow and heats up again in the sunshine, suffering thermal contraction and expansion. The changing cross-section that the particle presents to solar radiation pressure, plus a time lag due to thermal inertia, lead to a net along-track force. The effect causes outward drift for rocky particles in circular orbits. For particles in the size range ∼0.002–0.02 m orbiting the inner planets, particle orbits can outwardly evolve at the rate of ∼0.1RPlan per million years for Mars to ∼1RPlan per million years for Mercury for distances ∼2RPlan from the body, where RPlan is the planet’s radius. Poynting–Robertson dominates thermal expansion beyond a few RPlan for the inner planets. Hence there are distances from a planet where the effects balance, depending on particle size. Orbits evolving outward from the thermal expansion effect would stop there, as well as those inwardly evolving from Poynting–Robertson. Thus particles would accumulate in these places, assuming the absence of other forces. Mars appears to be the best candidate for the operation of the thermal expansion effect. Particles in the size range considered here and orbiting in the Phobos–Deimos region would tend to be collected by the moons, sweeping the particles up and perhaps helping keep the region free of dust. The thermal expansion effect is overwhelmed by Poynting–Robertson for rocky particles orbiting Jupiter and Saturn and thus is unimportant; these planets are not considered here. For particles orbiting small asteroids, the thermal expansion effect is much larger than the Poynting–Robertson effect, but both are overwhelmed by ordinary solar radiation pressure, which increases orbital eccentricities rapidly. Meteoroids in eccentric orbits about the Sun also suffer the thermal expansion effect, but with only ∼0.0003e2 AU change in semimajor axis over a million years for a 2 m meteoroid orbiting between Mercury and Earth.
    Icarus 01/2014; 239:96–104. · 3.16 Impact Factor
  • David Parry Rubincam
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    ABSTRACT: The Poynting–Robertson effect from sunlight impinging directly on a particle which orbits a Solar System body (planet, asteroid, comet) is considered from the Sun's rest frame. There appear to be no significant first-order terms in Vb/c for circular orbits, where Vb is the body's speed in its orbit about the Sun and c is the speed of light, when the particle's orbital semimajor axis is much smaller than the body's orbital semimajor axis about the Sun as is mainly the case in the Solar System.
    Icarus 11/2013; 226(2):1618-1623. · 3.16 Impact Factor
  • David Parry Rubincam, Stephen J. Paddack
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    ABSTRACT: YORP torques, where “YORP” stands for “Yarokovsky–O’Keefe–Radzievskii–Paddack,” arise mainly from sunlight reflected off a Solar System object and the infrared radiation emitted by it. We show here, through the most elementary demonstration that we can devise, that secular torques from impinging solar photons are generally negligible and thus cause little secular evolution of an asteroid’s obliquity or spin rate.
    Icarus 01/2010; · 3.16 Impact Factor
  • Stephen J. Paddack, D. P. Rubincam
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    ABSTRACT: Solar radiation pressure acting on small celestial bodies in heliocentric orbit can alter rotation and cause significant orbital changes via the YORP effect. YORP has a long history. The concept of light pressure causing motion of matter in space was suggested by Kepler in the seventeenth century. After a hiatus of about 200 years a variety of different of persons have done theoretical, laboratory and observational work on the effects of radiation pressure on small celestial bodies, among them the YORP quartet of Yarkovsky, O'Keefe, Radzievskii, and Paddack. Yarkovsky suggested an irradiation and re-radiation process to cause orbital changes. Radzievskii proposed that variations in albedo across an orbiting body could cause it to spin to its bursting point. Paddack, after discussions with O'Keefe, suggested and did laboratory work to show that shape was much more important than albedo in altering the spin of small celestial objects. Rubincam and later authors such as Vokrouhlicky, Bottke, Nesvorny, Morbidelli, Scheeres, and Margot, applied YORP to the spin of small asteroids and showed it to be significant. Thanks to the work of Lowry et al., Taylor et al., and Kaasalainen et al. it now appears that YORP has now been observed to change asteroid rotation rates; in fact, the asteroid 2000 PH5 has recently been renamed YORP by the IAU. Cuk and Burns have applied YORP to the orbital evolution of binary asteroids, which they call BYORP. Lately it has been shown that if 99942 Apophis has a north-south asymmetry in its shape that it could affect whether this object poses a hazard the Earth. We expect future missions to small asteroids will routinely measure YORP and other physical properties as well as gravity, composition, and topography.
    10/2007;
  • David P Rubincam, Stephen J Paddack
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    ABSTRACT: Rotational force produced by sunlight may help explain the movement of small asteroids, unusual asteroid orbits, and asteroid pairs.
    Science 05/2007; 316(5822):211-2. · 31.20 Impact Factor
  • David Parry Rubincam
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    ABSTRACT: Photon thrust from shape alone can produce quasi-secular changes in an asteroid's orbital elements. An asteroid in an elliptical orbit with a north–south shape asymmetry can steadily alter its elements over timescales longer than one orbital trip about the Sun. This thrust, called here orbital YORP (YORP = Yarkovsky–O'Keefe–Radzievskii–Paddack), operates even in the absence of thermal inertia, which the Yarkovsky effects require. However, unlike the Yarkovsky effects, which produce secular orbital changes over millions or billions of years, the change in an asteroid's orbital elements from orbital YORP operates only over the precession timescale of the orbit or of the asteroid's spin axis; this is generally only thousands or tens of thousands of years. Thus while the orbital YORP timescale is too short for an asteroid to secularly journey very far, it is long enough to warrant investigation with respect to 99942 Apophis, which might conceivably impact the Earth in 2036. A near-maximal orbital YORP effect is found by assuming Apophis is without thermal inertia and is shaped like a hemisphere, with its spin axis lying in the orbital plane. With these assumptions orbital YORP can change its along-track position by up to ±245 km, which is comparable to Yarkovsky effects. Though Apophis' shape, thermal properties, and spin axis orientation are currently unknown, the practical upper and lower limits are liable to be much less than the ±245 km extremes. Even so, the uncertainty in position is still likely to be much larger than the ∼0.5 km “keyhole” Apophis must pass through during its close approach in 2029 in order to strike the Earth in 2036.
    Icarus 01/2007; 192(2):460-468. · 3.16 Impact Factor
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    ABSTRACT: The Yarkovsky and YORP (Yarkovsky-O'Keefe-Radzievskii-Paddack) effects are thermal radiation forces and torques that cause small objects to undergo semima-jor axis drift and spin vector modifications, respectively, as a function of their spin, orbit, and material properties. These mechanisms help to (a) deliver asteroids (and meteoroids) with diameter D < 40 km from their source locations in the main belt to chaotic resonance zones capable of transporting this material to Earth-crossing or-bits; (b) disperse asteroid families, with drifting bodies jumping or becoming trapped in mean-motion and secular resonances within the main belt; (c) modify the rota-tion rates and obliquities of D < 40 km asteroids; and (d) allow asteroids to enter into spin-orbit resonances, which affect the evolution of their spin vectors and feed-back into the Yarkovsky-driven semimajor axis evolution. Accordingly, we suggest that nongravitational forces should now be considered as important as collisions and gravitational perturbations to our overall understanding of asteroid evolution.
    Annu. Rev. Earth Planet. Sci. 01/2006; 34:157-91.
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    D. P. Rubincam
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    ABSTRACT: Saturn's icy ring particles, with their low thermal conductivity, are almost ideal for the operation of the Yarkovsky effects. The dimensions of Saturn's A and B rings may be determined by a near balancing of the seasonal Yarkovsky effect with the Yarkovsky-Schach effect. The two effects, which are photon thrust due to temperature gradients, may confine the A and B rings to within their observed dimensions. The C ring may be sparsely populated with icy particles because Yarkovsky drag has pulled them into Saturn, leaving the more slowly orbitally decaying rocky particles. Icy ring particles ejected from the B ring and passing through the C ring, as well as some of the slower rocky particles, should fall on Saturn's equator, where they may create a luminous "Ring of Fire" around Saturn's equator. This predicted Ring of Fire may be visible to Cassini's camera. Curiously, the speed of outwards Yarkovsky orbital evolution appears to peak near the Cassini Division. The connection between the two is not clear. D. Nesvorny has speculated that the resonance at the outer edge of the B ring may impede particles from evolving via Yarkovsky across the Division. If supply from the B ring is largely cut off, then Yarkovsky may push icy particles outward, away from the inner edge of the A ring, leaving only the rocky ones in the Division. The above scenarios depend delicately on the properties of the icy particles.
    Icarus 10/2004; 36:1079. · 3.16 Impact Factor
  • David Parry Rubincam
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    ABSTRACT: Polar wander may occur on Triton and Pluto because of volatile migration. Triton, with its low obliquity, can theoretically sublimate volatiles (mostly nitrogen) at the rate of ∼1013 kg year−1 from the equatorial regions and deposit them at the poles. Assuming Triton to be rigid on the sublimation timescale, after ∼105 years the polar caps would become large enough to cancel the rotational flattening, with a total mass equivalent to a global layer ∼120–250 m in depth. At this point the pole wanders about the tidal bulge axis, which is the line joining Triton and Neptune. Rotation about the bulge axis might be expected to disturb the leading side/trailing side cratering statistics. Because no such disturbance is observed, it may be that Triton’s surface volatile inventory is too low to permit wander. On the other hand, its mantle viscosity might be low, so that any uncompensated cap load might be expected to wander toward the tidal bulge axis. In this case, the axis of wander passes through the equator from the leading side to the trailing side; rotation about this wander axis would not disturb the cratering statistics. Low-viscosity polar wander may explain the bright southern hemisphere: this is the pole which is wandering toward the sub-Neptune point. In any case the “permanent” polar caps may be geologically very young. Polar wander may possibly take place on Pluto, due to its obliquity oscillations and perihelion-pole geometry. However, Pluto is probably not experiencing any wander at present. The Sun has been shining strongly on the poles over the last half of the obliquity cycle, so that volatiles should migrate to the equator, stabilizing the planet against wander. Spacecraft missions to Triton and Pluto which measure the dynamical flattening could give information about the accumulation of volatiles at the poles. Such information is best obtained by measuring gravity and topography from orbiters, as was done for Mars with the highly successful Mars Global Surveyor.
    Icarus 01/2003; 163(2):469-478. · 3.16 Impact Factor
  • David Parry Rubincam
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    ABSTRACT: Gravitational core-mantle coupling may be the cause of the observed variable acceleration of the Earth's rotation on the 1000-year timescale. Density inhomogeneities which randomly come and go in the liquid outer core may gravitationally attract density inhomogeneities in the mantle (and crust), torquing the mantle and changing its rotation state. The corresponding torque by the mantle on the core may also explain the westward drift of the magnetic field of 0.2° yr-1. Gravitational core-mantle coupling would stochastically affect the rate of change of the Earth's obliquity by just a few percent. Its contribution to polar wander would only be ~0.5% the presently observed rate.
    Journal of Geophysical Research 01/2003; 108. · 3.17 Impact Factor
  • David Parry Rubincam, David D. Rowlands, Richard D. Ray
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    ABSTRACT: Asteroid 951 Gaspra appears to be in an obliquity resonance with its spin increasing due to the Yarkovsky-O'Keefe-Radzievskii-Paddack effect (YORP effect, for short). Gaspra, an asteroid 5.8 km in radius, is a prograde rotator with a rotation period of 7.03 hours. A 3 × 106 year integration indicates that its orbit is stable over at least this time span. From its known shape and spin axis orientation and assuming a uniform density, Gaspra's axial precession period turns out to be nearly commensurate with its orbital precession period, which leads to a resonance condition with consequent huge variations in its obliquity. At the same time, its shape is such that the YORP effect is increasing its spin rate. YORP may be a reason for small asteroids entering resonances in the first place: they speed up or slow down and fall into resonances. The continued action of YORP probably ultimately causes asteroids to leave resonances, so that they are quasi-stable states.
    Journal of Geophysical Research 09/2002; 107(E9):5065-. · 3.17 Impact Factor
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    William F. Bottke, David P. Rubincam, Joseph A. Burns
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    ABSTRACT: In the Yarkovsky effect, the recoil from asymmetric, reradiated thermal energy causes objects to undergo semimajor axis drift as a function of their spin, orbit, and material properties. We consider the role played by this mechanism in delivering meteoroids from parent bodies in the main belt to chaotic resonance zones where they can be transported to Earth-crossing orbits. Previous work has approximated the dynamical evolution of meteoroids via Yarkovsky forces, mostly through the use of the perturbations equation and simplified dynamics (e.g., Monte Carlo codes). In this paper, we calculate more precise solutions by formulating the seasonal and diurnal variants of this radiation force and incorporating them into an efficient N-body integrator capable of tracking test bodies for tens of millions of years with all relevant planetary perturbations included. Tests of our code against published benchmarks and the perturbation equations verify its accuracy.Results from long-term numerical integration of meter-sized bodies started from likely meteoroid parent bodies (e.g., 4 Vesta) indicate that dynamical evolution in the inner main belt can be complex. Chaotic effects produced by weaker planetary resonances allow many meteoroids to reach Mars-crossing orbits well before entering the 3:1 mean-motion resonance with Jupiter or the ν6 secular resonance. Outward-evolving meteoroids sometimes become captured in these weaker resonances, increasing e and/or i while a stays constant. Conversely, inward-evolving meteoroids frequently jump across mean-motion resonances with Jupiter, bypassing potential “escape hatches” from the main belt. Despite these effects, our simulations indicate that most stony meteoroids reach Earth-crossing orbits via the 3:1 or ν6 resonance after tens of Myr of evolution in the main belt. These time scales correspond well to the measured cosmic ray exposure ages of chondrites and achondrites. The source of these meteorites, however, is less clear, since Yarkovsky drift allows nearly any body in the main belt to add to the cumulate meteoroid flux. Our results suggest that small parent bodies dominate the meteoroid flux if the main belt size distribution at sub-km sizes is in collisional equilibrium, while big parent bodies dominate if observed population trends for km-sized bodies persist to smaller sizes.
    Icarus. 06/2000;
  • David Parry Rubincam
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    ABSTRACT: The Yarkovsky–O'Keefe–Radzievskii–Paddack (YORP) effect may spin up or spin down 5-km-radius asteroids on a 108-year timescale. Smaller asteroids spin up or down even faster due to the radius-squared dependence of the YORP timescale. The mechanism is the absorption of sunlight and its re-emission as thermal radiation from an irregularly shaped asteroid. This effect may compete with impacts and tidal encounters as a way of changing rotation rates for small asteroids, especially in the near-Earth region. The YORP effect may explain the rapid rotation of 1566 Icarus and the slow tumbling of 4179 Toutatis. It may explain to some extent the slow rotation of 253 Mathilde. Meteoroids spin up or down on timescales fast compared to their cosmic ray exposure ages.
    Icarus. 01/2000;
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    David Parry Rubincam
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    ABSTRACT: Pluto may be the only known case of precession-orbit resonance in the solar system. Pluto's precession caused by Charon about their orbital plane might have a period of 250.8 Earth years, the same as the orbital period of the Pluto-Charon system about the Sun. A Pluto flyby mission might refute or provide more evidence for the resonance. It is not clear how the planet would get in to such a resonance. Present-day Earth-based is observations appear to rule out Pluto's being in a resonance associated with half of its orbital period about the Sun unless Pluto has a large nonhydrostatic component to its flattening.
    Journal of Geophysical Research 05/1999; · 3.17 Impact Factor
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    David Parry Rubincam
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    ABSTRACT: Mars may have substantially changed its average axial tilt over geologic time due to the waxing and waning of water ice caps through the phenomenon of climate friction (also called obliquity-oblateness feedback). Depending upon Mars' climate and internal structure, water caps of the order of 1017–1018 kg cycling with the obliquity oscillations could have either increased or decreased the average obliquity by possibly tens of degrees. This is in contrast to previous results, which indicated that 1017 kg carbon dioxide caps only increased the axial tilt. Since the south polar cap appears to be mostly uncompensated, Mars may be largely rigid on the obliquity timescale. Further, Mars may be a water-rich planet so that there is a large phase angle between insolation forcing and the size of the obliquity-driven water caps. A stiff, water-rich planet indicates the obliquity may have decreased over the eons. Such a decrease might account for the apparent youthfulness of the polar layered terrain, the idea being that fewer volatiles were available to be cycled into and out of the terrain at high obliquity because of more even insolation between equator and pole, so that the movement of volatiles produced thin layers or perhaps no layers at all. As the obliquity decreased, the insolation contrast between high and low latitiudes increased, and more volatiles might have shuttled into and out of the polar regions, forming the observed thick layers. In another but perhaps less likely scenario, Mars' average obliquity may have either increased or decreased until it became “stuck” at its present value of ∼24°. In this case the idea is that Mars' climate dynamics altered as the average tilt changed. Once the rate of increase in tilt caused by the deformation of the solid planet equaled the rate of decrease caused by the caps, the obliquity evolution ceased, leaving Mars at its present tilt.
    Journal of Geophysical Research 01/1999; 104:30765-30771. · 3.17 Impact Factor
  • David Parry Rubincam
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    ABSTRACT: There is an optimal size for the delivery of small asteroids from Mars to the Earth by Yarkovsky thermal drag. Basaltic asteroids with radii of about 6 m take on the average 185 million years (Myr) for their semimajor axes to shrink by 0.52 AU, assuming circular orbits and ignoring planetary perturbations and collisions. All other sizes take longer. Bigger objects are slower because they are more massive, and smaller objects are slower because they are more isothermal. These results are based on treating the asteroids as spheres and solving the heat conduction equation using spherical Bessel functions. The small near-Earth asteroids show a concentration of sizes in the thermal drag range; thus some of them may come from Mars as survivors of gravitational mechanisms which eliminate them on the 10 Myr timescale. The possible role of thermal drag in Mars-Earth delivery will remain speculative until it is included in numerical integrations of the orbits of small asteroids.
    Journal of Geophysical Research 01/1998; 103:1725-1732. · 3.17 Impact Factor
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    David Parry Rubincam, Douglas G. Currie, John W. Robbins
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    ABSTRACT: Photon thrust from the solar heating of the LAGEOS I satellite appears to explain much of the eccentricity variations seen in the satellite's orbital elements. We invoke a thermal model of LAGEOS I in which the photon thrust from solar heating is directed along the satellite's spin axis and functionally depends only on the cosine of the angle between the Sun's position and the spin axis. We calibrated the amplitude of the force from the 1980-1983 equivalent along-track acceleration derived from the observed orbital perturbations; during this time the spin axis position is assumed to be known and to be that at orbit injection. The photon thrust from this simple thermal model, plus later spin axis positions obtained from Sun glint data (which show LAGEOS I to be processing), give reasonable agreement with the observed along-track acceleration in the time period of 1988-1995. Thus much of the eccentricity variations seem to be due to thermal thrust and do not have a geophysical origin (atmospheric tides) as has been proposed. However, our solar heating model does not appear to explain the highest peaks and deepest troughs seen in the along-track acceleration, indicating the need for a better thermal model and consideration of other forces, such as that due to anisotropic reflection.
    Journal of Geophysical Research 01/1997; 102:585-590. · 3.17 Impact Factor
  • Chreston F. Martin, David P. Rubincam
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    ABSTRACT: For several years, Earth albedo has been one of the leading candidates for explaining the anomalous along-track acceleration experienced by the LAGEOS satellites, with reasonable reflection models having been shown to give acceleration peaks comparable to those observed. The effects of Earth albedo on LAGEOS I have been studied for the period March 1985 to June 1989, during which time measurements of reflected radiation from the Earth were made by one to three Earth Radiation Budget Experiment (ERBE) satellites. Data taken during this experiment were processed into hourly radiation exitances for the entire Earth divided into 2.5°×2.5° blocks. These ERBE data were used, along with detailed models of reflectance characteristics of the Earth, to calculate the accelerations which reflected radiation would induce on LAGEOS I. The along-track component of the acceleration was averaged over 10 revolutions in order to average out the short-period effects. The results showed that the albedo effect on along-track acceleration did not exceed 0.5 pm/s2, or about 20% of the anomalous acceleration. Even this acceleration showed no correlation in phase with the observed acceleration. The albedo accelerations were also used to calculate the effects on the LAGEOS Keplerian orbital elements. The effects on the LAGEOS node and inclination excitations were significant, having amplitudes of several milliarc seconds (mas) per year. The largest effects were found to be on the eccentricity excitation function, having amplitudes at the 50-100 mas/yr level. The patterns also correlate well with the observed eccentricity vector excitations, but with a difference in sign, suggesting that some parameters estimated with LAGEOS data, such as ocean tide parameters, may have been corrupted by albedo effects.
    Journal of Geophysical Research 01/1996; 101:3215-3226. · 3.17 Impact Factor
  • David Parry Rubincam
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    ABSTRACT: Thermal drag, a variant of the Yarkovsky effect, may act on small asteroids with sizes from a few meters to a few tens of meters. Yarkovsky thermal drag comes from an asteroid's absorbing sunlight in the visible and reradiating it in the infrared. Since the infrared photons have momentum, by action-reaction, they kick the asteroid when they leave its surface. The reradiation, which is asymmetric in latitude over the asteroid, gives a net force along the asteroid's pole. Due to the asteroid's thermal inertia, averaging this force over one orbital period produces a net drag if the spin axis has a component in the orbital plane. Thermal drag tends to circularize orbits. It can increase or decrease orbital inclinations. An object whose spin axis points in random directions over its lifetime displays little change in orbital inclination. Thermal drag appears to have little to do with the delivery of chondrites from the asteroid belt; the thermal drag timescale (10(exp 8) years for meter-sizzed objects) is long compared with their cosmic ray exposure ages, and aphelia in the asteroid belt are not expected for mature thermal drag orbits. However, Yarkovsky thermal drag may act on the recently discovered near-Earth asteroids, which have radii of 10-30 m. Asteroid 1992 DA, for instance, might have its orbit shrunk by 0.1 AU in 3 x 10(exp 7) years, removing it from an Earth-crossing orbit. The near-Earth asteroids also tend to have small to moderate orbital eccentricities, as expected for highly evolved thermal drag objects. However, the time needed to bring them in from the asteroid belt (about 10(exp 9) years) is long compared with the collisonal and dynamical lifetimes (both about 10(exp 8) years) for Earth-crossing objects, arguing against their emplacement by thermal drag.
    02/1995;
  • David Parry Rubincam, Anthony Mallama
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    ABSTRACT: We examine spatial variability of attenuation in the Earth's atmosphere as a cause of asymmetrical eclipses and consequent acceleration of LAGEOS, i.e., the solar radiation pressure on LAGEOS due to the Earth's penumbra. Measurements of atmospheric attenuation derived from the satellite-borne Stratospheric Aerosol and Gas Experiment after the eruption of Mount Pinatubo were used to simulate the largest expected aerosol content of the atmosphere. In our experiment one hemisphere was loaded with volcanic aerosols, while the other was not. The difference between attenuation in the two hemispheres sets a maximum reasonable limit to the size of eclipse asymmetry. This condition would accelerate LAGEOS only about 0.2 picometers per second squared (pm s-2 or 10-12 m s-2) and indicates that eclipse asymmetry can only account for about 40-50% of the remaining unmodeled residuals. This is slightly less than the penumbral acceleration found by Vokrouhlicky et al. (1994). .
    Journal of Geophysical Research 01/1995; 100:20285-20290. · 3.17 Impact Factor