David Parry Rubincam

NASA, Вашингтон, West Virginia, United States

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Publications (52)222.32 Total impact

  • David Parry Rubincam
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    ABSTRACT: The dynamical evolution of the Earth-Moon system due to tidal friction is treated here. George H. Darwin used Laplace planes (also called proper planes) in his study of tidal evolution. The Laplace plane approach is adapted here to the formalisms of W.M. Kaula and P. Goldreich. Like Darwin, the approach assumes a three-body problem: Earth, Moon, and Sun, where the Moon and Sun are point-masses. The tidal potential is written in terms of the Laplace plane angles. The resulting secular equations of motion can be easily integrated numerically assuming the Moon is in a circular orbit about the Earth and the Earth is in a circular orbit about the Sun. For Earth-Moon distances greater than ~10 Earth radii, the Earth's approximate tidal response can be characterized with a single parameter, which is a ratio: a Love number times the sine of a lag angle divided by another such product. For low parameter values it can be shown that Darwin's low-viscosity molten Earth, M. Ross's and G. Schubert's model of an Earth near melting, and Goldreich's equal tidal lag angles must all give similar histories. For higher parameter values, as perhaps has been the case at times with the ocean tides, the Earth's obliquity may have decreased slightly instead of increased once the Moon's orbit evolved further than 50 Earth radii from the Earth, with possible implications for climate. This is contrast to the other tidal friction models mentioned, which have the obliquity always increasing with time. As for the Moon, its orbit is presently tilted to its Laplace plane by 5.2°. The equations do not allow the Moon to evolve out of its Laplace plane by tidal friction alone, so that if it was originally in its Laplace plane, the tilt arose with the addition of other mechanisms, such as resonance passages.
    No preview · Article · Nov 2015 · Icarus
  • David Parry Rubincam
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    ABSTRACT: Drag from hydrogen in the interstellar cloud which formed Gould's Belt may have sent interplanetary dust particle (IDPs) and small meteoroids with embedded helium to the Earth, perhaps explaining part the helium-3 flux increase seen in the sedimentary record near the Eocene-Oligocene transition. Assuming the Solar System passed through part of the cloud, IDPs in the inner Solar System may have been dragged to Earth, while dust and small meteoroids in the asteroid belt up to centimeter size may have been dragged to the resonances, where their orbital eccentricities were pumped up into Earth-crossing orbits; however, this hypotheses does not explain the Popigai and Chesapeake Bay impacts.
    No preview · Article · Sep 2015 · Icarus
  • David Parry Rubincam
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    ABSTRACT: Space erosion from dust impacts may set upper limits on the cosmic ray exposure (CRE) ages of stony meteorites. A meteoroid orbiting within the asteroid belt is bombarded by both cosmic rays and interplanetary dust particles. Galactic cosmic rays penetrate only the first few meters of the meteoroid; deeper regions are shielded. The dust particle impacts create tiny craters on the meteoroid’s surface, eroding it away by abrasion at a particular rate. Hence a particular point inside a meteoroid accumulates cosmic ray products only until that point wears away, limiting CRE ages. The results would apply to other regolith-free surfaces in the Solar System as well, so that abrasion may set upper CRE age limits which depend on the dusty environment. Calculations based on N. Divine’s dust populations and on micrometeoroid cratering indicate that large stony meteoroids in circular ecliptic orbits at 2 AU will record 21Ne CRE ages of ∼176 × 106 y if dust masses are in the range 10−21–10−3 kg. This is in broad agreement with the maximum observed CRE ages of ∼100 × 106 y for stones. High erosion rates in the inner Solar System may limit the CRE ages of Near-Earth Asteroids (NEAs) to ∼120 × 106 y. A characteristic of erosion is that the neon concentrations tend to rise as the surface of the meteorite is approached, rather than drop off as for meteorites with fixed radii. Pristine samples recovered from space may show the rise. If the abrasion rate for stones were a factor of ∼6 larger than found here, then the ages would drop into the 30 × 106 y range, so that abrasion alone might be able to explain many CRE ages. However, there is no strong evidence for higher abrasion rates, and in any case would probably not be fast enough to explain the youngest ages of 0.1–1 × 106 y. Further, space erosion is much too slow to explain the ∼600 × 106 y ages of iron meteorites.
    No preview · Article · Jan 2015 · Icarus
  • 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.
    No preview · Article · Sep 2014 · Icarus
  • 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 V-b/c for circular orbits, where V-b 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. Published by Elsevier Inc.
    No preview · Article · Nov 2013 · Icarus
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    David Parry Rubincam
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    ABSTRACT: The seasonal polar caps of Mars can be used to test the equivalence principle in general relativity. The north and south caps, which are composed of carbon dioxide, wax and wane with the seasons. If the ratio of the inertial (passive) to gravitational (active) masses of the caps differs from the same ratio for the rest of Mars, then the equivalence principle fails, Newton’s third law fails, and the caps will pull Mars one way and then the other with a force aligned with the planet’s spin axis. This leads to a secular change in Mars’s along-track position in its orbit about the Sun, and to a secular change in the orbit’s semimajor axis. The caps are a poor Eötvös test of the equivalence principle, being 4 orders-of-magnitude weaker than laboratory tests and 7 orders-of-magnitude weaker than that found by lunar laser ranging; the reason is the small mass of the caps compared to Mars as a whole. The principal virtue of using Mars is that the caps contain carbon, an element not normally considered in such experiments. The Earth with its seasonal snow cover can also be used for a similar test.
    Preview · Article · Aug 2011 · Physical review D: Particles and fields
  • 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.
    No preview · Article · Oct 2010 · Icarus
  • 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.
    No preview · Article · Dec 2007 · Icarus
  • 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.
    No preview · Article · Oct 2007
  • S.J. Paddack · D.P. Rubincam

    No preview · Article · Aug 2007
  • Stephen J. Paddack · David P. Rubincam

    No preview · Article · Aug 2007 · Science
  • 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.
    No preview · Article · May 2007 · Science
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    William F. Bottke · David Vokrouhlic · David P. Rubincam · David Nesvor
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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.
    Preview · Article · May 2006 · Annual Review of Earth and Planetary Sciences
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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.
    Preview · Article · Oct 2004 · Icarus
  • D. P. Rubincam
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    ABSTRACT: The temperature T of a black or gray body orbiting the Sun can be expressed in terms of spherical harmonics in latitude and longitude, its Keplerian orbital elements, and a variable describing rotation about its axis. Assuming that the Earth is a black or gray body without thermal inertia, the resulting equation for T exhibits previously unrecognized odd-degree zonal terms dubbed “Seversmith psychroterms.” They cause a hemispheric temperature difference which depends upon e sin ωS , where e is the orbital eccentricity and ωS is the Sun’s argument of perigee measured in an Earth-centered frame. The hemisphere containing perihelion is the cooler. For a gray body with the Earth’s average albedo of 0.3, an emissivity of unity, and an obliquity of 23.5°, the pole-to-pole temperature difference for the combined first and third degree spherical harmonic psychroterms can reach 3.4 K for the present eccentricity of 0.016, and 12.9 K for the maximum eccentricity of 0.06. While a thermally inertia-less black or gray body with boiling hot subsolar points and nights at absolute zero are poor models for the Earth, the Seversmith psychroterms will survive in more realistic models (although with smaller amplitudes) because the Earth radiates nonlinearly in T. The psychroterms acts in the direction opposite to the Milankovitch precession index, which also depends on e sin ωS : by warming the cool northern summers, the psychroterms make it harder for the traditional Milankovitch mechanism to operate. The Seversmith psychroterms could in fact be responsible for the ice sheets that cycle with e sin ωS , instead of the Milankovitch mechanism. By cooling the southern hemisphere for thousands of years when perihelion is in the south, the psychroterms may somehow cause the southern hemisphere to control the northern ice sheets associated with the 23 kyr and 19 kyr periods (kyr = 103 years), possibly through ice-albedo feedback in the sea ice surrounding Antarctica. Two other unexpected features besides the psychroterms are: while the average insolation increases with increasing e, the average temperature of the Earth paradoxically decreases; and the equator-to-pole temperature difference of 21 K on a gray body with an albedo equal to 0.3 and an emissivity of unity is actually smaller than the observed difference of 28 K on the real Earth.
    No preview · Article · Jan 2004 · Theoretical and Applied Climatology
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    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.
    Preview · Article · Jul 2003 · Journal of Geophysical Research Atmospheres
  • 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.
    No preview · Article · Jun 2003 · Icarus
  • David Parry Rubincam
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    ABSTRACT: Asteroid 951 Gaspra appears to be in an obliquity resonance with its spin increasing due to the YORP effect. Gaspra, an asteroid 5.8 km in radius, is a prograde rotator with a rotation period of 7.03 hours. A 3 million year integration indicates 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 Yarkovsky-O'Keefe-Radzievskii-Paddack effect (YORP effect for short) is increasing its spin rate. The YORP cycle normally leads from spin-up to spin-down and then repeating the cycle; however, it appears possible that resonance trapping can at least temporarily interrupt the YORP cycle, causing spin-up until the resonance is exited. This behavior may partially explain why there is an excess of fast rotators among small asteroids. YORP may also be a reason for small asteroids entering resonances in the first place.
    No preview · Article · Nov 2001 · Journal of Geophysical Research Atmospheres
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    Preview · Article · Jan 2001
  • 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.
    No preview · Article · Nov 2000 · Icarus