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Size-selective concentration of particles in a weakly turbulent protoplanetary nebula may be responsible for the initial collection of chondrules and other constituents into primitive body precursors. This paper presents the main elements of this process of turbulent concentration. In the terrestrial planet region, both the characteristic size and size distribution of chondrules are explained. "Fluffier" particles would be concentrated in nebula regions which were at a lower gas density and/or more intensely turbulent. The spatial distribution of concentrated particle density obeys multifractal scaling, suggesting a close tie to the turbulent cascade process. This scaling behavior allows predictions of the probability distributions for concentration in the protoplanetary nebula to be made. Large concentration factors (> 10 5) are readily obtained, implying that numerous zones of particle density significantly exceeding the gas density could exist. If most of the available solids were actually in chondrule sized particles, the ensuing particle mass density would become so large that the feedback effects on gas turbulence due to mass loading could no longer be neglected. This paper describes the process, presenting its basic elements and some implications, without including the effects of mass loading.

Ca-A1 rich refractory mineral inclusions (CAIs) found at 1-6% mass fraction in primitive chondrites appear to be 1-3 million years older than the dominant (chondrule) components which were accreted into the same parent bodies. A prevalent concern is that it is difficult to retain CAIs for this long against gas-drag-induced radial drift into the sun. We reassess the situation in terms of a hot inner (turbulent) nebula context for CAI formation, using analytical models of nebula evolution and particle diffusion. We show that outward radial diffusion in a weakly turbulent nebula can overwhelm inward drift, and prevent significant numbers of CAI-size particles from being lost into the sun for times on the order of lo6 years. CAIs can form early, when the inner nebula was hot, and persist in sufficient abundance to be incorporated into primitive planetesimals at a much later time. Small ( 5 0.1 mm diameter) CAIs persist for longer times than large (2 5mm diameter ones. To obtain a quantitative match t o the observed volume fractions of CAIs in chondrites, another process must be allowed for: a substantial enhancement of the inner hot nebula in silicate-forming material, which we suggest was caused by rapid inward drift of meter-sized objects. This early in nebula history, the drifting rubble would have a carbon content probably an order of magnitude larger than even the most primitive (CI) carbonaceous chondrites. Abundant carbon in the evaporating material would help keep the nebula oxygen fugacity low, plausibly solar, as inferred for the formation environment of CAIs. The associated production of a larger than canonical amount of COZ might also play a role in mass-independent fractionation of oxygen isotopes, leaving the gas rich in l60 as inferred from CAIs and other high temperature condensates.

We address the thermal history of the Earth after the Moon-forming impact, taking tidal heating and thermal blanketing by the atmosphere into account. The atmosphere sets an upper bound of ∼100 W/m 2 on how quickly the Earth can cool. The liquid magma ocean cools over 2-10 Myr, with longer times corresponding to high angular-momentum events. Tidal heating is focused mostly in mantle materials that are just beginning to freeze. The atmosphere's control over cooling sets up a negative feedback between viscosity-dependent tidal heating and temperature-dependent viscosity of the magma ocean. While the feedback holds, evolution of the Moon's orbit is limited by the modest radiative cooling rate of Earth's atmosphere. Orbital evolution is orders of magnitude slower than in conventional constant Q models, which promotes capture by resonances. The evection resonance is encountered early, when the Earth is molten. Capture by the evection resonance appears certain but unlikely to generate much eccentricity because it is encountered early when the Earth is molten and Q ⊕ Q $ . Tidal dissipation in the Earth becomes more efficient (Q ⊕ Q $ ) later when the Moon is between ∼20R ⊕ and ∼40R ⊕ .If lunar eccentricity grew great, this was when it did so, perhaps setting the table for some other process to leave its mark on the inclination of the Moon.Published by Elsevier B.V.

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Abstract. Aerodynamic roughness (z0) is an important parameter in studies of sand and dust transport, as well as atmospheric circulation models. Aerodynamic roughness is a function of the size and spacing of surface roughness elements and is typically determined at point locations in the field from wind velocity profiles. Because field measurements require complex logistics, z0 values have been obtained for very few localities. If radar can be used to map z0, estimates can be obtained for large areas. In addition, because aerodynamic roughness can change in response to surface processes (e.g., flooding of alluvial surfaces), radar remote sensing could obtain new measurements on short timescales. Both z0 and the radar backscatter coetficient cr ø are dependent on topographic roughness at the submeter scale, and correlation between these two parameters was developed based on radar data obtained from aircraft (AIRSAR). The Spaceborne Radar Laboratory (SRL) afforded the opportunity to test the correlation for data obtained from orbit. SRL data for sites in Death Valley, California; Lunar Lake, Nevada; and Gobabeb, Namibia, were correlated with wind data and compared with previous radar z0 relations. Correlations between cr ø and z0 for L band (X: 24 cm) HV (H, vertically and V,vertically polarized modes) L band HH, and C band (X -5.6 cm) HV compare favorably with previous studies. Based on these results, maps of z0 values were derived from SRL data for each site, demonstrating the potential to map z0 for large vegetation-free areas from orbit using radar systems. IntroductionAeolian processes are prominent in arid and coastal regions but can occur wherever loose particles are available for movemcnt by the wind. In addition to hazards created by sand and dust storms, the migration of sand over roads, agricultural fields, and other cultural features has negative economic impacts. Moreover, because aeolian processes involve the interaction of the atmosphere and Earth's surface. they can influence the climate. Aeolian processes can occur frequently and on short timescales, resulting in rapid surface changes. Remote sensing affords the opportunity to monitor these changes and, in some cases, allows the prediction of potential aeolian activity. Remote sensing in the visible spectrum has been used to map sand dune fields [e.g., Breed et al.

The dynamics of the Pluto‐Charon system are reviewed from a historical perspective. Although Pluto‧s orbit crosses Neptune‧s, an intricate system of nested resonances keeps these planets apart. Pluto‧s orbit is apparently chaotic as well. Pluto always keeps the same face turned toward Charon, and vice versa. Tides also damp Charon‧s orbital eccentricity and inclination. Precession of Pluto‧s orbital plane causes Pluto‧s obliquity to vary periodically from formally prograde to retrograde. Pluto is probably an original member of the Solar system, but not an escaped satellite of Neptune. The Voyager II encounter with Neptune, the final Pluto‐Charon mutual events, and the next generation of telescopes are bound to reveal some surprises.

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