La Côte-Saint-André, France
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Murdoch N.,Laboratoire Lagrange | Murdoch N.,Open University Milton Keynes | Rozitis B.,Open University Milton Keynes | Nordstrom K.,University of Maryland University College | And 4 more authors.
Physical Review Letters | Year: 2013

We investigate the role of gravity on convection in a dense granular shear flow. Using a microgravity-modified Taylor-Couette shear cell under the conditions of parabolic flight microgravity, we demonstrate experimentally that secondary, convective-like flows in a sheared granular material are close to zero in microgravity and enhanced under high-gravity conditions, though the primary flow fields are unaffected by gravity. We suggest that gravity tunes the frictional particle-particle and particle-wall interactions, which have been proposed to drive the secondary flow. In addition, the degree of plastic deformation increases with increasing gravitational forces, supporting the notion that friction is the ultimate cause. © 2013 American Physical Society.


Veras D.,University of Warwick | Jacobson S.A.,Laboratoire Lagrange | Jacobson S.A.,University of Bayreuth | Gansicke B.T.,University of Warwick
Monthly Notices of the Royal Astronomical Society | Year: 2014

Although discs of dust and gas have been observed orbiting white dwarfs, the origin of this circumstellar matter is uncertain. We hypothesize that the in situ break-up of small bodies such as asteroids spun to fission during the giant branch phases of stellar evolution provides an important contribution to this debris. The YORP (Yarkovsky-O'Keefe-Radviesvki-Paddock) effect, which arises from radiation pressure, accelerates the spin rate of asymmetric asteroids, which can eventually shear themselves apart. This pressure is maintained and enhanced around dying stars because the outward push of an asteroid due to stellar mass loss is insignificant compared to the resulting stellar luminosity increase. Consequently, giant star radiation will destroy nearly all bodies with radii in the range 100 m-10 km that survive their parent star's main-sequence lifetime within a distance of about 7 au; smaller bodies are spun apart to their strongest, competent components. This estimate is conservative and would increase for highly asymmetric shapes or incorporation of the inward drag due to giant star stellar wind. The resulting debris field, which could extend to thousands of au, may be perturbed by remnant planetary systems to reproduce the observed dusty and gaseous discs which accompany polluted white dwarfs. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Fraser W.C.,Herzberg Institute for Astrophysics | Fraser W.C.,California Institute of Technology | Brown M.E.,California Institute of Technology | Morbidelli A.,Laboratoire Lagrange | And 2 more authors.
Astrophysical Journal | Year: 2014

Here we measure the absolute magnitude distributions (H-distribution) of the dynamically excited and quiescent (hot and cold) Kuiper Belt objects (KBOs), and test if they share the same H-distribution as the Jupiter Trojans. From a compilation of all useable ecliptic surveys, we find that the KBO H-distributions are well described by broken power laws. The cold population has a bright-end slope, , and break magnitude, (r′-band). The hot population has a shallower bright-end slope of, , and break magnitude . Both populations share similar faint-end slopes of α2 0.2. We estimate the masses of the hot and cold populations are 0.01 and 3 × 10-4 M ⊕. The broken power-law fit to the Trojan H-distribution has α1 = 1.0 ± 0.2, α2 = 0.36 ± 0.01, and H B = 8.3. The Kolmogorov-Smirnov test reveals that the probability that the Trojans and cold KBOs share the same parent H-distribution is less than 1 in 1000. When the bimodal albedo distribution of the hot objects is accounted for, there is no evidence that the H-distributions of the Trojans and hot KBOs differ. Our findings are in agreement with the predictions of the Nice model in terms of both mass and H-distribution of the hot and Trojan populations. Wide-field survey data suggest that the brightest few hot objects, with , do not fall on the steep power-law slope of fainter hot objects. Under the standard hierarchical model of planetesimal formation, it is difficult to account for the similar break diameters of the hot and cold populations given the low mass of the cold belt. © 2014. The American Astronomical Society. All rights reserved.


Jacobson S.A.,University of Colorado at Boulder | Jacobson S.A.,Laboratoire Lagrange | Jacobson S.A.,University of Bayreuth | Scheeres D.J.,University of Colorado at Boulder | McMahon J.,University of Colorado at Boulder
Astrophysical Journal | Year: 2014

We propose and analyze a new mechanism for the formation of the wide asynchronous binary population. These binary asteroids have wide semimajor axes relative to most near-Earth and main belt asteroid systems. Confirmed members have rapidly rotating primaries and satellites that are not tidally locked. Previously suggested formation mechanisms from impact ejecta, from planetary flybys, and directly from rotational fission events cannot satisfy all of the observations. The newly hypothesized mechanism works as follows: (1) these systems are formed from rotational fission, (2) their satellites are tidally locked, (3) their orbits are expanded by the binary Yarkovsky-O'Keefe- Radzievskii-Paddack (BYORP) effect, (4) their satellites desynchronize as a result of the adiabatic invariance between the libration of the secondary and the mutual orbit, and (5) the secondary avoids resynchronization because of the YORP effect. This seemingly complex chain of events is a natural pathway for binaries with satellites that have particular shapes, which define the BYORP effect torque that acts on the system. After detailing the theory, we analyze each of the wide asynchronous binary members and candidates to assess their most likely formation mechanism. Finally, we suggest possible future observations to check and constrain our hypothesis. © 2014. The American Astronomical Society. All rights reserved..


Jacobson S.A.,Laboratoire Lagrange | Jacobson S.A.,University of Bayreuth
Proceedings of the International Astronomical Union | Year: 2014

Recently, the discovery of small unbound asteroid systems called asteroid pairs have revolutionized the study of small asteroid systems. Observations with radar, photometric and direct imaging techniques have discovered that multiple asteroid systems can be divided clearly into a handful of different morphologies. Simultaneously, new theoretical advances have demonstrated that solar radiation dictates the evolution of small asteroids with strong implications for asteroid internal structure. We review our current understanding of how small asteroid systems evolve and point to the future. © Copyright 2014 International Astronomical Union.


Jacobson S.A.,Laboratoire Lagrange | Jacobson S.A.,University of Bayreuth
Proceedings of the International Astronomical Union | Year: 2016

Rotationally fissioned asteroids produce unbound asteroid pairs that have very similar heliocentric orbits. Backward integration of their current heliocentric orbits provides an age of closest proximity that can be used to date the rotational fission event. Most asteroid pairs follow a predicted theoretical relationship between the primary spin period and the mass ratio of the two pair members that is a direct consequence of the YORP-induced rotational fission hypothesis. If the progenitor asteroid has strength, asteroid pairs may have higher mass ratios or faster rotating primaries. However, the process of secondary fission leaves the originally predicted trend unaltered. We also describe the characteristics of pair members produced by four alternative routes from a rotational fission event to an asteroid pair. Unlike direct formation from the event itself, the age of closest proximity of these pairs cannot generally be used to date the rotational fission event since considerable time may have passed. Copyright © 2016 International Astronomical Union.


Bec J.,Laboratoire Lagrange | Homann H.,Laboratoire Lagrange | Krstulovic G.,Laboratoire Lagrange
Physical Review Letters | Year: 2014

Heavy inertial particles transported by a turbulent flow are shown to concentrate in the regions where an advected passive scalar, such as temperature, displays very strong frontlike discontinuities. This novel effect is responsible for extremely high levels of fluctuations for the passive field sampled by the particles that impacts the heat fluxes exchanged between the particles and the surrounding fluid. Instantaneous and averaged heat fluxes are shown to follow strongly intermittent statistics and anomalous scaling laws. © 2014 American Physical Society.


Tanga P.,Laboratoire Lagrange | Mignard F.,Laboratoire Lagrange
Planetary and Space Science | Year: 2012

The Gaia cornerstone mission of the European Space Agency, scheduled for launch in mid-2013, is expected to produce a breakthrough in our understanding of the Galaxy, providing a full characterisation of all sources by extremely accurate astrometry and complementary spectral data. The continuous scanning of the sky and the fully automated selection of the sources also ensure that nearly all Solar System objects brighter than V=20 will be observed by Gaia. We describe the expectations of the mission in Solar System science and the peculiar properties of asteroid data, requiring appropriate data reduction procedures currently being implemented. Recent estimates of the number of observed sources and other statistical properties of the sample are presented. © 2012 Elsevier Ltd. All rights reserved.


Krstulovic G.,Laboratoire Lagrange
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

We study the statistical properties of the Kelvin waves propagating along quantized superfluid vortices driven by the Gross-Pitaevskii equation. No artificial forcing or dissipation is added. Vortex positions are accurately tracked. This procedure directly allows us to obtain the Kevin-wave occupation-number spectrum. Numerical data obtained from long time integration and ensemble average over initial conditions support the spectrum proposed in L'vov and Nazarenko. Kelvin-wave modes in the inertial range are found to be Gaussian as expected by weak-turbulence predictions. Finally the dissipative range of the Kelvin-wave spectrum is studied. Strong non-Gaussian fluctuations are observed in this range. © 2012 American Physical Society.


Bitane R.,Laboratoire Lagrange | Homann H.,Laboratoire Lagrange | Bec J.,Laboratoire Lagrange
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

Tracers in a turbulent flow separate according to the celebrated t3 /2 Richardson-Obukhov law, which is usually explained by a scale-dependent effective diffusivity. Here, supported by state-of-the-art numerics, we revisit this argument. The Lagrangian correlation time of velocity differences increases too quickly for validating this approach, but acceleration differences decorrelate on dissipative time scales. Phenomenological arguments are used to relate the behavior of separations to that of a "local energy dissipation," defined as the average ratio between the cube of the longitudinal velocity difference and the distance between the two tracers. This quantity is shown to stabilize on short time scales and this results in an asymptotic diffusion t1 /2 of velocity differences. The time of convergence to this regime is shown to be that of deviations from Batchelor's initial ballistic regime, given by a scale-dependent energy dissipation time rather than the usual turnover time. It is finally demonstrated that the fluid flow intermittency should not affect this long-time behavior of the relative motion. © 2012 American Physical Society.

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