Patrick Michel - Academia.edu (original) (raw)
Papers by Patrick Michel
Astronomy & Astrophysics, 2000
We have integrated backward and forward in time the orbits of 20 very bright bolides (with visual... more We have integrated backward and forward in time the orbits of 20 very bright bolides (with visual magnitude brighter than -10) over a time span of 5 Myr or more. The sample was mainly selected among events observed during the period between 1993 and 1996, but we have included also three older, particularly interesting events (Abee, 1952; Glanerbrug, 1990; and
Comptes Rendus Physique, Apr 1, 2005
The population of Near-Earth Objects (NEOs) evolves on orbits which can cross the orbit of the Ea... more The population of Near-Earth Objects (NEOs) evolves on orbits which can cross the orbit of the Earth. Most NEOs come from the asteroid belt via unstable zones associated with powerful or diffusive resonances. Their evolutionary paths and the statistical properties of their dynamics have been determined by massive numerical integrations. A steady-state model of their orbital and magnitude distributions has been elaborated which indicates that 1000 NEOs are kilometre-size with an impact frequency with the Earth around 0.5 Myr. A non-gravitational mechanism, the Yarkovsky thermal drag, plays the dominant role in delivering material in the NEO source regions, explaining how this population is maintained in a steady-state and why its size distribution is shallower than expected if NEOs were created through the direct injection of fresh fragments from collisional break ups into resonances. To cite this article: P. Michel et al., C. R. Physique 6 (2005).
Planetary and Space Science, 2015
We performed impact disruption experiments of porous sintered glass beads targets. The results of... more We performed impact disruption experiments of porous sintered glass beads targets. The results of these experiments and comparing with previous study suggested that not only the porosity but also the impact velocity strongly influence the outcome.
ABSTRACT Much of the evolution of small solar system bodies (SSSBs) is dominated by collisions, w... more ABSTRACT Much of the evolution of small solar system bodies (SSSBs) is dominated by collisions, whether from the initial build-up of planetesimals or the subsequent impacts between remnant bodies that exist today. In the quasi-steady-state collisional system of a protoplanetary disk, impact speeds are of order the escape speed of the largest body. Until the largest body becomes protoplanet sized, impacts typically will be at speeds less than the sound speed of the assumed rocky material (here we focus on asteroids). Since the dominant source of confining pressure for planetesimal-sized SSSBs is self-gravity, rather than material strength, they can be treated as gravitational aggregates. A rotating body has lower effective surface gravity than a non-rotating one (with the difference increasing with decreasing latitude) and therefore might suffer more mass loss as the result of a collision. What is less obvious, however, is whether rotation systematically increases mass loss on average regardless of the impact trajectory. This has important implications for the efficiency of planet formation via planetesimal growth, and also more generally for the determination of the impact energy threshold for catastrophic disruption (leading to the largest remnant having 50% of the original mass), as this has generally only been evaluated for non-spinning bodies. Here we carry out a systematic exploration of the effect of pre-impact rotation on the outcomes of rubble-pile collisions. We use pkdgrav, a cosmology code adapted to collisional problems and recently enhanced with a new soft-sphere collision algorithm that includes more realistic contact forces and permits simulations with many more particles than the older hard-sphere algorithm. We find that for most collision scenarios, rotation lowers the threshold energy for catastrophic dispersal. Furthermore, we discuss our results in the context of scaling laws that may be used to predict collision outcomes for planetary formation studies.
Monthly Notices of the Royal Astronomical Society, 2014
ABSTRACT Out of the handful of asteroids that have been imaged, some have distributions of blocks... more ABSTRACT Out of the handful of asteroids that have been imaged, some have distributions of blocks that are not easily explained. In this paper, we investigate the possibility that seismic shaking leads to the size sorting of particles in asteroids. In particular, we focus on the so-called Brazil Nut Effect (BNE) that separates large particles from small ones under vibrations. We study the BNE over a wide range of parameters by using the N-body code PKDGRAV, and find that the effect is largely insensitive to the coefficients of restitution, but sensitive to friction constants and oscillation speeds. Agreeing with the previous results, we find that convection drives the BNE, where the intruder rises to the top of the particle bed. For the wide-cylinder case, we also observe a "whale" effect, where the intruder follows the convective current and does not stay at the surface. We show that the non-dimensional critical conditions for the BNE agree well with previous studies. We also show that the BNE is scalable for low-gravity environments and that the rise speed of an intruder is proportional to the square root of the gravitational acceleration. Finally, we apply the critical conditions to observed asteroids, and find that the critical oscillation speeds are comparable to the seismic oscillation speeds that are expected from non-destructive impacts.
The Astronomical Journal, 1998
Planetary and Space Science, 2009
Physical Review Letters, 2013
Astronomy & Astrophysics, 2000
We have integrated backward and forward in time the orbits of 20 very bright bolides (with visual... more We have integrated backward and forward in time the orbits of 20 very bright bolides (with visual magnitude brighter than -10) over a time span of 5 Myr or more. The sample was mainly selected among events observed during the period between 1993 and 1996, but we have included also three older, particularly interesting events (Abee, 1952; Glanerbrug, 1990; and
Comptes Rendus Physique, Apr 1, 2005
The population of Near-Earth Objects (NEOs) evolves on orbits which can cross the orbit of the Ea... more The population of Near-Earth Objects (NEOs) evolves on orbits which can cross the orbit of the Earth. Most NEOs come from the asteroid belt via unstable zones associated with powerful or diffusive resonances. Their evolutionary paths and the statistical properties of their dynamics have been determined by massive numerical integrations. A steady-state model of their orbital and magnitude distributions has been elaborated which indicates that 1000 NEOs are kilometre-size with an impact frequency with the Earth around 0.5 Myr. A non-gravitational mechanism, the Yarkovsky thermal drag, plays the dominant role in delivering material in the NEO source regions, explaining how this population is maintained in a steady-state and why its size distribution is shallower than expected if NEOs were created through the direct injection of fresh fragments from collisional break ups into resonances. To cite this article: P. Michel et al., C. R. Physique 6 (2005).
Planetary and Space Science, 2015
We performed impact disruption experiments of porous sintered glass beads targets. The results of... more We performed impact disruption experiments of porous sintered glass beads targets. The results of these experiments and comparing with previous study suggested that not only the porosity but also the impact velocity strongly influence the outcome.
ABSTRACT Much of the evolution of small solar system bodies (SSSBs) is dominated by collisions, w... more ABSTRACT Much of the evolution of small solar system bodies (SSSBs) is dominated by collisions, whether from the initial build-up of planetesimals or the subsequent impacts between remnant bodies that exist today. In the quasi-steady-state collisional system of a protoplanetary disk, impact speeds are of order the escape speed of the largest body. Until the largest body becomes protoplanet sized, impacts typically will be at speeds less than the sound speed of the assumed rocky material (here we focus on asteroids). Since the dominant source of confining pressure for planetesimal-sized SSSBs is self-gravity, rather than material strength, they can be treated as gravitational aggregates. A rotating body has lower effective surface gravity than a non-rotating one (with the difference increasing with decreasing latitude) and therefore might suffer more mass loss as the result of a collision. What is less obvious, however, is whether rotation systematically increases mass loss on average regardless of the impact trajectory. This has important implications for the efficiency of planet formation via planetesimal growth, and also more generally for the determination of the impact energy threshold for catastrophic disruption (leading to the largest remnant having 50% of the original mass), as this has generally only been evaluated for non-spinning bodies. Here we carry out a systematic exploration of the effect of pre-impact rotation on the outcomes of rubble-pile collisions. We use pkdgrav, a cosmology code adapted to collisional problems and recently enhanced with a new soft-sphere collision algorithm that includes more realistic contact forces and permits simulations with many more particles than the older hard-sphere algorithm. We find that for most collision scenarios, rotation lowers the threshold energy for catastrophic dispersal. Furthermore, we discuss our results in the context of scaling laws that may be used to predict collision outcomes for planetary formation studies.
Monthly Notices of the Royal Astronomical Society, 2014
ABSTRACT Out of the handful of asteroids that have been imaged, some have distributions of blocks... more ABSTRACT Out of the handful of asteroids that have been imaged, some have distributions of blocks that are not easily explained. In this paper, we investigate the possibility that seismic shaking leads to the size sorting of particles in asteroids. In particular, we focus on the so-called Brazil Nut Effect (BNE) that separates large particles from small ones under vibrations. We study the BNE over a wide range of parameters by using the N-body code PKDGRAV, and find that the effect is largely insensitive to the coefficients of restitution, but sensitive to friction constants and oscillation speeds. Agreeing with the previous results, we find that convection drives the BNE, where the intruder rises to the top of the particle bed. For the wide-cylinder case, we also observe a "whale" effect, where the intruder follows the convective current and does not stay at the surface. We show that the non-dimensional critical conditions for the BNE agree well with previous studies. We also show that the BNE is scalable for low-gravity environments and that the rise speed of an intruder is proportional to the square root of the gravitational acceleration. Finally, we apply the critical conditions to observed asteroids, and find that the critical oscillation speeds are comparable to the seismic oscillation speeds that are expected from non-destructive impacts.
The Astronomical Journal, 1998
Planetary and Space Science, 2009
Physical Review Letters, 2013