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"Benz, Derek"
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The Brimstone Key
As the four friends known as the Grey Griffins begin school at Iron Bridge Academy, where children with special powers like theirs are trained to fight evil beings, rumors surface that a mad scientist known as the Clockwork King is back, and the Griffins must defeat his robotic war machines before total devastation is unleashed upon the world.
Book
The relic hunters
Tragedy divides the Grey Griffins, but their united quest to capture Von Strife continues, pitting them against killer clockworks, spider-like beasts, and an army of animated dead as they work together to prevent the building of The Paragon Engine.
Book
Collisions and Gravitational Reaccumulation: Forming Asteroid Families and Satellites
Numerical simulations of the collisional disruption of large asteroids show that although the parent body is totally shattered, subsequent gravitational reaccumulation leads to the formation of an entire family of large and small objects with dynamical properties similar to those of the parent body. Simulations were performed in two different collisional regimes representative of asteroid families such as Eunomia and Koronis. Our results indicate that all large family members must be made of gravitationally reaccumulated fragments; that the post-collision member size distribution and the orbital dispersion are steeper and smaller, respectively, than for the evolved families observed today; and that satellites form frequently around family members.
Journal Article
Disruption of fragmented parent bodies as the origin of asteroid families
Asteroid families are groups of small bodies that share certain orbit
1
and spectral properties
2
. More than 20 families have now been identified, each believed to have resulted from the collisional break-up of a large parent body
3
in a regime where gravity controls the outcome of the collision more than the material strength of the rock. The size and velocity distributions of the family members provide important constraints for testing our understanding of the break-up process, but erosion and dynamical diffusion of the orbits over time can erase the original signature of the collision
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,
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. The recently identified young Karin family
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provides a unique opportunity to study a collisional outcome almost unaffected by orbit evolution. Here we report numerical simulations modelling classes of collisions that reproduce the main characteristics of the Karin family. The sensitivity of the outcome of the collision to the internal structure of the parent body allows us to show that the family must have originated from the break-up of a pre-fragmented parent body, and that all large family members formed by the gravitational reaccumulation of smaller bodies. We argue that most of the identified asteroid families are likely to have had a similar history.
Journal Article
Fragment properties at the catastrophic disruption threshold: The effect of the parent body's internal structure
Numerical simulations of asteroid break-ups, including both the fragmentation of the parent body and the gravitational interactions between the fragments, have allowed us to reproduce successfully the main properties of asteroid families formed in different regimes of impact energy, starting from a non-porous parent body. In this paper, using the same approach, we concentrate on a single regime of impact energy, the so-called catastrophic threshold usually designated by Q*D, which results in the escape of half of the target's mass. Thanks to our recent implementation of a model of fragmentation of porous materials, we can characterize Q*D for both porous and non-porous targets with a wide range of diameters. We can then analyze the potential influence of porosity on the value of Q*D, and by computing the gravitational phase of the collision in the gravity regime, we can characterize the collisional outcome in terms of the fragment size and ejection speed distributions, which are the main outcome properties used by collisional models to study the evolutions of the different populations of small bodies. We also check the dependency of Q*D on the impact speed of the projectile. In the strength regime, which corresponds to target sizes below a few hundreds of meters, we find that porous targets are more difficult to disrupt than non-porous ones. In the gravity regime, the outcome is controlled purely by gravity and porosity in the case of porous targets. In the case of non-porous targets, the outcome also depends on strength. We then propose some power-law relationships between Q*D and both target's size and impact speed that can be used in collisional evolution models.
Paper