Benefits of space research to the natural sciences

The use of space technology to develop techniques and devices to help support the American dollar and determine the origin of the moon and solar system is discussed

Tektites

Detection, identification, and structural analyses of tektite

Impact ejecta on the moon

The partitioning of energy and the distribution of the resultant ejecta on the moon is numerically modeled using a Eulerian finite difference grid. The impact of an iron meteoroid at 15 km/sec on a gabbroic anorthosite lunar crust is examined. The high speed impact induced flow is described over the entire hydrodynamic regime from a time where the peak pressures are 6 Mbar until the stresses everywhere in the flow are linearly elastic, and less than 5 kbar. Shock-induced polymorphic phase changes, (plagioclase and pyroxene to hollandite and perovskite), and the subsequent reversion to low pressure phases are demonstrated to enhance shock wave attenuation. A rate-dependent equation of state is used for describing the hysteretic effect of the phase change. Ballistic equations for a spherical planet are then applied to material with net velocity away from the moon

Impact of an asteroid or comet in the ocean and extinction of terrestrial life

Finite difference calculations describing the impact mechanics associated with a 10 to 30 km diameter silicate or water object impacting a 5 km deep ocean overlying a silicate solid planet demonstrate that from 12 to 15% of the bolide energy resides in the water. It is speculated that minimal global tsunami run-up heights on the continents would be 300-400 meters, and that such waves would inundate all low altitude continental areas, and strip and silt-over virtually all vegetation. As a result the terrestrial animal food chain would be seriously perturbed. This could in turn cause extinction of large terrestrial animals

Impact and explosion crater ejecta, fragment size, and velocity

A model was developed for the mass distribution of fragments that are ejected at a given velocity for impact and explosion craters. The model is semi-empirical in nature and is derived from (1) numerical calculations of cratering and the resultant mass versus ejection velocity, (2) observed ejecta blanket particle size distributions, (3) an empirical relationship between maximum ejecta fragment size and crater diameter and an assumption on the functional form for the distribution of fragements ejected at a given velocity. This model implies that for planetary impacts into competent rock, the distribution of fragments ejected at a given velocity are nearly monodisperse, e.g., 20% of the mass of the ejecta at a given velocity contain fragments having a mass less than 0.1 times a mass of the largest fragment moving at that velocity. Using this model, the largest fragment that can be ejected from asteroids, the moon, Mars, and Earth is calculated as a function of crater diameter. In addition, the internal energy of ejecta versus ejecta velocity is found. The internal energy of fragments having velocities exceeding the escape velocity of the moon will exceed the energy required for incipient melting for solid silicates and thus, constrains the maximum ejected solid fragment size

Oblique impact: A process for providing meteorite samples of other planets

Cratering flow calculations for a series of oblique to normal impacts of silicate projectiles onto a silicate halfspace were carried out to determine whether the gas produced upon shock vaporizing both projectile and planetary material could entrain and accelerate surface rocks and thus provide a mechanism for propelling SNC meteorites from the Martian surface. The difficult constraints that the impact origin hypothesis for SNC meteorites has to satisfy are that these meteorites are lightly to moderately shocked and yet were accelerated to speeds in excess of the Martian escape velocity. Two dimensional finite difference calculations demonstrate that at highly probable impact velocities, vapor plume jets are produced at oblique impact angles of 25 deg to 60 deg and have speeds as great as 20 km/sec. These plumes flow nearly parallel to the planetary surface. It is shown that upon impact of projectiles having radii of 0.1 to 1 km, the resulting vapor jets have densities of 0.1 to 1 g/cu.cm. These jets can entrain Martian surface rocks and accelerate them to velocities 5 km/sec. It is suggested that this mechanism launches SNC meteorites to Earth

Melting and its relationship to impact crater morphology

Shock-melting features occur on planets at scales that range from micrometers to megameters. It is the objective of this study to determine the extent of thickness, volume geometry of the melt, and relationship with crater morphology. The variation in impact crater morphology on planets is influenced by a broad range of parameters: e.g., planetary density, thermal state, strength, impact velocity, gravitational acceleration. We modeled the normal impact of spherical projectiles on a semi-infinite planet over a broad range of conditions using numerical techniques

The size distributions of fragments ejected at a given velocity from impact craters

The mass distribution of fragments that are ejected at a given velocity for impact craters is modeled to allow extrapolation of laboratory, field, and numerical results to large scale planetary events. The model is semi-empirical in nature and is derived from: (1) numerical calculations of cratering and the resultant mass versus ejection velocity, (2) observed ejecta blanket particle size distributions, (3) an empirical relationship between maximum ejecta fragment size and crater diameter, (4) measurements and theory of maximum ejecta size versus ejecta velocity, and (5) an assumption on the functional form for the distribution of fragments ejected at a given velocity. This model implies that or planetary impacts into competent rock, the distribution of fragments ejected at a given velocity is broad, e.g., 68% of the mass of the ejecta at a given velocity contains fragments having a mass less than 0.1 times a mass of the largest fragment moving at that velocity. The broad distribution suggests that in impact processes, additional comminution of ejecta occurs after the upward initial shock has passed in the process of the ejecta velocity vector rotating from an initially downward orientation. This additional comminution produces the broader size distribution in impact ejecta as compared to that obtained in simple brittle failure experiments