Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEjecta distribution and momentum transfer from oblique impacts on asteroid surfaces
56
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
NASAs Double Asteroid Redirection Test (DART) mission will impact its target asteroid, Dimorphos, at an oblique angle that will not be known prior to the impact. We computed iSALE-3D simulations of DART-like impacts on asteroid surfaces at different impact angles and found that the the vertical momentum transfer efficiency, $beta$, is similar for different impact angles, however, the imparted momentum is reduced as the impact angle decreases. It is expected that the momentum imparted from a 45$^circ$ impact is reduced by up to 50% compared to a vertical impact. The direction of the ejected momentum is not normal to the surface, however it is observed to `straighten up with crater growth. iSALE-2D simulations of vertical impacts provide context for the iSALE-3D simulation results and show that the ejection angle varies with both target properties and with crater growth. While the ejection angle is relatively insensitive to the target porosity, it varies by up to 30$^circ$ with target coefficient of internal friction. The simulation results presented in this paper can help constrain target properties from the DART crater ejecta cone, which will be imaged by the LICIACube. The results presented here represent the basis for an empirical scaling relationship for oblique impacts and can be used as a framework to determine an analytical approximation of the vertical component of the ejecta momentum, $beta-1$, given known target properties.
rate research
Read More
We describe systematic ranging, an orbit determination technique especially suitable to assess the near-term Earth impact hazard posed by newly discovered asteroids. For these late warning cases, the time interval covered by the observations is generally short, perhaps a few hours or even less, which leads to severe degeneracies in the orbit estimation process. The systematic ranging approach gets around these degeneracies by performing a raster scan in the poorly-constrained space of topocentric range and range rate, while the plane of sky position and motion are directly tied to the recorded observations. This scan allows us to identify regions corresponding to collision solutions, as well as potential impact times and locations. From the probability distribution of the observation errors, we obtain a probability distribution in the orbital space and then estimate the probability of an Earth impact. We show how this technique is effective for a number of examples, including 2008 TC3 and 2014 AA, the only two asteroids to date discovered prior to impact.
The NASA Double Asteroid Redirection Test (DART) spacecraft will impact the secondary member of the [65803] Didymos binary in order to perform the first demonstration of asteroid deflection by kinetic impact. Determination of the momentum transfer to the target body from the kinetic impact is a primary planetary defense objective, using ground-based telescopic observations of the orbital period change of Didymos and imaging of the DART impact ejecta plume by the LICIACube cubesat, along with modeling and simulation of the DART impact. LICIACube, contributed by the Italian Space Agency, will perform a flyby of Didymos a few minutes after the DART impact, to resolve the ejecta plume spatial structure and to study the temporal evolution. LICIACube ejecta plume images will help determine the vector momentum transfer from the DART impact, by determining or constraining the direction and the magnitude of the momentum carried by ejecta. A model is developed for the impact ejecta plume optical depth, using a point source scaling model of the DART impact. The model is applied to expected LICIACube plume images and shows how plume images enable characterization of the ejecta mass versus velocity distribution. The ejecta plume structure, as it evolves over time, is determined by the amount of ejecta that has reached a given altitude at a given time. The evolution of the plume optical depth profiles determined from LICIACube images can distinguish between strength-controlled and gravity-controlled impacts, by distinguishing the respective mass versus velocity distributions. LICIACube plume images discriminate the differences in plume structure and evolution that result from different target physical properties, mainly strength and porosity, thereby allowing inference of these properties to improve the determination of momentum transfer.
Gaia Data Release 2 includes observational data for 14,099 pre-selected asteroids. From the sparsely sampled G band photometry, we derive lower-limit lightcurve amplitudes for 11,665 main belt asteroids in order to provide constraints on the distribution of shapes in the asteroid main belt. Assuming a triaxial shape model for each asteroid, defined through the axial aspect ratios a > b and b=c, we find an average b/a=0.80+-0.04 for the ensemble, which is in agreement with previous results. By combining the Gaia data with asteroid properties from the literature, we investigate possible correlations of the aspect ratio with size, semi-major axis, geometric albedo, and intrinsic color. Based on our model simulations, we find that main belt asteroids greater than 50 km in diameter on average have higher b/a aspect ratios (are rounder) than smaller asteroids. We furthermore find significant differences in the shape distribution of main belt asteroids as a function of the other properties that do not affect the average aspect ratios. We conclude that a more detailed investigation of shape distribution correlations requires a larger data sample than is provided in Gaia Data Release 2.
The (153591) 2001 SN263 asteroid system, target of the first Brazilian interplanetary space mission, is one of the known three triple systems within the population of NEAs. One of the mission objectives is to collect data about the formation of this system. The analysis of these data will help in the investigation of the physical and dynamical structures of the components (Alpha, Beta and Gamma) of this system, in order to find vestiges related to its origin. In this work, we assume the irregular shape of the 2001 SN263 system components as uniform density polyhedra and computationally investigate the gravitational field generated by these bodies. The goal is to explore the dynamical characteristics of the surface and environment around each component. Then, taking into account the rotational speed, we analyze their topographic features through the quantities geometric altitude, tilt, geopotential, slope, surface accelerations, among others. Additionally, the investigation of the environment around the bodies made it possible to construct zero-velocity curves, which delimit the location of equilibrium points. The Alpha component has a peculiar number of 12 equilibrium points, all of them located very close to its surface. In the cases of Beta and Gamma, we found four equilibrium points not so close to their surfaces. Then, performing numerical experiments around their equilibrium points, we identified the location and size of just one stable region, which is associated with an equilibrium point around Beta. Finally, we integrated a spherical cloud of particles around Alpha and identified the location on the surface of Alpha were the particles have fallen.
The observationally complete sample of the main belt asteroids now spans more than two orders of magnitude in size and numbers more than 64,000 (excluding collisional family members). We undertook an analysis of asteroids eccentricities and their interpretation with simple physical models. We find that Plummers (1916) conclusion that the asteroids eccentricities follow a Rayleigh distribution holds for the osculating eccentricities of large asteroids, but the proper eccentricities deviate from a Rayleigh distribution: there is a deficit of eccentricities smaller than $sim0.1$ and an excess of larger eccentricities. We further find that the proper eccentricities do not depend significantly on asteroid size but have strong dependence on heliocentric distance: the outer asteroid belt follows a Rayleigh distribution, but the inner belt is strikingly different. Eccentricities in the inner belt can be modeled as a vector sum of a primordial eccentricity vector of random orientation and magnitude drawn from a Rayleigh distribution of parameter $sim0.06$, and an excitation of random phase and magnitude $sim0.13$. These results imply that a late dynamical excitation of the asteroids occurred, it was independent of asteroid size, it was stronger in the inner belt than in the outer belt. We discuss implications for the primordial asteroid belt and suggest that the observationally complete sample size of main belt asteroids is large enough that more sophisticated model-fitting of the eccentricities is warranted and could serve to test alternative theoretical models of the dynamical excitation history of asteroids and its links to the migration history of the giant planets.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
