Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Excited Spin State of Dimorphos Resulting from the DART Impact
90
0
0.0
(
0
)
Authors
Harrison F. Agrusa
Ask ChatGPT about the research
No Arabic abstract
The NASA Double Asteroid Redirection Test (DART) mission is a planetary defense-driven test of a kinetic impactor on Dimorphos, the satellite of the binary asteroid 65803 Didymos. DART will intercept Dimorphos at a relative speed of ${sim}6.5 text{ km s}^{-1}$, perturbing Dimorphoss orbital velocity and changing the binary orbital period. We present three independent methods (one analytic and two numerical) to investigate the post-impact attitude stability of Dimorphos as a function of its axial ratios, $a/b$ and $b/c$ ($a ge b ge c$), and the momentum transfer efficiency $beta$. The first method uses a novel analytic approach in which we assume a circular orbit and a point-mass primary that identifies four fundamental frequencies of motion corresponding to the secondarys mean motion, libration, precession, and nutation frequencies. At resonance locations among these four frequencies, we find that attitude instabilities are possible. Using two independent numerical codes, we recover many of the resonances predicted by the analytic model and indeed show attitude instability. With one code, we use fast Lyapunov indicators to show that the secondarys attitude can evolve chaotically near the resonance locations. Then, using a high-fidelity numerical model, we find that Dimorphos enters a chaotic tumbling state near the resonance locations and is especially prone to unstable rotation about its long axis, which can be confirmed by ESAs Hera mission arriving at Didymos in late 2026. We also show that a fully coupled treatment of the spin and orbital evolution of both bodies is crucial to accurately model the long-term evolution of the secondarys spin state and libration amplitude. Finally, we discuss the implications of a post-impact tumbling or rolling state, including the possibility of terminating BYORP evolution if Dimorphos is no longer in synchronous rotation.
rate research
Read More
The ac-susceptibility of the electron doped single-layered manganite La$_{1.1}$Sr$_{0.9}$MnO$_4$ is analyzed in detail. A quasi two-dimensional (2$D$) antiferromagnetic (AFM) order with Ising anisotropy is stabilized below $T_N$ $sim$ 80K. We show that below $T_N$, a rare 2$D$ spin-glass (SG) correlation develops with the same Ising anisotropy as the AFM state. Using simple scaling arguments of the droplet model, we derive a scaling form for the ac-susceptibility data of a 2$D$ SG, which our experimental data follows fairly well. Due to simplifications in this 2$D$ case, the proposed scaling form only contains two unknown variables $psi u$ and $tau_0$. Hence, the logarithmic growth law of the SG correlation predicted by the droplet model is convincingly evidenced by the scaling of our experimental data. The origin and nature of this 2$D$ SG state is also discussed.
Impacts between planetary-sized bodies can explain the origin of satellites orbiting large ($R>500$~km) trans-Neptunian objects. Their water rich composition, along with the complex phase diagram of water, make it important to accurately model the wide range of thermodynamic conditions material experiences during an impact event and in the debris disk. Since differences in the thermodynamics may influence the system dynamics, we seek to evaluate how the choice of an equation of state (EOS) alters the systems evolution. Specifically, we compare two EOSs that are constructed by different approaches: either by a simplified analytic description (Tillotson), or by interpolation of tabulated data (Sesame). Approximately $50$ pairs of Smoothed Particle Hydrodynamics impact simulations were performed, with similar initial conditions but different EOSs, in the parameter space in which the Pluto-Charon binary is thought to form (slow impacts between Pluto-size, water rich bodies). Generally, we show that impact outcomes (e.g., circumplanetary debris disk) are consistent between EOSs. Some differences arise, importantly in the production of satellitesimals (large intact clumps) that form in the post-impact debris disk. When utilizing an analytic EOS, the emergence of satellitesimals is highly certain, while when using the tabulated EOS it is less common. This is because for the typical densities and energies experienced in these impacts, the analytic EOS predicts very low pressure values, leading to particles artificially aggregating by a tensile instability.
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.
With the goal of understanding why X-rays have been reported near some high velocity clouds, we perform detailed 3 dimensional hydrodynamic and magnetohydrodynamic simulations of clouds interacting with environmental gas like that in the Galaxys thick disk/halo or the Magellanic Stream. We examine 2 scenarios. In the first, clouds travel fast enough to shock-heat warm environmental gas. In this scenario, the X-ray productivity depends strongly on the speed of the cloud and the radiative cooling rate. In order to shock-heat environmental gas to temperatures of > or = 10^6 K, cloud speeds of > or = 300 km/s are required. If cooling is quenched, then the shock-heated ambient gas is X-ray emissive, producing bright X-rays in the 1/4 keV band and some X-rays in the 3/4 keV band due to O VII and other ions. If, in contrast, the radiative cooling rate is similar to that of collisional ionizational equilibrium plasma with solar abundances, then the shocked gas is only mildly bright and for only about 1 Myr. The predicted count rates for the non-radiative case are bright enough to explain the count rate observed with XMM-Newton toward a Magellanic Stream cloud and some enhancement in the ROSAT 1/4 keV count rate toward Complex C, while the predicted count rates for the fully radiative case are not. In the second scenario, the clouds travel through and mix with hot ambient gas. The mixed zone can contain hot gas, but the hot portion of the mixed gas is not as bright as those from the shock-heating scenario.
The flashes from meteoroid impacts on the Moon are useful in determining the flux of impactors with masses as low as a few tens of grams. A routine monitoring program at NASAs Marshall Space Flight Center has recorded over 300 impacts since 2006. A selection of 126 flashes recorded during periods of photometric skies was analyzed, creating the largest and most homogeneous dataset of lunar impact flashes to date. Standard CCD photometric techniques were applied to the video and the luminous energy, kinetic energy, and mass are estimated for each impactor. Shower associations were determined for most of the impactors and a range of luminous efficiencies was considered. The flux to a limiting energy of 2.5E-6 kT TNT or 1.05E7 J is 1.03E-7 km-2 hr-1 and the flux to a limiting mass of 30 g is 6.14E-10 m-2 yr-1 at the Moon. Comparisons made with measurements and models of the meteoroid population indicate that the flux of objects in this size range is slightly lower (but within error bars) than flux at this size from the near Earth object and fireball population by Brown et al. 2002. Size estimates for the crater detected by Lunar Reconnaissance Orbiter from a large impact observed on March 17, 2013 are also briefly discussed.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
