ﻻ يوجد ملخص باللغة العربية
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.
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 th
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 wi
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
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 thic
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 s