Surface Properties, Orbital Dynamics, and Thermophysical Modeling of the Primitive Asteroid (269) Justitia

Abstract

The Emirates Mission to the Asteroid Belt (EMA) will study the ultra-red asteroid (269)~Justitia. In this work, we present the first detailed investigation of Justitia's surface dynamics using the newly developed 3-D polyhedral shape model with 574 vertices and 1,144 faces. We analyze its geopotential, surface acceleration, escape speeds, slopes, and equilibrium points, and we also search for planar symmetric periodic orbits using an equivalent ellipsoidal approximation. Our results indicate that the lowest geopotential values occur at the poles, which also correspond to regions of maximum surface acceleration. The global slope distribution suggests preferred zones of material accumulation or migration, offering clues to Justitia's long-term morphological evolution. Most slopes remain below $40^\circ$, implying that loose particles may settle stably across large portions of the surface. We identify five equilibrium points consistent with Justitia's estimated density and slow rotational period. Two external points (E$_2$ and E$_4$) exhibit linear stability, and all equilibrium locations lie relatively far from the surface due to the body's slow spin. Additionally, we discover 28 new families of planar symmetric periodic orbits, then classify their topologies and determine their linear stability, providing a dynamical framework relevant to future spacecraft operations near Justitia. Finally, thermal modeling reveals how thermal inertia and heliocentric distance shape Justitia's temperature distribution. The south pole receives more insolation than the north pole, reaching minimum temperatures of about 102~K and 87~K, respectively. These combined dynamical and thermal results offer valuable insights for the EMA mission and for understanding slowly rotating small bodies.

Figures (48)

• Figure 1: 3-D polyhedral shape model of asteroid Justitia presented in six perspective views ($\pm$x, $\pm$y, and $\pm$z). The shape model consisted of 574 vertices and 1,144 triangular faces. The color code indicates the distance from the centroid of each face to the asteroid's center of mass, in km.
• Figure 2: Geopotential distribution over the surface of asteroid Justitia, assuming a bulk density of 1.0 g cm$^{-3}$ and a rotational period of 33.12962 h, shown from views $-$x, $-$y, and $-$z. The color scale indicates the computed values from Eq. \ref{['eq:1']}, expressed in km$^{2}$ s$^{-2}$.
• Figure 3: Equipotential surface of Justitia and its contour lines in the xOy plane. The color box denotes the gravitational potential, $U(\mathbf{r})$, in km$^{^2}$ s$^{-2}$ around Justitia (black).
• Figure 4: The surface acceleration distribution across asteroid Justitia is presented from three orthogonal perspectives ($-$x, $-$y, and $-$z). The color bar represents the magnitude of the vector sum of the gravitational and centrifugal acceleration vectors $\mid\mid-\nabla V(\mathbf{r})\mid\mid$ at the barycenter of the facet, in km s$^ {-2}$.
• Figure 5: Gravitational acceleration around and inside Justitia in three orthogonal projections: xOy, xOz, and yOz planes. The contour lines represent lines of force. The color bar indicates the magnitude of the gravitational acceleration vector $\mid\mid-\nabla U(\mathbf{r}) \mid\mid$, measured in km s$^{-2}$.