Extended Data Fig. 3: Simulations of obliquity and orientation evolution taking into account sublimation torques. | Nature Astronomy

Extended Data Fig. 3: Simulations of obliquity and orientation evolution taking into account sublimation torques.

From: Sublimation as an effective mechanism for flattened lobes of (486958) Arrokoth

Extended Data Fig. 3

These simulations are performed with reduced assumption of pure CH4 icy bodies in order to get the upper limit of the sublimation torques. This reduces the time to reach the volume of the SHAPE-ORIG from the initial states (SHAPE-SYN and SHAPE-REV) to about 1 Myr. Due to the computationally intensive integral needed to solve the Euler equation, we present a tendency of the simulated spin state evolution for around 0.05 to 0.1 Myr. In panel A we show the obliquity change for both initial shapes as a function of time (for approx. 320 orbits or 0.1 Myr), starting with the current obliquity of Arrokoth. The relevant movement of the spin axis’ orientation in the space is shown in panel B in terms of right ascension and declination (Ra, Dec). The initial (Ra, Dec) state is in the lower right corner of the plot. These simulations show that obliquity, Ra. and Dec. changes are within 0.4, 0.3 and 0.5 deg respectively. The spin axis has a tendency to stay near the orbital plane, which is demonstrated in panels C and D, for two cases of obliquity close to 90° (89.99° and 90.002°) starting with SHAPE-SYN. The orientation changes of the spin axis are presented again in Ra. Dec. space for a simulation time of 200 orbits (about 0.06 Myr), during which the variation is less than 10−3 deg for both angles. A strong stability of orientation is preserved when the spin axis lies closely to the orbital plane and perihelion because the net torque in the inertial frame is minimized32,33.

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