Extended Data Fig. 5: Torque efficiency of SHAPE-SYN (upper panels) and SHAPE-REV (lower panels). | Nature Astronomy

Extended Data Fig. 5: Torque efficiency of SHAPE-SYN (upper panels) and SHAPE-REV (lower panels).

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

Extended Data Fig. 5

Here we provide additional information on surface torque efficiency \(-{\mathbf{r}}_i \times \hat n_{vi}\) in x, y and z direction for both initial shapes to assess whether to expect pronounced sublimation driven torques on the body. Here, ri and \(\hat n_{vi}\) are the radius and the unit vector in the direction of gas ejection of i-th facet. The distribution of positive (red) and negative (blue) values of torque efficiency indicating increasing or decreasing of the spin rate along the corresponding spin axis, are perfectly ‘symmetric’ on the surface of SHAPE-SYN. When the body is in a circular orbit with an obliquity of 90° (or 0°), the orbital averaged solar flux distribution on its surface is even between ‘red’ and ‘blue’ regions, resulting in a balance between the torques induced by mass loss in both regions This balance could not be perfectly achieved for SHAPE-REV since it exhibits a small degree of asymmetry, but the resulted non-zero torque is also of small absolute value in the case of circular orbit and an obliquity of 90°. Since Arrokoth has an obliquity close to 99° and small orbital eccentricity, the illumination distribution on its surface is evenly distributed in positive and negative regions and, hence, leads to a low magnitude of the sublimation induced torques. The red, green and blue arrows point in the direction of +x, +y and +z respectively, as labeled in the plots.

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