The tumbling spin state of (99942) Apophis
P. Pravec et al. (2014)
- Published
- May 1, 2014
- Journal
- Icarus · Vol. 233
- DOI
- 10.1016/j.icarus.2014.01.026
At a GlanceAI
Lightcurves show Apophis is a mildly excited tumbler with a near‑prolate inertia ellipsoid, constraining its precession/rotation periods.
SummaryAI
Using a densely calibrated multi-telescope lightcurve campaign, the authors show (99942) Apophis is in non-principal-axis rotation (tumbling) in a Short-Axis Mode state. They invert the full-apparition photometry to jointly solve for spin state and a convex shape, finding a near-prolate inertia structure (I2≈I3, much larger than I1) that yields sizeable wobble even though the excitation energy is low (E/E0≈1.024). The model provides distinct precession and spin periods (Pφ≈27.38 h, Pw≈263 h) and a retrograde angular-momentum direction, which narrows the plausible Yarkovsky drift range relevant to post-2029 impact-keyhole predictions. More broadly, Apophis is placed in the “slow tumbler” population, where observed PA/NPA transitions appear to track roughly constant damping time, hinting either multiple excitation pathways or size-dependent dissipation (lQ).
Method SnapshotAI
Convex lightcurve inversion with rigid-body NPA (Euler-equations) dynamics fits multi-epoch photometry to solve for Apophis’s tumbling state and shape.
BackgroundAI
Background in asteroid lightcurve photometry plus rigid-body rotation (principal moments, precession in SAM/LAM) is needed to follow the tumbling/shape inference.
Apophis physical model
— SA