Thermal infrared observations of asteroid (99942) Apophis with<i>Herschel</i>
T. G. Müller et al. (2014)
- Published
- Jun 1, 2014
- Journal
- Astronomy & Astrophysics · Vol. 566
- DOI
- 10.1051/0004-6361/201423841
At a GlanceAI
Herschel far-IR data plus a tumbling spin/shape model constrain Apophis’ elongated size (~375 m) and high thermal inertia.
SummaryAI
Using Herschel-PACS thermal infrared measurements taken before and after opposition, the authors thermophysically model Apophis while explicitly accounting for its non-principal-axis (tumbling) rotation and elongated convex shape. The combined geometry and shape-dependent flux changes across the two epochs require substantial heat retention, yielding a high thermal inertia (most likely 250–800, best ~600 J m−2 s−0.5 K−1) and a larger effective diameter than many earlier estimates (375+14−10 m) with pV≈0.30. The high inertia and Itokawa-like surface/physical similarities are interpreted as evidence for a rubble-pile–like body, implying a higher mass (≈4.4–6.2×10^10 kg) and correspondingly different Yarkovsky-driven orbit evolution and impact-risk modeling.
Method SnapshotAI
Fit a thermophysical model to multi-epoch Herschel far-IR photometry using a lightcurve-derived convex polyhedral shape and tumbling spin-state solution.
BackgroundAI
Background in asteroid thermophysical modeling, radiometry (size–albedo inference), and non-principal-axis rotation/shape modeling of small bodies.
Apophis physical model
— SA