Surface thermophysical properties investigation of the potentially hazardous asteroid (99942) Apophis

Abstract

In this work, we investigate the surface thermophysical properties (thermal emissivity, thermal inertia, roughness fraction and geometric albedo) of asteroid (99942) Apophis, using the currently available thermal infrared observations of CanariCam on Gran Telescopio CANARIAS and far-infrared data by PACS of Herschel, on the basis of the Advanced thermophysical model. We show that the thermal emissivity of Apophis should be wavelength dependent from $8.70\mu m$ to $160\mu m$, and the maximum emissivity may arise around $20\mu m$ similar to that of Vesta. Moreover, we further derive the thermal inertia, roughness fraction, geometric albedo and effective diameter of Apophis within a possible 1$\sigma$ scale of $\Gamma =100_{-52}^{+100}\mathrm{J}{\mathrm{m}}^{-2}{\mathrm{s}}^{-0.5}{\mathrm{K}}^{-1}$, $f_{\mathrm{r}}=0.78\sim 1.0$, $p_{\mathrm{v}}=0.286_{-0.026}^{+0.030}$, $D_{\mathrm{eff}}=378_{-25}^{+19}\mathrm{m}$, and 3$\sigma$ scale of $\Gamma =100_{-100}^{+240}\mathrm{J}{\mathrm{m}}^{-2}{\mathrm{s}}^{-0.5}{\mathrm{K}}^{-1}$, $f_{\mathrm{r}}=0.2\sim 1.0$, $p_{\mathrm{v}}=0.286_{-0.029}^{+0.039}$, $D_{\mathrm{eff}}=378_{-29}^{+27}\mathrm{m}$. The derived low thermal inertia but high roughness fraction may imply that Apophis could have regolith on its surface, and less regolith migration process has happened in comparison with asteroid Itokawa. Our results show that small-size asteroids could also have fine regolith on the surface, and further infer that Apophis may be delivered from the Main Belt by Yarkovsky effect.

15 pages, 6 figures, 6 tables, accepted to Research in Astronomy and Astrophysics

References in corpus (5)

• Thermal inertia of near-Earth asteroids and implications for the magnitude of the Yarkovsky effect
• Thermal Infrared Observations of Asteroid (99942) Apophis with Herschel
• Shape, Thermal and Surface Properties determination of a Candidate Spacecraft Target Asteroid (175706) 1996 FG3
• Surface Thermophysical Properties determination of OSIRIS-REx target asteroid (101955) Bennu
• The astrometric Gaia-FUN-SSO observation campaign of 99 942 Apophis

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