GTC/CanariCam observations of (99942) Apophis

Abstract

Context. The potentially hazardous asteroid (PHA) (99942) Apophis is one of the most remarkable near-Earth asteroids (NEA) in terms of impact hazard. A good determination of its surface thermal inertia is very important in order to evaluate the Yarkovsky effect on its orbital evolution. Aims. We present thermal infrared observations obtained on January 29, 2013, with CanariCam mid-infrared camera/spectrograph attached to the Gran Telescopio CANARIAS (GTC, Roque de los Muchachos Observatory, La Palma, Spain) using the Si2-8.7, Si6-12.5, and Q1-17.65 filters with the aim of deriving Apophis' diameter (D), geometric albedo (p V ), and thermal inertia (Γ). Methods. We performed a detailed thermophysical model analysis of the GTC data combined with previously published thermal data obtained using Herschel Space Observatory PACS instrument at 70, 100, and 160 μm.Results. The thermophysical model fit of the data favors low surface roughness solutions (within a range of roughness slope angles rms between 0.1 and 0.5), and constrains the effective diameter, visible geometric albedo, and thermal inertia of Apophis to be D eff = 380-393 m, p V = 0.24-0.33 (assuming absolute magnitude H = 19.09 ± 0.19) and Γ = 50-500 Jm −2 −0.5 K −1 , respectively.

Impact probability under aleatory and epistemic uncertainties

“…Müller et al (2014) obtain p V = 0.30 +0.05 −0.06 from far-infrared observations with ESA's Herschel space observatory. Recent thermal infrared observations put p V in the range 0.24-0.33 (Licandro et al, 2016), in accordance with radar observations that gives p V = 0.35 ± 0.10 (Brozović et al, 2018). Farnocchia et al (2013a) used p V = 0.23 ± 0.02.…”

“…Müller et al (2014) use full range of Γ of 250-800 Jm −2 s −0.5 K −1 , with best solution at Γ = 600 Jm −2 s −0.5 K −1 , giving log 10 (Γ ) = 2.7 ± 0.25. Licandro et al (2016) constrain the thermal inertia of Apophis to lie in the range 50-500 Jm −2 s −0.5 K −1 , giving log 10 (Γ ) = 2.2 ± 0.5. Farnocchia et al (2013a) used a generic relationship between the thermal inertia and the diameter which led to log 10 (Γ ) = 2.65 ± 0.08.…”

Secular light curves of NEAs 2201 Oljato, 3200 Phaethon, 99942 Apophis, 162173 Ryugu, 495848 and 6063 Jason

“…According to Delbo et al (2007), it has a diameter of 270±60 m, an absolute magnitude H=19.7±0.4, and a geometric albedo pv=0.33±0.08. Licandro et al (2015) find effective diameter D=380-393 m, pv=0.24- Figure 7. The Secular Light Curve of 3200 Phaethon.…”

Surface thermophysical properties on the potentially hazardous asteroid (99942) Apophis

“…Until by now, the available thermal infrared measurements of Apophis are the far-IR data observed by the Herschel Space Observatory (Müller et al, 2014), and three mid-IR data measured by CanariCam of Gran Telescopio CANARIAS (Licandro et al, 2016). All these data are used in this work to be compared with the theoretical flux simulated from the so-called Advanced thermophysical Model so as to derive the possible scale of surface thermophysical properties.…”

“…Licandro et al (2016) used the same TPM like Müller et al (2014), but added three new mid-infrared data measured by CanariCam of Gran Telescopio CANARIAS. Both the work of Müller et al (2014) and Licandro et al (2016) assumed constant thermal emissivity to derive the surface thermophysical properties, but actually the thermal emissivity may be wavelength dependent from mid-infrared to far infrared (Müller & Lagerros, 1998), which should be taken into account when deriving the surface thermophysical properties.…”