Characterization of of (98943) 2001 CC${}_{21}$, the target of Hayabusa2$\#$

Abstract

The near-Earth asteroid (98943) Torifune, previously designated 2001 CC${}_{21}$, is the flyby target of the Hayabusa2 extended mission, nicknamed Hayabusa2$\#$ (SHARP: Small Hazardous Asteroid Reconnaissance Probe). The ground-based telescope observations offer a key science input for the mission's scientific investigation. During 2022 - 2024 this asteroid was at visible apparent magnitudes brighter than 18.5, allowing for a detailed characterization using ground-based telescope observations. We determined its rotation period $P=5.021516\pm 0.000106$ h and its absolute magnitude H = 18.78 $\pm$ 0.14 and. The large number of lightcurves allows to estimate its axes ratio, its convex shape and its pole orientation $\lambda =301^{\circ }\pm 35^{\circ }$, $\beta ={89_{-6}^{+1}}^{\circ }$ and $\epsilon =5^{\circ }\pm 3^{\circ }$ which indicate a prograde rotation. We report the semi-axis of the equivalent ellipsoid, $a$ = 0.42${}_{0.06}^{+0.08}$ km, $b$ = 0.16${}_{0.04}^{+0.05}$ km, and $c$ = $0.17\pm 0.03$ km. Consequently, the volume equivalent diameter is $D_{eq}$ = $0.44\pm 0.06$ km . Using observations conducted simultaneously with four broadband filters, we determined $(g-r)=0.663\pm 0.022$ mag, $(r-i)=0.177\pm 0.012$ mag, and $(i-z_s)=-0.061\pm 0.032$ mag. Additionally, we found that Torifune exhibits no detectable large-scale heterogeneity. We classified the object using a high signal-to-noise ratio spectrum (over the visible and near-infrared region) as Sq-type in the Bus-DeMeo taxonomy. We estimate a mineralogy similar to LL/L ordinary chondrites, with an ol/(ol+px) = 0.60, a Fa content of 28.5 mol$\%$, and a Fs content of 23.4 mol$\%$. The spectral data indicate a surface affected by moderate space weathering effects.

Accepted for publication in PSJ, 29 page, 15 figures

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