We investigated the physical properties of the comet-like objects 107P/ ( 4015 ) Wilson–Harrington ( 4015WH ) and P/2006 HR30 ( Siding Spring ; HR30 ) by applying a simple thermophysical model ( TPM ) to the near-infrared spectroscopy and broadband observation data obtained by AKARI satellite of JAXA when they showed no detectable comet-like activity .
We selected these two targets since the tendency of thermal inertia to decrease with the size of an asteroid , which has been demonstrated in recent studies , has not been confirmed for comet-like objects .
It was found that 4015WH , which was originally discovered as a comet but has not shown comet-like activity since its discovery , has effective size D = 3.74–4.39 km and geometric albedo p _ { V } \approx 0.040–0.055 with thermal inertia \Gamma = 100–250 J m ^ { -2 } K ^ { -1 } s ^ { -1 / 2 } .
The corresponding grain size is estimated to 1–3 mm .
We also found that HR30 , which was observed as a bare cometary nucleus at the time of our observation , have D = 23.9–27.1 km and p _ { V } = 0.035–0.045 with \Gamma = 250–1,000 J m ^ { -2 } K ^ { -1 } s ^ { -1 / 2 } .
We conjecture the pole latitude -20 ^ { \circ } \lesssim \beta _ { s } \lesssim + 60 ^ { \circ } .
The results for both targets are consistent with previous studies .
Based on the results , we propose that comet-like objects are not clearly distinguishable from asteroidal counterpart on the D – \Gamma plane .