Comet 289P/Blanpain: Near-Perihelion Activity and the Phoenicids

Abstract

We present NEOWISE observations of Jupiter family comet 289P/Blanpain, the parent body of the Phoenicid meteoroid stream. Near-infrared images at 3.4$\mu$m ($W1$) and 4.6$\mu$m ($W2$) were obtained near perihelion on two occasions: UT 2019-10-30 (inbound, heliocentric distance $R_{\rm h}$ = 1.20 au) and UT 2020-01-11/12 (outbound, $R_{\rm h}$ = 1.01 au). To assess faint activity, we establish constraints on dust production driven by the limited sublimating area of water ice, based on studies of the 1956 Phoenicids. The ejected dust mass is $M_{\rm d}$ = 4100 $\pm$ 200 kg (inbound) and 1700 $\pm$ 200 kg (outbound), respectively. The dust production rates are $Q_{\rm dust}$ = 0.01$-$0.02 kg s$^{-1}$, corresponding to dust-to-gas production ratio 2 $\leqslant\,f_{\rm dg}\,\leqslant$ 6. The resulting fractional active area, $f_{\rm A}$ = 3.8 $\pm$ 1.9 $\times 10^{-5}$, is the smallest yet reported. The absence of 4.6$\mu$m ($W2$) excess suggests that 289P contains negligible amounts of CO$_2$ and CO. Time-resolved analysis of weighted mean of $W1$ and $W2$ magnitudes finds a distinctive peak amplitude in the light curve having a rotational period $P_{\rm rot}$ = 8.8536 $\pm$ 0.3860 hr, however, further verification is needed. The perihelion-normalized nongravitational acceleration, $\alpha_{\rm NG}^\prime$ = 3.1 $\times$ 10$^{-6}$, is approximately an order of magnitude smaller than the trend observed for well-studied comets, consistent with weak outgassing. Current dust production from 289P, regardless of plausible assumptions for particle size and distribution, is an order of magnitude too small to produce the Phoenicid stream within its $\sim$300 yr dynamical lifetime. This suggests another mass supply, probably in 1743$-$1819, rapid rotational destruction of a sub-km precursor body, resulting in fragments equaling the mass of an object with radius $\sim$ 100 m.