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We present a deep imaging and spectroscopic search for emission from (3200)Phaethon, a large near-Earth asteroid that appears to be the parent of thestrong Geminid meteoroid stream, using the 4.3 m Lowell Discovery Telescope.Observations were conducted on 2017 December 14-18 when Phaethon passed only0.07 au from the Earth. We determine the $3\sigma$ upper level of dust and CNproduction rates to be 0.007-0.2 $\mathrm{kg~s^{-1}}$ and$2.3\times10^{22}~\mathrm{molecule~s^{-1}}$ through narrowband imaging. Asearch in broadband images taken through the SDSS $r'$ filter shows no100-m-class fragments in Phaethon's vicinity. A deeper, but star-contaminatedsearch also shows no sign of fragments down to 15 m. Optical spectroscopy ofPhaethon and comet C/2017 O1 (ASASSN) as comparison confirms the absence ofcometary emission lines from Phaethon and yields $3\sigma$ upper levels of CN,C$_2$ and C$_3$ of $\sim10^{24}$-$10^{25} \mathrm{molecule~s^{-1}}$, 2 ordersof magnitude higher than the CN constraint placed by narrowband imaging, due tothe much narrower on-sky aperture of the spectrographic slit. We show thatnarrowband imaging could provide an efficient way to look for weak gas emissionfrom near-extinct bodies near the Earth, though these observations requirecareful interpretation. Assuming Phaethon's behavior is unchanged, our analysisshows that the DESTINY$^+$ mission, currently planning to explore Phaethon in2026, may not be able to directly detect a gas coma.

A Deep Search for Emission From "Rock Comet" (3200) Phaethon At 1 AU