Complex organic molecules tracing the comet-forming zones in protoplanetary disks

Resolved emission from gas-phase methanol can reveal the abundance and distribution of the comet-forming ice reservoir in protoplanetary disks. ALMA Cycle 4 observations of four transitions of gas-phase methanol in TW Hya allow the first model-independent determination of the rotational temperature of methanol in a prototoplanetary disk. The data confirm that the methanol is rotationally cold (T_rot < 50 K), and well constrain the column density to 2 × 10¹² cm^-2. Astrochemical models will constrain the chemical origin of methanol in TW Hya.