  The presence of numerous complex organic molecules (COMs; defined as those
containing six or more atoms) around protostars shows that star formation is
accompanied by an increase of molecular complexity. These COMs may be part of
the material from which planetesimals and, ultimately, planets formed. Comets
represent some of the oldest and most primitive material in the solar system,
including ices, and are thus our best window into the volatile composition of
the solar protoplanetary disk. Molecules identified to be present in cometary
ices include water, simple hydrocarbons, oxygen, sulfur, and nitrogen-bearing
species, as well as a few COMs, such as ethylene glycol and glycine. We report
the detection of 21 molecules in comet C/2014 Q2 (Lovejoy), including the first
identification of ethyl alcohol (ethanol, C2H5OH) and the simplest
monosaccharide sugar glycolaldehyde (CH2OHCHO) in a comet. The abundances of
ethanol and glycolaldehyde, respectively 5 and 0.8% relative to methanol (0.12
and 0.02% relative to water), are somewhat higher than the values measured in
solar- type protostars. Overall, the high abundance of COMs in cometary ices
supports the formation through grain-surface reactions in the solar system
protoplanetary disk.
