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One of the least understood properties of comets is the compositionalstructure of their nuclei, which can either be homogeneous or heterogeneous.The nucleus structure can be conveniently studied at millimeter wavelengths,using velocity-resolved spectral time series of the emission lines, obtainedsimultaneously for multiple molecules as the body rotates. Using thistechnique, we investigated the sources of CH3OH and HCN in comet 103P/Hartley2, the target of NASA's EPOXI mission, which had an exceptionally favorableapparition in late 2010. Our monitoring with the IRAM 30 m telescope showsshort-term variability of the spectral lines caused by nucleus rotation. Thevarying production rates generate changes in brightness by a factor of 4 forHCN and by a factor of 2 for CH3OH, and they are remarkably well correlated intime. With the addition of the velocity information from the line profiles, weidentify the main sources of outgassing: two jets, oppositely directed in aradial sense, and icy grains, injected into the coma primarily through one ofthe jets. The mixing ratio of CH3OH and HCN is dramatically different in thetwo jets, which evidently shows large-scale chemical heterogeneity of thenucleus. We propose a network of identities linking the two jets withmorphological features reported elsewhere, and postulate that the chemicalheterogeneity may result from thermal evolution. The model-dependent averageproduction rates are 3.5x10**26 molec/s for CH3OH and 1.25x10**25 molec/s forHCN, and their ratio of 28 is rather high but not abnormal. The rotationaltemperature from CH3OH varied strongly, presumably due to nucleus rotation,with the average value being 47 K.

The Sources of HCN and CH3OH and the Rotational Temperature in Comet 103P/Hartley 2 from Time-Resolved Millimeter Spectroscopy