One of the least understood properties of comets is the compositional structure 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 , obtained simultaneously for multiple molecules as the body rotates .
Using this technique , we investigated the sources of CH _ { 3 } OH and HCN in comet 103P/Hartley 2 , the target of NASA ’ s EPOXI mission , which had an exceptionally favorable apparition in late 2010 .
Our monitoring with the IRAM 30 m telescope shows short-term variability of the spectral lines caused by nucleus rotation .
The varying production rates generate changes in brightness by a factor of 4 for HCN and by a factor of 2 for CH _ { 3 } OH , and they are remarkably well correlated in time .
With the addition of the velocity information from the line profiles , we identify the main sources of outgassing : two jets , oppositely directed in a radial sense , and icy grains , injected into the coma primarily through one of the jets .
The mixing ratio of CH _ { 3 } OH and HCN is dramatically different in the two jets , which evidently shows large-scale chemical heterogeneity of the nucleus .
We propose a network of identities linking the two jets with morphological features reported elsewhere , and postulate that the chemical heterogeneity may result from thermal evolution .
The model-dependent average production rates are 3.5 \times 10 ^ { 26 } molec s ^ { -1 } for CH _ { 3 } OH and 1.25 \times 10 ^ { 25 } molec s ^ { -1 } for HCN , and their ratio of 28 is rather high but not abnormal .
The rotational temperature from CH _ { 3 } OH varied strongly , presumably due to nucleus rotation , with the average value being 47 K .