Title: Measurement of the distribution and excitation of cometary volatiles using ALMA

Abstract:
Comets are believed to have accreted at around the time the planets formed (c. 4.5 Gyr ago), 
and many have remained in a frozen, relatively quiescent state since then. Studies of cometary 
compositions using Earth and space-based instruments thus provide unique information 
regarding the physical and chemical conditions of the early Solar System. Use of gas-phase 
coma observations as a probe of cometary ice requires a complete understanding of the gas-
release mechanisms. However, previous observations have been unable to ascertain the precise 
origins of fundamental coma species such as H2CO, HCN and HNC, and details regarding the 
possible formation of these species in the coma are not well understood. In this work, we report 
results from the first cometary observations using the Atacama Large Millimeter Array (ALMA), 
and present measurements of spatially and spectrally-resolved distributions of HCN, HNC, 
H2CO, CH3OH and dust within the comae of three comets: C/2012 F6 (Lemmon), C/2012 S1 
(ISON) and C/2012 K1 (PanSTARRS). Our observations reveal an unprecedented level of detail 
in the distribution and excitation of these fundamental cometary molecules, and highlight the 
importance of high signal-to-noise, sub-arcsecond imaging for the derivation of cometary 
compositions. The powerful spectral imaging capabilities of ALMA and next-generation ground-
based telescopes such as the E-ELT will provide a crucial framework for the interpretation of 
results from current and future space-based comet observing missions.

Co-authors:
Anthony Remijan, Jeremie Boissier, Stefanie Milam, Michael Mumma, Steven Charnley, Lucas 
Paganini, Geronimo Villanueva, Dominique Bockelee-Morvan, Nicolas Biver, Yi-Jehng Kuan, 
Dariusz Lis, Jacques Crovisier, Iain Coulson, Dante Minniti