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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.04.015 Byline: Sho Fukuzaki (a), Yasuhito Sekine (a), Hidenori Genda (b), Seiji Sugita (a), Toshihiko Kadono (c), Takafumi Matsui (d) Keywords: Titan; Atmospheres, Evolution; Impact processes; Satellites, Atmospheres Abstract: Chemical reactions and volatile supply through hypervelocity impacts may have played a key role for the origin and evolution of both planetary and satellite atmospheres. In this study, we evaluate the role of impact-induced N.sub.2 production from reduced nitrogen-bearing solids proposed to be contained in Titan's crust, ammonium sulfate ((NH.sub.4).sub.2SO.sub.4), for the replenishment of N.sub.2 to the atmosphere in Titan's history. To investigate the conversion of (NH.sub.4).sub.2SO.sub.4 into N.sub.2 by hypervelocity impacts, we measured gases released from (NH.sub.4).sub.2SO.sub.4 that was exposed to hypervelocity impacts created by a laser gun. The sensitivity and accuracy of the measurements were enhanced by using an isotope labeling technique for the target. We obtained the efficiency of N.sub.2 production from (NH.sub.4).sub.2SO.sub.4 as a function of peak shock pressure ranging from [approximately equal to]8 to [approximately equal to]45GPa. Our results indicate that the initial and complete shock pressures for N.sub.2 degassing from (NH.sub.4).sub.2SO.sub.4 are [approximately equal to]10 and [approximately equal to]25GPa, respectively. These results suggest that cometary impacts on Titan (i.e., impact velocity v.sub.i [approximately equal to]8km/s) produce N.sub.2 efficiently; whereas satellitesimal impacts during the accretion (i.e., v.sub.i Author Affiliation: (a) Department of Complexity Science and Engineering, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8561, Japan (b) Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo 113-0033, Japan (c) Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita 565-0871, Japan (d) Planetary Explorations Research Center, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino 275-0016, Japan Article History: Received 23 November 2009; Revised 21 April 2010; Accepted 21 April 2010