↑ "The World Factbook". www.cia.gov. Retrieved 2016-03-17. ↑ Altwegg, K.; Balsiger, H.; Bar-Nun, A.; Berthelier, J. J.; Bieler, A.; Bochsler, P.; Briois, C.; Calmonte, U.; Combi, M. (2015-01-23). "67P/Churyumov-Gerasimenko, a Jupiter family comet with a high D/H ratio".