Afonin, V., McKenna-Lawlor, S., Gringauz, K., Kecskemety, K., Keppler, E., Kirsch, E., Richter, A., O'Sullivan, D., Somogyi, A., Thompson, A., Varga, A., & Witte, M. (1989). Energetic ions in the close environment of Mars and particle shadowing by the planet. Nature, 341, 616-618.