On the Cover: We study rocks to discover clues about a planet's geologic and climatic history. On Earth, gray hematite (center) is commonly formed in liquid water. When scientists detected gray hematite on Mars, they pondered whether it, too, formed in water—could it be evidence of a warmer, wetter past?
Gray hematite has been identified in three locations on Mars—Valles Marineris (background), Meridiani Planum (left), and Aram crater (bottom). Background: JPL/NASA; left: NASA/JPL/Arizona State University; center: John Betts Fine Minerals; bottom: Kees Veenenbos
6 The MarsDial: A Sundial for the Red Planet: Woody Sullivan and Jim Bell channel Bill Nye's enthusiasm for sundials.
12 Mars Rocks! Deciphering Minerals on Mars: Melissa Lanetells us how we figure out what Mars is made of.
3 Members' DialogueGalileo, Planetary Society political advocacy, and SETI@home
4 We Make it Happen! Secret messages from Mars; building sundials
20 Q&A Why can't we see gravity? Where is Mercury 10?
22 Society News Scholarships, thank yous, and the annual audit
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