Kevin Williams may have found one of the best places on Mars to look for past or present life. The region lies at the merger of two ancient riverbeds, the Samara and Paraná-Loire Valles systems. But the past presence of water is only part of the reason why the area intrigues Williams and his colleagues at the Smithsonian Institution in Washington, D.C.
Visible and infrared images taken by two Mars-orbiting spacecraft reveal that a kilometer-high edifice, probably a volcano, lies at the confluence. Moreover, the appearance of soil at the site indicates that when the volcano erupted, its lava encountered liquid or frozen water. Williams presented the findings March 15 at the annual Lunar and Planetary Science Conference in Houston.