<jats:title>Mars' Atmosphere from Curiosity</jats:title> <jats:p> The Sample Analysis at Mars (SAM) instrument on the Curiosity rover that landed on Mars in August last year is designed to study the chemical and isotopic composition of the martian atmosphere. <jats:bold> Mahaffy <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6143" page="263" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1237966">263</jats:related-article> ) present volume-mixing ratios of Mars' five major atmospheric constituents (CO <jats:sub>2</jats:sub> , Ar, N <jats:sub>2</jats:sub> , O <jats:sub>2</jats:sub> , and CO) and isotope measurements of <jats:sup>40</jats:sup> Ar/ <jats:sup>36</jats:sup> Ar and C and O in CO <jats:sub>2</jats:sub> , based on data from one of SAM's instruments, obtained between 31 August and 21 November 2012. <jats:bold> Webster <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6143" page="260" related-article-type="in-this-issue" vol="341" xlink:href="10.1126/science.1237961">260</jats:related-article> ) used data from another of SAM's instruments obtained around the same period to determine isotope ratios of H, C, and O in atmospheric CO <jats:sub>2</jats:sub> and H <jats:sub>2</jats:sub> O. Agreement between the isotopic ratios measured by SAM with those of martian meteorites, measured in laboratories on Earth, confirms the origin of these meteorites and implies that the current atmospheric reservoirs of CO <jats:sub>2</jats:sub> and H <jats:sub>2</jats:sub> O were largely established after the period of early atmospheric loss some 4 billion years ago. </jats:p>