While
photographers had to improvise to include clouds in their views for most of the
19th century, by the late 20th century it was possible for robotic cameras to
successfully record these weather patterns—all without direct human contact. Landing on July 4, 1997, the Mars Pathfinder was
a spacecraft sent by NASA to explore the red planet. Its six-wheeled robotic
rover, Sojourner, helped analyze the climate and geology of Mars and conduct
experiments with its atmosphere and soil composition. As in the survey expeditions
in the American West of the 1860s and 1870s, photography played a vital role in
this massive effort to gather data about an unknown land. Sojourner was
equipped with a camera on an expandable pole that sent images of Mars back to Earth.
This view of the Martian sky shows stratus clouds, consisting of ice condensed on
reddish dust particles, suspended low in the atmosphere.