Free Astronomy Magazine March-April 2021

MARS ROVERS tion, which had its last communication session on September 27, 1997. That final communication also marked the end of So- journer’s mission, which up to that point had covered a distance of just over 100 meters. During that jour- ney, the rover had made a series of analyses, the first of which was on a rock called “Barnacle Bill.” The Alpha Proton X-ray Spec- trometer (APXS) was used to determine its composi- tion. The instrument took about ten hours to per- form a full scan of the sam- ple, finding many elements but only a small amount of hydrogen, which made up only 0.1 percent of the TOP MARS PATHFINDER SCIENCE FINDINGS • Rounded pebbles and cobbles at the landing site, and other observations, suggested conglomerates that formed in run- ning water during a warmer past in which liquid water was stable. • Radio tracking of Mars Pathfinder provided a precise measure of the lander's location and Mars' pole of rotation. The measurements suggested that the radius of the planet's central metallic core is greater than 800 miles (1,300 kilometers) but less than roughly 1,250 miles (2,000 kilometers). • Airborne dust is magnetic, and its characteristics suggest the magnetic mineral is maghemite, a very magnetic form of iron oxide, which may have been freeze-dried on the particles as a stain or cement. An active water cycle in the past may have leached out the iron from materials in the crust. • Dust devils were seen and frequently measured by temperature, wind and pressure sensors. Observations suggested that these gusts are a mechanism for mixing dust into the atmosphere. • Early morning water ice clouds were seen in the lower atmosphere. • Abrupt temperature fluctuations were recorded in the morning, suggesting that the atmosphere is warmed by the planet's surface, with heat convected upward in small eddies.