Opportunity: travel diary

8 July 2003: Launch from Cape Canaveral, Florida, for a seven-month journey to Mars, where nobody will greet us. Sol 1, 25 January 2004: We cross the atmosphere in seven minutes and land in the small Eagle crater. Sedimentary rocks lie ten metres away. Seven sols of rest. Sol 13: We discover stone spherules, later found scattered widely. Their bluish appearance earns them the name blueberries. About four millimetres across, they contain hematite and jarosite formed in acidic waters toxic to humans. Some say the spherules fall from the sky. Sol 45: Phobos crosses the Sun. Sol 55: We try to climb out, slip on the steep slope and try somewhere else the following day. Sol 134: We descend cautiously into Endurance crater on a thirty-degree slope. Its sedimentary rocks can be drilled, and contain minerals formed in salt lakes on Earth. Sol 251: At Wopmay, spherules protrude from sandstone. Sols 284–297: We study the seven-metre Burns Cliff, named after Roger Burns, who predicted Martian jarosite. Its layers formed in a dry, windblown dune environment with fluctuating groundwater and temporary lakes that repeatedly dried. Sols 330–335: We pass the aluminium heat shield. Beware its sharp edges: it is turned inside out. Sol 339: In the dust we discover a hollow iron meteorite, Heat Shield Rock, officially Meridiani Planum MP001. Sols 446–484: At Purgatory Ripple, climbing a dune causes the wheels to sink into soft sand below a hard, brittle desert crust. While trapped, we make the Rub-al-Khali panorama.

Sol 654, Erebus crater: Layered rocks deposited underwater cracked after drying. Dark material in the cracks is sand. Sol 952: We reach Victoria crater at the spectacular Cape Verde viewpoint, then spend roughly a year circling the rim to find a safe way down. Sol 1160: Updated autonomous driving software is tested over sixteen metres. The rover independently avoids rocks on a surface carpeted with small spherules. From sol 1205, 2007, Ls 258°: The Mars Year 28 dust storm strikes. The sky darkens and instruments shut down. On sol 1236 only one percent of sunlight penetrates the dust, with optical depth 5.5. Days become 10–20 °C cooler and nights warmer. The final image before the storm shows the darkening landscape on sol 1224. Sol 1716: Solar conjunction blocks communication. Weather observations produce 6,448 files, which must be transmitted and deleted promptly to avoid Spirit’s sol-18 fault. Sol 2681, 2011: We reach Endeavour crater and name the rim Spirit Point for the rover whose career has just ended. Sol 2769, Homestake: A gypsum vein two by forty-five centimetres marks water once flowing through cracks. Sol 2811: Four Martian years of accumulated dust block the panels. We hope spring wind will clean them. Meanwhile we winter on a sixteen-degree, south-facing slope at Greeley Haven, named for planetary scientist Ronald Greeley, and study wind. Sol 3058, Cape York: Clay minerals preserve ancient traces of drinking-quality water. Sol 3061, Matijevic Hill: Kirkwood spherules—newberries—differ from blueberries. Sol 3773, 2014: A faulty memory cell repeatedly restarts the computer. For three months, only data transmitted to Earth that day can be kept. Sol 3894: We climb Cape Tribulation, the highest summit. Sol 3968, 24 March 2015: The odometer reaches 42.2 km—a marathon in 3,968 sols. Sol 3973: Three-metre rock spires stand in the unusual elongated Spirit of St Louis crater. Sol 4079: We enter Marathon Valley to find clay minerals previously detected from orbit. Sol 5104, Mars Year 34: An unusually early, powerful dust storm removes 99% of solar energy. Optical depth reaches 10.8, compared with 0.5 in clear weather: almost complete darkness for days. Sol 5111, 10 June 2018: Opportunity communicates for the last time. Its final returned image shows the Sun. We leave the rover in Perseverance Valley. Return to mission control for a new assignment.