English: NASA's Perseverance Mars rover dropped the last of 10 tubes at the "Three Forks" sample depot on Jan. 28, 2023, the 690th Martian day, or sol, of the mission. This image of the 10th tube was taken by the WATSON (Wide Angle Topographic Sensor for Operations and eNgineering) camera on the end of the rover's 7-foot-long (2-meter-long) robotic arm. This final sample is what's called a "witness" tube – one of three collected by the rover so far and the only one deposited at the depot. Witness tubes are similar to the sample tubes that hold Martian rock and sediment, except they have been preloaded with a variety of materials that can capture molecular and particulate contaminants. They are opened on the Martian surface to "witness" the ambient environment near sample collection sites. With samples returned to Earth in the future, the witness tubes would be used to determine if samples being collected might be contaminated with materials that traveled with the rover from Earth. The Three Forks depot, the first sample depot on another world, is a crucial milestone in the NASA-ESA (European Space Agency) Mars Sample Return campaign, which aims to bring Mars samples to Earth for closer study. The Perseverance rover will be the primary means to convey the collected samples to a future robotic lander as part of the campaign. The lander would, in turn, use a robotic arm to place the samples in a containment capsule aboard a small rocket that would blast off to Mars orbit, where another spacecraft would capture the sample container and return it safely to Earth. Hosting the duplicate set, the Three Forks depot will serve as a backup if Perseverance can't deliver its samples. A key objective for Perseverance's mission on Mars is astrobiology, including the search for signs of ancient microbial life. The rover will characterize the planet's geology and past climate, pave the way for human exploration of the Red Planet, and be the first mission to collect and cache Martian rock and regolith (broken rock and dust). Subsequent NASA missions, in cooperation with ESA (European Space Agency), would send spacecraft to Mars to collect these sealed samples from the surface and return them to Earth for in-depth analysis. The Mars 2020 Perseverance mission is part of NASA's Moon to Mars exploration approach, which includes Artemis missions to the Moon that will help prepare for human exploration of the Red Planet. https://photojournal.jpl.nasa.gov/catalog/PIA25340