Sample-return mission

The "Genesis Rock", returned by the Apollo 15 lunar mission in 1971.

A sample-return mission is a spacecraft mission with the goal of collecting and returning tangible samples from an extraterrestrial location to Earth for analysis. Sample-return missions may bring back merely atoms and molecules or a deposit of complex compounds such as loose material ("soil") and rocks. These samples may be obtained in a number of ways, such as soil and rock excavation, mining, or a collector array used for capturing particles of solar wind or cometary debris.

Up to the present, humanity has collected samples of six identified Solar System bodies, as well as samples of the solar wind. These samples were acquired through three methods: the collection of samples of Earth itself, the collection of meteorites that have fallen on Earth, and the collection of samples through sample-return missions. Samples of Moon rock from Earth's Moon were collected both from meteorites and through robotic and crewed sample-return missions. The comet Wild 2 and the asteroid 25143 Itokawa were visited by a robotic spacecraft, which returned samples to Earth. Furthermore, samples for three identified Solar System bodies were only collected by means other than sample-return missions: samples from Earth itself, samples from Vesta in the form of HED meteorites, and samples from Mars in the form of Martian meteorites.

Scientific use

A meteorite from Vesta that fell on Africa

Samples available on Earth can be analyzed in laboratories, so we can further our understanding and knowledge as part of the discovery and exploration of the Solar System. Until now many important scientific discoveries about the Solar System were made remotely with telescopes, and some Solar System bodies were visited by orbiting or even landing spacecraft with instruments capable of remote sensing or sample analysis. While such an investigation of the Solar System is technically easier than a sample-return mission, the scientific tools available here on Earth to study such samples are far more advanced and diverse than those that can go on spacecraft. Analysis of samples on Earth allows to follow up any findings with different tools, including tools that have yet to be developed; in contrast, a spacecraft can carry only a limited set of analytic tools, and these have to be chosen and built long before launch.

Samples analyzed on Earth can be matched against findings of remote sensing, for more insight into the processes that formed the Solar System. This was done, for example, with findings by the Dawn spacecraft, which visited the asteroid Vesta from 2011 to 2012 for imaging, and samples from HED meteorites (collected on Earth until then), which were compared to data gathered by Dawn.[1] These meteorites could then be identified as material ejected from the large impact crater Rheasilvia on Vesta. This allowed deducing the composition of crust, mantle and core of Vesta. Similarly some differences in composition of asteroids (and, to a lesser extent, different compositions of comets) can be discerned by imaging alone. However, for a more precise inventory of the material on these different bodies, more samples will be collected and returned in the future, to match their compositions with the data gathered through telescopes and astronomical spectroscopy.

One further focus of such investigation—besides the basic composition and geologic history of the various Solar System bodies—is the presence of the building blocks of life on comets, asteroids, Mars or the moons of the gas giants. Several sample-return missions to asteroids and comets are currently in the works. More samples from asteroids and comets will help determine whether life formed in space and was carried to Earth by meteorites. Another question under investigation is whether extraterrestrial life formed on other Solar System bodies like Mars or on the moons of the gas giants, and whether life might even exist there today. The result of NASA's last "Decadal Survey" was to prioritize a Mars sample-return mission, as Mars has a special importance: it is comparatively "nearby", might have harbored life in the past, and might even be able to sustain life today. Jupiter's moon Europa is another important focus in the search for life in the Solar System. However, due to the distance and other constraints, Europa might not be the target of a sample-return mission in the foreseeable future.