# Sources of Extraterrestrial Rare Earth Elements: To the Moon and Beyond
## 3 Earth's Moon: Missions to Our Nearest Neighbor  
Study of Earth's Moon began several centuries ago in 1609 as [PERSON] made the first telescopic observations of Earth's nearest neighbor in space [23]. Observations, exploration, and the study of Moon formation and evolution have continued ever since the first spacecraft landed on the lunar surface in 1959 as part of the Soviet Union's Space Program (Luna 2). The most recent lunar landing occurred in 2013 through the China National Space Administration (the Chang'e 3 mission) and a follow-up mission, Chang'e 5, is scheduled to be launched November 2017. This will be the first lunar sample return mission since 1976 (Luna 24). The sources of raw materials, on which the human race depends, have to date originated from one planet, Earth. Advances in space exploration technology however have the potential to expand our \"closed planetary economy\" to include extraterrestrial resources [24]. Efforts to map and characterize the lunar surface have been extensive, and are ongoing: SMART-1 (European Space Agency, 2004); Kaguya (Japan, 2007); Chang'e-1 (China, 2007); Chandrayaan-1 (India, 2008); Lunar Reconnaissance Orbiter (LRO, United States of America, 2009); Chang'e-2 (China, 2010); the Gravity Recovery and Interior Laboratory (GRAIL, United States of America, 2012); and Chang'e-3 (which included a lander and rover, the first lunar landing since 1976, China, 2013). Yet, not since the mission of the Luna 24 mission in August 1976, has a spacecraft designed for sample return landed on the Moon, and not since December 1972 has humankind set foot on the lunar surface (Apollo 17) [25]. The Earth's Moon has previously been described as an \"Earth-orbiting Space Station\" [26] on which exist, natural resources that have the potential to be practically, and sustainably, used by humanity. The Earth's Moon is fundamental to advancing our understanding of the evolution of terrestrial planets and is the only other Solar System object for which a rich data set of geology, mineralogy, petrology, geochemistry, geochronology, and internal architecture exists. The exploration of the Moon and its resources is a fundamental step in furthering the exploration of our Solar System [26; 27]. The potential use of Earth's Moon as a resource is thus an important discussion to have within the context of sustaining human society and the planning of future space investigations. If humankind is to one day live on extraterrestrial bodies, such as the Moon or Mars, then the dependency on Earth as a resource source needs to be minimized, and the development of in situ resource dependency maximized [28]. The establishment of a base station on the lunar surface may one day be required in order to facilitate humankinds' exploration of our Solar System to, and beyond, to Mars. This would require a self-sufficient operational base where fundamental life support materials existed, fuel components were available, and construction materials were accessible (e.g., [29; 30; 31]). A decade ago, 14 space agencies developed a vision for human space exploration and established a network through which this could be communicated, and ultimately achieved [32]. This is The Global Exploration Strategy: The Framework for Coordination. The first target is the nearest one in our Solar System, the Earth's Moon. The Earth's Moon has been the focus of geoscientific and cosmoscientific investigations for decades. It is a window into early Solar System processes which were fundamental to the geological and chemical evolution of Earth, and it provides insights into the evolution of planetary bodies (e.g., [33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59]). Numerous scientific, technological, socio-economical, and political rationales exist that justify our study and exploration of Earth's nearest neighbor in space, but in order to maximize the potential of the Moon as a resource, stakeholders and nations will have to effectively and sustainably collaborate [22].