Volatile Lunacy

editorial Volatile lunacy

Over the past six years an increasingly complex view of water inside and on the surface of the Moon has emerged. Lunar water has moistened sticky questions, and so renewed lunar exploration efforts are needed to deepen our knowledge of the Earth–Moon system.

Only six years ago, much of what we Just one month later, the hypothesis thought we knew about the Moon suddenly was confirmed when a spent Centaur seemed doubtful. A significant quantity rocket disconnected from NASA’s of water molecules, trapped within Lunar Crater Observation and Sensing small beads of volcanic glass in Apollo Satellite (LCROSS) spacecraft and samples1, seemed irreconcilable with a deliberately crashed into a permanently body born from the hot debris of a giant shadowed crater. Within the plume of impact, without enough gravity to hold an material thrown up by the impact, the atmosphere and with a surface exposed LCROSS spectrometer detected about to a harsh space weathering environment. 150 kilograms of water5. The water ice Unlike rocks found on Earth, early analyses stored in polar regions could have been of the Apollo samples did not reveal any implanted in the lunar regolith by the 6 water-bearing minerals, or any evidence / ALAMY © NAGELESTOCK.COM solar wind or delivered by meteorite or for aqueous alteration. For decades, lunar cometary impacts. scientists assumed that the Moon was dry. Earth, but the retention of so much water The discoveries of water inside and As discussed in a web focus published with in the lunar interior is more than can be on the surface of the Moon are fuelling this issue (http://www.nature.com/ngeo/ accommodated easily by many Moon renewed passion for lunar exploration focus/lunar-water/index.html), the 2008 formation models3. in an increasingly diverse crowd. As discovery of lunar water was not an isolated Volatile elements are a central constraint the Chinese Chang’e 3 spacecraft — case. And the presence of water, even in in our understanding of planet formation representing the first soft landing on sparse amounts, has the potential to stir up and evolution. For example, the apparent the Moon since 1976 — and its rover lunar science. dearth of water on the Moon and the Yutu sit on the lunar surface studying Modern analytical techniques, applied abundance of it on Earth was one line of the surrounding terrain (page 391), to the decades-old lunar sample collection, evidence for the Moon’s formation in a privately funded teams across the world have also revealed appreciable amounts giant impact. Furthermore, as we know are scrambling for the $30 million Google of water in apatite minerals from vast from terrestrial studies, volatile elements Lunar XPRIZE, promised to the first team basaltic plains that arise from deep mantle affect mantle dynamics, volcanism, with a spacecraft that lands safely on the sources, as well as in other lunar crustal seismicity and other geological processes. lunar surface, travels 500 metres and beams rocks thought to be later-stage magmatic For example, there is evidence that the images back to Earth7. And the Shackleton intrusions. And water bound to minerals ancient Moon had a complex lunar dynamo Energy company in Texas, USA, plans that formed in the lunar interior and were (page 409), the enigmatic longevity of to mine the Moon’s surface water to fuel then exposed by impacts has been remotely which could be attributed to a water- space exploration8. sensed from orbit2. As Robinson and enriched reservoir near the core–mantle ‘Follow the water’ has long been NASA’s Taylor demonstrate in a Review Article on boundary (page 400). motto for Mars exploration9. Unlike on page 401, the emerging picture of water in The discovery of lunar water has Mars, it is doubtful that the Moon’s water the Moon’s interior is one of heterogeneity. also triggered a reassessment of surface ever existed in liquid form, let alone Lunar models face a daunting challenge processes. A year after the discovery of supported life. But, as is the case for Mars10, to explain a Moon within which water bound within lunar igneous rocks, deciphering the presence of lunar water wetness varies. traces of water were remotely detected with targeted exploration efforts can help Lunar water has been detected as across the lunar surface, especially at to unravel the formation and evolution of molecules locked up within rocks’ mineral high latitudes. In September 2009, NASA the Moon, and by extension its companion structures, and not as pools of liquid as on reported that its Moon Mineralogy Mapper from birth, the Earth. ❐ Earth, but there are perplexing similarities spectrometer aboard the Indian Space to the Earth’s interior. Although the water Research Organization’s Chandrayaan-1 References 1. Saal, A. E. et al. Nature 454, 192–195 (2008). content of the volcanic glasses — a few spacecraft had detected absorption features 2. Klima, R., Cahill, J., Hagerty, J. & Lawrence, D. Nature Geosci. 6, 4 parts per million — was enough to dampen consistent with water or hydroxyl , a 737–741 (2012). the notion of a bone-dry Moon, the glasses result supported by detections from the 3. Canup, R. Nature 504, 27–29 (2013). would have lost water during eruption, and Deep Impact and Cassini spacecraft. This 4. http://www.nasa.gov/topics/moonmars/features/ moon20090924.html the source regions in the lunar mantle may indicated that active surface processes 5. Colaprete, A. et al. Science 330, 463–468 (2009). contain as much water as mid-ocean ridge were forming and preserving water and 6. Liu, Y. et al. Nature Geosci. 5, 779–782 (2012). basalts on Earth1. Mid-ocean ridge basalts hydroxyl on the Moon, and suggested that 7. http://www.googlelunarxprize.org/ 8. http://www.shackletonenergy.com/ are relatively dry, so this does not mean permanently shadowed polar regions could 9. http://www.hq.nasa.gov/mars/presentations/FTW/index.html that the Moon contains as much water as host water ice reservoirs. 10. Grotzinger, J. Nature Geosci. 2, 231–233 (2009).

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