CosmoELEMENTS

Meteorite hunting is a lot like football (soccer) … just run with us on this. Success requires skill, a cracking team, a whole lot of luck … and, historically, England (and the UK) are not very good at it … we were just unlucky … the (fire)ball always seems to miss the goal! Meanwhile, around the world, meteorite fall recoveries are becoming more and more frequent; but in the UK, to put it in the style of the famous English football anthem by the band the Lightning Seeds, it’s been “30 years of hurt” since our last meteorite fall.

Diamond is the most illustrious of all minerals. Made of pure carbon atoms packed into a dense isometric structure, diamond is treasured as a gemstone for its brilliant (adamantine) luster and supreme hardness, and is in demand for many industrial applications because of these same properties. On Earth, most natural diamonds form deep (>160 km) under continental cratons, where high static pressures (>45 kilobars) stabilize diamond relative to graphite, which is the low-pressure polymorph of pure carbon. Such diamonds are only fortuitously brought to the surface, carried as xenoliths or xenocrysts in explosive volcanic pipes known as kimberlites. To geoscientists, diamonds provide invaluable records of the extreme conditions and otherwise inaccessible environments in which they formed. Diamonds can also probe exotic extraterrestrial environments. Nanometer-sized diamonds also occur as a rare component of the most primitive carbonaceous chondrite meteorites, rocks which preserve the original components of the Solar System.

Silicon carbide (SiC) minerals, which were argued to condense in stellar winds, were first isolated and imaged in 1987 (Bernatowicz et al. 1987). However, their existence in meteorites had been speculated from extensive noble gas studies. These studies suggested that SiC minerals are the carrier phases of the exotic 128,130Xe and 22Ne isotopic anomalies that can be found in primitive meteorites (e.g., Anders and Zinner 1993). In fact, SiC stardust does carry large isotopic anomalies, up to 4 orders of magnitude, both in light mass elements (e.g., carbon, nitrogen) and in medium mass elements (e.g., magnesium, iron, titanium). These anomalies can only be produced in stars through nuclear reactions occurring at extreme temperatures, by which the structure of the atomic nucleus is altered. The extreme isotopic anomalies in the SiC dust grains were not completely homogenized during the first 10 million years of planet formation and Solar System evolution, so they have kept their compositions intact until today. The dust grains carrying these enormous anomalies can be identified in extraterrestrial rocks that fall to Earth.

Similar in size to the Earth, Venus differs from our planet by its extreme surface temperature (470 °C), suffocating atmospheric pressure (about 92 times that of the Earth’s), and caustic atmosphere (mostly CO2, with sulfuric acid rain). Venus is Earth’s hellish twin sister. However, there are some similarities. As for the Earth, Venus has also had a very complex geologic history. During the early 1990s, NASA’s Magellan spacecraft imaged the surface of Venus with radar and gave us a panorama of a volcanic wonderland (Fig. 1). The surface of Venus is dotted with some of the largest volcanoes in the solar system, complete with summit calderas and extensive lava flows. Volcanoes on Venus resemble many of those on Earth, particularly those formed from the eruption of basaltic magma, such as Mauna Kea (Hawaii, USA) and Mount Etna (Italy). One of the biggest unresolved scientific questions about Venus concerns its style and rate of volcanism during its geologic past. Did volcanic eruptions on Venus occur locally and constantly in time? Or did the planet undergo sporadic events of global and catastrophic volcanism which rejuvenated its entire crust in a short amount of time?

Between 1969 and 1972, Apollo mission astronauts explored the lunar surface, collecting geologic materials and returning them to Earth for careful study. After consideration of many lines of evidence, one of the many major results of studying the Apollo rocks is the broad scientific consensus that the Moon formed from the debris of a giant impact of a large body with the proto-Earth (e.g., Stevenson 1987). This left the Moon depleted in highly volatile elements such as hydrogen, relative to Earth. So it was thought.

Comets, and some primitive asteroids, preserve the microscopic remnants of the basic building blocks of rocky bodies in our solar system. Analyzing these building blocks can provide important clues both to the source of the water for Earths’ oceans and to the inventory of organic matter delivered to the early Earth. In general, samples from comets preserve a greater abundance of organic matter and primordial presolar dust grains from the protosolar molecular cloud, and generations of stars older than the sun, than do samples from asteroids. Meteorites, which come from asteroids, generally have less organic matter and preserve fewer presolar grains. This is because asteroids and comets formed at different places in the solar nebula, and, thus sampled different distributions of organic and mineral components. Furthermore, the warmer conditions on asteroids allowed for liquid water and greater subsequent physical and chemical alteration of the accreted material.

The digital age has transformed the ways by which we live and work. Surprisingly, it is still challenging to agree on a general definition of what digital really means. There is a telltale picture taken by film director Stanley Kubrick in 1946 of people in the New York City (USA) subway. In this picture, almost all the commuters are looking down and into their newspapers. If you now replace the newspapers with smartphones, then the scene might have been shot on a subway today. But there is at least one crucial difference between the two pictures: information density. A newspaper holds only a few tens of kilobytes (kB) of information, whereas a smartphone can hold up to a terabyte (TB). This is six to eight orders of magnitude more than a newspaper. Furthermore, almost all the exabytes (260) of information by humankind has become accessible to us via the internet and through our smartphones. In combination with apps, this vast amount of information is structured and tailored to all our various daily needs. This is the power and attractiveness of digital: the vastness of the information has been condensed, structured, and made accessible through digital devices such as smartphones. Hence, if we use computers solely for calculations – their initial purpose – this is not what we mean by digital.

In 2019, we are celebrating the 50th anniversary of NASA’s momentous Apollo expeditions to the Moon. The samples brought back by the astronauts, and the fieldwork those astronauts performed on the lunar surface, cemented the Moon’s status as the cornerstone of the solar system. It is not an exaggeration to say that the Apollo expeditions transformed our understanding of our solar system, and, in fact, most of the discoveries made in planetary science since the 1960s can trace directly, or indirectly, from the scientific results of those Apollo expeditions.

The Apollo program was the seminal moment in modern human history and the crowning technological achievement of the 20th century. In addition to the obvious historical, cultural, and technological significance of the Apollo program, scientific results from the Apollo lunar samples have had a lasting impact on a range of scientific fields, none more so than on the fields of planetary science and cosmochemistry. Over the past five decades, studies of these lunar samples have yielded significant insights into planetary bodies throughout the solar system. Despite the Apollo samples being a static collection, recent and ongoing studies continue to make new significant discoveries. Here, we will discuss the collection, curation, and study of the Apollo lunar samples and look forward to some expected new developments in the coming years.

When one mentions the word “geology”, most people will likely think of volcanoes, glaciers, or majestic mountain ranges. Beginning in the late 18th century with the work of pioneering Scottish geologist James Hutton (1726–1797), uniformitarianism emerged as a central tenet of geology and remained so well into the 20th century. Central to the idea of uniformitarianism is the concept of gradualism, whereby processes throughout time occur at the same or similar rates, leading to the famous concept that “The present is the key to the past.”