Hands-on Astronomy: Meteorites and Cosmochemistry

Historically the information for observational astronomers has largely been provided by electromagnetic radiation, and the arrival of astronomy via neutrinos and gravitational waves has led to the term “multimessenger astronomy”. But we have already seen that cosmic rays, which have been known for over a century, are a different messenger, and in this chapter we deal with another messenger, which has been somewhat overlooked in the excitement. This is material from outside the Earth: mostly meteorites, but also rocks from the Moon, more recently from comets, asteroids, and even Mars. This material can be analysed in the laboratory by chemical and radiochemical techniques. The basic composition of meteorites includes chondrules, which crystallised in space, refractory inclusions, which incorporate particles similar to that of the gas forming the solar nebula, and a matrix including pre-solar dust grains. Isotope ratios and the composition of the radioactive nuclides can be used to infer developments in the history and pre-history of the solar system. Specific large meteorites provide a particularly rich field of exploration. The composition of different types of meteorites is checked against the predictions of stellar “dust factories”, notably stars in the “asymptotic giant branch (AGB) phase of evolution. In this chapter I discuss the results of the examination of meteorites, but also outline specific missions to bring back material from comets and asteroids, and some key results of the analysis of the Moon rocks brought to Earth by the Apollo astronauts, and results from the penultimate NASA mission to Mars.