22 October 2020

Rachel Kirby is a PhD candidate in the Geochemistry and Cosmochemistry group at RSES.  Her current research focusses on the role of gases and high temperature processes in the formation of early solar system materials.

When people ask what my field of research is, the quick answer is cosmochemistry and planetary geology.  But what does that mean? 

Cosmochemistry evokes images of nebulas, the swirling colours punctuated by bright stars and the beginnings of new planetary systems.  The term cosmochemistry means the study of the chemical and isotopic composition of the cosmos.  In practice, most of the work done by cosmochemists focusses on our own little corner of the universe – our Solar System.  Cosmochemists hope to answer questions such as: what is our Solar System made of?  How, and when, did the planets form?  Is our Solar System, amongst the countless planetary systems in the universe, special?  Cosmochemists use many of the same tools that geochemists use to analyse the chemistry of Earth rocks, such as mass spectrometry and infrared spectroscopy, however we apply them to meteorites and samples collected from space instead of terrestrial rocks. 

Planetary geology is the study of celestial bodies other than the Earth, including planets, moons, asteroids, comets and meteorites, and the processes that have shaped them.  Planetary geologists seek to understand the geological history of celestial bodies.  While cosmochemistry is focussed more on the chemical composition of cosmic bodies, planetary geology has more of a focus on the physical processes that have shaped them.  Cosmochemistry and planetary geology go hand in hand, and together they help us understand the history of the Solar System.

Cosmochemists and planetary geologists rely primarily on analysing samples from space to provide data.  These samples are mostly meteorites, i.e. rocks which have fallen to Earth from outer space.  Meteorites have the advantage of being more easily accessible than samples collected in space, but the disadvantage of being physically and chemically altered as they are heated during entry into our atmosphere.  A few samples have been collected directly from space, for example those collected by astronauts in the Apollo missions.  As this blog post is being published, the OSIRIS-REx mission will have just attempted its first Touch-And-Go (TAG) sample collection from the asteroid Bennu.  This mission, along with Hayabusa2, another sample return mission to the asteroid Ryugu, are important because they will provide pristine material to study.  By sampling meteorites and material returned to Earth, cosmochemists and planetary geologists can make discoveries about not just other places in our solar system, but moments in time, frozen in the rock for sometimes billions of years.


Apollo 17 scientist-astronaut Harrison H. Schmitt collecting lunar samples.  Source: Planetary Science Research Discoveries, University of Hawai’i.

As technology develops, remote study of planetary bodies is becoming more feasible.  Along with missions to land on other bodies (including the Moon, Mars, comets and asteroids), orbiting satellites have been launched into the Solar System.  Spectacular images of far off worlds such as Pluto have been beamed back to Earth, where we have marvelled over their beauty and contemplated their genesis.  Further improvements in technology have allowed us to image alien planets outside our Solar System, increasing both our understanding and the number of questions we have of how worlds form across the cosmos.  All from our small, blue home.

Header image: The Soul Nebula. Source: NASA Jet Propulsion Laboratory.