Why do we collect and study meteorites? Well, have you ever wondered how old our solar system is? Or, what it was like in the solar system just after star formation but before planets got big? How about, how similar is our solar system to others regarding the formation of Earth-like planets? Meteorites are essential to addressing these questions. Chondrites, meteorites from bodies that have not separated, or differentiated, into metallic and silicate layers, are the key. Being undifferentiated is so important because the components within the chondrites have not changed too drastically since their original accretion (aqueous and thermal alteration on the parent body are common but pristine samples exist). Thus, they reflect the chemical and physical conditions within the early solar system. Chondrites come in several types (ordinary, enstatite, carbonaceous, etc.) categorized broadly based on their chemistry. I’m going to focus on carbonaceous chondrites as they hold relevant information to the questions posed above. In fact, it is hard to say exactly how old our solar system is but we can determine, rather precisely nowadays, the age of the first solids. Our solar system started as a disk of gas and dust distributed around a newly formed star. The temperature of this mixture was quite hot meaning that the elements within the disk were perfectly happy in their non-solid state. If this lasted forever we would not be here. At some point the gas and dust began to cool and as it did so different elements decide to combine and transitions from gaseous to solid (well, not ‘decide’ exactly, thermodynamic properties drive the order and reactions). This process is called condensation. So, to know the age of the first solids you have to date the minerals formed at the highest temperatures in the disk. Chondritic components called calcium- and aluminum-rich inclusions (CAI) are what you want for this measurement. CAIs are full of primitive, high temperature minerals. While not all CAIs are the same, several in pristine carbonaceous chondrites have been given the age of 4.57Ga (that is, 4.57 billion years old). This is the age of the first solids and therefore, the most concrete age we can assign to our solar system.

So, we can get the age of our solar system, no big deal. Can chondrites tell us anything else about our early solar system conditions or anything about other star systems? Of course they can. Together the components of chondrites weave a tale of chemical and physical complexity. For example, planetary scientists look at isotopic signatures to investigate interactions between the pre-accreted solids and remaining disk gas or amounts of processing on the parent body to name a few. Combinations of mineral chemical data, component size and type distributions, and other measurable parameters are used to categorize chemical reservoirs and the extent to which mixing within the disk occurred. Some of the components of chondrites have been partially or completely melted, namely chondrules. This means that a heating mechanism within the disk is required to heat up and melt the condensed material. Current collaborations between planetary scientist and astrophysicists are addressing the temperatures, timing, and extent of heating so that potential mechanisms can be narrowed down. By studying chondrites from many different angles we, as a planetary community, are better able to put constraints on what is going on in the solar system before parent bodies got big enough to destroy the evidence.

Enough about our solar system, what about others? Technology (Hubble, ALMA, etc) has permitted us to observe other star systems. From these observations we learn whether planets surround the star, at what distance, their relative size, and sometimes a little about their chemistry. Other times, much younger star systems are observed and imaged. These star systems are sometimes in the stages closely linked to when we believe solids are starting to form and the process of planet formation beginning. While we cannot necessarily draw a concrete link between these systems and the chondrites we study from our solar system, we can ask the question could the conditions in the observed system produce the samples we study on Earth? If the building blocks of Earth are some combination of the chondrite samples (controversial and hotly debated) could these systems then produce Earth-like bodies? The jury is still out.

So end the convoluted musings of a PhD candidate trying to figure out the context of the samples used for their thesis. In other news, we had a day of extremes today at South Miller. We found both the smallest, smaller than pinky finger-nail size, and the largest, nearly the size of a basketball, meteorites both preliminarily determined to be ordinary chondrites. And, it was the coldest day so far at South Miller -5F with 15mph winds. So far all fingers and toes are accounted for but the wind is picking up….

– the rambling PhD candidate, Ellen from the increasingly windy South Miller Range, Antarctica 9 January 2016