The Winchcombe Meteorite by Anthony Rowett
By now, you may have heard about a meteorite that fell in and around Winchcombe, just outside Cheltenham. It’s caught the attention of the media, who’ve spent plenty of time discussing where and when it fell, and some of its basic characteristics. But what about the interesting, but not journalist friendly details of the meteorite; the information that may not be deemed accessible enough to put on the average news website (but of course, it is understandable, really)?
Let’s explore why the Winchcombe Meteorite is catching the attention of scientists, for reasons beyond its unexpectedness.
The Winchcombe Meteorite is of the Carbonaceous Chondrite type, but what do those words actually mean? A chondrite is a very common type of meteorite, being non-metallic and containing a significant number of ‘chondrules’. Chondrules are small, pebble like parts inside the object, which began as molten lumps, and, in the process of the meteorite’s formation, gathered together, along with the rest of its dusty mass. Chondrites are, as you may have inferred, formed by the merging together of small pieces of material, and have not been affected by either melting or other processes of change that would occur on a long-lived celestial body. These characteristics of forming by accumulation of particles and having not been modified mean that the objects have changed little since the formation of the Solar System.
Chondrites may be the most common type of meteorite that falls to earth, but there are many, many subtypes, which vary from being extremely common to extremely rare. As you may have read, not just here, but elsewhere, this meteorite is carbonaceous, which sounds simple enough; it must be made a of carbon, mustn’t it? Well, maybe, but there are several different groups, some of which defy the rules of chondrites that you’ve just read, by having no chondrules, or being largely metallic (the science couldn’t be less straight forward).
Carbonaceous chondrites are rare as far as meteorite groundings go, and as this is written, there has been no word on which subgroup our object falls into. The CI group of chondrites is one of the most significant; they have a high-water content and have the closest composition to that of the solar system in its first days. The CI group often contain amino acids and other essential parts of life, like polycyclic aromatic hydrocarbons (thought by some to be the first materials used in forming life, and they unfortunately have no relation to smell). CH chondrites seemingly defy the non-metallic rule, sometimes being almost half made up of metals, as are the CB chondrites, which contain the largest chondrules of all, being as much as 10 mm in diameter!
The CV Group of chondrites contain many pieces of metallic material that are resistant to decomposition and damage and can survive for a long time. One of the most interesting groups are the CM specimens, which are both the most common carbonaceous chondrite, and contain the most organic material of any group, including sugars.
To which of these groups does the Winchcombe Meteorite belong? Let’s consider that the CM group is the most common, but also that the CI group is particularly dark in colour, lacks chondrules (some think they once had these, but lost them) and can be extremely fragile, and susceptible to our weather. If you’ve seen the images from Winchcombe, you’ll probably have seen the dusty pile, lying in someone’s front drive, or a transparent bag, with what appears to be an ash like substance inside, aspects which, from the description of each group, make it likely to be of the organically rich CI group. If it is indeed a CI or CM object, it’s likely to contain organic material, so Winchcombe really has been the centre of an alien invasion. According to the movies, alien invasions are supposed to happen in America; perhaps Netflix should set their next sci-fi film in Gloucestershire.
(The accompanying image shows the dustjacket of the book ‘The Worst Journey in the World’ by Apsley Cherry-Garrard which can be viewed in the Emery Walker Library.)