## Missing meteorites in Antarctica

Over the last few years I’ve been lucky enough to be invited along to a small get-together of applied mathematicians from the University of Manchester, seeking interesting earth science problems to tackle. These meetings are a lot of fun and make me feel like a scientist in a movie as the situation usually unfolds a bit like this: Earth scientists show pictures and tell stories of some phenomena we think is curious or important, but difficult to quantify, and then the mathematicians fill walls of backboards with equations, while much banter flies in the room, and then eventually the blackboard of equations is reduced to a set of simple governing equations that we hope meet the requirements of the earth system. The characters involved in this make it all particularly fun, and often funny. We then go for a run, drink some beer and poke fun at each other before doing more of the same the next day.

Though not involving me, one of the coolest outputs of these meetings is a paper published in February. The conundrum it seeks to solve is this: Antarctica offers rich pickings of meteorites because ice flow brings them to the surface where they can be easily seen, but whats weird is that even though these conditions mean that most of the meteorites collected on earth are from Antarctica, there is a marked absence of iron-rich meteorites in the Antarctic samples as compared to the ratio of iron-rich to rocky meteorites found over the rest of the earths surface. As the meteorites, and type of meteorites, are expected to be more or less evenly distributed over the planet, why are the iron-rich meteorites missing? What could be going on?

The discussion in the mathematicians pow-wow was about whether the iron-rich meteorites could be absorbing enough sunlight that they could heat up and melt the ice around them so that they sink downwards from the surface, and therefore cannot be found.

Interesting eh?

Well, they used a they model developed earlier to explain melting of ice beneath a surface cover of rocks along, with a tidy little physical lab test to show that indeed it is possible for these meteorites to stay buried due to melting the ice around them. So while ice flow in the meteorite stranding zones in Antarctica is carrying all the meteorites towards the surface, and all the meteorites begin to get heated from the sunlight penetrating the ice, the iron-rich ones are darker and more thermally conductive and so heart up more and also conduct this heat from he upper surface to through the meteorite mass more efficiently. So efficiently in fact that the ice below the iron-rich meteorite melts a little and by this process the meteorite can effectively tunnel downwards at a rate that offsets the surface-ward transport of the ice flow, meaning that the iron-rich meteorites get stuck just below the surface, thus evading the searching eyes of the meteorite-hunting scientists. The image is taken from the publication in Nature Communications, which is open access and you can look at the pdf yourself for the details of the experiment, but it shows an example of the laboratory experiments in which an iron meteorite is sinking through the ice as it is heated by a lamp from above.

G. W. Evatt et al. A potential hidden layer of meteorites below the ice surface of Antarctica, Nature Communications (2016). DOI: 10.1038/ncomms10679

In case the paper is a bit much, the University of Manchester press release can be read here: http://www.manchester.ac.uk/discover/news/meteorites