Mathematicians and Earth Scientists from The University of Manchester have joined forces to solve a problem which has long puzzled meteorite hunters recovering samples from Antarctica: fewer iron-rich meteorites have been found in Antarctica than anywhere else on Earth.
Rocky material from the asteroid belt, the Moon and planets like Mars are found here on Earth as meteorites. Although meteorites fall evenly across the Earth’s surface, over two thirds (about 35,000) of the world’s total number of collected specimens have been recovered from Antarctica. This is primarily because ice flow dynamics transport meteorites, buried at depth in the ice for hundreds of years, up to localised surface regions, known as Meteorite Stranding Zones (MSZs), allowing for efficient recovery and scientific study. Only 0.7% of the meteorites recovered from Antarctica are iron-based, compared with 5.5% from 'witnessed falls' in the rest of the world.
The researchers studied the problem using mathematical modelling combined with a series of lab-based experiments where ice-encased meteorites were exposed to simulated solar radiation. They found that meteorites a few tens of centimetres below the ice surface are commonly warmed by the incoming radiation, but melt the ice around them to a different extent determined by their thermal conductivity. This means that the under-representation of iron-based meteorites could be because the Sun’s rays penetrate the clear ice in MSZs during the summer months causing melting of the samples at different rates. In fact the iron-containing meteorites can sink at a rate sufficient to offset the total annual upward ice transport, permanently trapping them below the ice surface.
Tantalisingly, this means that there may be a sparse layer of iron-rich meteorites trapped buried at depths of about 30 cm in the Antarctic ice, waiting to be discovered!
- Meteorites originate from bodies in the asteroid belt or from large bodies like the Moon or Mars. These important samples provide us with an understanding of the origin and evolution of the Solar System and the formation of planets.
- Meteorites are collected as ‘falls’, when they are witnessed falling as fireball events, or recovered as ‘find’ samples from hot and cold deserts by meteorite search teams. We find most of our meteorites in Antarctica where they are well preserved on the ice.
- However, there is a statistical difference between the types of meteorites we find in Antarctica and those that are seen falling in other parts of the world. Specifically, we seem to find more types of iron-based meteorites in the rest of the world compared to Antarctica.
- We ask why this is the case, and test our ideas using lab experiments and mathematical modelling to investigate how meteorites behave when they are trapped in ice.
- We showed that the amount of iron in the meteorite sample effects is responsible for how efficiently it heats up (i.e., how it thermally conducts heat). The iron-richer meteorites heat up more than the iron-poorer meteorites.
- This implies that the iron richer types of meteorites may sink more effectively, trapping them at depth in the Antarctic ice. This hides them from meteorites collection teams, meaning that we need to think of new methods to recover buried meteorites in Antarctica.
- “Iron meteorites 'buried in Antarctica' by the Sun” on BBC News
- Blog about this research on the Earth and Solar System blog
- “Treasure Trove Of Iron Meteorites May Be Hiding Beneath Antarctica's Ice” on IFLScience.com
- “Iron Meteorites Play Hide-and-Seek Under Antarctic Ice” on Smithsonian.com
- “Iron Meteorites Just Below the Icy Surface” on Cosmosparks blog
Funding bodies: I.D.A. acknowledges the support of a Royal Society Wolfson Research Merit Award. K.H.J. acknowledges the help of the Leverhulme Trust (#2011-569), Royal Society (RS/UF140190) and the Science and Technology Facilities Council grant ST/M001253/1. Funding for this project was also received from the Engineering and Physical Sciences Research Council, UK, via the MAPLE platform grant EP/I01912X/1.