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meteorites

Image of the Week – The Lost Meteorites of Antarctica…

Image of the Week – The Lost Meteorites of Antarctica…

 When most people think of Antarctica, meteorites aren’t the first things that come to mind. Perhaps they imagine the huge ice shelves, the desolate interior, or perhaps penguin colonies near one of the scientific bases — but usually not meteorites. So why is our project looking for meteorites in Antarctica, and besides, aren’t they all lost until they are found?


Let’s start with the Antarctic part. Surprisingly, Antarctica is a great place to hunt for meteorites, with two-thirds of all known meteorites found there (see also this previous post). Despite the difficult searching conditions, the dark meteorites show up well on the bright white surface of the ice sheet. Also, due to the cold conditions, the weathering of meteorites is slower than in warmer regions, such as hot deserts. However, Antarctica is vast and most meteorites are small (a few cm in size) so finding them is still difficult. One thing that helps in this case is the presence of mountain ranges and nunataks near the perimeter of the continent. These slow the ice flow and cause stagnation points — blue ice areas (see Fig.1) — where meteorites can collect and accumulate on the surface usually at elevations of 1500m to 2500m or so.

To understand the “lost” part, you need to know that not all meteorites are created equally – some are stony, somewhat like the rocks found in the Earth’s crust, whilst others are more metallic, having a high iron content perhaps close to 90%. The latter tell a meteoriticist (yep, this is a real job definition!) about the cores of planets and the early formation of the solar system. In the rest of the world these rarer and more interesting iron meteorites usually make up about 5.2% of all samples found — but on the ice sheet, they only represent about 0.6%, an order of magnitude less.

This under-representation is a little odd and unexpected. We don’t expect any particular bias due to delivery to Earth, and if you’re out hunting for meteorites on your skidoo and spot a dark rock that’s potentially a meteorite, you’re still going to pick it up: so no bias in collection.

So where are the missing iron meteorites?

About 3 years ago a team from Manchester were looking at this problem and came up with a hypothesis that might explain it: as sunlight enters the blue ice and gets scattered below the surface it gets absorbed by meteorites and heats them up. This happens more on their upper surface, and due to the higher conductivity of iron meteorites in comparison to their stony counterparts, the heat is transferred to the ice below. Given the right conditions during the Austral summer, this process can provide enough energy so that iron meteorites melt the ice underneath them and sink a few centimetres below the surface whilst the stony ones stay on top. Though we put this on a mathematical footing by way of a model and confirmed the mechanism by some laboratory experiments, the only way to be sure that there is a layer of iron meteorites hiding below the surface is to go out and find them.

Fig. 2: Meteorite close-up: partially embedded in the blue ice surface [Credit: Katherine Joy/Lost Meteorites of Antarctica].

The current project

If you’re going to try and find iron meteorites hidden below the ice surface in Antarctica, then you’re going to need a new way of doing things. Ordinarily, searches are carried out by systematically searching an area of blue ice on skidoo and looking for dark rocks that might be potential meteorites (see Fig. 2). Obviously this won’t work for samples below the surface, so we had to come up with a new method that allows a good sized area to be covered (even in a relatively productive area we estimate the density of irons is <1 km-2) and can cope with the conditions up on the Antarctic plateau. Given that the key discriminating characteristic of the subsurface meteorites is their metallic content, it makes sense to use a system based on metal detector technology.

Our system is somewhat different to what you might use for hunting for archaeological coins or have to walk through at the airport, and instead the detector coils are embedded into an array of large polymer panels (the same material the British Antarctic Survey use for transporting fuel drums on). It’s entirely bespoke, including the pulse and detection electronics, data acquisition and analysis, and importantly, it’s designed to be able to deal with the conditions we expect down South.

Fig 3: The prototype detection system being tested at Sky-Blu Field Station during the 2018/19 season. Panels are on the left of the image, control electronics are beneath the photovoltaic panel in the centre, and an indicator box on the skidoo shows when something metallic is detected [Credit: Geoff Evatt/Lost Meteorites of Antarctica].

Even so, given the logistical challenges of remote working in Antarctica (the area we want to search is ~700 km from the nearest base), we thought it prudent to do some tests of the prototype equipment closer to home. To that end, we’ve had two field trips to the UK Arctic Research Station in Ny Ålesund on Svalbard for the initial testing of the detection equipment.

In addition, we need to figure out exactly where to search. We therefore need to confirm an area has surface meteorites before we can hope to find the subsurface layer. That was the point of last Austral summer’s expeditions: while one team kept close to the Sky-Blu base for the first Antarctic test of full detector array, the other team went out to the Recovery Glacier region for a visual search of surface meteorites. Thankfully both were a success, with our meteorite hunting team bringing back a total of 36 surface meteorites.

Fig 4: The meteorite search team’s home for a few weeks. 700 km from Halley and poor weather meant return to civilisation was delayed until the Twin Otter could fly in [Credit: Katherine Joy/Lost Meteorites of Antarctica].

A bit more planning and we’re lined up for next year’s expedition where it all comes together and we find out if the hidden layer is there – or there’s something else at work…

You can find out more about the project and what we’re up to on the project blog: https://ukantarcticmeteorites.com/blog/

Further reading

Edited by Clara Burgard


Andy Smedley trained as an atmospheric scientist measuring and modelling how sunlight interacts with the atmosphere. Recently his research interests have expanded to include sunlight’s interaction with, and impacts on, the cryosphere. He is currently working on the Leverhulme Trust funded “Lost Meteorites of Antarctica” project at the University of Manchester where he deals with the logistics of Antarctic field expeditions, mapping and analysis to select the field sites, and trying to better understand how solar radiation interacts with blue ice and light absorbing particles – including meteorites.

Image of the Week – Searching for clues of extraterrestrial life on the Antarctic ice sheet

Fig. 1: A meteorite in the Szabo Bluff region of the Transantarctic mountain range, lying in wait for the 2012 ANSMET team to collect it [Credit: Antarctic Search for Meteorites Program / Katherine Joy].

Last week we celebrated Antarctica Day, 50 years after the Antarctic Treaty was signed. This treaty includes an agreement to protect Antarctic ecosystems. But what if, unintentionally, this protection also covered clues of life beyond Earth? In this Image of the Week, we explore how meteorites found in Antarctica are an important piece of the puzzle in the search for extraterrestrial life.


Meteorites in Antarctica

Year after year, teams of scientists from across the globe travel to Antarctica for a variety of scientific endeavours, from glaciologists studying flowing ice to atmospheric scientists examining the composition of the air and biologists studying life on the ice, from penguins to cold-loving microorganisms. Perhaps a less conspicuous group of scientists are the meteorite hunters.

Antarctica is the best place on Earth to find meteorites. Meteorites that fall in this cold, dry desert are spared from the high corrosion rates of warmer, wetter environments, preserving them in relatively pristine condition. They are also much easier to spot mainly due to the contrast between their dark surfaces on the white icy landscape (see our Image of the Week), but also because the combination of Antarctica’s climate, topography and the movement of ice serves to concentrate meteorites, as if lying in wait to be found.

The targeted search for meteorites has taken place annually since the late 1960s, leading to the recovery of over 50,000 specimens from the continent, and counting. The most prolific of these search teams is the US-led Antarctic Search for Meteorites ANSMET), which lay claim to over half of these finds. Comprising only a handful of enthusiasts, this team camps out on the slopes of the Transantarctic Mountains for around 6 weeks hunting for meteorites. The finds include rocks originating from asteroids, the Moon and Mars.

 

Evidence of life in a meteorite?

There has long been a link between meteorites and the potential for life beyond Earth. Perhaps the most famous, or rather infamous, meteorite found in Antarctica is the Alan Hills 84001 meteorite (ALH84001). Found by the 1984 ANSMET team, this meteorite was blasted from the surface of Mars some 17 million years ago as a result of an asteroid or meteorite impact, falling to Earth around 13,000 years ago. This piece of crystallised Martian lava is roughly 4.5 billion years old. The reason for its infamy is the widely publicised claim made a decade after its discovery that it harbours evidence of Martian life [McKay et al 1996]. Specifically, application of high resolution electron microscopy unearthed microstructures comprising magnetite crystals that looked, to the NASA scientist David McKay and his team, like fossilised microbial life, albeit at the nanoscale (see Fig. 2).

Fig.2: A nanoscale magnetite microstructure that was interpreted as fossilised microbial life from Mars [Credit: D McKay (NASA), K. Thomas-Keprta (Lockheed-Martin), R. Zare (Stanford), NASA].

Such a finding of evidence for extraterrestrial life has huge implications for the presence of life beyond Earth, a subject that has captivated humankind since ancient times. This extraordinary claim made headline news across the globe. It even gained acknowledgement by the then US president Bill Clinton. In the words popularised by Carl Sagan, “extraordinary claims require extraordinary evidence”, and this one garnered considerable controversy that endures today. At the time, there was no known process that did not involve life that could result in these types of structures. Subsequent research, triggered by this claim, has since indicated otherwise. The debate rolls on, and it seems we will never really know whether the crystals structures are fossils of Martian life or not, with no conclusive evidence on either side of the argument. Nevertheless, the interest and attention gained through this story kick-started a flurry of hugely successful Mars exploration missions, as well as reinvigorated the search for life beyond Earth.

 

Meteorites as microbial fuel

The ALH840001 is an unusual connection between meteorites and the search for extraterrestrial life. Much subtler, but more wide-reaching, is the potentially important connection between organic-containing meteorites and the existence of life elsewhere. The chondrite class of meteorites originates from the early solar system, specifically from primitive asteroids that formed from the accretion of dust and grains. They are the most common type of meteorite that falls to Earth, and contain a wide array of organic compounds, including nucleotides and amino acids, the so-called building blocks of life. In addition, a number of organic compounds that reside in these meteorites are also common on Earth, and are known to fuel microbial life by serving as a source of energy and nutrients for an array of microorganisms [Nixon et al 2012]. These meteorites have fallen to Earth and Mars for billions of years, since before the emergence and proliferation of life as we understand it. A significant quantity of these meteorites, and the organic matter contained within them, has therefore accumulated on Mars. In fact, owing to the thinner atmosphere of Mars, a larger quantity is expected to have accumulated there than on Earth, and with more of its organic content intact. It is a therefore a distinct possibility that these meteorites may play an important role in the emergence, or even persistence, of life on Mars, if such life has ever existed [Nixon et al 2013].

The search for life on Mars is very much an active pursuit. As we continue this search using robotic spacecraft, such as NASA’s Curiosity rover and the upcoming European Space Agency’s ExoMars rover, we seek to better define whether environments on Mars are habitable for life. But our understanding of habitability on Mars and beyond is defined by our knowledge of the limits of life here on Earth, such as the microbial lifeforms that can make a living on and under the Antarctic ice sheet (see this previous post), but also in terms of the chemical energy able to support life. The search for meteorites on Antarctica has an important role to play here, and long may the hunt continue.

 

References and further reading

Edited by Joe Cook and Clara Burgard


Sophie Nixon is a postdoctoral research fellow in the Geomicrobiology group at the University of Manchester. She completed her PhD in Astrobiology in 2014 at the University of Edinburgh, the subject of which was the feasibility for microbial iron reduction on Mars. Sophie’s research interests since joining the University of Manchester are varied, focussing mainly on the microbiological implications of anthropogenic engineering of the subsurface (e.g. shale gas extraction, nuclear waste disposal), as well as life in extreme environments and the feasibility for life beyond Earth. Contact: sophie.nixon@manchester.ac.uk