New paper: The spatial flux of Earth’s meteorite falls found via Antarctic data

By Geoff Evatt:

So, how many new meteorites are landing from space each? How much total mass of them are we gaining? And where about’s on Earth are we most likely to be hit? (especially timely this week given the news story about a 1 km asteroid passing within 4 million km of the Earth! ) This are just some of the questions answered in our latest publication, as published by the journal Geology this week.

In this study, we combined glaciology, mathematics and physics, and sprinkled it all with meteorite collection data, to produce an accturate estimate of these quantities. The headline figure being we estimate over 17,000 falls each year weighing over 50 gr (that is to say, some 17,000 objects fall from space and hit the earth every year, where each component fragment is known as a meteorite, and the summed mass of these meteorites are over 50 gr), and this equates to over 16,000 kg per year landing on the Earth. As for the regions most likely to be impacted, then this, it turns out, appears to be at the equator, where the poles receive about 60% of the equatorial flux.

The first part of the study was to work out the flux of extraterrestrial material in Antarctica. With it having the most documented meteorites on earth, and collected in a very systematic fashion, this meant we were able to harness the data from thousands of samples. However the nature of meteorites in Antarctica means that working out the area they originally landed on is not simple (because the ice is flowing). Combining mathematics with glaciology, we were able to invert for the effective surface area of ice which feeds into Meteorite Stranding Zones (the areas from which they are collected). And since we know flow speeds of the ice, and the number of meteorites collected from them, we were then able to solve for the flux of meteorites falling on a typical square kilometre of ice. Such a figure is useful, but beggars the question: how does that relates to elsewhere on Earth?

Schematic of meteorite stranding zone ice flow and loss used to help build our model of Antarctic meteorite stranding zone data. Image Andrew Smedley (as published in the supplementary materials of Evatt et al., 2020)

Solving for the places most likely to be impacted (the latitudinal variation) was a lovely problem, as the answer was not obvious because competing effects pulled the result to either the poles or the equator. Why the poles? Well, because material orbiting the sun might do so above/below the Earth, yet when in the vicinity of the Earth gravitational attraction, the  objects would be deviated towards the polar regions. Conversely, the equatorial regions face head-on into the asteroid belt, and thus more surface area is available for receiving the material. As it turns out (after much old-school orbital mechanics) the equator still dominate for earth, but with the polar region receiving a decent whack – about 60% of the equatorial flux. This computed variation ties in very neatly with observations of the spatial distribution of fireballs across the globe – which was extremely reassuring.  With us knowing a good estimate for the flux at the poles, is was then straight forward to use the derived latitudinal variation curve to estimate it for everywhere else.

Now, despite the equator being more likely to be hit, in regards being hit by anything dangerously big, this is not anything to worry about for many many years. This is because such events are extremely rare. And since the whole planet is receiving so many non-dangerous falls each year (17,000+), and each event creating a glorious fireball (much brighter than the shooting stars we see which are formed from dust-sized grains) it really tells us to head outside and look up: there is a good chance of seeing such a fireball event if you give it just a few nights. 

Stay safe and look up!

Read the article (open access): G.W. Evatt, A.R.D. Smedley, K.H. Joy, L. Hunter, W.H. Tey,I.D. Abrahams, and L. Gerrish (2020) The spatial flux of Earth’s meteorite falls found via Antarctic data Geology https://doi.org/10.1130/G46733.1

Read a BBC Science online news story about the study

Avoiding the Italian Job

Geoff Evatt | 19 Dec 2018

At the end of the Italian Job, the looted gold is left at the rear of a coach that dangles dangerously over a precipice; tangentially close, yet also so far away: “Hang on boys, I’ve got an idea….”. Well, I too have had an idea. Chainsaws. OK, so that might not have helped Michael Caine in his predicament, but hopefully it’ll help us should we locate any englacial meteorites.

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Essential course material: chainsaw, underlying theory, vape… [Credit: G W Evatt]

To be ready for sawing out some meteorites in a year’s time, I will give it a practise this coming January down at the BAS base, Sky-Blu. (the chainsaw bar length is 40 cm, the meteorites could be 50 cm deep: hmmm). And before I can even practise in the field, I was sent on a chainsaw course on an industrial estate in Chesterfield. Yes, it was a long long way from Antarctica, but it was freezing and the corrugated iron all around had a certain monotonous colouring, so maybe that will all come in useful. More importantly, I learned a lot about fixing basic chainsaw issues, how to sharpen chains, and how to cut logs the correct way (I’ve done a reasonable amount of chainsawing at home, but now I know sooo much more). The course instructor, James, also gave good suggestions as to how to cut ice and deal with the cold. In short, I feel much more prepared and confident about using the saw down there.

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Tools of the trade. [Credit: G W Evatt]

And what if it’s a total failure (as in does not let me extract lumps of ice)? Well, I’ve also sent down a farm-shop of ironmongery, saws and ice drills. Between these, I hope that we will find an efficient method that allows us to extract any iron meteorites we detect. After all I want be prepared and confident, and we don’t wan’t to face any Italian Job conundrums….

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Practising for Antarctica [Credit: G W Evatt]

PS For those of you really into their chainsaws, I’ll be using battery powered DeWalt one. Whilst it cut the Chesterfield logs very effectively, it may be a totally different matter in the cold, in which case I’ll have to opt to using a petrol one instead next season.

Finalising the field procedures

Katie Joy | 13 Dec 2018

We have done a final run through of the metal detector electronic assembly system that connects up to our five detector panel array. Practice makes perfect and it is much easier to do a dry run through in the electronics lab in Manchester before getting to the cold and windy field site. Liam, John and Wouter (our fab electronic engineers) carefully ran Geoff and Mike through which cables to connect to which connector so that the instrument powers up in the right order in the field (marginally less complicated than booting up the Apollo 13 command module), and the procedure has been documented.

Andy and Katie have been working hard finalise our fieldsite maps and ensure that our GPS system is working well for logging our skidoo tracks and meteorite collection locations.

Our fieldwork is nearly upon us – Katie heads out next Tuesday on the 18th December and Geoff in the New Year.

Training for life on the Ice (Sept 2018)

Katie Joy | 01 Oct 2018

Fieldwork in Antarctica is a massive logistical and human challenge – from getting scientists to the continent, ensuring that they are trained to go out into the middle of the continent, and actually living and working on the ice, it takes a vast number of highly trained people. Fortunately, BAS are really good at this and have an amazing bunch of people that we are working with – from their Cambridge headquarters, on the bases we will visit and into the field.

To help get us prepared for our upcoming trip Geoff and I joined the new BAS staff for pre-season training. During our four-day intensive course we met a wide range of people from vehicle mechanics, chefs, science support crews, boat swains, base managers and field guides, seal and penguin tagging and monitoring teams, doctors – many of whom have signed up for an amazing 18 month stints down on the ice. We also met some of the other science crews who in the 2018 austral season will be undertaking deep ice drilling and hot ice drilling operations to study past climate on the continent, and others who are studying seal populations on South Georgia Island to understand communities and breeding patterns.

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Locations of the BAS bases [Image: BBC]

The training was split into several sessions. First up was and introduction to BAS history, operations, science and practice: BAS operate out of five bases – Rothera, on the peninsula, Halley, on the eastern side of the Weddell Sea, Bird Island and King Edward Point on South Georgia island and  Signy island. People on the bases, on the ships and in the field undertake different science projects – some (like ours) are very seasonal, some run all year round. We got a chance to hear from BAS scientists who run some of these longer term projects,  looked around the Cambridge BAS building and met people who run the archive facility, ice core storage facility and the geology prep and rock stores.

We also got a chance to try on our field kit and check that it all fitted – from insulating boots (very important to get the size and fit right), through to thermal underwear, outer layers and woolly hats – everything was reviewed and items swapped out as needed.


BAS issued polar insulating boots and field kit bags

The last couple of days focused on an intensive and rapid introduction to medical situations and protocols. The polar medical office (British Antarctic Survey Medical Unit ) is run out of Plymouth NHS Hospital and the team travelled up to Cambridge for the training event. In small groups we ran over recognition of life signs and medical problems through to how to bandage up a broken limb, deliver an injection (into an orange!), learn about pain relief options, and about mental health in remote, often stressful, environments. The course were rounded off by undertaking practicals where actors delivered a series of medical scenarios for our group to try and deal with (imagine fending off an imaginary seal whilst trying to deal with someone with a broken leg – that sort of thing…).  Frankly I hope that I never have to put anything I learnt as part of the sessions into practice – but it was an incredibly useful quick fire overview of what to do and how to relay information with people back on station and back in Plymouth if needed.

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Geoff and Katie practising how to get out of a Scott polar tent without creating a medical emergency

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For further information:

BAS science projects https://www.bas.ac.uk/science/our-research/research-projects/

BAS fieldwork https://www.bas.ac.uk/polar-operations/life-in-the-polar-regions/camping-and-deep-field-working/