To catch a falling star
When a priceless meteorite hit the UK it sparked a nationwide search that led to a driveway in the Cotswolds. But how do you go about finding a fragment of space rock and what might the fallout from the ‘Winchcombe fireball’ mean for our understanding of life on Earth?
9th March 2021 (Taken from: #42)
For seven spectacular seconds at 9.54pm on Sunday 28th February 2021 a dazzling fireball ignited the skies above the British Isles. Captured on meteor-monitoring cameras from Galway to Manchester, it was streaking towards the Cotswolds, a fittingly genteel destination for what would turn out to be a distinguished and rare type of meteorite – with a mineralogical make-up that could hold clues to how life emerged on our planet.
The 4.6 billion-year-old space rock’s arrival took Britain’s planetary science community completely by surprise – including fireball tracker Jim Rowe, who had been on a two-year personal mission to upgrade the UK’s meteorite-recovery capabilities. On 6th January, in a webinar to the British Astronomical Association, Rowe had showcased the newly minted protocols he and his collaborators had developed for salvaging cosmic debris, wrapping up his talk with a wistful thought: “Hopefully, when we come out of lockdown it’ll coincide with a nice meteorite landing.” He got his wish, a good month ahead of schedule with by far the most important fall in UK astronomical history.
When the story was reported on 9th March, a good deal was made in the British press of two of its most fortuitous aspects. First was the fact that one of the biggest intact clumps of meteorite turned up in the Gloucestershire village of Winchcombe, in the driveway of the Wilcock family – who identified the 300g of rock and black powder they found splattered across their tarmac as something worthy of investigation. They carefully scooped what they could into a plastic Waitrose freezer bag, and then emailed a photo to the UK Meteor Observation Network (UKMON).
The second tremendous stroke of luck that caught the media’s attention – with an uncharacteristic flurry of excitement over mineralogy – was the rock’s carbon content. “Carbonaceous chondrite is a slightly misleading name,” says Ashley King, referring to the rock’s prized scientific classification. King had been one of the first scientists on the scene, and took custody of the Wilcocks’ samples. With lockdown in full swing, he first shepherded the precious cargo to the Holiday Inn in Cheltenham, where he says there were “two people – and this bag of meteorites!” He then took them to the Natural History Museum in London, where he works as a research fellow in the Planetary Materials Group, specialising in exactly this exotic class of planetary material.
Most meteorites are 4.6 billion years old. They are the building blocks of everything we see now”
“People hear ‘carbonaceous’ and they think, ‘Ah, it’s 100 percent carbon,’ and it’s not – it’s a few percent,” explains King. “But it’s still higher than most meteorites; it’s what gives it that really dark colour.” Some of that carbon is in its carbonate minerals, which formed thanks to water – the Winchcombe meteorite has already been identified as belonging to a particular subgroup of ‘CM’ chondrites, stones that come from water-rich asteroids.
But a lot of the carbon is held in what scientists often refer to, tantalisingly, as ‘organics’. In analyses of similar meteorites in the past, simple compounds such as amino acids have been detected – the building blocks of proteins, the complex organic molecules that are fundamental to the composition of biological cells.
“I suspect that’s what we’re going to see in Winchcombe as well,” says King. “Things like carbon and hydrogen, oxygen, nitrogen, bound together in really simple structures.” These volatile elements (that is, elements that easily react and combine with other chemicals) “wouldn’t have been abundant as complex molecules in the inner solar system when the Earth was forming”.
For living things to occur, along with oceans, atmospheric gases and so many other familiar features of our planet, says King, a starter kit of chemical ingredients would have had to be “potentially delivered to the Earth quite early on. These types of asteroids and these types of meteorites are one of the ways that we can [explain] that.”
The Earth and its atmosphere are the end destination for around 50,000kg of hurtling cosmic crumbs every year, most of it dust left in the wake of comets. The larger specimens that survive descent to land as meteorites might have broken off from comets too, or other planets in our solar system. But they are far more likely to hail from asteroids, the metallic and stony remnants from the great swirl of rock and dust that originally clumped together to form the sun and its retinue of planets. The majority of these unclumped leftovers settled into a holding pattern between Mars and Jupiter – our solar system’s version of the M25, otherwise known as the asteroid belt. Occasionally, either a collision or a gravitational nudge from Jupiter, or local traffic, will throw material off course and towards the inner solar system, where we reside.
For this reason, says King, “Most meteorites are 4.6 billion years old; they come from these asteroids where not much happened – and so they really are the materials that were there at time zero in our solar system. They are the building blocks of everything we see now.”
Just how important these primordial lumps are to understanding the solar system’s early history is illustrated by the fact that the world’s space agencies currently have two very active, and very expensive, retrieval missions on the go. Nasa has invested around $1 billion in its OSIRIS-REx spacecraft, which touched down on the carbonaceous near-Earth asteroid Bennu in October 2020, and is now ferrying back chips from the surface, which are expected to arrive in the autumn of 2023. Meanwhile a similar Japanese mission, Hyabusa2, has already returned its carbonaceous samples to Earth; its sample-return capsule touched down in Australia in December 2020, after a six-year round-trip to the asteroid Ryugu.
“I’m on the team for the analysis of the Hayabusa2 sample, which is kicking off this summer,” says King. “That was my plan for the year – but now we’ve got Winchcombe!” A sample that’s come to him direct, minus stopovers in the outback and Japan on the way, and approximately $300 million cheaper.
While the Winchcombe rocks won’t be as pristine as those lifted from the extraterrestrial sources, they are nevertheless, says King, “pretty much as good as we can get it for a meteorite fall”. Having been collected properly, within hours of driveway impact and without being tainted by typical earthly contaminants such as rain or oily human fingers, the Wilcocks’ contribution to planetary science represents a rare coup for researchers.
The world has been systematically identifying and collecting meteorites for only the past 200 years or so. In that time we have amassed nearly 70,000 samples. Of those, a mere 500 – some 0.7 percent – are CM carbonaceous chondrites. They’re the tiny subset of an already elite cohort among this particularly crumbly, friable class of rocks: those lucky few survivors of the caustic descent through the Earth’s atmosphere, and which were found before they were absorbed into the chemical environment of their new home. “Most meteorites, even if they’re seen to fall, are not collected for several days after the event,” says King. “And some of this material, probably less than 12 hours after the fall, was actually sealed up in a bag… It’s probably the quickest ever CM chondrite fall collected.”
So when the Winchcombe rock plummeted out of the Gloucestershire sky that Sunday night, the stars aligned. Or, more accurately, the British Isles’ six disparate networks of fireball-tracking cameras aligned – and this is where the serendipitous intervention of Jim Rowe in meteorite science comes in.
A solar farm developer by trade, Rowe had in recent years switched his focus to the solar system instead – specifically a wildly ambitious hunt for meteorites hitting the UK. “Other 50-something guys with a bit of money to spare might buy a sports car,” he jokes. “I bought a fireball network.”
Successful retrievals following fireballs are exceptionally rare in the UK; historically they have been once-in-a-generation events. Prior to Winchcombe, the last such British recovery took place 30 years ago, in the village of Glatton, Cambridgeshire, when an ordinary, stony ‘L6’ chondrite whistled into Arthur Pettifor’s conifer hedge one Sunday morning, while the pensioner was out planting onions nearby. Before that, on Christmas Eve 1965 44kg of seasonal stones rained down on the residents of Barwell, Leicestershire. And for a confirmed fall recovery in Great Britain prior to that you have to go back to 1949 and then to 1930 (oddly enough, both in Wales).
Other 50-something guys with a bit of money might buy a sports car, I bought a fireball network”
In all, the British and Irish Meteorite Society lists just 27 official recoveries across Great Britain and Ireland since the first recorded English fall in 1623, near Ermington in Devon: “a stone of twenty three pounds weight, which in falling made a fearful noise, first like a rumbling of a piece of ordinance…”
With that sort of hit rate, six camera networks – two run by academic institutions and four by amateur organisations – all scanning the skies nightly for incoming shrapnel might seem like overkill. But according to Rowe, there are nowhere near enough. He wants to see the current combined array of 60 cameras more than doubled, with a special focus on Scotland and the North of England where coverage is relatively sparse.
The past few years have been a sky-high learning curve for Rowe. Having sold some of his solar businesses in early 2016, he found himself with both time and resources on his hands. And it was just at this point that a widely reported shooting star – the St Patrick’s Day meteor, an appropriately green flash above southern England – reignited his passion for meteoroids. That fireball sparked memories of his school days in New Zealand, when he had become fascinated with one of the exhibits in Christchurch’s Canterbury Museum: a huge chunk of the Canyon Diablo meteorite, the iron behemoth that carved out Meteor Crater in Arizona 50,000 years ago.
The starry-eyed youngster had written off to no less an authority than the curator of the Smithsonian Institution’s vast meteorite collection in the US, Brian Mason. He’d naively asked Mason if he knew much about the specimens held there (“I thought that ‘curator’ was the person who made sure the cabinets were locked”). It turned out that Mason hailed from Christchurch too. Tickled, the eminent geochemist wrote to Rowe saying he had duly inducted him into the prestigious International Meteoritical Society. “He got me seconded, got me a subscription to their magazines, and I was the only New Zealand-based member for a while.”
On re-entering the orbit of meteorite science some three or four decades later, Rowe was to have a sizeable impact of his own. First of all, he adapted a camera to conform to the technical specifications of the French-led survey the Fireball Recovery and InterPlanetary Observation Network (FRIPON). Having stuck that on his chimney and got it working, he started building FRIPON’s UK network. With his own money, Rowe began acquiring similar kit to extend its coverage: “I bought another half dozen or so and gave them away to institutions that were engaged and interested in this.”
As he encountered like-minded people from the various other camera arrays, he began to see huge drawbacks in so many projects working independently, and decided to do something about it. “I realised that all the different networks were missing stuff. With five other networks, each would get one capture – which the others would ignore… and the thinking was to try and coordinate that.”
The result was the UK Fireball Alliance (UKFAll), which Rowe launched in 2018 with the help of the Natural History Museum (and Ashley King in particular); Richard Kacerek of UKMON, the country’s largest amateur meteorite network; and Drs Luke Daly and Sarah McMullan, who ran the UK branch of the Australian Desert Fireball Network. Rowe describes UKFAll as a “loose coordination and collaboration” between the six hobbyist and professional groups, but it’s become so much more than a data-sharing exercise. “I worked with a lot of the different networks and system designers to come up with a common data-exchange format,” he says. Concocting code that could allow a variety of systems and software languages to talk to each other, and thus easily share information on meteor trajectories, size, fragmentation history, impact locations and projected orbits was, he notes, “a long way from developing solar farms”.
This newfound ability to “mix and match” data proved instrumental in rapidly pinpointing Winchcombe as the centre of the ‘strewn field’ (astrogeology lingo for crash zone) in the early hours of 1st March. That morning the UKFAll coordinators already knew where the fragments were likely to be, had an early sense of which part of the solar system the meteor had come from (“Not too far away from Jupiter,” according to Ashley King; “the outer part of the main asteroid belt”) and even had an inkling that it might be of the carbonaceous variety. Armed with their data, the team could kick into gear their pre-prepared media strategy (with certain modifications to account for lockdown restrictions), and “by lunchtime,” says Rowe, “several UKFAll members were on national television explaining what to do with suspected meteorites and who to contact”.
More of a challenge than getting the cameras to work in concert, perhaps, has been coordinating the human side of UKFAll’s recovery strategy – actually getting bodies in the field to hunt for those elusive celestial nuggets.
Nagging back-to-earth issues such as public liability, health-and-safety protocols, the risk of trespassing and the like had paralysed attempts to mobilise the community to track down falls in the past. But by the time Winchcombe became a target, UKFAll had spent a full year resolving all those “really boring micro-details”, as Rowe calls them, as well as coordinating a proactive approach to public engagement – perhaps captured best by a disarmingly hopeful call-out on the UKFAll website:
Report a fireball
Have you seen a really bright meteor? Or heard a sonic boom that isn’t related to aircraft movement? If so, please click the button below to report it.
They also had professionals with experience in the field on hand, like Dr Luke Daly of Glasgow University (UKFAll’s treasurer) and Dr Katherine Joy of the University of Manchester. “Coordinating an enthusiastic group of scientists who just want to run around and look everywhere is a little bit like herding cats,” says Joy, who has spotted meteorites in locations as diverse as Antarctica and Chile’s Atacama Desert, and who helped comb the countryside in the days following the Winchcombe fall. “It gets a lot easier once everyone learns how to do it properly.”
In the fields of Gloucestershire, that meant arranging the searchers “a little bit like a police search line. The knowledge comes from how you organise the line – thinking about lighting conditions, where the sun is, how can I best see the surface I’m searching, tracking it with GPS…” But it also came with topographical challenges that Joy hadn’t confronted when tramping the Chilean desert or zipping across the snow on a Skidoo: “In Antarctica it’s relatively easy to find the meteorites because they’re easy to spot.” Searching the Atacama on foot, meanwhile, was trickier because the meteorites tended to blend in with terrestrial rocks – “that’s just a case of tuning your eyes. But searching in wet soggy fields where there’s livestock and sheep poo and rabbit poo and dog poo and brambles and nettles and members of the public… It presented much more of a challenge than I’d anticipated.”
Nevertheless, the team came back with a different kind of dropping – a 150g meteoric lozenge discovered in a field by Luke Daly’s group from Glasgow, and dating back to the beginning of the solar system, 4.6 billion years ago. “It’s a real privilege and a bit of a buzz when you find one,” says Joy. “And it’s always quite interesting to think, ‘What has this rock seen in its time and travels?’”
In offering answers to questions about how the Earth emerged as a habitable oasis, says Dr Joy, ancient carbonaceous chondrites are “an important part of the puzzle… And they will hopefully fill that gap of understanding what types of volatiles came to Earth – and to other planetary bodies as well.”
Also working on that puzzle are scientists from a number of different fields trying to connect the dots between the delivery of water and other chemical ingredients to Earth and the emergence of life. “We can say, ‘This is what’s in the meteorite,’” says King, “and go to the biologists and ask, ‘Right, what could you do if you mixed this up?’”
It’s always quite interesting to think, ‘What has this rock seen in its time and travels?’”
Carbonaceous chondrites from Winchcombe and from the Hayabusa2 mission have landed right in the middle of a lively decades-long debate over how, and where, on Earth life came about. For many years the orthodoxy among biochemists and geneticists was that the complex sequence of reactions that created the first cells must have taken place in the oceans, somewhere near the surface. But a big problem with the classic ‘primordial soup’ idea – put forward most famously by the British geneticist JBS Haldane in 1929 – has always been that water, as a particularly volatile ingredient, demolishes many of those early molecular interactions. For this reason, many other candidates for the cradle of cellular replication have been proposed over the years – such as alkaline vents on seabeds or volcanic hot springs – and in the last 12 years or so, a case has been gathering for life having begun inland rather than in the seas.
Among those working on this theory is John Sutherland of Cambridge’s MRC Laboratory of Molecular Biology, who has produced evidence in favour of warm, shallow pools as places where a carbon-based, prebiotic molecular mix would be exposed to UV radiation from the sun and, crucially, undergo cycles of first being immersed in water and then drying out. In 2020 Sutherland’s team showed this process could, under the right conditions, produce chemical precursors to proteins and DNA, while in 2019 biochemist Moran Frenkel-Pinter at the Center for Chemical Evolution in Atlanta demonstrated that certain life-associated amino acids spontaneously form protein-like chains when they undergo a similar drying-out process.
And Sutherland’s working model for a ‘Goldilocks’ location where such a synthesis might occur? A meteorite impact crater – ideally flanked by streams that form a pool in its base. In such a crater some of the required ingredients might just have been delivered by the rock itself, into an environment that would have allowed these and other chemicals to be alternately dissolved in shallow water then dried out by the sun.
“You can say with some degree of confidence we need to be on the surface, we can’t be deep in the ocean or 10 kilometres down in the crust,” explained Sutherland in the December 2020 issue of Nature. “Then we need phosphate, we need iron. A lot of those things are very easily delivered by iron-nickel meteorites.” It’s a hypothesis that’s been resisted by many working in the field, but the inland-puddle view appears to have been factored in to Nasa’s choice of landing site for its Perseverance mission to Mars – whose rover and onboard helicopter touched down in the Jezero impact crater on 18th February 2021 with the express purpose of seeking out residual signatures of previous life and water on the planet.
“I think the choice of the Perseverance landing site is tackling the question: was Mars habitable in the past?” says Joy, whose research, when not out scouring fields, deserts and snow, is focused on analysing meteorites from both the Moon and Mars. “Explicitly picking sites where there seems to be evidence of a delta deposit” – signs of a sediment build-up where two bodies of water meet – “which indicates there was water-flow – is key to thinking about whether there could have been types of conditions where life could have been stable under a good pH [alkaline or acidic] environment, presumably when Mars still had an atmosphere.” If there are clues to be found by Perseverance in the Martian subsurface, astrobiologists might have to wait a while before they find them – as yet there is no confirmed date for a ‘fetch’ mission that would return the rover’s samples to Earth.
“People always talk about meteorite impacts killing off life,” says King, reflecting on the discourse among biochemists. While that debate is a long way from the Winchcombe rock in terms of chemical evolution, he says it’s fascinating to speculate on ways in which the opposite might also be true, and that “actually impacts could create little hydrothermal systems” – that is, places where both water and warmth were present – “and things that would be really favourable to creating life”.
Meanwhile, three months after the Winchcombe impact, he and the whole UK community of planetary scientists and meteorite enthusiasts are still experiencing shellshock from the remarkable rock that somehow dropped perfectly into their lap. For Joy, who happens to have already analysed very similar kinds of meteorites, from samples found on the Moon by Apollo astronauts, “It’s one of these beautiful cosmic connections… one of this type just happens to land in Gloucestershire! Sometimes I struggle to explain some of these things.” When UKFAll was established, recalls Rowe, “I’d jokingly promised Ashley King a carbonaceous chondrite as the first one, because it’s his field of study.” When that prediction later proved accurate, “that struck Ashley as quite uncanny”.
Amplified by these otherworldly conjunctions, the astronomical achievement of the Winchcombe operation has left Rowe feeling a little adrift in the universe. After the adrenaline of the fall and the media aftershocks had passed, he says he was left with a feeling of “almost depression”. While acknowledging a deeper sense of satisfaction at the magnitude of the project’s first big test, and excitement at the prospect of a sharp increase in the frequency of UK meteorites being safely salvaged from now on, Rowe acknowledges the melancholy of success: “If you look at what we could have achieved that was better than this, there isn’t anything. This is like the hole-in-one for the beginner golfer. And they say, ‘OK, so what do I do next?’ on the second hole, and you go, ‘Yeah, do that again if you can.’”
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