METEORITE MEDLEY
2021 has been a good year for meteors and meteorites – although one or two landed a bit too close for comfort
WINCHCOMBE METEORITE
On the evening of 28 February this year a bright, fiery, meteor was visible across much of the south of England, causing a sonic boom as it passed. It was tracked by the UK Meteor Network, who received almost 800 sighting reports from Liverpool down to Cornwall, which, along with videos from CCTV, dashcams and video doorbells, enabled them to plot the meteor’s path. They concluded that it had hit the ground somewhere between SwindonVillage and Bourtonon-the-Hill in Gloucestershire, sparking a search for meteorite fragments across the area.
The next day, what the local paper had described as a “huge space object” was found to be of rather more modest proportions and embedded in the tarmac front drive belonging to the Wilcock family in the Cotswold village of Winchcombe. Hannah Wilcock, 25, said: “When I heard it drop, I stood up and looked out the window to see what was there, but because it was dark I couldn’t see anything. It was only the next morning when we went out that we saw it on the drive
– a bit like a kind of splatter. And in all honesty, my original thought was – has someone been driving around the Cotswolds lobbing lumps of coal into people’s gardens?” The family did, however, contact the Natural History Museum (NHM), who had been inundated with pictures by hopeful meteorite hunters.
On seeing the Wilcocks’ picture, planetary scientist Richard Greenwood said: “It was one of those moments when your legs start going wobbly. I saw this thing; it was like a splat across the [Wilcocks’] drive; and it had all these rays coming off it; and I just thought – that is a meteorite. It was instantaneous.” This was the first time in 30 years that a piece of a meteor that had been observed crossing the sky had been successfully recovered from the ground in the UK. It was swiftly retrieved by the NHM and found to be a rare carbonaceous chondrite, prized by researchers because they contain pristine material from the formation of our Solar System 4.6 billion years ago and so can give insights into the process of planet formation. Out of 65,000 known meteorites that have been found, only 1,206 have been witnessed to fall; of these, only 51 are carbonaceous chondrites, and it is the first time this type of meteorite had been found in the UK.
In all, 319g (11.3 oz) of material was collected from the Wilcock’s driveway and lawn and the fact that it was retrieved so quickly, within 12 hours of landing, and hadn’t been rained on, meant that the quality of the specimen was
“We went out and saw it on the drive – a bit like a kind of splatter”
comparable to what is expected from sampling missions sent to asteroids. Over the next few days additional pieces were retrieved from nearby farmland with the final haul totalling 548g (19.3oz). While scientists are now analysing most of the fragments, some are on display at the Natural History Museum in London, along with the patch of tarmac from the Wilcocks’ drive where the first piece was found, carefully excised, and added to the museum collection. gloucestershirelive.co.uk, 1+9 Mar 2021; nhm.ac.uk/discover/ news/2021/September.
FLASHES AND BOOMS
In recent months there have been a number of spectacular meteors reported streaking across the night sky (when the objects are airborne, they are meteors, once they hit the ground, meteorites). In July, south-east Norway was treated to a display by a meteor that produced several strong flashes of light and a series of loud bangs. Researchers used video footage from dashcams and security cameras to track its path, and believe it fell to earth in Finnemarka, a wooded region 60km (40 miles) west of Oslo where a group of campers saw the fireball and reported “a large explosion just above their heads”. A day later, the American Meteor Society received more than 213 reports of a glowing meteor that was visible from Texas, Arkansas, Louisiana, Oklahoma and Missouri, accompanied by loud booms, with an unconfirmed report that part of the object had hit the ground near a rural road in Rockwell, Texas. In early September, it was the turn of Brittany and Normandy in France, where another glowing meteor crossed the sky. It was also visible from Southampton and is believed to have fallen in the Channel. Later in the month, North Carolina residents saw a meteor travelling across the state at an estimated 32,000mph (8,889km/h) before disintegrating 28 miles (45km) above Morehead City. More mysteriously, on 10 October New Hampshire was treated to an earth-shaking boom that disturbed people across the state. Initial speculation suggested it was an earthquake, but the US Geological Survey said that none had taken place, and sonic booms from military aircraft were ruled out by the Air
Force. Some flippant commenters thought it might have been a gender reveal party gone wrong (see p6-7), but John Ebel from the Weston Observatory said: “I would look for a natural event, something coming into the atmosphere past the speed of sound, meteor, meteorite, probably causing enough energy to be released that people heard it here down on the ground.” Greg Cornwell of the National Weather Service later confirmed this suspicion, reporting that the geostationary weather satellite GOES-16 showed a blue dot flashing over New Hampshire around 11.21am, consistent with a meteorite exploding. BBC News, 25 Jul; [UPI] 26 Jul; oust-france.fr, 6 Sept; cbsnews.com, 28 Sept; yahoo. com/news, 11 Oct; boingboing.net, 13 Oct 2021.
METEORITIC NEAR MISS
Ruth Hamilton of Golden in British Columbia, Canada, was asleep at home when she became vaguely aware of her dog barking; the next thing she knew, she was shocked fully awake by a huge explosion and a shower of debris hitting her in the face. On turning on the lights, she realised something had punched a hole in her bedroom ceiling. She called the police: “Talking to the operator, she was asking me all kinds of questions, and at that point, I rolled back one of the two pillows I’d been sleeping on and in between them was the meteorite.” It was melon-sized and had landed just inches from Ruth’s head; clearly, it could have been fatal had it struck her. Police initially suspected it was a rock from blasting taking place locally at Kicking Horse Canyon, but construction staff said there had been no blasting going on, although some of the crew had seen a bright light in the sky that exploded and caused some booms. Professor Peter Brown at Western University in London, Ontario, confirmed the rock was a meteorite: “Everything about the story was consistent with a meteorite fall, and the fact that this bright fireball had occurred basically right at the same time made it a pretty overwhelming case.” [UPI] 12 Oct 2021.
METEORITE HUNTERS
It is estimated that about 500 meteorites survive their fall through the Earth’s atmosphere and hit the ground each year. The majority of these are quite small and do not conveniently deposit themselves on someone’s pillow. They are of considerable scientific interest but only about two per cent of them are ever recovered; on average, it takes 100 man-hours to find each meteorite fragment. As a result, Robert Citron and his team at the University of California, Davis, have been working on a way to drastically increase the percentage of meteorites recovered. Citron and his team have been using drones to fly a grid pattern over the likely area of a meteorite fall, taking systematic high-resolution pictures of the ground. These are then processed by an artificial intelligence that has been trained on photographs of meteorites and their impact sites to pinpoint the likely positions of fragments within the search area. The system has performed well in tests where it had to identify meteorites placed by researchers in a lakebed in Nevada and Citron is optimistic about the potential of the system, particularly for finding meteorites in remote regions. universetoday.com, 9 Jul 2021.
PULVERISE IT!
While finding small meteorites on the ground is difficult, finding and dealing with much bigger rocks in space that could pose a future threat to the whole planet is even more challenging. While scientists now keep watch for potentially destructive asteroids to give us advance warning of the kind of object that caused the Tunguska Event in 1908 ( FT1:12, 189:4), destroyed Tall elHammam in antiquity ( FT412:14) or wiped out the dinosaurs, they completely missed the meteor that caused extensive damage by exploding over Chelyabinsk in 2014 ( FT300:7, 58-59). As a result, even if we are lucky, we may only get short notice of something potentially disastrous coming our way, so we need to be able to respond quickly if we are to do something about it. Now Philip Lubin and his team at the University of California, Santa Barbara, have come up with a new way to defend our planet, a project known as PI (short for “Pulverise It”). Instead of deflecting an incoming space rock, PI involves laying an array of penetrator rods 4-12in (10-30 cm) in diameter and six to 10ft (1.8-3m) long, possibly loaded with explosives, in the object’s path. Impact with these penetrators would shatter the object into house-size chunks that would still hit the Earth but would now burn up in the atmosphere, producing a spectacular light show instead of the apocalypse. “If you can reduce the big events, which are dangerous, into a bunch of little events that are harmless, you’ve ultimately mitigated the threat,” said Alexander Cohen, a member of Lubin’s team. The advantage of this approach is it does not require any dedicated infrastructure and could be launched at objects some days away using rockets that exist today, or even minutes before impact using ICBM missiles. “Humanity could finally control its fate and prevent a future mass extinction like that of the previous tenants of the Earth who did not bother with planetary defence, the dinosaurs,” said Lubin. phys.org/news, 13 Oct 2021.