Chicken Little got bonked on the noggin by an acorn and thought the sky was falling. As if.
Except there really is stuff falling from the sky, from way higher up than a big old oak tree. It is estimated that 29 to 57 tonnes of rock rain down on earth from space every day.
Most people know of the potential threat to the planet posed by a large asteroid. Besides being the thing that resulted in the demise of the dinosaurs, it has been the subject of movies starring Bruce Willis. But while we know that these big asteroids are a potential threat, few people realise that we are routinely running into space rocks that don’t quite measure up to that planet-killer status.
Most people are, however, quite excited to see a star streak across the sky. They squeal. They point. Wishes get made.
If there is a ‘well, actually’ type person present, they will let you know that these are not, in fact, shooting stars, but meteors.
What we are seeing is a bit of space rock that has gotten in our way. Travelling merrily on its way minding its own business , unimpeded by the vacuum of space, it suddenly finds itself plowing into our atmosphere, which slows it down suddenly, and friction from the air makes it heat up A LOT making it glow very brightly, producing the streak of light we see. Most of these bits of space rock are small enough that they completely vapourise in the atmosphere, but some are large enough that bits will fall to the ground, and at this point we call them meteorites.
Don’t panic though, because to date there is only a single account of a meteorite actually hitting someone. Her name was Henny Penny Ann Hodges, the date was November 30, 1954, and she was having a nap when a meteorite crashed through the roof of her house, into a radio, and then onto her leg where it left a sizable bruise.
Other notable meteors have caused damage to property. Back in 2013, a very large meteor shattered the skies above Chelyabinsk, the fireball it produced creating shockwaves that shattered windows over a large area, resulting in 1200 people being injured. The bright flash and detonation made people think a nuclear weapon had exploded, and indeed it is estimated that the energy released was equivalent to between 20- and 30-times the Hiroshima explosion. About 600kg of meteorite was recovered, and it is estimated that the rock was about 19m across with a mass of 12,000,000 kg before it crashed into our atmosphere. 99.995% burned up in the atmospheric explosion.
So with these dramatic events being part of our historical record, perhaps it is surprising that the amount of space rock entering the atmosphere is estimated to be somewhere between 29,000 and 53,000 kg per day. That seems like a pretty rough estimate, right? There is a good reason for that. We simply do not have enough data to make a half-decent estimate.
There are sky surveys making concerted efforts to map the sky and find all the Potentially Hazardous Near Earth Objects, but these are focussed on the largest and most dangerous stuff, the pretty rare big chunks of space rock from about the Chelyabinsk-sized meteoroids up to asteroids hundreds of metres or kilometres in size. The stuff smaller than that is way more common, but much harder to see until we actually run into it.
We can also learn a lot about our local solar system environment if we study this smaller stuff too. Until recently, there have only been sporadic efforts to monitor the sky for meteors so these can also be studied. Developments in camera sensors and small single-board-computers have made it feasible to deploy a planet-wide meteor monitoring system, to collect much more data and expand our understanding of meteors. We can also use this data to track down and locate meteorites!
In February 2021, a search was undertaken to find meteorite material after a large fireball was caught on meteor cameras across the UK. In total, about 548g of meteorite material was recovered in the village of Winchcombe, Gloucestershire, by people who searched areas suggested by people triangulating the course of the meteor on the meteor camera network and from footage captured on people’s doorbell-cameras. This was the first bit of meteorite recovered in the UK since 1991, but some believe that good coverage of the night skies using meteor-detection cameras could result in recovering a meteorite annually from a land area the size of the UK or NZ. Check out how excited these searchers were:
The cool thing is, just about anyone can be involved in this project. Getting a meteor camera set up costs about NZ$350 and once set up it chugs away collecting data for this citizen science project, without your active involvement. Whenever you like, you can connect to your camera and see what meteors it was able to detect the previous night.
Dashboards share cool information that the network has been able to derive from your camera and those around nearby.
When a fireball big enough to actually drop a meteorite is seen, the data on your meteor camera can be used to figure out where it came from, which direction it was heading and how fast, and where any meteor might be able to be located – down to as small as a 15m target!
This fireball meteor was captured by GMN RMS station CA0011 in January 2020. Overlaid over the whole stream is a frame-by-frame capture of the meteor streaking across the sky, with the brightness adjusted in the moving box to see better. Note how it flares and flickers as bits disintegrate off the rock.
Would you like to know more about how you can start collecting and contributing meteor data as part of this science project? Head over to globalmeteornetwork.org and check out the wiki which has information on how to get started and build your own RMS meteor camera, and sign up for the newsgroup forum on groups.io.