- Meteorites contain materials from the earliest days of our Solar System and even from before the planets began to form.
- Scientists need to collect meteorite samples as swiftly as possible when they impact Earth, using networks such as the UK Fireball Alliance (UKFALL) and public support.
- At the University of Glasgow in the UK, planetary scientists Professor Martin Lee, Dr Luke Daly, and Dr Sammy Griffin have dedicated their time to the extensive study of meteorites.
- The scientists’ long list of achievements includes the analysis of the Winchcombe meteorite which contains water with a similar chemical signature to water on Earth.
- By collecting and analysing Martian meteorites, called nakhlites, the team aim to further elucidate the possibility of life on Mars.
While the enigmas surrounding life and the universe continue to befuddle us, scientists are unlocking clues to address many important questions about Earth and our Solar System by studying meteorites. As fragments of asteroids or comets, the Moon or even Mars, meteorites have much to tell us about the formation of planets and the distribution of water and biological molecules.
There are around a million known asteroids in the Solar System, most of which are found in the asteroid belt between Mars and Jupiter. These icy, rocky, or metallic objects have no atmosphere and were formed billions of years ago just as the planets were developing. Scientists are especially interested in asteroids as they preserve a unique snapshot of the earliest years of our Solar System.
Finding meteorites
At the University of Glasgow in the UK, planetary scientists Professor Martin Lee, Dr Luke Daly, and Dr Sammy Griffin specialise in tracking, collecting, and studying meteorites. Meteorites are constantly falling to Earth from space. The meteorites found long after they have fallen, called ‘finds’, are usually contaminated by interactions with the Earth’s environment, absorbing water and other molecules and obscuring important information about the early Solar System. If the fireball – the bright light from a meteorite as it decelerates rapidly through Earth’s atmosphere – is seen and the surviving meteorite is collected within a few days of landing on Earth, it is called a ‘fall’. Falls are ideal for laboratory analysis as they have had minimal opportunity to be contaminated by their short time on Earth.
With the help of local residents, volunteers, and scientists, the team were able to collect the Winchcombe meteorite in less than seven days after the fall.
There have been fireballs recorded throughout history, but modern technology has enabled easier sighting, reporting, and collection of meteorites. In February 2021, a fireball was detected by 16 dedicated meteor cameras in the UK that were part of a meteorite monitoring network. In addition, it was also captured on numerous doorbell cameras and dashcam videos besides being reported by over 1,000 eyewitnesses. The footage was widely shared on social media.
Dr Luke Daly, who helps coordinate the UK Fireball Alliance (UKFALL), and the rest of the team quickly realised that the fireball dropped a meteorite over the UK. By using the sighting data alongside computer modelling of the meteorite’s path, they were able to identify a probable location for the meteorite sample in Gloucestershire, Central England. With the help of local residents, volunteers, and scientists from across the country, the team were able to collect over 530g of meteorite material, now named the Winchcombe meteorite, in less than seven days after the fall – some was even collected within 12 hours.
Traveller from the outer Solar System
The Winchcombe meteorite was a big success for the UKFALL team. Its atmospheric entry was documented on multiple cameras, meaning scientists could pinpoint exactly where in the Solar System it came from. Since it was collected swiftly, it serves as a near pristine example of a rare type of meteorite, called a carbonaceous chondrite. These are meteorites that are rich in clay, contain water and organic compounds (molecules that contain carbon), and are some of the oldest solid materials found in the Solar System.
The planetary scientists at the University of Glasgow conducted laboratory analysis of the Winchcombe meteorite samples to discover that the water contained within the meteorite minerals has a similar isotopic signature to water on Earth. This means that our planet’s water was probably brought here by asteroids, potentially triggering the origin of life on Earth.
Analysing Martian meteorites
There are a range of Martian meteorites. Those known as the nakhlites were created when there was a large-impact event on Mars that caused rocks from the surface to be ejected into space. They are made of igneous rocks formed by volcanic activity around 1,400 million years ago. By analysing their crystal structures, scientists can learn about how these rocks were originally formed on Mars.
The team at the University of Glasgow have studied nakhlites using a scanning electron microscope-based technique, called electron backscatter diffraction. Using a beam of electrons (a small particle that is part of an atom) to illuminate crystals within a meteorite sample, this technique gives information about the material’s structure at a micro-scale. The scientists discovered that there were two impacts that created the nakhlite meteorites. The first impact dates back to about 630 million years ago and deformed the original rocks from which the meteorites were produced, while also generating liquid water through the melting of ice. The second impact that occurred around 11 million years ago ejected the nakhlites from Mars.
Water on Earth was probably brought here by asteroids, potentially triggering the origin of life on Earth.
Lee, Daly, and Griffin emphasise that Martian meteorites are pivotal for improving our comprehension of the history of water on Mars, as well as volcanic activity and the processes caused by meteorite impacts. The team have used two more types of analytical techniques to study nakhlite meteorites – atom probe tomography (a method that can make a 3D compositional map of the individual atoms of each element within a sample) and transmission electron microscopy (a beam of electrons is transmitted through a sample to create an image). The team’s extraordinary work on Martian meteorites has led to the discovery that some of the water generated from the melting of the ice around the meteorite impact is still trapped within the minerals that make up the rocks.
Meteorite material is one of the most challenging types of geological samples to collect. It requires a precise collaboration across the country to recover recent falls, or spacecraft that is capable of directly collecting samples from asteroids and returning them to Earth. However, Lee, Daly, and Griffin are persistent in their study and efforts, firmly believing that meteorites can help us answer some of the most important questions about our Solar System.
What spurred your interest in meteorites?
We are geologists by training and very passionate about rocks, and what they can tell us about how our Earth works. It was then a natural progression into studying meteorites which are the coolest rocks around and can tell us so much about how our Solar System formed. Meteorites even contain small mineral grains, including diamonds, that formed during the death of stars in other parts of the galaxy.
Can you describe the UKFALL network?
UKFALL is an amazing international collaboration between meteorite researchers, museums, and citizen scientists all coming together to image fireballs, find meteorites, curate them, and study them in the UK. It is a collaboration with six different camera networks participating, from professional academic networks, such as SCAMP and the Global Fireball Observatory, to amateur astronomers, such as UKMON and Nematode. We are all working together imaging the night sky for fireballs, sharing data so we can quickly figure out if a meteorite has landed, where it landed, and where it came from in the Solar System. Our most notable success is the recovery of the Winchcombe meteorite in 2021.
What are the legal issues faced when collecting meteorites off land – who owns a meteorite?
Our working hypothesis is that if it is public land, the finder owns it and if it is private land, the landowner owns it. However, this has never actually been tested in a UK court of law and there are no specifics about meteorite ownership in the UK legal system. Other countries do have set regulations enshrined in law about meteorite ownership ie, Morocco – if you found it it’s yours – and Australia – it belongs to the King.
What are the differences between the main types of meteorites and what questions can they each answer?
There are three main types of meteorite: iron, stony iron, and stony. As the name suggests, iron meteorites are made of iron nickel metal. We think iron meteorites are from the cores of early planetary embryos that have melted and separated into a core, mantle, and a crust similar to the Earth’s internal structure. But unlike the Earth, the iron meteorite parents got busted open early in the Solar System, producing iron asteroids and iron meteorites.
Stony iron meteorites are made of fragments of rocks or minerals embedded in an iron nickel metal matrix. We think these form in some of the most cataclysmic events in our Solar System – a planet-planet collision. The metallic core of one planetary embryo merges with the upper mantle made of a beautiful green mineral called olivine. The metal melts and injects itself along grain boundaries in the upper mantle, producing an exquisite patchwork of bright green crystals floating in metal.
Finally, the stony meteorites which we spend most of our time studying are split into two groups: the chondrites and achondrites. The achondrites have melted and lost all their initial metal to the core of their parent planet or planetary embryo. They are typically igneous or volcanic rocks from the crust of differentiated bodies like the Moon, Mars, and asteroid Vesta, and by studying them we can learn about volcanism on other planets, moons, and asteroids. Last but best are the chondrites. These amazing wee stones are loose agglomerations of all the grains and minerals that formed in the Solar nebular – before there were planets. These dust particles stuck together to make asteroids, but they never got big enough to melt and separate out. In fact, beyond being exposed to heat and water, almost nothing has happened to these rocks since they formed 4.567 billion years ago when the Sun first started to shine. By studying them, we can learn about the environment in our Solar System before there were planets and how life-giving water and organic material could have been delivered to the Earth and other terrestrial planets.
