Meteorites: Windows into our solar system’s beginnings

Our space scientists are working on answering some very big questions.

Professor Sara Russell, one of our planetary scientists, reveals “our group has been focused on trying to understand how we got to have a habitable world. The origins of Earth, how it got to be a water world and how the organic material that eventually became life was first delivered.”

Earth is about 4.5 billion years old, which means the answers to these questions are hidden somewhere in the distant past. No one’s managed to recreate Doc’s DeLorean from Back to the Future yet, but that’s not a problem for our scientists, they have their own time machines – meteorites!

Meet the meteorites

Every day rocks travel through space towards Earth. Most of this material is very fine grained and lots gets vaporised as it falls through our planet’s atmosphere. Only a few rocks survive to land on the surface, becoming what we call meteorites.

We care for a collection of around 5,000 meteorites. According to Sara, it’s one of the world’s best meteorite collections.

There are several different types of meteorite. The most common are made of stone. Of those, a type called chondrites falls most often. These are filled with flecks of metal and little blobs called chondrules. Billions of years ago these blobs floated about in the dusty disk from which the planets of our solar system formed.

Then there are heavy iron meteorites covered in regmaglypts – marks that look like big thumbprints pressed in all over their surface.

There are also pallasites meteorites, which are a mix of stone and iron. These probably formed in collisions between stony and iron meteorites. The stunning Imilac meteorite on display in our Hintze Hall is a pallasite.

The collection we house also contains objects that were formed by meteorites landing on Earth. When a huge meteorite fell in a desert in what’s now Libya, “it caused so much heat that the sand actually melted and formed glass,” Sara explains, pointing out a translucent, pale yellow piece of glass.

Then there’s tektites – now-solidified, black, teardrop-shaped rocks. When massive meteorites landed, the heat and power of their impact sprayed molten rock into the air that then cooled forming tektites.

Where did life come from?

Where meteorites fall is quite random.

However, the UK’s been particularly unlucky. Until the Winchcombe meteorite landed in 2021, the last to fall here was the Glatton meteorite in 1991.

“In the middle of the COVID-19 lockdown, the Winchcombe meteorite splatted onto someone’s driveway,” recalls Sara. “But it turns out to be a really unusual type of meteorite.”

The Winchcombe meteorite is a carbonaceous chondrite. This type of meteorite is full of carbon and water – although this isn’t sloshing around inside it. We think these types of meteorites come from the outermost parts of our solar system. In these cold and distant places, far away from the risk of evaporation, material such as water can condense into rock.

“We think meteorites like this would have hit early Earth and brought water and the ingredients for life,” says Sara.

The very rare carbonaceous chondrites in the collection we care for, including the Winchcombe meteorite, are kept as pristine as possible by storing them inside a high-tech, well-lit glovebox. This is a sealed cabinet with built-in gloves that allows the scientists to work with the specimens in a carefully controlled environment.

Oxygen is vital for us but awful for carbonaceous chondrites, which formed in the airless conditions of space. Elements in them, such as carbon and iron, deteriorate quickly in our atmosphere. To keep these important specimens safe, the atmosphere inside the glovebox is high in nitrogen, with only 1.5 parts of oxygen per million. The air we breathe is 200,000 parts of oxygen per million.

But it doesn’t matter how quickly you collect a new meteorite specimen that’s fallen to Earth, it will always be contaminated by terrestrial materials.

While all the space rocks we care for are important, there’s no denying that a recent arrival has been a game-changer. Sara points out a small glass dish inside the glovebox. The few tiny grains of black rubble it holds may look inconsequential, but they’re part of groundbreaking science.

The grains come from a near-Earth asteroid called Bennu. They were scooped up by the OSIRIS-Rex spacecraft on its 3.5-billion-kilometre round trip from Earth. When it returned in 2023, some of the incredibly special material it gathered was sent to us to be studied.

Unlike meteorites, these samples from Bennu are uncontaminated, having been collected out in space and then carefully protected once arriving on Earth. Recently, our scientists were part of a team that identified some of the building blocks needed for life to develop tucked away inside the samples.

How to study a space rock

“Meteorites have been around for so long. They’re a witness to everything that’s happened in the solar system,” says Sara.

To get an ancient space rock to give up its secrets, scientists start by looking at it under a regular microscope.

“Then we’ll make it into a polished mount,” Sara explains, pulling out an example, where a tiny piece of the Winchcombe meteorite has been embedded in clear epoxy – a type of resin.

“It’s been polished down to make a very, very flat surface, and then coated with carbon to make it electrically conductive. We use this in scanning electron microscopes,” reveals Sara.

From these you get very close-up, high-resolution images of the meteorite’s surface. Scientists also use a technique called Energy Dispersive X-ray spectroscopy, or EDX for short, to identify the different minerals in a specimen.

“That can tell us a lot about the environment in which it formed. Different minerals form under different levels of oxygen, different pressures and different temperatures. It tells us an awful lot about where it came from,” Sara explains.

Using our CT-scanners, our scientists can look at a meteorite’s internal structure. This can, for example, allow them to investigate how the original material came together in space and how it might have changed when it was part of an asteroid.

Meteorites are rare and one of a kind. This is something that’s always in the minds of our scientists when they’re working with the collection. They make sure to use the smallest amounts of meteorite specimens possible when carrying out their research.

“We make sure that we preserve the meteorites for future generations to use as well. The equipment is developing over time, so people can do new things on smaller and smaller samples,” says Sara.

Why do we study meteorites?

Meteorites from asteroids are all about 4.5 billion years old. They date back to the time when our solar system was forming.

“They’re kind of telling us what was happening then. We can use them to learn about how the planets formed, what the environment was like then, what the structure of the solar system was like and how long everything took to form,” Sara explains.

Nearly all meteorites come from asteroids, but a rare few come from Mars and the Moon.

While we’ve been able to return samples from asteroids, there’s not yet been a sample-return mission to Mars. NASA’s Perseverance Rover is busy collecting rocks from the Jezero Crater on the red planet. It’s patiently waiting for us to arrange a mission to bring them to Earth.

Until then, Martian meteorites, such as those in the collections we house, are the only way for us to work hands-on with rocks from Mars. That makes them a really important tool for answering questions about this fascinating other world.

For example, the red planet is one of the places in our solar system where we’re searching for signs of life. Mars was thought to be a dry planet until our scientists found evidence of water inside a Martian meteorite called Nakhla. Water is a vital ingredient for life.

Moon rocks are also having a resurgence right now! With plans for a lunar base as part of NASA’s upcoming Artemis missions, there are lots of questions around how much water there is on the Moon and where it is. Lunar meteorites can help answer these questions.

Astronauts brought back rocks from the Moon during the Apollo missions in the 1960s and 1970s. They only collected samples from the near side of the Moon, so the meteorite collection we care for can actually give us a better idea of the Moon as a whole. “Lunar meteorites come from all over the surface, so we’re using them to learn how the composition of the Moon is different from one place to another,” Sara details.

Our scientists are also working with micrometeorites. Thousands of tonnes of extraterrestrial material fall from space to Earth every year and most of this is in the form of dust. We get far more micrometeorites arriving on Earth from asteroids, comets and other bodies than we do larger meteorites.

“They can give us a much better idea of what’s out there,” explains Sara. “By looking at micrometeorites, we can learn about how Earth is kind of growing over time – the flux of Earth.”

“You can also look at fossil micrometeorites by dissolving up rock and looking at the micrometeorites in them. The atmosphere changes them a little bit, so it can also tell you how the atmosphere has changed over time.”

There are so many questions to answer about the origins of our solar system and life on Earth. The research going on right now only scratches the surface of what meteorites might be able to tell us.

“A lot of meteorites come from different places to Earth,” says Sara. “Most of them come from further out and then some come from inwards, so they can tell you about this whole range of space.”

“They’re like a time machine and a spacecraft all in one!”