‘It’s almost like a dream’: Sample of asteroid Bennu arrives at the Natural History Museum

After spending seven years whizzing around the solar system, the OSRIS-REx space mission finally reached its climax as its precious cargo ripped through Earth’s atmosphere and touched down in the scrubland of Utah.

The charred capsule contained fine material collected from the surface of the asteroid Bennu.

Orbiting the Sun roughly 120,000,000 kilometres away, this near-Earth asteroid is of intense interest to scientists for a number of reasons. For a start, it is thought to be an untouched time capsule from the beginning of the solar system, providing clues as to the origin of Earth and the life it supports. But it also has the potential to harm Earth, as it is considered to be the ‘most dangerous’ asteroid in the solar system.  

Now an incredibly special sample of Bennu has made its way to the Natural History Museum.

Here, a team of researchers will start studying the black, rocky powder in extraordinary detail. They will be exposing the extraterrestrial grains to a whole host of experiments and tests to vastly expand our knowledge of how asteroids like Bennu formed, what material they might contain, and fundamentally whether they played any role in bringing the building blocks of life to Earth itself.

The next few years will be a fantastically exciting time for these researchers.  

Bennu arrives at the Museum

‘We're really lucky,’ says Dr Ashley King, a meteorite researcher at the Natural History Museum, who will be part of the team studying the pieces of Bennu. ‘We're one of the first people to get our hands on the Bennu samples.’

‘And here at the Museum we have a team of researchers that are going to start studying these samples to understand their mineralogy and chemical composition.’

This is exciting, because Bennu is thought to have coalesced from material that formed during the birth of the solar system some 4.56 billion years ago. 

Before the formation of the Sun, a series of chain reactions kicked off, leading to the creation of ever more complex elements and molecules. All this matter eventually formed what is known as an ‘protoplanetary disk’ around the youthful star, in a way not dissimilar to the rings of Saturn today. 

This matter, formed of things like water and iron, eventually started to come together. As more and more matter combined, its gravity increased and so it attracted more material, eventually building up to form the beginnings of planets. 

The asteroid Bennu also formed in this disk at the same time, meaning that it is built from the same material that created our own planet, and will give scientists an unprecedented glimpse back to the very start of Earth’s life.

‘It's kind of like the leftover building block of our solar system,’ explains Ashley. ‘When we think about how planet Earth formed, all the ingredients are also locked up within Bennu. So we want to disentangle the story of Bennu and learn about the origin of the solar system and then the history of Earth.’

Untouched by Earth’s atmosphere

One of the most significant things about this sample is its pristine nature.

Up until the first asteroid return mission completed by the Japanese Space Agency in 2010, the only way for scientists to study material from elsewhere in space was to look at meteorites. But these pose a problem.

The very act of a space rock streaming through Earth’s atmosphere and then landing on the ground irreversibly changes it. The extreme heat as it crashes down as well as the damp nature of the surface of our planet alters the chemistry in these rocks, meaning that it is no longer a perfect representation of what it came from. 

By visiting asteroids still careening around space and collecting samples, scientists are able to get a much better picture of what these objects are made from.

‘Meteorites are brilliant,’ says Ashley. ‘But they're all contaminated to some extent. For Bennu, we have samples that we know exactly which asteroid and whereabouts on the asteroid they came from, so we have that geological context. And then the samples have come back to us and they're in a completely pristine state.’

To maintain this pristine condition means that the handling and movement of these samples must occur in a very controlled manner.

When OSIRIS-REx first made contact with Bennu, it blasted a jet of nitrogen gas onto the surface to kick up little bits of the rocky layer into a container, before backing off and sealing the tube shut. It is this capsule that the spacecraft then sent back down to Earth.

Scientists picked this container up from where it landed in Utah, and opened it in a sealed nitrogen environment with no oxygen and very low humidity. After they assessed that the mission had indeed been a success, and did a stock take of the material, the scientists removed a small sample and sealed it in a stainless steel tube.

It was this sample they then sent to the Natural History Museum, where it is now stored in yet another nitrogen environment to await study.

Unpicking Bennu’s secrets

The sample doesn’t look like much. Maybe a teaspoon of fine jet-black dust within a glass vial. But its origin is truly extraordinary, and it could help scientists at the Natural History Museum answer some of the big questions about the origins of life on Earth.

‘The sample, we believe, comes from the sort of asteroid that we think might be responsible for bringing water to Earth,’ explains Dr Helena Bates, a researcher at the Natural History Museum who will be studying the sample in minute detail.

‘So, when Earth formed it was quite a dry environment, and we think that water was delivered from an extraterrestrial source at some point during Earth's later evolution. We think that Bennu could be representative of the type of asteroid that delivered water to Earth.’

This means that Helena and her colleagues are keen to peer into the tiny grains to see if they contain any extraterrestrial water, and then compare it to the water we have on Earth. This could give them clues as to the origin of the life-sustaining substance. 

But it could also provide clues as to the origin of life itself.

‘We're going to be looking at the organic content,’ says Helena. ‘When I say organics, I don't mean life, but carbon-bearing molecules.’

‘We're obviously made up of organic molecules built into life. But we find organic material in some meteorite samples that are similar to Bennu. So we're going to be looking at the organic complement of this sample, trying to see if maybe these samples from Bennu - or samples like the samples from Bennu - could have acted like a stock cube for life and were delivered to Earth.’

To do this, the team will be applying a number of techniques to the material. This will include putting the grains in electron microscopes to probe its structure on a micron-scale, as well as grinding bits of the asteroid up before firing x-rays at the dust and looking at the way the waves bend as they interact with the grain’s surface to get an idea of its mineralogy.

But even before these samples are analysed, Bennu has already been surprising scientists.

Its surface, for example, was found to be strewn with large boulders over ten metres in size, whilst simultaneously, the fine rocky layer on the asteroid’s exterior astonished researchers by how loosely compacted it was. When OSIRIS-REx flew into to collect a sample from Bennu, the team suspect that if the spacecraft hadn’t fired its reverse thrusts, it would have simply sunk into the asteroid's surface.

‘I think these samples are going to transform our understanding of how the solar system formed,’ says Ashley. ‘I'm pretty sure when we start unpicking these samples, we're going to see all sorts of interesting stuff that we maybe haven't seen in our meteorite records before.’

The future of natural history

For over a decade, Professor Sara Russell has been involved in the OSIRIS-REx mission. She was there from the very start, when researchers were just sitting around musing about how great it would be to one day do an asteroid return mission. She has since seen this idle chit-chat turn into reality.

‘It's almost unbelievably exciting,’ says Sara. ‘It’s almost like a dream to have the sample back, because we've been thinking about it for so long.’

‘There has been so much planning. And we've spent years talking about what the sample might be like and speculating. To actually have a bit of the sample here at our Museum and to be able to analyse it in our own labs is really a dream come true.’

She has been part of a team made up of hundreds of scientists all around the world, each one adding their expertise and knowledge to make those early conversations a reality. This mission simply would not be possible without these huge, international collaborations.

But Sara expects that this mission will only be the start and hopes that it will inspire a new generation to start exploring space and creating new, extraterrestrial natural history collections. 

‘It's almost like a second era of voyages of exploration,’ says Sara. ‘We're starting to explore the solar system around us and bring back materials from space.’

‘I see this as being the next era of natural history collections.’