Incoming: A Pinch of Pristine Asteroid

It’s just a tiny 100 mg. Which really is not much when you think about it. 

Yup, that is the estimate of how much material from the asteroid Ryugu is being brought back by Hayabusa-2, and is the exact amount the team from JAXA originally planned to get.  

We actually won’t know exactly how much has been captured until the Japanese scientists open up the capsule after it lands in Woomera in the early hours of this Sunday morning, though.  Assuming all goes well with the landing,  those tiny shards of rock, equivalent in amount to a generous pinch of salt, will become the most valuable material on Planet Earth.

It is also going to be the first time we’ll have a sub-surface sample from an asteroid to study. The significance? This material has not experienced any weathering as the asteroid has travelled around the Solar system for the last 4.5 billion years. It is hoped that this will be the pristine material created before the Earth and other planets were formed - material from the original solar nebula.

Hayabusa-2 has already made startling discoveries about the asteroid Ryugu, as well as its place in the solar system. We know that the asteroid is made up of materials similar to the carbonaceous chondrite meteorites that have landed on Earth.  

These rocks are from the very beginning of our solar system and give us a glimpse into these early tumultuous years of our planets forming.  This information, as well as a discovery that Ryugu has perhaps changed how far it is from the Sun, has come from the onboard instruments on the spacecraft.

So why then is it so important to bring back a piece to Earth?  

This comes down to the sheer accuracy of measurements that can be done in the labs here on Earth, even with tiniest amounts of material collected.  The fantastic opportunity of Hayabusa-2 is that it can pair its larger-scale observations of the asteroid's surface, with samples that they collected from it. This helps planetary scientists have two different sets of data to build their conclusions.

During 2019, Hayabusa-2 obtained samples from two distinct areas on Ryugu, both times touching down on the asteroid and firing a projectile at the surface so that the material would fly up into a funnel and be collected.  The first of these sample grabs was from the surface of the asteroid, but the second managed to sample a little deeper into the asteroid with a bit of a clever idea. 

Before the second sampling, Hayabusa-2 actually fired a bigger projectile (2.5 kg of copper) into the asteroid, creating an artificial crater.  The spacecraft was then maneuvered back to sample from that crater - providing researchers with the opportunity to see how the variation of chemistry and materials between the surface of the asteroid, which is constantly exposed to the solar radiation environment, and the rocks that are buried and sheltered away from the harshness of space.   

Both samples have been stored onboard in separate capsules, and within these, they have already been sorted into ‘big’ grains (about 1 mm), fine grains (about 0.01 mm) and gases. One of the most exciting things about this mission is that the first sampling of the gases will occur here in Australia, by the teams that recover the samples from the red sands of the Australian landing location. 

Give them a good sniff while the samples are fresh! 

Getting a fresh look at these asteroid samples is particularly important for the sample collected from the crater Hayabusa-2 made. The hope that this has sample pristine carbonaceous chondrite material, and enable us to see what volatiles and organic molecules make up the components of this material.  

Previously, there’s been hints in the meteorites that have fallen to Earth and been studied that these carbonaceous chondrites molecules are there - but the Hayabusa-2 is going to give scientists a fresh whiff of material will really be able to confirm things.  Then we can feed this information into how much material was available at the beginning of the solar system to form, well everything we live on!

After this initial atmospheric test in Australia, the samples will go back to Japan, to a facility built to make sure every speck of dust is recovered from the containers. So careful are they about these samples, there has already been enormous work done to prepare including working out how to identify and extract any soot from the explosive used with the projectile they used to get the samples.  

Once the Hayabusa-2 team have recovered everything they can, portions of the samples will be sent to labs all over the world for detailed analysis.  Everything from every single element they contain, how these have formed into minerals and how these minerals lie in relation to each other is going to be poured over.  

And Australia will be getting some of the samples too. Prof Trevor Ireland from the Australian National University (ANU) is particularly excited about getting some of the material sampled from the crater.  Using his machines, in a basement of the School of Earth Sciences at ANU, he and his team will be able to discover the exact chemistry and look to date each of the minerals they find.  He’ll then work with teams from around the world to do a bit of detective work on the history of this asteroid.  

The following timeline has been outlined by the Japanese Space Agency, JAXA.

The capsule will separate from the Hayabusa-2 spacecraft on 5 December 2020, when the craft is approximately 220,000 km away from the Earth. Within a couple of hours of capsule release - the spacecraft will administer an orbital control correction around 200,000 km - 160,000 km from the Earth, which will lead the Hayabusa-2 onto its next mission - the exploration of two more asteroids (with no sample returns) over the next 11 years

In the early hours of Sunday morning (6 December 2020), the sample return capsule will enter Earth’s atmosphere at an altitude of 200 km, where it will descend and slow down. The parachutes are expected to open a few minutes later at an altitude of roughly 10 km, which will eventually return the precious cargo to Earth’s surface. JAXA scientists and Australian authorities will then retrieve the capsule. 

The expected re-entry flight is from the Northwest direction, with the precious capsule landing in the Woomera Prohibited Area (WPA). This area does not allow civilian access. It is expected that the re-entry fireball will appear in the sky between 3:30 am - 4:30 am South Australia local time, with further refining of this time closer to the landing time. 

You can watch the return on the JAXA YouTube Channel (once the broadcast begins)