﻿When we imagine aliens visiting Earth, we often picture an evil crew on a spaceship -
scary, threatening and weirdly humanoid. But what if aliens end up slipping onto our
planet in much smaller and subtler ways - on a microscopic scale, unnoticed?
Now flip that question. When we send spacecraft across the solar system,
land on distant asteroids, and bring pieces of them home,
how can we be sure we aren’t leaving traces of ourselves behind?
Traces that future scientists might one day misinterpret as something... alien?
That’s one of the reasons sample return missions are so fascinatingly delicate.
When we venture out there to bring a piece of the universe back here,
we need to touch without leaving fingerprints. And in the case of asteroid Ryugu,
what came back to Earth wasn’t just a handful of ancient dust,
but a lesson in just how easy it is to confuse what’s truly alien with what’s all too familiar.
I’m Alex McColgan, and you’re watching Astrum.
Join me today as we explore why asteroids like Ryugu are so scientifically valuable,
how the Hayabusa2 mission successfully brought home a piece of it,
and the hidden threat right here at home that almost ruined the whole thing.
Why study asteroids in the first place? Far more than lifeless rocks,
they’re really more like time capsules. You see, our solar system was created over
4.5 billion years ago. Its planets, moons,
and all other celestial bodies are thought to be made from some primordial material.
But it’s hard to tell what that material may have been just by studying Earth rocks.
On Earth, erosion, tectonic activity, and the weather
modify the material’s physical and chemical properties beyond recognition.
That’s not the case with asteroids, where this material remains largely unperturbed by time,
like a window into the earliest days of our solar system.
There’s also evidence to suggest asteroid collisions with Earth
might have delivered organic compounds to our planet
when the conditions for life were starting to emerge.
Asteroids might hold insights we can’t get elsewhere
about the origins of our solar system and the life in it.
Yet, getting to asteroids isn’t easy. Most of them are found in the asteroid belt,
circling the Sun in an orbit between Mars and Jupiter.
A trip out there, though it has been done before, would take a long time.
Not worth it just to collect a small sample. It is much more efficient to send a spacecraft
to an asteroid that crosses Earth’s orbit – so that’s exactly what the Japanese Aerospace
Exploration Agency (JAXA) did. In 2010, the Hayabusa mission returned
the first ever asteroid samples to Earth. Taken from asteroid Itokawa and weighing
less than a gram, it set the stage
for the sequel mission — Hayabusa2. On December 3rd, 2014, the Hayabusa2 spacecraft
launched from the Tanegashima Space Center in Japan.
The mission aimed to gain insight into the origin and evolution of the Solar System,
including the beginnings of life. It would do this by collecting samples from
the near-Earth asteroid, Ryugu. Discovered in 1999,
it measures 900 metres across, a nd comes within 195 million km from
the Sun, or 45 million km of Earth’s orbit — a quarter of the distance to the asteroid belt.
After almost four years of travel, Hayabusa2 arrived at Ryugu on June 27th, 2018.
The spacecraft consisted of an orbiter equipped with instruments including
optical navigation cameras, a near-infrared spectrometer (NIRS3),
a thermal infrared imager (TIR), and a laser altimeter (LIDAR).
These tools mapped Ryugu’s surface, composition, and thermal properties
from an orbital altitude of 20km. Soon after arrival, Hayabusa2
deployed two small MINERVA-II rovers — the first to successfully land on an asteroid.
Rover-1A and Rover-1B used internal rotating masses to hop in Ryugu’s low gravity,
capturing images and temperature data of the surface.
Soon after, the MASCOT lander was released.
Because Ryugu’s gravity was too weak to “pull” MASCOT toward it,
the lander was “pushed” out of the spacecraft by a spring,
and then free-fell from a height of 51m. 6 minutes later, it touched down on the asteroid,
bouncing several times before coming to a halt. It operated on Ryugu’s surface for 17 hours,
collecting magnetic, thermal, and spectroscopic data.
A third rover, MINERVA-II-2, was released in October 2019 but failed
before deployment. Instead, it was released into orbit as a gravitational experiment
before crashing into Ryugu 5 days later. Hayabusa2 retrieved samples from Ryugu
during two brief touchdowns in 2019. The first touchdown gathered surface samples,
close to the equatorial ridge, by firing a small projectile.
The impact ejected surface material into the sampler horn,
which then funneled it into sealed containers within the spacecraft’s return capsule.
The second sample came from firing a Small Carry-on Impactor (SCI) on touchdown
to create an artificial crater and expose subsurface material.
The reasoning behind the two sample types was that the surface samples
had been exposed to the regular radiation, micrometeoroid impacts,
and temperature cycles of space, whereas the subsurface material
had been shielded from this cosmic weathering, providing a more comprehensive picture of
Ryugu’s composition. By November 2019,
the spacecraft had everything it needed. With its precious cargo loaded,
it wrapped up its time at Ryugu and started the return journey home. Over
a year later, in December 2020, Hayabusa2 emerged above our pale blue dot. As it soared past us,
it dropped a landing capsule containing the 5.4 grams of asteroid sample, which parachuted down
to a soft landing in South Australia. NASA and JAXA are sharing samples
between the Hayabusa2 mission and the similar OSIRIS-REx mission which returned samples of
the Bennu asteroid in 2023, maximizing research potential and opportunities for peer-review.
As the spacecraft continued on its extended mission to another, smaller asteroid, scientists
on Earth scrambled to extract and analyze this little piece of our Universe’s history.
The heavy weight of hope was placed on this tiny asteroid sample — and it didn’t disappoint.
We already knew that Ryugu belonged to the C-type or carbonaceous asteroids,
which tend to be found in the outer region of the asteroid belt and contain similar materials to
those from the time our Solar System formed. But what we didn’t know, and to researchers’ delight,
Ryugu’s composition was found to be very similar to a rare class of meteorites known as CI
chondrites. CI chondrites are the most chemically primitive meteorites known, and are characterised
by the presence of carbonaceous material other than pure carbon, like diamond or graphite.
They contain chondrules, which are small, round grains that formed in the solar nebula,
when our Sun was still very young. It seemed JAXA had hit the nail on the head — their mission had
gotten them up close and personal with the birth of the solar system, just as they had aimed for.
Today, Ryugu orbits our Sun relatively close to Earth – scraping by at a distance of just
114,000 km at its closest. But it didn’t always call this galactic neighbourhood home. Using an
X-Ray technique called Mössbauer spectroscopy, the team put together a timeline of Ryugu’s past
by meticulously analyzing minute chemical changes in each sample particle fragment.
What they found is convincing enough to place Ryugu’s origins in the outer solar system.
The asteroid’s surface properties support this theory. If Ryugu had originated closer to the Sun,
where temperatures are higher, researchers would expect to see coarser grains. Additionally,
the grain fragments are porous. This is exactly what you’d expect to see in asteroids that once
held water and carbon dioxide ice. In order for those compounds to be solid,
Ryugu’s parent body would’ve been three to four times farther from the Sun than Earth is.
Research places Ryugu's formation about 2 million years after the solar system itself.
Over the next 3 million years, its parent body lost its ice, leaving behind a hydrated interior
and dry surface. About one billion years later, a cosmic impact fragmented it. Those fragments
eventually coalesced into today's Ryugu. Sample analysis also showed the asteroid
contains a rich mix of organic molecules. This is huge, as it implies that the fine-grain surface of
an asteroid as old as Ryugu is able to shield organic molecules from the harsh environment
of interstellar space. Hiroshi Naraoka of Kyushu University in Japan confirms that these molecules
could be transported throughout the solar system, and even be potentially dispersed
as interplanetary dust by impacts that eject the uppermost layer of the asteroid. It seems to add
weight to the hypothesis that abiotic chemical reactions on asteroids might play a role in
creating some of life’s ingredients. But beyond just organic molecules,
one research team at Imperial College London also found something a lot more exciting — organic
matter. Not exactly “life,” but rods and filaments similar to the size and shapes of
microorganisms here on Earth. If these were true extraterrestrial organisms, it would finally prove
that the idea of “panspermia”, a.k.a that life originating from elsewhere in the universe can
survive the transfer between planetary bodies, is possible. But before they shouted ‘alien’,
the team did what any good scientists would do – they double checked their work.
Space agencies have very tight protocols when it comes to preventing contamination. The
Ryugu sample traveled to Earth in a hermetically sealed chamber and was opened in a class 10,000
clean room using sterilized tools before being stored in airtight containers under nitrogen.
When scientists went to retrieve the sample to begin testing, they first performed an X-ray
nanotomography analysis — basically X-ray on steroids. It allows researchers to image
internal structures at scales smaller than a micrometre, without sectioning or damaging
the specimen. This was to check that Ryugu’s sample didn’t fall prey to any contamination
in the process of transferring it from the landing capsule into its storage facility.
The results came in — Ryugu was clean. So where did the microorganisms come from?
Upon arrival on Earth, the primary Ryugu samples were carefully subdivided into
multiple portions in JAXA's specialized facility. Some remained sealed in their pristine state for
future analysis, while others were distributed to different research teams worldwide for immediate
study. This standard practice allows scientists to maximize research potential while preserving
portions of the irreplaceable material. Subsample A0180, measuring just 1 by 0.8 mm,
travelled to Imperial College London, where — despite the meticulous protocols and cutting-edge
containment systems — the impossible happened. During their first observation by scanning
electron microscopy, the researchers noticed something strange – rods and filaments of
organic matter scattered across the sample. Cylindrical and carbon-rich, these specimens
were mainly observed on the surface of the sample, though 28% were found within porous cavities. They
counted eleven rods and filaments in total — a number which rose to 147 at the second scanning
electron microscopy examination 19 days later. Just to be sure, they surveyed common fabrics
and fibres in the lab, to compare them to these filaments. Hair,
clothing, wipes — nothing seemed to match. They paid close attention to the rate of
population growth and decline, and concluded that based on population statistics, the specimens
were living and had infiltrated the Ryugu rock after sample preparation. In order to examine a
rock under a microscope, the sample must first be cut, ground, and polished to create a flat,
mirror-like surface for examination — also known as preparation of the polished block.
The research team deduced it was at this point that the rods and filaments appeared,
a conclusion supported by the earlier findings of the nano X-ray tomography, which came out clean.
This pointed to one explanation – the rods and filaments were most likely microorganisms
of terrestrial origin. Earthly bacteria had contaminated our pristine asteroid sample.
The team didn’t attempt to sequence the bacteria’s DNA,
so we don’t know exactly what species it was, but it was likely a single
spore of some kind of prokaryote — probably a Bacillus – that started forming a colony.
Luckily, the team was able to control the spread. Once they repolished the block,
the microorganism population disappeared for good, and analysis could go on as planned.
Despite the contamination setback, Ryugu’s sample has proven incredibly valuable.
Combined with NASA’s much larger sample from Bennu, which weighs 121.6g and arrived in 2023,
it has given us a glimpse into the early days of the solar system, and new findings
about both asteroids are still coming to light. As we prepare for more ambitious sample return
missions — including potential trips to Mars — the stakes get even higher. If we're looking for signs
of life, we need to be completely certain we're not just finding hitchhikers from our own planet.
Space agencies do have planetary protection guidelines in place to minimize the risk of
forward contamination (us taking microbes to other planets), and back contamination (setting
alien life loose on our planet). And Hayabusa2 is a great example of how space exploration is
as much about the challenges here on Earth as it is about the challenges out there in space.
Each mission teaches us something new about our target subjects, as well as our own methods. And
despite the unexpected hiccup, Ryugu’s ancient material continues to improve our understanding
of our celestial origins. I’m excited to see what new findings will come out in the next 5-10 years.
Until then, we’ll just have to sit tight. Thanks for watching! If you enjoyed this
video, you might want to check out my other videos on asteroid Bennu. Until next time.
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