When Japan’s JAXA Hayabusa2 mission returned from asteroid Ryugu, it didn’t just bring back samples—it brought home the secrets of the solar system’s beginnings.

But what if the samples we brought back weren’t as pristine as we thought? The Hayabusa2 mission faced an unexpected twist that threatened the integrity of their findings.

What happens when we’re not just exploring space, but also carrying the possibility of contamination from Earth itself? This is the story of how a microscopic hitchhiker nearly ruined an extraordinary mission and what it means for the future of space exploration.

Why Asteroids Like Ryugu Hold the Key to Understanding Our Origins
Asteroids are more than just floating rocks—they are time capsules of our solar system’s early days.

Formed over 4.5 billion years ago, they hold clues to the materials that make up everything in our solar system, including Earth.

Unlike Earth, where weathering and geological activity have altered its surface over time, asteroids remain relatively unchanged.

By studying asteroids like Ryugu, we can unlock secrets about the building blocks of life and the origins of the solar system itself.

The study of these celestial bodies isn’t just about understanding space; it’s about understanding life on Earth.

Ryugu, in particular, is a C-type asteroid, which is rich in carbon—one of the fundamental elements needed for life.

By analyzing samples from Ryugu, scientists hoped to discover not just the composition of the asteroid, but also clues about the formation of the solar system and the potential for life beyond Earth.

The Hayabusa2 Mission: A Journey to Ryugu
The Hayabusa2 mission began in 2014, with the spacecraft launched from Japan’s Tanegashima Space Center.

Its goal was to reach Ryugu, a near-Earth asteroid, and bring back samples that could offer a snapshot of our solar system’s birth.

Ryugu is unique because it’s part of a group of asteroids that cross Earth’s orbit, making it an ideal target for a sample-return mission.

After nearly four years of travel, Hayabusa2 reached Ryugu in 2018.

Upon arrival, Hayabusa2 deployed two rovers—MINERVA-II—and a lander, MASCOT, which studied the asteroid’s surface and took measurements.

The rovers even hopped around Ryugu, gathering data on its surface and temperature.

This was the first time such a feat had been accomplished, and it set the stage for the spacecraft’s sample collection.

The mission was well on its way to making history.

The Two Touchdowns: Collecting Surface and Subsurface Samples
Hayabusa2’s sample collection process was meticulous.

The first touchdown, in February 2019, involved firing a small projectile into the surface of Ryugu to eject material into the spacecraft’s collector.

This provided surface samples, which had been exposed to space weathering, radiation, and micrometeoroid impacts over time.

The second touchdown was even more ambitious.

Hayabusa2 fired a larger projectile to create an artificial crater in Ryugu’s surface, exposing subsurface material that had been shielded from the harsh conditions of space.

This collection would give researchers a more complete picture of Ryugu’s composition, offering insights into the pristine materials hidden beneath its surface.

A Surprising Discovery: Contamination and the Search for Life
When the samples finally returned to Earth in December 2020, scientists were eager to study the ancient material from Ryugu.

The asteroid’s surface properties suggested that it had originated in the outer solar system, where temperatures were low enough to preserve water and carbon-based molecules.

But as scientists began analyzing the samples, something unexpected happened.

In an X-ray analysis, researchers at Imperial College London discovered what appeared to be rods and filaments within the asteroid samples.

At first, they thought these structures might be microorganisms—something that could provide evidence for panspermia, the theory that life might travel between planets.

The possibility of alien life on an asteroid seemed within reach.However, after careful analysis, the team realized that these microorganisms were more likely to be terrestrial contaminants.

Despite the strict protocols used to prevent contamination, it appeared that some Earthly bacteria had hitchhiked on the samples.

The team had followed all the necessary precautions, including using sterilized tools and storing the samples in airtight containers under nitrogen, yet somehow, a microscopic organism had made its way into the pristine samples.

The Implications of the Contamination: A Missed Opportunity or a Cautionary Tale?
While the discovery of contamination was disappointing, it wasn’t the end of the story.

The contamination setback highlighted just how careful we must be when returning samples from space.

It was a sobering reminder that the line between Earth and space is not as clear as we thought, and that even the smallest hitchhiker can complicate our search for extraterrestrial life.

Despite this, the sample from Ryugu has already provided invaluable insights into the early solar system.

The asteroid’s composition, rich in organic molecules, supports the idea that asteroids may have played a role in delivering the building blocks of life to Earth.

The discovery that Ryugu’s surface is similar to a rare class of meteorites, CI chondrites, only deepens the mystery of how life began.

The fact that these ancient molecules have survived for billions of years is extraordinary, and it adds weight to the theory that asteroids like Ryugu may have been crucial in the formation of life on Earth.

The Future of Asteroid Sample Missions: Maximizing Potential, Minimizing Risk
The Hayabusa2 mission was a success, but it also provided important lessons for future sample-return missions.

The contamination issue faced by JAXA is a reminder of the challenges that come with space exploration.

As agencies like NASA continue their asteroid missions, including the OSIRIS-REx mission which returned samples from the Bennu asteroid in 2023, planetary protection protocols will become even more critical.

With more ambitious missions planned, including future trips to Mars, it’s clear that the search for life beyond Earth is as much about safeguarding our own planet as it is about exploring the cosmos.

The lessons learned from Hayabusa2 will help shape future space missions, ensuring that we leave as little trace as possible on the planets and asteroids we visit.