Early Sunday morning, the sky over a remote military complex in central Australia will be lit up by a fireball that plunges to Earth. It’s going to be a flamboyant homecoming for the monster return capsule of Hayabusa2, a Japanese spacecraft launched almost exactly six years ago on a mission to shoot down an ancient asteroid and steal some of its dirt. If the capsule survives its fiery descent, its cargo of pristine space rock will help scientists understand the earliest days of our solar system, shed light on the mysterious origins of meteorites, and perhaps even provide clues to the origin of life on Earth.
By the time it lands under a parachute in the Australian outback, the monster will have traveled more than 180 million miles from Ryugu, a diamond-shaped asteroid orbiting the sun between Earth and Mars. Scientists believe that Ryugu broke off from a larger parent body just a few million years ago, but the rocks that make up it are closer to 4 billion years old. Hayabusa2 camped around Ryugu for over a year and a half, studying the asteroid from a distance and sending robotic scouts to the surface to prepare for a sample collection. His main mission was to collect just a few grams of dust and pebbles from this cosmic time capsule that has been preserved for centuries in the frigid vacuum of space.
“We hope to learn a lot about how a giant cloud of gas and dust turned into planets 4.5 billion years ago in our solar system,” said Larry Nittler, a cosmochemist at the Carnegie Institution for Science and one of nine US scientists selected by NASA to participate in the Japanese mission. “Ryugu and other similar asteroids are basically the leftover building blocks that didn’t grow into planets and have been floating around ever since.”
Ryugu looks like a piece of charcoal the size of several city blocks, and it spins like a spinning top once every eight hours. One of the darkest asteroids ever discovered, its inky complexion is the result of all the carbon trapped in organic compounds smeared across its surface. Some of these prebiotic compounds, such as amino acids, are the building blocks of life, and it may well have been asteroids like Ryugu that seeded the Earth with the molecular grist that set evolution in motion.
Carbonaceous asteroids like Ryugu are abundant in our solar system, but they mostly orbit the outer planets. Every now and then they collide, break apart, and the pieces are sent on an orbit to the innermost sanctuary of the sun. If those pieces happen to collide with Earth, we call them meteorites. Almost everything we know about them comes from the bits and pieces that surface. But by the time these rocks have crashed to Earth, they’ve been cooked crisp and damaged by Earth’s chemistry. Sending a probe to a still-orbiting asteroid is the best way to collect a clean sample. As the first spacecraft to visit a carbonaceous asteroid, Hayabusa2 could help determine the origin of meteorites discovered on Earth and shed some light on the processes that formed the organic compounds in the early solar system.
“Are there any samples of the organics that we don’t have in our collection because they didn’t survive the atmosphere? We don’t know,” said Harold Connolly, a geologist at Rowan University and a member of the sample analysis team for Hayabusa2 and NASA’s own asteroid sample return mission, OSIRIS-REx. But he hopes Hayabusa2 can help solve the mystery.
There is also a pragmatic reason to visit Ryugu. NASA researchers have identified it as a potentially dangerous asteroid, meaning its orbit will get close enough to Earth to create a non-negligible chance of a collision. While the risk is small, the complex forces acting on asteroids as they orbit the sun make it difficult to accurately predict their orbits more than a few decades into the future. For example, when exposed to the sun, an asteroid can release volatile compounds such as water, and this outgassing can produce thrust that subtly alters its orbit. “We don’t quite understand how asteroids move in detail because we don’t quite know their composition,” says Connolly. “This will help us better predict dangerous asteroids and when they might hit Earth.”
Second time is the charm
Hayabusa2 is a sequel to Hayabusa, a Japanese mission launched in 2003. It was the world’s first return mission to an asteroid sample, but a malfunction in the collection mechanism meant that only a few micrograms of dust returned to Earth. Like its predecessor, Hayabusa2 was designed to collect samples and deploy small robots on the asteroid’s surface. Hayabusa2 arrived in Ryugu in late 2018 after traveling through the solar system for three years, and a few months later the spacecraft deployed a lander named Mascot and the first of two small Minerva-II rovers. The cylindrical rover spent five weeks hopping over the surface to collect data and send incredible photos back to Earth. The shoebox-sized lander only lasted 17 hours to run out of battery. During its short life, Mascot used a range of instruments to analyze the composition and structure of the asteroid’s regolith.
By the end of 2018, the rover and lander had completed their missions and set the stage for Hayabusa2’s descent to the surface. Scooping up some asteroid dirt is harder than it sounds, because Ryugu isn’t solid. Like most asteroids, it’s more of a mess, a loose collection of dust and rocks held together by their own gravity. This makes it tricky to get to the surface to collect a sample without shaking up a lot of rocks that could damage the spacecraft. Ryugu also turned out to be made up of more large boulders — some as high as 10 stories — than the mission’s scientists had expected. “Safe landing sites were limited by the large amount of rocks,” said Tomokatsu Morota, a planetary scientist at the University of Tokyo and one of the researchers who worked on Hayabusa2’s navigation camera. He says the team had to manually count more than 10,000 rocks and measure more than 100 remotely to determine suitable landing sites on the asteroid’s rough surface. “It was very hard work,” Morota says.
“A whole history lesson from just a small example”
By early 2019, the team had picked a landing spot and Hayabusa2 made its first descent. The spacecraft’s sample-collecting horn tapped the surface for only about a second before returning to orbit the asteroid. During that brief encounter, Hayabusa2 fired a small bullet into the asteroid to throw up some dust and locked it in a collection chamber. A few months later, Hayabusa2 was preparing for another collection run by dropping a small plastic explosive from its orbit to create an artificial crater more than 10 meters across, exposing the older rock beneath Ryugu’s surface. lie. After the debris settled around the asteroid, the spacecraft made its second short descent to collect a sample from the crater. Just a few weeks before Hayabusa2 left Ryugu, his second Minerva-II rover failed before being deployed. But instead of losing the rover, mission controllers released it and performed a few gravity measurements before hitting the asteroid.
Hayabusa2 will jettison its monster container when it is about 100,000 miles from Earth, about half the distance between our planet and the moon. Once the capsule has landed, it will be recovered by a team of Japanese researchers stationed in the burning Australian desert. It is immediately taken to a temporary cleanroom built on site so that it can be analyzed for volatile substances such as water that may have been present in the sample. Within hours of the capsule being recovered, the researchers will pierce the hull and bottle and store any gases released by the sample for analysis. After that, the sample will be returned to Japan, where researchers from the Japan Aerospace Exploration Agency will distribute small portions to research teams around the world for further investigation.
“By examining samples with lab instruments, we can tell their composition, how much heating they experienced, shocks, water flows, and so on. You can get a whole history lesson from just one small sample,” said Bill Bottke, a planetary scientist at the Southwest Research Institute. who was not involved in the Hayabusa2 mission.” Only some of this information can be determined by spacecraft in orbit. It’s like the difference between seeing a mountain from a distance and studying one of the rocks in the lab.”
The Hayabusa2 researchers won’t know how much asteroid debris the spacecraft has collected until they pry open the capsule, but they are optimistic it will be about 10 grams. A significant portion of the sample will be given to NASA researchers, who have worked closely with Japan on Hayabusa2 and OSIRIS-REx. In fact, NASA and the Japanese space agency each tapped into a few of their own researchers to help the other agency. Connolly, one of the researchers who worked on both missions, is optimistic that research on the Hayabusa2 sample will improve research on the much larger OSIRIS-REx sample when it returns to Earth in 2023.
“We can apply the lessons learned in the analytical process and the factual information we manage to extract from these whispering rocks so that we as a community can better prepare for the analysis of OSIRIS-REx samples,” says Connolly. “My expectation is that they will be complementary and give us a better idea of the limitations of the earliest solar system processes.”
The return of the Hayabusa2 capsule to Earth marks a major milestone for the mission, but it’s not the end of the spacecraft’s journey. After it jettisons its monster this weekend, it will continue on a bonus mission to another asteroid that could last up to 10 years. This time it won’t collect samples, but it will collect valuable data as it orbits the asteroid.
You can watch a live stream of the fiery finale of Hayabusa2’s main mission on the Japan Aerospace Exploration Agency YouTube channel. The capsule is scheduled to begin its atmospheric entry Saturday at 12:30 p.m. EST (or 2:30 a.m. Sunday in Japan) and land approximately 15 minutes later.
This story originally appeared on wired.com.