Early sunday In the morning, the sky over an isolated military complex in central Australia will be lit by a fireball plunging down to Earth. It will be a blazing homecoming for the sample return capsule of Hayabusa2, a Japanese spacecraft launched almost exactly six years ago with the aim of shooting an ancient asteroid and stealing some of its dirt. If the capsule survives its fiery descent, its payload of pristine space rocks will help scientists understand the early days of our solar system, shed light on the mysterious origins of meteorites, and may even provide clues to the emergence of life on Earth.
By the time it lands by parachute in the Australian outback, the sample will have traveled more than 180 million miles to Ryugu, a diamond-shaped asteroid orbiting the sun between Earth and Mars. Scientists believe that Ryugu broke away from a larger parent body only a few million years ago, but the rocks that make it up 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 its surface to prepare for sample collection. Its main mission was to collect only a few grams of dust and pebbles from this cosmic time capsule that has been preserved for eons in the freezing void 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,” says Larry Nittler, cosmochemist at the Carnegie Institution for Science and one of nine American scientists selected by NASA to participate in the Japanese mission. “Ryugu and other asteroids like him are basically the remaining building blocks that didn’t become 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 high every eight hours. It is one of the darkest asteroids ever discovered, its ink complexion is the result of all carbon trapped in organic compounds spread over its surface. Some of these prebiotic compounds, such as amino acids, are the building blocks of life, and it may very well be asteroids like Ryugu that seeded Earth with the molecular grain that started evolution.
Carbonaceous asteroids like Ryugu are abundant in our solar system, but they mostly hang around the outer planets. Every now and then they collide, break apart, and the pieces are sent on a path to the inner sanctum of the sun. If these pieces collide with Earth, we call them meteorites. Almost everything we know about them comes from the bits and pieces that bring them to the surface. But by the time these stones crashed into Earth, they were baked until they were crisp and were corrupted by Earth chemistry. Sending a probe to an asteroid still in orbit is the best way to get a clean sample. As the first spacecraft to visit a carbonaceous asteroid, Hayabusa2 can help determine the provenance of meteorites discovered on Earth and shed light on the processes that formed organic compounds early in the solar system.
“Are there any samples of organic material that we don’t have in our collection because they haven’t survived through the atmosphere? We don’t know, ”says Harold Connolly, a geologist at Rowan University and a member of the sample analysis team for Hayabusa2 and NASA’s asteroid sample return mission. OSIRIS-REx. But he hopes Hayabusa2 can help solve the mystery.