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Early Sunday morning, the skies over a secluded military complex in central Australia will be illuminated by a fireball crashing to Earth. It will be a blazing homecoming for the Champion Return Capsule from Hayabusa2, a Japanese spacecraft launched almost exactly six years ago on a mission to shoot 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 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.
When he lands under the parachute in the Australian outback, the champion will have traveled more than 180 million miles from Ryugu, a diamond-shaped asteroid orbiting the sun between Earth and Mars. Scientists believe Ryugu separated from a larger parent body just a few million years ago, but the rocks that make it up are more than 4 billion years old. Hayabusa2 has been camping around Ryugu for more than a year and a half, studying the asteroid from a distance and sending robotic scouts to its surface to prepare for a 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 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,” says Larry Nittler, cosmochemist at the Carnegie Institution for Science and one of nine American scientists selected. from NASA to participate in the Japanese mission. “Ryugu and other asteroids like this are basically the advanced building blocks that did not become planets and have been floating around ever since.”
Ryugu looks like a lump of coal the size of several blocks and spins like a top once every eight hours. It is one of the darkest asteroids ever discovered, its ink-like complexion is the result of all the carbon trapped in organic compounds smeared on its surface. Some of these prebiotic compounds, such as amino acids, are the building blocks of life, and it may very well have been asteroids like Ryugu that seeded the Earth with the molecular dust that set evolution in motion.
Carbonaceous asteroids such as Ryugu are abundant in our solar system, but are mostly found around the outer planets. From time to time, they collide, break, and pieces are sent on a trajectory to the inner sanctuary of the sun. If these pieces collide with Earth, we call them meteorites. Almost everything we know about them comes from the fragments that come to the surface. But when these stones crashed to Earth, they were crunchy baked and corrupted by Earth’s chemistry. Sending a probe to an asteroid still in orbit is the best way to collect 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 in the early solar system.
“Are there any samples of organic substances that we don’t have in our collection because they didn’t survive by crossing 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.
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