The Hayabusa2 provided researchers with a unique opportunity to observe the asteroid Ryugu from many angles, including the most inaccessible spots. The refrigerator-sized spacecraft maneuvered to take images while the asteroid and the sun were on either side of each other, an alignment that allows the sun's rays to reflect directly onto the camera without casting shadows.
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This way, anything with a rough surface that reflects light will appear brighter when it is in contrast. This means that small and distant asteroids can only be seen in contrast. In fact, they are so dark that we cannot see them like we can with the Moon. Dominguez and Yokotafound that Ryugu is one of the darkest celestial bodies: It reflects only 3.5 percent of sunlight, which is darker than other types of asteroids and even darker than a piece of carbon.
But taking close-up, high-contrast images allowed researchers to get a detailed picture of the asteroid's surface. The mostly shadow-free images allowed researchers to map the structure of Ryugu's surface, at least on one side.
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The Ryugu exploration is part of a broader effort to investigate many types of asteroids to learn more about their shapes, contents, and origins. Ryugu is similar to another near-Earth asteroid, Bennu, which was recently visited by NASA's Osiris Rex. Both are C-shaped asteroids with ridges, though they have different prominent central edges. The first Hayabusa mission encountered a rockier S-type asteroid.
Andy Rifkin, an astronomer at Johns Hopkins University in Baltimore, says that asteroids in the main asteroid belt, a scattered collection of space rocks that Jupiter never allowed to become a planet, have stable orbits for billions of years. In contrast, asteroids near Earth have unstable orbits.
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Ryugu likely formed when something collided with a much larger asteroid, scattering a mass of rocky debris that later accumulated and drifted in different directions. By comparing Ryugu's structure, topography, and composition to a variety of larger asteroids, researchers believe it may have come from a "parent body" called Eulalia, which is also dark and carbon-rich.
Researching near- Earth helps scientists understand the objects that could one day collide with our planet.
