Asteroid · Near-Earth asteroid (Apollo) · orbits Sun
Ryugu is a kilometre-wide, diamond-shaped rubble pile so dark it reflects less than 5% of the sunlight that hits it. Japan’s Hayabusa2 spacecraft orbited it in 2018-19, fired a copper projectile into it to expose fresh material, and brought samples home that turned out to hold water-bearing minerals and the building blocks of life.
Hayabusa2 returned 5.4 g of Ryugu in December 2020 - the first large sample of a carbon-rich asteroid.
Its samples contain amino acids and even uracil, one of the four building blocks of RNA.
It reflects only ~4.5% of incoming light - about as dark as charcoal.
Sunlight can spin an asteroid
Ryugu’s spinning-top shape, with its raised equatorial ridge, is thought to be a relic of a time when it spun much faster and material migrated toward the equator. The likely culprit is sunlight itself: photons absorbed and re-emitted unevenly from a lumpy surface exert a tiny torque - the YORP effect - that over millions of years can spin a small asteroid up or slow it down.
Hayabusa2 touched down twice on the carbon-rich asteroid Ryugu, even firing an impactor to blast open a crater and grab pristine subsurface material. It parachuted 5.4 g of asteroid to Earth in December 2020 and is now cruising toward the tiny fast-spinning asteroid 1998 KY26, arriving in 2031.