Near-Earth Asteroid Ryugu Was Born in the Outer Solar System: Shedding Light on the Origin of Celestial Neighborhood

The Solar System is more than just a family composed of the Sun and the planets that we know of. It also includes other celestial bodies bound to the Sun by gravity such as asteroids, comets, meteors, and moons. The characteristics of these object give us a glimpse into the origin of our star system.

On May 10, 1999, an asteroid named Ryugu was discovered by scientists with the Lincoln Near-Earth Asteroid Research at the Lincoln Lab's ETS in New Mexico. Recently, a study was conducted regarding the origin of this near-Earth object.

What Is Ryugu?

Ryugu is a 900-meter chunk of space rock assigned with asteroid number 162173. Unlike other minor planets, it is not a single big chunk of rock but rather a rubble pile or a collection of loose small rocks that are bound together by gravity.

Unlike other C-type (carbonaceous) asteroid which are scattered throughout the region between Mars and Jupiter, Ryugu is not located in the main asteroid belt. Instead, its orbit is very close to that of the Earth, suggesting that there could be a disruption which sent it out of the asteroid belt.

Planet in the Making

From 2018 to 2019, Ryugu was surveyed by the Hayabusa2 probed which was launched in 2014 by the Japan Aerospace Exploration Agency (JAXA). On December 5, 2020, the mission brought home samples of the asteroid collected after its five-year-long space journey. The grains and pebbles reached the Earth in perfect shape from their source nearly 9 million kilometers away.

The experts performed an analysis of the ancient grains of dust which reveal its life story as an asteroid in the Solar System. It was found out that part of the body of the carbon-rich rock began its formation at the farther region away from the Sun before it ended up in the asteroid belt. The samples were also thought to be more than 4.5 billion years old, possibly containing the ancient materials that once formed the Solar System.

The result of the analysis also suggests that asteroid could have complex histories of multiple migrations throughout our star system before they settled in their current spots. Their historical data may contain important information about the periods in the history of the Solar System.

Ryugu shares similarities with other asteroids in the main belt, such as Polana and Eulalia families. However, studies of the samples brought from this space rock reveal that some of its components are more consistent with the materials in the outer regions of the Solar System. For instance, Ryugu contains a lot of organic matter like comets and has isotopes of oxygen which are both consistent with the outer Solar System.

These unusual properties of Ryugu suggests that its primary parent body was a planetesimal, a solid object that could grow into a planet, which was formed in the outer part of Solar System. However, its growth might have been disrupted by something that broke it apart and sent it to the main asteroid belt where it was affected by water leading to its transformation.