Study of ancient asteroids reveals the Solar System’s tumultuous past

The early solar system

A reorganization of the outer planets of the Solar System would have taken place during the early stages of its formation, according to a recent study of two Trojan asteroids of Jupiter.

The American astrophysicist David Nesvorny and his colleagues at the Southwest Research Institute have studied a rare pair of asteroids named Patroclus and Menoetius, which are about the same distance from the Sun as Jupiter, one in orbit in front and the another behind the gas giant.

These asteroids will be the focus of NASA’s Lucy mission to be launched in 2021. According to the researchers, they are remnants of the primordial material that led to the formation of the outer planets (Saturn, Jupiter, Neptune Uranus). They would thus be witnesses of the birth of the solar system more than 4 billion years ago.

Patroclus and Menoetius are about 113 km wide and orbit around each other as they circle the Sun. They are the only known binary system in the Trojan asteroid population of Jupiter. In astronomy, the term “Trojan” is used to refer to a small object that shares a relationship with two other larger bodies.

Current work shows that the presence of Patroclus and Menoetius, as well as others in the orbit of Jupiter, would be the result of an early planetary rearrangement in our system. The pair would have formed from the initial disk of material beyond Neptune.

Simulations suggest that the presence of the celestial couple today at this location indicates that the dynamic instability between the giant planets must have occurred in the first 100 million years of solar system formation. These objects were probably captured during a dramatic period of dynamic instability during a collision between the giant planets of the Solar System.

This great upheaval would have pushed Uranus and Neptune outward, where they met a large population of small bodies that would be the origin of the current objects of the Kuiper Belt, which orbit at the edge of the Solar System.

According to the researchers, several small bodies of this primordial Kuiper belt were scattered inward, and some of them became Trojan asteroids. Indeed, recent simulations of the formation of small bodies suggest that binary systems like Patroclus-Menoetius are remnants of the very first moments of the birth of the system.

Current observations of the Kuiper belt show that these binary systems would have been common during the genesis of the system. “There are only a few left in Neptune’s orbit. The question is how did they survive until today,” says researcher William Bottke.

The dynamic model of early instability of the Solar System put forward in the present works also has important consequences for the rocky planets, in particular with regard to the origin of the large craters of impact on the Moon, Mercury and Mars, which formed about 4 billion years ago.

According to this model, the meteorites that dug these craters are less likely to reach outlying areas of the Solar System. This could mean that they were made by remnants of small bodies from the process of forming rocky planets. The details of these works are published in the journal Nature Astronomy.

Shakes Gilles

Editor of The Talking Democrat. He enjoys bike riding, kayaking and playing soccer. On a slow weekend, you'll find him with a book by the lake.