Asteroid Families Shed Light on Early Solar System

(CN) — The discovery of an ancient family of darkly colored asteroids could shed light on the processes that led to the birth of our solar system, which has been a point of debate among planetary scientists.

The space rocks in the main asteroid belt, between the orbits of Mars and Jupiter, are nearly as old as the solar system itself, which formed about 4.6 billion years ago.

In the early phase of the solar system, rocky material combined to form bodies known as planetesimals. Some of these planetesimals clumped together to form planets, while others mostly went on to inhabit the asteroid belt, according to the Thursday report in the journal Science.

Determining what the planetesimals were originally like is challenging, as countless collisions have fractured almost every one of these cosmic bodies into asteroids.

“This family was indeed the largest missing piece of a gigantic puzzle,” lead author Marco Delbo, an astrophysicist at the University of the Cote d’Azur in Nice, France, said in an email to Courthouse News. “They allow us to understand what were the sizes and the composition of the planetesimals that formed our planets.

“These original asteroids are the ‘holy grail’ of planetary formation.”

In addition to fracturing, the asteroids have spread out over time, which led the team to use a computer model to search for V-shaped groups of the cosmic rocks – a pattern that reflects a single-parent body that fragmented into pieces of varying sizes and spread out over time. This allowed the researchers to determine the size of the asteroids and their lineage.

“(W)e can now identify all the asteroids that are members of our (family) and other families in the portion of the main belt that is closest to Earth,” Delbo said.

The newfound family consists of asteroids that average 7.15 miles in diameter, which confirms theories that the cosmic rocks were “born big” and not small, as some explanations suggest, according to Delbo.

After analyzing the family, the team estimated that the original planetesimals were all larger than 15.5 miles wide, which supports the traditional view of asteroid formation: that most were born as fragments of larger chunks of rock. This is in contrast to some recent theories that suggest that planetesimals were much smaller chunks of rock, Delbo said.

“The big surprise is that we could for the first time tell which are the asteroids that were born as fragments of other asteroids and which are the asteroids that could not be born as fragments,” he said. “So these are the original asteroids, those that must have formed by coagulation of dust from the protoplanetary disk.”

A protoplanetary disk is a rotating disk of dense gas and dust that surrounds a newly formed star.

The team plans to use their new method to search for asteroid families in other areas of the asteroid belt.

“In order to have the asteroid impact to form the primordial family, the main belt must have been massive enough and excited enough to make this impact happen,” Delbo said. “This is very cool, as we can derive precious information about the orbital and mass distribution of planetesimals at the time when the planets were forming.

“There are more families yet to be discovered!”

(Computer-generated photo by NASA shows Earth as viewed from an asteroid.)

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