Astronomers identifies the oldest known asteroid family

Researchers have found a previously unknown family of darkly colored asteroids, which may be the oldest objects in the known universe. A newfound ancient family of asteroids is nearly as old as the solar system, a new study finds. 

Asteroids are rocky, airless worlds that orbit our sun but are too small to be called planets. Tens of thousands of these minor planets are gathered in the main asteroid belt, a vast doughnut-shaped ring between the orbits of Mars and Jupiter. Asteroids that pass close to Earth are called near-earth objects. The main belt contains a vast number of irregularly shaped asteroids, also known as planetesimals, orbiting the Sun between mars and Jupiter.

By identifying all the families in the main belt, we can figure out which asteroids have been formed by collisions and which might be some of the original members of the asteroid belt," said SwRI astronomer Kevin Walsh.

"We identified all known families and their members and discovered a gigantic void in the main belt, populated by only a handful of asteroids," said Walsh, a co-author of the research published in the journal Science.

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"These relics must be part of the original asteroid belt. That is the real prize, to know what the main belt looked like just after it formed," he said.

Identifying the very oldest asteroid families, those billions of years old, is challenging, because, over time, a family spreads out, researchers said. As asteroids rotate in orbit around the Sun, their surfaces heat up during the day and cool down at night. This creates radiation that can act as a sort of mini-thruster, causing asteroids to drift widely over time.

After billions of years, family members would be almost impossible to identify, until now. The team used a novel technique, searching asteroid data from the inner region of the belt for old, dispersed families. They looked for the "edges" of families, those fragments that have drifted the furthest."Each family member drifts away from the center of the family in a way that depends on its size, with small guys drifting faster and further than the larger guys," said team leader Marco Delbo, an astronomer from the Observatory of Cote d'Azur in Nice, France. 

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