SKY TECHNOLOGY

Astronomers discover the oldest known asteroid family

WASHINGTON: Astronomers have identified the oldest known asteroid family, which extends throughout the inner region of the main asteroid belt, using a new search technique.

The main belt contains vast numbers of irregularly shaped asteroids, also known asplanetesimals, orbiting the Sun between Mars and Jupiter.

As improved telescope technology finds smaller and more distant asteroids, astronomers at Southwest Research Institute (SwRI) in the US identified clusters of similar- looking bodies clumped in analogous orbits.

These familial objects are likely fragments of catastrophic collisions between larger asteroids eons ago, researchers said.

Finding and studying asteroid families allows scientists to better understand the history of main belt asteroids.

"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 coauthor of the research published in the journal Science.

"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 centre 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.