Tackling mysteries of colliding planetesimals

Why astronomers are seeing both of these debris clouds so physically close to each other is a mystery. If the collisions between asteroids and planetesimals were random, cs1 and cs2 should appear by chance at unrelated locations. Yet, they are positioned intriguingly near each other along the inner portion of Fomalhaut’s outer debris disk.

Another mystery is why scientists have witnessed these two events within such a short timeframe. “Previous theory suggested that there should be one collision every 100 000 years, or longer. Here, in 20 years, we've seen two,” explained Paul. “If you had a movie of the last 3000 years, and it was sped up so that every year was a fraction of a second, imagine how many flashes you'd see over that time. Fomalhaut’s planetary system would be sparkling with these collisions.”

Collisions are fundamental to the evolution of planetary systems, but they are rare and difficult to study.

“The exciting aspect of this observation is that it allows researchers to estimate both the size of the colliding bodies and how many of them there are in the disk, information which is almost impossible to get by any other means,” said co-author Mark Wyatt at the University of Cambridge in England. “Our estimates put the planetesimals that were destroyed to create cs1 and cs2 at just 30 km in size, and we infer that there are 300 million such objects orbiting in the Fomalhaut system.”

“The system is a natural laboratory to probe how planetesimals behave when undergoing collisions, which in turn tells us about what they are made of and how they formed,” explained Mark.