An international team of researchers studying meteor showers has found that not all comets crumble the same way when they approach the Sun. The differences in how comets break up are attributed to the conditions in the protoplanetary disk where comets formed 4.5 billion years ago. The meteoroids we see as meteors in the night sky are the same size as the pebbles that collapsed into comets during the formation of our solar system. As our solar system formed, small particles in the disk around the young Sun gradually grew larger until they became small pebbles, which eventually gave rise to comets and asteroids.
When comets approach the Sun today, they crumble into smaller pieces called meteoroids, which co-orbit with the comet for a while before creating meteor showers when they hit Earth’s atmosphere. The size distribution and physical properties of these meteoroid streams still contain information about the conditions in the protoplanetary disk during the collapse. The researchers use special low-light video cameras in networks around the world to track meteors in a NASA-sponsored project called “CAMS,” which helps measure the meteoroids’ paths, altitude, and composition as they enter Earth’s atmosphere.
The team studied 47 young meteor showers, most of which are the remnants of Jupiter-family comets from the Scattered Disk of the Kuiper Belt beyond Neptune and long-period comets from the Oort Cloud surrounding our solar system. Long-period comets tend to crumble into meteoroids indicative of gentle accretion conditions, with a low density and poor in certain elements. On the other hand, Jupiter-family comets produce smaller, denser meteoroids with a higher content of solid materials and more diversity in their composition.
The differences in how comets and asteroids break up suggest that long-period comets formed under more gentle particle growth conditions near the edge of the Trans Neptunian Disk, while Jupiter-family comets formed closer to the Sun where fragmentation played a more significant role. Primitive asteroids formed even closer to the Sun, outside the orbit of Jupiter, producing meteor showers with even smaller particles due to aggressive fragmentation of their pebble building blocks. This information sheds light on the processes that shaped the formation and evolution of comets, asteroids, and other celestial bodies in our solar system.
The outward movement of Neptune during the formation of the giant planets likely scattered comets and asteroids from the protoplanetary disk, creating the Scattered Disk of the Kuiper Belt and the Oort Cloud. However, the properties of long-period and Jupiter-family comets suggest that Oort Cloud comets may have been perturbed by early interactions with stars and molecular clouds in the birth region of the Sun, while Jupiter-family comets have always been on shorter orbits and sample objects scattered by Neptune. These findings provide valuable insights into the complex dynamics and evolution of our solar system over billions of years.