Various theories explain the creation of the solar system's moons. Predominantly, it is believed that they formed from disks of gas, dust, and pebbles that encircled nascent planets, similar to planetary formation around stars. Alternative theories propose that moons originated from massive planetary rings or the remnants of collisions between earlier moons.
Crater counting offers insights into the age of moon surfaces, thereby constraining the ages of the moons themselves and validating theories of their formation. This method involves imagining the early, tumultuous conditions of the solar system around 4.5 billion years ago.
Shortly after the solar system's formation, as Neptune migrated outward, it disrupted a disk of planetesimals, propelling nearly all these icy objects throughout the solar system, with a small fraction forming the Kuiper Belt. This event initiated an extended period of bombardment evident on the outer moons' surfaces.
Recent research led by William Bottke of the Southwest Research Institute involved dating the surfaces of 26 moons. The team modeled the bombardment process, considering the size and frequency of impacts over time, which influenced crater sizes.
The study revealed that early, significant impacts on these moons are not recorded due to extensive resurfacing from melting, shattering, or complete disruption, which obscured large early craters. The oldest identified surfaces, such as those on Iapetus and Oberon, date back just a few million years after bombardment began, whereas the surfaces of larger moons are potentially much younger.
The lack of early impact evidence complicates efforts to conclusively determine moon formation processes. However, the findings support the disk formation theory for larger moons. Upcoming missions with advanced gravity measurement capabilities might uncover more about this obscured epoch of solar system history.
Research Report:The Bombardment History of the Giant Planet Satellites
Related Links
Southwest Research Institute
The million outer planets of a star called Sol
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