A team of researchers from Tokyo Institute of Technology, Japan's National Institute of Polar Research, and ETH Zurich, Switzerland, have discovered that the evolutionary history of Vesta, the brightest asteroid visible from Earth, has been profoundly impacted by a massive 'hit-and-run' collision. The finding of these researchers deepens the understanding of protoplanet formation more than 4.5 billion years ago, in the early infancy of the Solar System.
The team has determined the precise timing, in a remarkable feat of astronomical detective work, of a large-scale collision on Vesta that helps explain the asteroid's irregular shape. The researchers published their finding in Nature Geoscience, and it pinpoints the crash to 4,525.4 million years ago.
The second most massive body in the asteroid belt is Vesta, and it is of immense interest to scientists investigating the origin and formation of planets. Unlike most asteroids, Vesta has kept its original, differentiated structure, meaning it has a crust, mantle, and metallic core, much like Earth.
Most of the knowledge about the asteroid had so far come from howardite-eucrite-diogenite (HED) meteorites, following studies in the 1970s that first proposed Vesta as the parent body of these meteorites.
Recently, NASA's Dawn mission, which orbited Vesta in 2011 to 2012, reinforced the idea that HED meteorites originate from Vesta and provided more insights into the asteroid's composition and structure. Careful mapping of Vesta's geology showed an unusually thick crust at the Asteroid's South Pole.
In the new research, the scientists provided a confident framework for understanding Vesta's geological timeline, including the massive collision that caused the formation of the thick crust.
One of the crucial factors to uncover this timeline was examining a rare mineral called zircon found in mesosiderites (stony-iron meteorites that are similar to HED meteorites in terms of texture and composition). Based on a reliable premise that both types of meteorites came from the same parent body, Vesta, the researchers focused on dating zircon from mesosiderites with unprecedented precision.
A specialist in geochemical and chronological studies of meteorites, Makiki Haba of Tokyo Institute of Technology (Tokyo Tech), and Akira Yamaguchi of Japan's National Institute of Polar Research (NIPR) were involved in sample preparation, a significant challenge, according to Haba, as fewer than ten zircon grains have been reported over the past few decades. She explained further that they developed how to find zircon in mesosiderites and eventually prepared enough grains for this study.
They joined forces with co-authors at ETH Zurich who developed a method to measure the age of the samples with the use of uranium-lead dating. The scientists pooled their expertise to propose a new evolutionary model for Vesta. Haba pointed out that this work could not be achieved without collaboration between Tokyo Tech, NIPR, and ETH Zurich.
The buildup on the study for Haba is to examine more precise conditions such as temperature and cooling rate during and after the large-scale collision on Vesta based on mesosiderite and HED meteorite measurements.
