Researchers completed the first global geological and tectonic map of the asteroid Vesta.
The map was created using images from NASA's Dawn spacecraft, which orbited the asteroid between June 2011 and September 2012, Arizona State University reported.
"The geologic mapping campaign at Vesta took about two and a half years to complete," said David Williams of Arizona State University's School of Earth and Space Exploration. "The resulting maps enabled us to construct a geologic time scale of Vesta for comparison to other planets and moons."
The analysis suggests Vesta endured a number of large impacts in its lifetime, creating features such as the large Veneneia and Rheasilvia craters. The mapping allowed the researchers to develop a relative chronology of events on the foreign object. Finding the time period in which events occurred is difficult because samples researchers have collected from Vesta do not reveal clear formation age as far as can be determined in a lab.
"So figuring out an actual date in years is a step-by-step-by-step process," Williams said. "We work with rock samples from the moon, mostly from Apollo missions decades ago. These give actual dates for large lunar impacts."
In order to estimate the surface age of Vesta researchers have created two models: one based on the lunar impact rate and the other on frequency of asteroid impacts. These two approaches ended up having different results. Despite the disparity, the team concluded the oldest surviving crust on Vesta predates the Veneneia impact, which is believed to be between 2.1 billion years old (asteroid system) or 3.7 billion years (lunar system). The Rheasilvia impact most likely has an age of around 1 billion years (asteroids) or 3.5 billion years (lunar).
"Vesta's last big event, the Marcia impact, has an age that's still uncertain," says Williams. "But our current best estimates suggest an age between roughly 120 and 390 million years." The difference, he explains, comes from which cratering model is used.
The findings appear in the December 2014 issue of the journal Icarus.
