The Dawn spacecraft left behind the giant asteroid Vesta last September, and is now en route to the even bigger dwarf planet Ceres, but scientists are still busy studying all of the data that was sent back to Earth while it was orbiting Vesta for over a year. And as often happens while exploring these new worlds, they have made a surprising discovery: long, sinuous gullies on the walls of geologically younger craters.
Actually, there are two types of gullies that have been seen so far—ones that are straighter, wider, and shorter, and other ones that are more sinuous, narrower, and longer, which end in lobe-shaped deposits.
The straighter ones aren’t as much of a surprise, as they resemble others seen elsewhere, such as on the Moon for example, and are thought to be caused by dry material flowing down the sides of craters. The sinuous, curvy ones though are different, and look more like ones formed by water on Earth and possibly Mars.
As Dawn team member Jennifer Scully explains, “The straight gullies we see on Vesta are textbook examples of flows of dry material, like sand, that we’ve seen on Earth’s moon and we expected to see on Vesta. But these sinuous gullies are an exciting, unexpected find that we are still trying to understand.”
What is causing the sinuous gullies on Vesta is a mystery still right now, since Vesta has no atmosphere or surface water. Could water be escaping from Vesta’s interior or is there some other explanation? Any water coming to the surface would quickly evaporate in the vacuum of space, but perhaps could run down crater walls a bit before doing so. Water and ice are now thought to be common inside larger asteroids and dwarf planets, so there is at least the possibility that is what is being seen on Vesta. Widespread hydrated minerals have also been previously identified on Vesta.
According to Christopher Russell, principal investigator for the Dawn mission, “On Earth, similar features—seen at places like Meteor Crater in Arizona—are carved by liquid water.” He adds, “On Mars, there is still a debate about what has caused them. We need to analyze the Vesta gullies very carefully before definitively specifying their source.”
Vesta is the second-most-massive known asteroid with a diameter of approximately 525 kilometres (326 miles), smaller only than the dwarf planet Ceres. Dawn is expected to reach Ceres in early 2015, which may have a thin atmosphere and water ice on its surface.