Vesta Never Had a Chance
May 14, 2012
Vesta, the third most massive object in the asteroid belt, is not an asteroid at all but a unique baby planet that has survived in the rough-and-tumble environment of the Main Belt since the formation of the solar system more than 4 billion years ago. That finding is one of several surprising discoveries about Vesta announced by scientists studying data collected by NASA’s Dawn space probe. According to the scientists, Vesta is the solar system’s only surviving planetesimal. Also known as protoplanets, planetesimals were asteroid-sized objects that collided and stuck together to form the planets, moons, and other solid or mostly solid objects of the solar system.
Vesta’s true identity was revealed after scientists discovered that Vesta has a unique internal structure. Much like the common rocks and minerals found on Earth, asteroids are usually made of the same materials throughout. However, measurements made by Dawn indicate that Vesta has three layers–a core, a mantle, and a crust. In this way, Vesta is more like the inner planets of the solar system than the asteroids. The inner planets, also called the terrestrial planets, are Mercury, Venus, Earth, and Mars. All of them, along with Earth’s moon, have a mostly iron metal core. They also have at least two more layers (Mercury may have three) called the mantle and the crust that consist of rocks and minerals. These layers were formed very early in the history of the solar system. Vesta has a metal core along with a rocky mantle and crust, indicating it, too, was formed in the early solar system.
The three layers also show that Vesta was on its way to becoming a planet when it stopped near its present size. Many scientists believe that the gravitational pull of Jupiter, the largest planet, probably prevented Vesta from combining with other planetesimals to form a full-sized planet. Common theories state that protoplanets in the solar system either combined to become full-sized planets or were destroyed in a collision with another object. Vesta’s amazing survival is a stroke of luck for scientists studying the formation of the planets and the early history of the solar system.
Launched in September 2007, Dawn is currently nearing the end of the first part of a two-part mission. The probe arrived at Vesta in July 2010 and will observe the asteroid for one year. Dawn is scheduled to leave Vesta and begin the journey to Ceres in July. It should arrive at the largest asteroid in 2015.