Dawn Probe to Rendezvous with Asteroid Vesta!

By Brendt Hyde, Mineralogy Technician

Our solar system is a very busy place! Aside from the 9 (no, make that 8!) major planets and their moons, there are 5 dwarf planets, 3 massive asteroid belts containing tens of thousands of smaller irregular bodies, and an untold number of comets.

Image taken July 9, 2011 from a distance of about 41,000 kilometers away from the protoplanet Vesta. NASA's Dawn Probe obtained this image with its framing camera. Each pixel in the image corresponds to roughly 3.8 kilometers. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

In September of 2007, NASA launched the space probe Dawn, its 8-year mission, to boldly go to the Asteroid Belt between Mars and Jupiter! This Saturday, July 16, the Dawn Probe will make the first rendezvous of its trip as it falls into orbit around Vesta, which, with a diameter of 520 kilometers (Km), is the second largest body in this highly populated region of our solar system.

Vesta was formed at the very beginning of our Solar System, more than 4.5 billion years ago. At some point in its early life, after it had stabilized and solidified into a regular spheroid body, Vesta experienced a collision so massive that it shattered the entire south pole of the asteroid, blasting it into space and leaving a crater 460 kilometers across and 13 kilometers deep! Small pieces from this explosion are still traveling through space and occasionally hit Earth in the form of meteorites. In honour of Dawn’s imminent arrival at Vesta, the Teck Suite Of Galleries: Earth’s Treasures has installed a display of the ROM’s world-class collection of meteorites believed to be from Vesta.

Olivine Diogenite (metorite NWA 5480), possibly from the lower mantle of Vesta. ROM ID: LM55998 and M53563

Vesta has a “differentiated body”, meaning that it has distinct layers composed of a core, a mantle, and a thin outer crust – similar to the Earth’s structure, but without an internal heat source or water. The collision was so powerful that it exposed the mantle layer deep within the asteroid. The ROM’s collection represents material that is thought to be from several of Vesta’s layers – Eucrites from the crust, Howardites which are a mixture of crustal and mantle material, Diogenites from the upper mantle, and even 2 Dunites from the lower mantle!

3AB Iron-Nickel meteorite (Henbury III AB), possibly from the core of Vesta. ROM ID: M17239

How will Dawn get to Vesta? Unlike conventional rocket fuel, Dawn’s ion propulsion thrusters expel atoms of ionized Xenon. Instead of providing a massive boost at the beginning of the mission (which Dawn received from the rocket that launched it into space), these thrusters gently increase the speed of Dawn every second of every day that they are in use. Dawn has enough Xenon fuel that its thrusters can remain on throughout its entire 8-year mission. The probe also received a giant speed boost when it used the gravitational force of Mars as a slingshot to increase its speed by 9,330 Km/h in February of 2009. Dawn is now travelling in the same orbit around the Sun as Vesta, at more than 74,000 Km/hour (!) and will slowly catch up to Vesta until it enters Vesta’s gravitational field. Dawn will orbit Vesta for a year, studying it with a variety of cameras, spectrometers, and gravity sensors. It will then use its ion propulsion system to travel to Ceres, another body in the Asteroid Belt.

Dawn's flight path (turqoise and brown) from Earth to Vesta to Ceres. Image credit: NASA and CalTech Jet Propulsion Lab

Ceres is so large (estimated 960 Km in diameter) that it has been classified as a Dwarf Planet (the only one closer to the Sun than Neptune). It is possible that Ceres is composed largely of water in the form of ice, so it is compositionally different from Vesta, yet dates from the same period near the formation of our Solar System. Scientists hope that Vesta and Ceres will provide a picture of the process of planetary formation from the very beginning of our solar system.