Grand plans for Dawn

Dawn carries an instrument ready to determine the elemental composition of the asteroid belt. The Los Alamos National Laboratory device, called GRaND (Gamma Ray and Neutron Detector), is set for an 8-year, 3.2-billion-mile odyssey to explore Vesta in 2011 and Ceres in 2015.

The Los Alamos device is one of three science payload instruments on board, accompanying a visual and infrared spectrometer and a framing camera, the mission's scientific imaging system.
GRaND will measure the elemental composition of the asteroids' surfaces using high-resolution spectroscopy and neutron detection. Radiation detected by GRaND is made by radioactive decay and cosmic ray interactions with the surfaces.

Dawn will be the first spacecraft to orbit two targets. At least 100,000 asteroids inhabit the asteroid belt, a reservoir of leftover material from the formation of our solar-system planets 4. 6 billion years ago. Dawn also will be the first satellite to tour a dwarf planet. The International Astronomical Union named Ceres one of three dwarf planets in 2006.

"GRaND will help us understand processes that shaped the surface of Vesta and Ceres, such as volcanism and aqueous alteration, providing new insights into how the asteroids evolved," said Tom Prettyman, lead scientist for the Los Alamos instrument and Dawn coinvestigator.

The GRaND instrument is designed to measure the chemical composition of the surfaces, mapping the near-surface abundance of major rock-forming elements, long-lived radioactive elements, and volatiles such as hydrogen, carbon, nitrogen and oxygen, which are the major constituents of ices. The gamma-ray spectrum provides a fingerprint of the elements within the surface that can be analyzed to determine their abundance. The neutrons provide information about light elements, such as hydrogen and carbon, as well as strong thermal neutron absorbers, such as iron, titanium, chlorine, gadolinium, and samarium.

Using proven technology from Lunar Prospector and 2001 Mars Odyssey missions, GRaND also includes new sensor technologies to improve the accuracy of elemental abundance measurements. The instrument can measure many rock-forming elements on Vesta and Ceres, in addition to its ice-analysis capability. From a circular, polar mapping orbit, GRaND will map the abundance of these elements over the entire surface of Vesta and Ceres.

Source: Los Alamos National Laboratory
	More on • Dawn