Dawn: Exploring Dichotomies across Space and Time

1. Dawn: Exploring Dichotomies across Space and Time DAWN Mission Speaker’s Kit Dawn EPO Teams

2. Dawn willuse ion propulsion to explore two complementary protoplanets, Vesta and Ceres, by: • Mapping their surfaces to understand their geology & composition • Determining how and when the bodies formed • And understanding the internal and external forces that shaped them • So why did Dawn’s scientists choose to look at the asteroid belt? • To explore the earliest stage of our solar system • To understand how planets like ours formed!

3. Why Ceres and Vesta? • Vesta and Ceres are protoplanets, the largest of the asteroids and survivors of the early solar system • They were amongst the first bodies to form • They are differentiated like bigger planets, but smaller than our moon • Vesta was volcanically active like our moon, while Ceres is made of ice and rock like Jupiter’s moons • Studying Ceres & Vesta together tells us about how a planet’s size and distance from the sun affect its formation

4. What is an asteroid, really? • There isn’t a good definition • Generally, a small, rocky body orbiting ~inside the orbit of Jupiter • Most are found in the main belt between Mars & Jupiter (which doesn’t look anything like this) --> Image credits: Lucasfilm

5. What are Asteroids made of? • Bright, dry, rocky asteroids like Vesta dominate the inner asteroid belt • Dark, hydrated, and icy asteroids like Ceres dominate the outer belt • Ceres and Vesta are big enough to differentiate (like the Earth), and thus are also called “protoplanets”

6. Asteroids come in all shapes & sizes…but protoplanets are round! Ida Eros Vesta Itokawa Ceres Gaspra Pallas 950 km Annefrank Image credits: NASA & STScI (HST)

7. Fiery Vesta: Differentiation and the HED meteorites

8. Vesta • Discovered by Heinrich Olbers in March 1807 • Largest basaltic asteroid • 265 km mean radius • Third largest asteroid! • Second most massive at 2.7×1020 kg • Density of 3750 kg/m3 • Differentiated • Basaltic (like Hawaii’s volcanoes) • Distinct surface regions • Implies early formation while 26Al was an energy source • Likely parent body of the HED meteorites! Image credit: STScI (HST)

9. Vesta Model rotated to show the south pole!

10. Fiery Vesta’s BasalticVisible & Infrared Spectrum

11. HED Meteorites • Howardites: • Clasts of Eucrite and Diogenite material • Eucrites: • plagioclase & pyroxene • Crust? • Diogenites: • Orthopyroxene & olivine • Mantle? Figure credits: Pieters et al. (2006) Dar al Gai 844, image courtesy R. Pellison-- http://www.saharamet.com

12. Vesta’s South Pole Figure credits: Pieters et al. (2006), after Takeda et al. 1997, Thomas et al. 1997

13. Icy Ceres: Dwarf Planet

14. Ceres • Discovered in 1801 by Piazzi • Orbital elements: • a=2.767 AU, • e=0.097, • i=9.73, • P=9.076 hrs • Largest body in asteroid belt • Mass: 9.46±0.04×1020 kg • 1/3 mass of asteroid belt! • Density: 2100 kg/m3 • Albedo 0.1 Image credit: STScI

15. Icy Ceres? • Size and shape- • Oblate spheroid—just like the Earth • Mean radius of 950 km • Other unique attributes: • Spectra of its surface look similar to clays • It has no obvious topography • It has no impact family and… • NO METEORITE ANALOG! • WHY? …it’s probably made of ICE! • Ceres’ density, 2100 kg/m3, and shape tells us its interior is a mixture of ice and rock. Image credit: STScI

16. Ceres’ Surface At one point, Ceres was thought to have frost on its surface, and though this now looks unlikely, there is still a strong case for water. • What is there: • Clays? • Brucite (Br), • Magnesium (Mg)? • Hydration (OH)? • Possibilities: • 3.3 μm- aromatic hydrocarbon or ammonium-bearing clays • 3.8 μm- carbonates • How do these minerals form? • Water-rock reactions! Figure credit: Rivkinet al 2011

17. Ceres’ Probable Interior Figure Credit: McCord & Sotin, 2005

18. The DAWN Spacecraft

20. Framing Camera Dawn’s Payload • Two redundant framing cameras (1024 x 1024 pixels, and 7 color filters plus clear) provided by Germany (MPS and DLR) • VIR, a visible and infrared mapping spectrometer (UV to 5 microns) provided by Italy (INAF and ASI) • GRaND, a Gamma Ray and Neutron Detector built by LANL and operated by PSI • A Radio Science Package provides gravity information • Topographic models will be derived from off-nadir imaging VIR GRaND

21. Spacecraft

22. Thrust Coast Dawn’s Interplanetary Trajectory Vesta departure July ‘12 Launch Sep ‘07 Earth today Vesta arrival July ‘11 Dawn today Mars gravity assist Feb ‘09 Ceres arrival Feb ‘15 Vesta today End of mission Jul ‘15

23. Dawn Mission Itinerary Vesta July 2011 – July 2012 Ceres Feb 2015 – July 2015 Mars Gravity Assist Feb 2009 • At each target, Dawn will: • Acquire color images • Compile a topographic map • Map the elemental composition • Map the mineralogical composition • Measure the gravity field • Search for moons Launch Sep 2007

24. Next up:Dawn at Vesta(Jul ‘11- Jul ‘12) • Dawn will explore Vesta using its specialized instrumentation. • Composition will be mapped by VIR (1.0 to 5.0 m) and FC color filters • Topography, impact history and geology will be mapped by the Framing Camera • Elemental abundances will be determined by GRaND • Crustal thickness and interior structure will be determined by gravity from radio science

25. Any Questions?? Dawn’s Launch, Sept. 27 2007