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

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! Dawn will use 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 2

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

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

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”

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

Fiery Vesta: Differentiation and the HED meteorites

Vesta Discovered by Heinrich Olbers in March 1807 Largest basaltic asteroid 265 km mean radius Third largest asteroid! Second most massive at 2.7×10 20 kg Density of 3750 kg/m 3 Differentiated Basaltic (like Hawaii’s volcanoes) Distinct surface regions Implies early formation while 26 Al was an energy source Likely parent body of the HED meteorites! Image credit: STScI (HST)

Vesta Model rotated to show the south pole!

Fiery Vesta’s Basaltic Visible & Infrared Spectrum

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--

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

Icy Ceres: Dwarf Planet

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±0.04×10 20 kg –1/3 mass of asteroid belt! –Density: 2100 kg/m 3 –Albedo 0.1 Image credit: STScI

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/m 3, and shape tells us its interior is a mixture of ice and rock. 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/m 3, and shape tells us its interior is a mixture of ice and rock. Image credit: STScI

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: Rivkin et al 2011

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

The DAWN Spacecraft

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 Dawn’s Payload Framing Camera VIR GRaND 20

Spacecraft

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

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 Dawn Mission Itinerary Launch Sep 2007 Mars Gravity Assist Feb 2009 Vesta July 2011 – July 2012 Ceres Feb 2015 – July 2015

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 Next up: Dawn at Vesta (Jul ‘11- Jul ‘12)

Any Questions?? 25 Dawn’s Launch, Sept