dawn: exploring dichotomies across space and time dawn mission speaker’s kit dawn epo teams
TRANSCRIPT
Dawn: Exploring Dichotomies across Space and Time
DAWN Mission Speaker’s KitDawn 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
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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 2.7×1020
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)
Vesta
Model rotated to show the south pole!
Fiery Vesta’s BasalticVisible & 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-- http://www.saharamet.com
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±0.04×1020 kg– 1/3 mass of asteroid belt!– Density: 2100 kg/m3
– 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/m3, and shape tells us its interior is a mixture of ice and rock.
Image credit: STScI
Ceres’ SurfaceAt 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 PayloadFraming Camera
VIR
GRaND
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Spacecraft
Dawn’s Interplanetary Trajectory
Thrust
Coast
Launch Sep ‘07
Mars gravity assistFeb ‘09
Vesta arrivalJuly ‘11
Vesta departureJuly ‘12
Ceres arrivalFeb ‘15
End of missionJul ‘15
Earth today
Dawn today
Vesta today
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At each target, Dawn will:Acquire color imagesCompile a topographic mapMap the elemental compositionMap the mineralogical compositionMeasure the gravity fieldSearch for moons
Dawn Mission Itinerary
LaunchSep 2007
Mars Gravity AssistFeb 2009
VestaJuly 2011 – July 2012
CeresFeb 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??
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Dawn’s Launch, Sept. 27 2007