American Astronautical Society, 2015 Robert H. Goddard Memorial Symposium, http://astronautical.org/goddard/2015

1. 1
Worlds Seen for the First Time
James L. Green
Director, Planetary Science
March 11, 2015

2. Galaxies
Have Formed
Collapsing
Gas & Dust
Conservations of
Angular Momentum
produces a disk of material From Dust to Planets Emerge
2

3. Growth of Planetesimals then Protoplanets
• When planetesimals collide they
can form even larger bodies called
protoplanets
• Massive enough for its shape to be
in hydrostatic equilibrium under its
own gravity due to heating
Animation from Tanga et al. (2003)
• Gravity causes dust to collect into
small bodies then larger objects
called planetesimals
• Many objects in the asteroid belt
are planetesimals (>1 km in size)
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4. Solar System Formation Models
Basic Principle: Objects closer to the Sun can grow faster
Comets
Primordial disk of icy bodies
• Gas giants and outer comets formed near present locations
Problem: Can’t form them even after ~4.5Byrs of evolution!
• Gas giants must form in a compact configuration (5-15 AU)
• Massive icy body population will then existed (15-30 AU)
5 AU 10 AU 20 AU 30 AU
15-30AU
4
15 AU

5. Destabilizing the Outer Solar System
Watch what happens after 850 My
Tsiganis et al. (2005); Morbidelli et al. (2005); Gomes et al. (2005)
The Late Heavy Bombardment
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6. Today
~4.2 Billion
Years
~3.8B Years
"Late Heavy
Bombardment"
What are they: Protoplanets, Dwarf Planets, or Kuiper Belt Object?
Purpose of the Dawn mission is to find out!
Vesta
••
Ceres

7. Dawn Arrives at Vesta
Dawn arrived: July 16, 2011
Dawn departed: Sept. 5, 2012
Vesta
Size: ~525 km diameter
Rotation: ~5.3 hours
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8. Dawn at Vesta
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9. Vesta Science Highlights
• Vesta is confirmed to be the parent body of the
HED meteorites found on Earth
• Vesta is differentiated: Iron core ~110 km radius
• Vesta is truly an intact survivor from the very
beginning of the solar system
• Vesta now appears to be a protoplanet!
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10. 10

11. 11
Ceres is a Planet Building Block

12. Is Ceres Active?
• ESA’s Herschel infrared
space telescope
between 2011 and 2013
observed a thin water-
vapor atmosphere
– A water absorption signal
detected by Herschel on
Oct. 11, 2012
• Scientists are interpreting these observations as
potential water/ice plumes (cryo-volcanos?)
12

13. 13
Best Structural Model of Ceres

14. Dawn’s Approach
Approach Trajectory
Sun
Capture (March 6)
1st science orbit
Rotation Characterization 3
(April 23, 2015)
Tick marks every 2 days
Ceres
Size: ~952 km diameter
Rotation: ~9 hours
Today
14

15. Ceres Approach
15

16. Ceres Approach Timeline
Date Activity Distance Pixels Comment
Dec 1, 2014 Calibration image of Ceres 1.12M km 8 Complete
Jan 13, 2015 First OpNav Image of Ceres
379,000
km
26 0.8x Hubble resolution
Jan 26, 2015 OpNav #2
201,000
km
43 1.4x Hubble resolution
Feb 4, 2015 OpNav #3
146,000
km
70 2.2x Hubble resolution
Feb 12, 2015 Rotation Characterization 1 84,000 km 121 3.8x Hubble resolution
Feb 20, 2015 Rotation Characterization 2 46,000 km 221 7x Hubble resolution
Feb 23, 2015 Closest Approach 38,000 km Begin high-phase Approach
Feb 25, 2015 OpNav #4 40,000 km 253 8x Hubble resolution
Mar 1, 2015 OpNav #5 49,000 km 207 6.5x Hubble resolution
Mar 6, 2015 Capture 60,000 km Capture into orbit
Apr 10, 2015 OpNav #6 33,000 km 304 9.5x Hubble resolution
Apr 15, 2015 OpNav #7 22,000 km 455 14x Hubble resolution
Apr 23, 2015
*
*
*
*
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17. Ceres – Our First Peek
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Taken December 1, 2014 at a distance of 1.2 million km
~3 times the Earth-Moon distance

18. Ceres at Hubble Resolution
18

19. RC 1
Feb 12
19
3.8 x Hubble
Resolution

20. RC 2
Feb 19
(4 km/pixel)
20
7 x Hubble
Resolution

21. The Types of Terrain
Older Cratered
Terrain
Basin with few
Craters (younger)
Unknown
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22. Mapping the Water Vapor to Ceres
• Herschel Space Observatory
found water vapor near Ceres
during it’s perihelion passage
• Is the flux steady with variable
intensity or periodic?
• Is there evidence for discrete
sources or widespread
sublimation?
• What do the surface materials
tell us about the history of
eruptions?
22

23. RC3
equator
RC3
south
HGA-to-Earth
HGA-to-Earth
Nadir
Nadir
Nadir
Nadir
Nadir
High Phase
south &
north
Limb
north
RC3
north
Limb
south
Ceres
Off-Nadir
Off-Nadir
Preview of RC 3
3 full rotations of the lit side are obtained in the north, at the equator, in
the south, as well as limbs and high phase imaging on the dark side.
RC 3 Orbit
(13,500 km)
23

24. Ceres Science Orbits
• Rotation Characterization 3 (RC3)
– Duration 1 orbit (20 days)
– Nadir rotation movies, high phase
observations
• Survey Orbit
– Duration 7 orbits (22 days)
– Nadir mapping, limb observations
• High Altitude Mapping Orbit (HAMO)
– Duration 70 orbits (56 days)
– Nadir & fixed off-nadir mapping
• Low Altitude Mapping Orbit (LAMO)
– Duration 404 orbits (92 days)
Total of 406 days of operations are planned at Ceres
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25. What will we find out?
• Is Ceres an active body?
– Models of Ceres interior suggest there could be
subsurface oceans and an outer ice-rich layer
• Is Ceres a protoplanet whose development into a
planet was disrupted by Jupiter’s gravity?
– Core, mantel, crust?
• Or is Ceres a Kuiper Belt object?
– Came into the asteroid belt during the LHB?
– An icy body more like Pluto than like Vesta
– On to Pluto to find out – we can compare the two!
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26. New Horizon Flyby
~55 AU
26
End of the
Kuiper Belt?

27. The New Pluto System
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28. Long-Range Imager Views Pluto-Charon
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29. Closest Approach On July 14, 2015
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30. Questions?
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