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Worlds Seen for the First Time

James L. Green Director, Planetary Science

March 11, 2015

GalaxiesHave Formed

Collapsing Gas & Dust

Conservations of Angular Momentum produces a disk of material From Dust to Planets Emerge

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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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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

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15 AU

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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Today

~4.2 Billion Years

~3.8B Years

"Late HeavyBombardment"

What are they: Protoplanets, Dwarf Planets, or Kuiper Belt Object?Purpose of the Dawn mission is to find out!

Vesta ••

Ceres

Dawn Arrives at Vesta

Dawn arrived: July 16, 2011Dawn departed: Sept. 5, 2012

VestaSize: ~525 km diameterRotation: ~5.3 hours

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Dawn at Vesta

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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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Ceres is a Planet Building Block

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?)

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Best Structural Model of Ceres

Dawn’s Approach

Approach Trajectory

Sun

Capture (March 6)

1st science orbit

Rotation Characterization 3(April 23, 2015)

Tick marks every 2 days

CeresSize: ~952 km diameterRotation: ~9 hours

Today

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Ceres Approach

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Ceres Approach TimelineDate Activity Distance Pixels Comment

Dec 1, 2014 Calibration image of Ceres 1.12M km 8 Complete

Jan 13, 2015 First OpNav Image of Ceres379,000

km26 0.8x Hubble resolution

Jan 26, 2015 OpNav #2201,000

km43 1.4x Hubble resolution

Feb 4, 2015 OpNav #3146,000

km70 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 Rotation Characterization 3 13,000 km 717 20x Hubble resolution

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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

Ceres at Hubble Resolution

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RC 1Feb 12

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3.8 x Hubble

Resolution

RC 2Feb 19

(4 km/pixel)

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7 x Hubble

Resolution

The Types of Terrain

Older Cratered Terrain

Basin with fewCraters (younger)

Unknown

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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?

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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)

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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 Ceres24

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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New Horizon Flyby

~55 AU

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End of theKuiper Belt?

The New Pluto System

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Long-Range Imager Views Pluto-Charon

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Closest Approach On July 14, 2015

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Questions?

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