Lunar and Planetary Science Conference March 18, 2019
New Horizons: Beyond Pluto Revealing the First Primordial Planetesimal
Dr. Alan Stern New Horizons Principal Investigator
Southwest Research Institute
Meet Ultima Thule (2014 MU69)
A Historic Journey To the Solar System’s Frontier
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Approach and Departure
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Flyby Overview
Prime B-Plane Target (EME2000): B · T = 452.0 km B · R = –3470.7 km
• Close approach distance: 3,500 kilometers (2,200 miles) from object center • Close approach time: 12:33 a.m. EST, Jan. 1, 2019 • Flyby speed: 14.4 km/s (32,200 mph) • Solar phase at C/A: 88.4º
Flyby Sequence
Meet Ultima Thule
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• A pristine Kuiper Belt object • 35 kilometers (22 miles) long • The first unquestionable primordial
contact binary • Apparently resulting from a gentle merger
Some Informal Terminology
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Ultima
Neck (or Collar)
Thule
Enigmatic Albedo Markings
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Bright Neck
Bright Curvilinear Lines (Lineation)
Bright Zones
Bright Spots
Dark Zones
Shape
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A Remarkably Shaped KBO
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range = 6,640 km, solar phase angle = 32.5°
Dr. Carly J.A. Howett New Horizons Science Team Southwest Research Institute
Surface Color
Old View
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• Resolution: 1.5 km/pixel
• Taken: Dec. 31, 2018 11:08:41 p.m. EST
• Distance: 73,000 kilometers (45,000 miles)
New View
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• Resolution: 0.3 km/pixel
• Taken: Jan. 1, 2019 12:13:45 a.m. EST
• Distance: 17,300 kilometers (10,700 miles)
MVIC LORRI Combined
Enhanced Color Composite
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Color Variation
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• Least red: neck, lineation and bluer spot regions
• Most red: center of Thule, spots near Ultima’s limb
• Subtle color variations with geology
More Red
Less Red
Neck
Bluer spot
NIR/Blue LORRI & MVIC Contrast Enhanced Color
Lineation
Color Comparison
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Dr. Silvia Protopapa New Horizons Co-Investigator Southwest Research Institute
Ultima Thule Surface Composition
Ralph/LEISA Image of Ultima Thule • Dec. 31, 2018
11:57:34 p.m. EST
• Distance: 31,200 km (19,400 miles)
• Spatial scale: 1.9 km/pixel
• Wavelengths co-added: 1.2–2.4 𝛍𝛍m
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Ralph/LEISA
MVIC, LEISA Images of Ultima Thule
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LORRI + Ralph/MVIC Ralph/LEISA Wavelengths co-added: 1.2–2.4 𝛍𝛍m
Ultima Thule Surface Composition
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LORRI + Ralph/MVIC Ralph/LEISA
MVIC LEISA
Ultima Thule Surface Composition
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LORRI + Ralph/MVIC Ralph/LEISA
Preliminary Composition Analysis
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LORRI + Ralph/MVIC Ralph/LEISA
CH3OH H2O
Tholins
H2O
Ultima Thule Surface Composition
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LORRI + Ralph/MVIC Ralph/LEISA
• Evidence for:
– Methanol
– Water ice
– Organic molecules
Dr. Kirby Runyon New Horizons Postdoctoral Scientist
Johns Hopkins Applied Physics Laboratory
Geology of Ultima Thule
Ultima Thule’s Complex Geology
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Rolling hills, troughs, pits, bright & dark areas
m Units: Early Building Blocks?
Comet 67P (Rosetta)
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Troughs and Craters
Maryland Crater
Troughs
Pit Craters Impact or Sublimation Craters
Stickney Crater (Phobos)
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Hills
Hills and Streaks
Streaks
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Animation Credit: Roman Tkachenko
Landscape Perspectives: Sheared Neck
Dr. William B. McKinnon New Horizons Co-Investigator
Washington University in St. Louis
Origin of Ultima Thule
Geometric Alignment of ‘Ultima’ and ‘Thule’
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• Major axes of both lobes are aligned
• Highly unlikely to be due to chance
• Indicates lobes once orbited one another – aligned by mutual tides
NASA/JHUAPL/SwRI/James Tuttle Keane
Different Lobes: Why Is Ultima so Flat?
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Atlas (Saturn) Hyperion (Saturn)
Ultima
Some satellites are almost as flat, but for different reasons (Sizes not to scale)
Gravitational Collapse of a Particle Cloud
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• 4.56 billion years ago – in a remote part of the solar nebula
• A swirling collection of icy particles begins to coalesce
NASA/JHUAPL/SwRI/James Tuttle Keane
…Two Bodies Form in Mutual Orbit
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Orbit shrinks due to:
• Tides with other bodies and/or
• Collisions with other bodies and/or
• Drag from nebular gas
NASA/JHUAPL/SwRI/James Tuttle Keane
… Slow Merger
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• Lobes appear undamaged by final merger – except at neck
• No evidence for catastrophic impacts or fragmentation
• Merger speed was gentle
NASA/JHUAPL/SwRI/James Tuttle Keane
Numerical Simulation of Merger
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• Impact at 2 meters/sec
• Hot (red) colors indicate max acceleration
• 200,000 particles in all, gravity and sliding friction included
Derek Richardson & Julian Marohnic (University of Maryland)
Acceleration
Min Max
What Is Ultima Thule Teaching Us?
• Our clearest look back to the era of planetesimal accretion
• Lobes are similar in color, composition
• Yet dissimilar in shape, assembly?
• Gentle merger of two separate planetesimals
• Alignment of lobes due to tides between co-orbiting bodies
• Consistent with origin in collapsing particle cloud
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• Media Contacts – JoAnna Wendel
NASA HQ [email protected] 202-358-1003
– Michael Buckley Johns Hopkins Applied Physics Lab [email protected] 443-567-3145
– Maria Stothoff Southwest Research Institute 210-522-3305 [email protected]
• On the Web
– www.nasa.gov/newhorizons
– http://pluto.jhuapl.edu
• Twitter: @nasanewhorizons
• Twitter: @NewHorizons2015
• Facebook: www.facebook.com/new.horizons1/
Follow New Horizons
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Back up slides
MVIC and LEISA Maps of Ultima Thule
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LORRI Ralph/LEISA
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