Ice Giant
Mission Status and Planning
15 September 2015
CAPS Meeting, Irvine, CA
Mark Hofstadter, Neil Murphy, and Kim Reh
(Jet Propulsion Laboratory, California Institute of Technology)
© 2015 California Institute of Technology. Government sponsorship acknowledged.
Neptune and Triton
from Voyager
Ground-Based Image of
Uranus. Sromovsky et al. 2012
Ice Giant Status: Neil Murphy
Outline
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Why Ice Giants are Important
Ice Giants in Visions and Voyages (V&V)
Science Since V&V
Technology Since V&V
Mission Proposals/Studies Since V&V
Current NASA Activities
Summary
Ice Giant Status: Neil Murphy
Why IG’s are Important (1/5)
Uranus and Neptune represent a distinct class of planet, commonly
referred to as “Ice Giants.” Their name derives from an astrophysicist’s
definition of:
• Gas: H2 and He.
• Ice: Things which could be solid or gas in the solar nebula, e.g. H2O, CH4,
NH3. (Other than in clouds, we do not believe these species are present as
solid ice in Ice Giants today.)
• Rock: Things that were solid almost everywhere in the solar nebula (e.g.
silicates).
Approximate Composition as a Percentage of Mass
Planet
Gas
Ice
Rock
Total Mass
(MEarth)
Earth
0%
0%
~100%
1
Jupiter/Saturn
95%
4%
1%
~300/100
Uranus/Neptune
10%
65%
25%
~15
Ice Giant Status: Neil Murphy
Why IG’s are Important (2/5)
Ice Giants are not small Jupiters
While the details are less certain, the composition and internal
structure of the Ice Giants are significantly different than Jupiter and
Saturn
Ice Giant Status: Neil Murphy
Why IG’s are Important (3/5)
In addition to their unique composition and interior structure (an expression
of their formation environment and evolution), IG’s
• Have complex asymmetric magnetic fields
Fig. courtesy F. Bagenal
• Show extremes of atmospheric energy balance.
Internal Heat /
Absorbed Solar
Jupiter
Saturn
Uranus
Neptune
0.7
0.8
0.08
1.6
Ice Giant Status: Neil Murphy
Why IG’s are Important (4/5)
• Ice Giant rings are different than the gas giant’s, potentially highlighting
different physical processes.
- Uranus has dense but thin and eccentric main rings. Outer rings are
intimately (and chaotically?) coupled to smaller moons (Showalter
and Lissauer 2006, Science).
- Neptune has “arcs” (really clumps).
Uranus rings, false color.
From de Pater et al. 2006,
Science.
• Ice Giant satellites are strange new worlds.
- Uranian satellites are a unique population of
icy, mid-sized satellites (see next slide),
including the tortured Miranda (left).
- Neptune’s satellites are dominated by Triton,
which is most likely a captured Kuiper Belt
object.
Ice Giant Status: Neil Murphy
Earth
Outer Planet Satellites
H2O, CO2
Europa
Ganymede
Callisto
Enceladus
Titan
NH3 , CO, CH4
N2
Triton
Ice Giant Status: Neil Murphy
Why IG’s are Important (5/5)
Summary
I) The Ice Giants are a distinct and important type of planet about
which little is known.
II) Ice Giants are abundant in our galaxy – most common known exoplanets.
III) The Ice Giants are a laboratory
for understanding fundamental
processes (e.g. atmospheric
energy balance; magnetosphereatmosphere interactions; icy
moon geology; solar system
formation).
As of February 2011
Ice Giant Status: Neil Murphy
Ice Giants in V&V (1/2)
Given their scientific importance, the Ice Giants
(and Uranus in particular) figured prominently in
Visions and Voyages.
• The Giant Planets Sub-panel of the Decadal
Survey ranked IG’s as their #1 priority.
• A Uranus mission was chosen as the third
Flagship for the decade.
Ice Giant Status: Neil Murphy
Ice Giants in V&V (2/2)
Science objectives include:
• Atmospheric composition (e.g. noble gas abundances
(He, Ne, Ar, Kr, and Xe) and isotopic ratios of H, C, N,
and O)
• Atmospheric structure and dynamics
• Internal structure
• Thermal emission
• Dynamo and magnetospheric structure, interaction
with the solar wind
• Satellite geology, geophysics, surface composition,
and interior structure
• Rings
Ice Giant Status: Neil Murphy
Science Since V&V
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Ground-based and 1 AU observations – e.g.:
- IR tracking of time and spatial stratospheric variations (Orton et al. 2015).
- Observations of Uranian aurora with Hubble (Lamy et al. 2012).
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Advances in seismology as a probe of giant planet interiors.
- The first reported direct detection on Jupiter (Gaulme et al. 2011), and
improved analyses of indirect detection via rings (Marley 2014).
- New instrumentation and techniques have the potential to revolutionize our
ability to probe both gas- and ice-giant interiors.
- Kepler observations of Neptune currently being analyzed.
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Theoretical work
- Large body of work on internal structure, magnetic field generation, satellites
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Two international ice giant workshops have been held, both
reaffirming the need for a dedicated mission.
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In Meudon, France (2013), hosted by the Observatoire de Paris.
In Columbia, Maryland (2014), hosted by APL.
Ice Giant Status: Neil Murphy
Technology Since V&V
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Advanced thermal protection systems for atmospheric
probes
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Aerocapture.
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Radioisotope power systems.
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More capable small satellite systems.
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low power electric propulsion
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Heavy Launch capabilities (e.g. SLS)
Ice Giant Status: Neil Murphy
Mission Proposals Since V&V
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Uranus flyby proposed to ESA M-Class call
(2010).
- Proposal reached second phase (request for
more information).
Uranus orbiter/probe proposed to ESA L-Class
call (2013).
- Major concerns involved the readiness of a
European Radioisotope Power System (RPS).
Uranus, Neptune, and dual-planet missions
proposed to ESA M-Class call (2014).
- While not selected for study, collaboration with
the U.S. was encouraged on a future mission.
Ice Giant Status: Neil Murphy
Mission Studies Since V&V
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NASA-sponsored studies:
- Reassessment of the Uranus mission contained in V&V
(2011). Identified issues in mass budget, particularly for
the probe.
- Studies of thermal protection system requirements for
Uranus probe (2014).
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Internal JPL studies.
- Range of mission sizes that might address a subset of
the V&V goals.
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Other institutions may have done similar internal studies.
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Planetary Science Summer School (2013 and 2014).
- Students selected Uranus and Neptune missions.
- A similar European school selected a Uranus mission
study in 2012.
Ice Giant Status: Neil Murphy
Current NASA Activity
At the Outer Planet Assessment Group meeting
on 24 August 2015, Planetary Science Division
Director Jim Green announced the start of an Ice
Giant study.
The following two slides have information from his
presentation.
In addition, an Ice Giant Workshop has been
approved for this November’s DPS meeting in
National Harbor, Maryland.
Ice Giant Status: Neil Murphy
Ice Giants Study
• Initiate an Ice Giants Study assigned to JPL
• Goal: Assess science priorities and affordable
mission concepts & options in preparation for the
next Decadal Survey
• Objectives:
• Identify mission concepts that can address science
priorities based on what has been learned since the
2013-2022 Decadal
• Identify potential concepts across a spectrum of price
points
• Identify enabling/enhancing technologies
• Assess capabilities afforded by SLS
Ice Giant Status: Neil Murphy
Study Ground-Rules
• Address both Uranus and Neptune Orbiters
• Target cost range NTE $2B (FY15$) per mission
• Technical aspects to investigate:
• Determine pros/cons in using one spacecraft design for both
missions (possibility of joint development of two copies)
• Evaluate use of realistic emerging enabling technologies:
distinguish mission specific vs. broad applicability
• Constrain missions to fit on a commercial LV
• Identify benefits/cost savings if SLS were available (e.g., time,
trajectory…)
• Identify clean-interface roles for potential
international partnerships
• Establish a Science Definition Team (SDT)
Ice Giant Status: Neil Murphy
Summary
• An ice giant mission remains a high scientific
priority, of interest to a broad community (planetary,
exoplanets, heliophysics) on both sides of the
Atlantic.
• A Flagship mission to Uranus and/or Neptune, as
outlined in V&V, would revolutionize our
understanding across a range of disciplines.
• Consistent with V&V recommendations, NASA has
recently initiated studies to examine affordable
concepts for Ice Giants missions.
Ice Giant Status: Neil Murphy
Backup
Ice Giant Status: Neil Murphy
Ice Giants in V&V (2/3)
V&V Uranus Mission Science Objectives (1 of 2)
Highest Priority Science Objectives:
1. Determine the atmospheric zonal winds, composition, and structure at high spatial
resolution, as well as the temporal evolution of atmospheric dynamics.
2. Understand the basic structure of the planet’s magnetosphere as well as the highorder structure and temporal evolution of the planet’s interior dynamo.
Medium Priority Science Objectives:
3. Determine the noble gas abundances (He, Ne, Ar, Kr, and Xe) and isotopic ratios of
H, C, N, and O in the planet’s atmosphere and the atmospheric structure at the
probe descent location.
4. Determine internal mass distribution.
5. Determine horizontal distribution of atmospheric thermal emission, as well as the
upper atmospheric thermal structure and changes with time and location at low
resolution.
6. Determine the geology, geophysics, surface composition, and interior structure of
large satellites.
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Ice Giant Status: Neil Murphy
Ice Giants in V&V (3/3)
V&V Uranus Mission Science Objectives (2 of 2)
Lower Priority Science Objectives:
7. Measure the magnetic field, plasma, and currents to determine how the
tilted/offset/rotating magnetosphere interacts with the solar wind over time.
8. Determine the composition, structure, particle-size distribution, dynamical stability,
and evolutionary history of the rings, as well as the geology, geophysics, and
surface composition of small satellites.
9. Determine the vertical profile of zonal winds as a function of depth in the
atmosphere, in addition to the presence of clouds as a function of depth in the
atmosphere.
Ice Giant Status: Neil Murphy