Report of the NASA Science Definition Team for the Jupiter Icy Moons Orbiter

Download full report (PDF 2.2 mb)

Executive Summary

The Jupiter Icy Moons Orbiter (JIMO) affords an exciting and unprecedented opportunity to
explore a part of the solar system identified by the National Academy of Sciences as critical in
the search for life’s origins and the understanding of planetary evolution. The Science Definition
Team (SDT, Appendix 1) for JIMO consisted of 38 scientists representing the community
interested in the exploration of the Jupiter system, with a focus on Europa, Ganymede, and
Callisto. The SDT was appointed by NASA in February 2003 to derive the scientific objectives
for the JIMO mission. Early in the process, the SDT determined that the approach to the study
should include the following guidelines:

The scientific foundations for the JIMO mission include recommendations from previous
studies by the National Research Council (NRC, 1999, 2003) and NASA (2003), which identify
Europa and the Jupiter system as high priority objects for solar system exploration and the search
for life’s origin. In addition to these documents, input to the SDT was obtained from a
community-wide meeting entitled “Forum on Concepts and Approaches for the Jupiter Icy
Moons Orbiter,” LPI (2003). After a series of presentations, the ~150 participants at the Forum
were organized into seven groups by scientific discipline to identify the high priority issues that
could be addressed by the JIMO mission. The results from the seven groups served as the basis
for subsequent SDT deliberations.

The goals presented in this document, and their detailed objectives and investigations, were which includes three crosscutting themes: Oceans (finding their locations, studying the structure
of their icy crusts, and assessing active internal processes), Astrobiology (determining the types
of volatiles and organics on and near the surfaces, and the processes involved in their formation
and modification), and Jovian System Interactions (studying the atmospheres of Jupiter and the
satellites and the interactions among Jupiter, its magnetosphere, and the surfaces and interiors of
the satellites).

The SDT has formulated four equally important goals for the JIMO mission. Within each
goal, the objectives, investigations and measurements have been identified and prioritized. The
goals are summarized as follow:

JIMO near-global high resolution imaging in the visible and infrared, with corresponding
topographic mapping and subsurface sounding, will enable the determination of the styles,
distribution, and importance of active processes that have shaped the icy satellites’ surfaces over
time. This information will provide further insight into why the evolutionary path of each moon
is different. These measurements will enable the determination of the places and processes by
which Europa’s putative ocean might communicate with the surface, and how erosional
processes operate. In addition, high resolution mapping of selected areas will enable the
identification of sites that are the most promising candidates for exploration on the surface.
Remote sensing observations of Io will provide insight into geologic and magnetospheric
processes, heat flow, and exchange of material among all of the satellites.

The primary objective in meeting this goal is to determine the presence and location of liquid
water beneath the moons’ icy crusts. This will involve understanding the extent of the satellites’
differentiation, establishing whether they contain subsurface oceans, characterizing and mapping
the location of possible water and brines, and measuring the thickness of the ice overlying any
putative oceans. Geophysical methods (gravity, altimetry, magnetic field) are the primary means
of making a global estimate of ice thickness. These techniques will be greatly enhanced by
making seismic measurements on the surface. A secondary objective is to assess the active
processes that have caused the moons to evolve internally. This objective involves searching for
evidence of current and past internal activity, as reflected by gravitational and magnetic fields,
topographic and subsurface changes, and evidence of thermal anomalies. A tertiary objective is
to understand the formation and evolution of the Jupiter system by investigating the composition
of Jupiter’s deep atmosphere, and by placing bounds on the orbital evolution of the satellites by
studying the orbital and rotational dynamics of all four large satellites, including measuring the
rate at which Io dissipates tidal energy in the form of heat.

The JIMO mission provides a unique opportunity to seek evidence of biotic or prebiotic
activity in an extraterrestrial environment. Liquid water is essential for all known living systems
and the icy satellites may contain some of the largest reservoirs in our solar system. Whether or
not icy satellites have ever provided an abode for biotic or prebiotic activity has important
implications for understanding the origin of life. The detection of signs of past or present life will
require measurements of certain biogenic organics with specific biological patterns and chirality

of atoms that constitute biomass. In addition, life generally leads to chemical disequilibrium in
the environment and, thus, in situ or remote sensing of metabolic byproducts can help detect
signs of life. To evaluate habitability it is important to determine the presence of liquid water, the
concentration of major biologically relevant ions as sources of energy and nutrients, and the
potential effects of radiation on life forms.

The planet, satellites, rings, dust, gas, particles and fields in the Jupiter system influence each
other through many complex interactions. Understanding these interactions provide insight into
the characteristics of other bodies in the Solar System. Measuring Jupiter’s elemental abundance
ratios will help determine the nature, history, and distribution of volatile and organic compounds
in the Solar System. Understanding of the dynamics of Jupiter’s atmosphere and magnetic field
provide insight into the deeper structure of Jupiter.

The icy moons interact with Jupiter’s magnetosphere through charged particle bombardment,
which modifies their surface chemistry, produces tenuous atmospheres and ionospheres, and
leads to rings of gas and dust circling Jupiter. These processes are generally harmful to life, but
they could also be a major source of energy for possible biota in the oceans of the icy moons.
Finally, observations of the charged particle bombardment on the chemistry of the environment
is important to studying their habitability. Measurements from JIMO on the electromagnetic
induction responses from the moons to Jupiter’s rotating field will reveal information about the
interiors of the moons, including the presence of liquid sub-ice oceans.

Based on the prioritizations within the four goals outlined above, the SDT has formulated a
set of science baseline investigations and measurements and science floor investigations and
measurements. The science floor is defined as the minimum science the JIMO mission must
accomplish in order to be viable from a scientific standpoint, while the baseline represents the
ideal JIMO mission the SDT believes should be undertaken. These are summarized in Table 1.1.

A critical element of the baseline mission is a small surface package for Europa, termed the
Europa Surface Science Package (ESSP). Many high-priority measurements can be made only
from the surface of Europa. The SDT crafted these high-priority measurements for a landed
package within the framework of the objectives and investigations for the overall mission and are
grouped into three science areas: 1) Astrobiology, in which measurements of organic materials,
inorganics (e.g., oxidants) relating to survival and recognizability of biochemical signatures of
life, and searches for patterns indicative of biology must be made in situ, 2) Geophysics, in
which acoustic/seismic measurements made from the surface enable constraints to be placed on
the interpretations of data taken from orbit regarding the presence of liquid water and the
structure of the icy crust, and 3) Geology-geochemistry in which in situ measurements of other
inorganic chemical species (e.g., sulfate hydrates) at the surface provide ground truth for remote
sensing data and insight into the structure of the surface at sub-meter scales and the possibility of
chemical exchange between the surface and a sub-surface ocean. Astrobiology and
geophysical measurements are of highest priority; while geology-chemistry measurements not directly related to the search for biochemical signatures are of lower priority but should be done
to determine composition of the non-ice materials thought to be sulfate hydrates and possibly
originating from the ocean. Data from the Galileo mission are sufficient to identify sites of
scientific interest for the ESSP. The SDT recommends that the final selection of a site be a
community-wide activity.

The overwhelming consensus of the SDT is that, given the high scientific potential from a
landed package and the large resources that would be committed to the JIMO mission, a surface
package to Europa should be included. Moreover, the SDT considers that up to ~25% of the
science resources, in particular, mass, could be devoted to the ESSP. However, in recognition of
the potential implementation uncertainty, the SDT has placed the ESSP in the baseline mission,
but not in the science floor. A study of the feasibility of the ESSP should be made, and the SDT
would assess the scientific trades in response to the study.

The SDT recognizes that the revolutionary nature of the JIMO spacecraft will require
significant technology development time before a payload is competitively selected. In order to
provide science requirements during that development, the SDT has worked closely with the
JIMO Project to derive the Payload Accommodation Envelope (PAE). The PAE is a set of
spacecraft requirements needed to accomplish the recommended science of the JIMO mission.
A particularly important element is the ability to change the trajectory of the spacecraft
repeatedly to orbit the icy moons individually. The SDT urges NASA to continue working with
the SDT to refine the PAE until such time that instruments teams are selected and can work
directly with the JIMO Project.

Based on previous studies by the National Academy of Sciences and NASA, results from the
community “Forum,” and discussions within the JIMO Science Definition Team, the SDT
recommends that:

1. JIMO be implemented to meet all science baseline and floor objectives, investigations and measurements elucidated in Section 3.
2. The JIMO project incorporate the science requirements defined in the PAE early in the design of the spacecraft, including a Payload Accommodation Envelope mass allocation of 1500 kg for science, capability for precise orbit determination and spacecraft electromagnetic cleanliness.
3. A Europa Surface Science Package be incorporated into the JIMO mission baseline design.
4. All the science instruments be competitively selected and flown as Principal Investigator provided investigations.
5. A planetary protection policy and implementation strategy be established for the exploration of icy satellites.
6. NASA select Interdisciplinary Scientists at an early stage in the mission development.
7. NASA consider a competitively selected augmentation to the science teams 2 to 4 years prior to operations at Jupiter.
8. An Outer Planets Data Analysis program be established.
9. A Fundamental Research program for the Outer Solar System be established.
10. A JIMO Data Analysis Program be established
11. The resources for science be identified for the full life cycle of the JIMO mission.
12. The JIMO project implement a ground data system to convert raw spacecraft data into useful science data products that are validated and archived.

The recommendations and details on scientific potential outlined in this report for the Jupiter
Icy Moons Orbiter represent the deliberations of the JIMO Science Definition Team. Although
some individuals of the 38-member team had different view points on some issues, the report
reflects the general consensus of the SDT. Because the JIMO concepts will continue to evolve
beyond the date of this report (February 2004), it is important that a dialog continue among
NASA Headquarters, project personnel, and the scientific community. In this context, there is the
potential for this report to be revised and augmented in the future.