Vision and Voyages for Planetary Science in the - Solar System ...

Titan Saturn System Mission
Many Titan mission concept studies have been conducted over the last decade including the most
recent Outer Planet Flagship Mission study. 72 In that study, completed in 2009, NASA and ESA worked
jointly to define a flagship-class mission that would achieve the highest priority science. The resulting
concept is called the Titan Saturn System Mission (TSSM) and has three overarching science goals:
1. Explore and understand processes common to Earth on another body, including the nature of
Titan’s climate and weather and their time evolution, its geological processes, the origin of its unique
atmosphere, and analogies between its methane cycle and Earth’s water cycle.
2. Examine Titan’s organic inventory; a path to pre-biological molecules. This includes
understanding the nature of atmospheric, surface, and subsurface organic chemistry, and the extent to
which that chemistry might mimic the steps that led to life on Earth.
3. Explore Enceladus and Saturn’s magnetosphere—clues to Titan’s origin and evolution. This
includes investigation of Enceladus’s plume for clues to the origin of Titan ices and a comparison of its
organic content with that of Titan, and understanding Enceladus’s tidal heating and its implications for the
Saturn system.
The intent of Goal 1 is to investigate the physical processes, many of which are similar to those
on Earth, that shape Titan’s atmosphere, surface and evolution.
Goal 2 investigates Titan’s rich organic chemistry. An extensive study is particularly important
because it will elucidate the chemical pathways that occur in two environments, which may resemble
those of early Earth. Measurements of the composition of the thermosphere will determine whether
amino acids are made in the upper atmosphere. The chemical pathways that lead to these prebiotic
molecules will be investigated to determine whether this formation mechanism is typical, and whether
prebiotic molecules are common in irradiated methane and nitrogen rich atmospheres, perhaps typical of
early Earth. Measurements of the surface will investigate the progress of Titan’s organic chemistry over
longer time periods.
Goal 3 investigates Enceladus, whose plumes provide a unique view of the composition and
chemistry of the interior, which is likely representative of the same types of icy materials that formed
Titan. This goal could possibly be addressed by a separate Enceladus mission as described below, but
Enceladus science remains high priority for a Titan mission, if Enceladus is not targeted separately. The
TSSM mission design includes Enceladus flybys prior to Titan orbit insertion, but some Titan mission
architectures, such as aerocapture directly from heliocentric orbit, might preclude Enceladus science
unless the spacecraft subsequently left Titan orbit for Enceladus, and these trades require further study as
mission concepts are developed further.
The study of such a complex system requires both orbital and in situ elements, and the TSSM
concept included three components—an orbiter, a balloon, and a lander.
The TSSM science was rated on an equivalent level with the Europa Jupiter System Mission by
both NASA and ESA science review panels. The science was rated as excellent and science
implementation rated as low risk, though the need for continued technology development for TSSM was
noted. Based on technical readiness, a joint NASA-ESA recommendation in 2009 prioritized, EJSM first,
followed closely by TSSM. The multi-element mission architecture is appropriate because it enables
complementary in situ and remote-sensing observations. The TSSM study demonstrated the effectiveness
of such an approach for accomplishing the diverse science objectives that are high-priorities for
understanding Titan. However the details of such an implementation are likely to evolve as studies
continue.
Technology needs for Titan, including surface sampling, balloons, and aerocapture, which may
enable delivery of additional mass to Titan, were prominent in OPAG’s technology recommendations. 73
Technology-development priorities for this mission are those needed to address the mission design risks
PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION
8-32