This second community announcement about the fourth New Frontiers Announcement of Opportunity (AO) provides information about the science objectives for the six mission themes listed in the first community announcement.

As previously announced, investigations for this opportunity are limited to the following mission themes (listed without priority):

• Comet Surface Sample Return,
• Lunar South Pole-Aitken Basin Sample Return,
• Ocean Worlds (Titan and/or Enceladus),
• Saturn Probe,
• Trojan Tour and Rendezvous, and
• Venus In Situ Explorer.

Investigations proposed to this opportunity must address at least one of the six mission themes above. These mission themes are briefly described below, including their science objectives.

The Comet Surface Sample Return mission theme is focused on acquiring and returning to Earth a macroscopic sample from the surface of a comet nucleus using a sampling technique that preserves organic material in the sample. The mission theme would also use additional instrumentation on the spacecraft to determine the geologic and geomorphologic context of the sampled region. Because of the increasingly blurred distinction between comets and the most primitive asteroids, many important objectives of an asteroid sample return mission could also be accomplished by this mission. The science objectives (listed without priority) of this mission theme are:

• Acquire and return to Earth for laboratory analysis a macroscopic comet nucleus surface sample;
• Characterize the surface region sampled; and
• Preserve sample complex organics.

The Lunar South Pole-Aitken Basin Sample Return mission theme is focused on returning samples from this ancient and deeply excavated impact basin to Earth for characterization and study. In addition to returning samples, this mission would also document the geologic context of the landing site. The science objectives (listed without priority) of this mission theme are:

• Elucidate the nature of the Moon’s lower crust and/or mantle by direct measurements of its composition and of sample ages;
• Determine the chronology of basin-forming impacts and constrain the period of late, heavy bombardment in the inner solar system and, thus, address fundamental questions of inner solar system impact processes and chronology;
• Characterize a large lunar impact basin through “ground truth” validation of global, regional, and local remotely sensed data of the sampled site;
• Elucidate the sources of thorium and other heat-producing elements to understand lunar differentiation and thermal evolution; and
• Determine the age and composition of farside basalts to determine how mantle source regions on the Moon’s farside differ from the basalts from regions sampled by Apollo and Luna

The Ocean Worlds mission theme is focused on the search for signs of extant life and/or characterizing the potential habitability of Titan and/or Enceladus. For Enceladus, the science objectives (listed without priority) of this mission theme are:

• Assess the habitability of Enceladus’ ocean; and
• Search for signs of biosignatures and/or evidence of extant life.

For Titan, the science objectives (listed without priority) of the Ocean Worlds mission theme are:

• Understand the organic and methanogenic cycle on Titan, especially as it relates to prebiotic chemistry; and
• Investigate the subsurface ocean and/or liquid reservoirs, particularly their evolution and possible interaction with the surface.

The Saturn Probe mission theme is intended to deploy one or more probes into Saturn’s atmosphere to directly determine the structure of the atmosphere, as well as noble gas abundances and isotopic ratios of hydrogen, carbon, nitrogen, and oxygen. The science objectives (listed without priority) of this mission theme are:

• Determine noble gas abundances and isotopic ratios of hydrogen, carbon, nitrogen, and oxygen in Saturn’s atmosphere; and
• Determine the atmospheric structure at the probe descent location.

The Trojan Tour and Rendezvous mission theme is intended to examine two or more small bodies sharing the orbit of Jupiter, including one or more flybys, followed by an extended rendezvous with a Trojan object. The science objective of this mission theme is:

• Visit, observe, and characterize multiple Trojan asteroids

The Venus In Situ Explorer mission theme is focused on examining the physics and chemistry of Venus’s atmosphere and crust by characterizing variables that cannot be measured from orbit, including the detailed composition of the lower atmosphere and the elemental and mineralogical composition of surface materials. The science objectives (listed without priority) of this mission theme are:

• Understand the physics and chemistry of Venus’s atmosphere through measurement of its composition, especially the abundances of sulfur, trace gases, light stable isotopes, and noble-gas isotopes;
• Constrain the coupling of thermochemical, photochemical, and dynamical processes in Venus’s atmosphere and between the surface and atmosphere to understand radiative balance, climate, dynamics, and chemical cycles;
• Understand the physics and chemistry of Venus’s crust;
• Understand the properties of Venus’s atmosphere down to the surface and improve understanding of Venus’s zonal cloud-level winds;
• Understand the weathering environment of the crust of Venus in the context of the dynamics of the atmosphere of Venus and the composition and texture of its surface materials; and
• Search for evidence of past hydrological cycles, oceans, and life and constraints on the evolution of Venus’s atmosphere.

Those responding to this opportunity may elect to reword these objectives as desired, but must define clear traceability from their science objectives to those listed above. Responders must also demonstrate linkages from their science objectives and associated investigations to the crosscutting themes and priority questions in Visions and Voyages for Planetary Science in the Decade 2013-2022, the most recent Decadal Survey (Chapter 3). Additionally, responders should demonstrate the extent to which their science objectives and investigations address the relevant science goals, objectives, and key questions described in the Decadal Survey (Chapters 4, 5, 7, and 8).

NASA recognizes that the science objectives may include more scope than can be accomplished in a single New Frontiers mission within the cost cap. Those responding to this opportunity should choose among the science objectives above and defend those choices.

NASA does not prescribe how any missions or investigations responsive to the six themes should actually be accomplished. However, NASA requires that any mission architecture achieve a preponderance of the science objectives listed above for the relevant mission theme. For the purpose of this AO, preponderance is defined to be superiority in number or influence. The requirement to address a preponderance of the science objectives (rather than a majority) recognizes that all science objectives are not necessarily equally important. The required justification of the choice of science objectives should make clear why the set of selected science objectives addresses a preponderance of the science goals.

For sample return missions, the condition of the sample and its volume (or mass) are not specified, but proposals must demonstrate that both the size and condition of the sample are sufficient to achieve a preponderance of the relevant science objectives stated above.

The time frame for the solicitation remains unchanged from the first community announcement.

NASA has not approved the issuance of the New Frontiers AO and this notification does not obligate NASA to issue the AO and solicit proposals. Any costs incurred by prospective investigators in preparing submissions in response to this notification or the planned draft New Frontiers AO are incurred completely at the submitter’s own risk.

Further information will be posted on the New Frontiers Program Acquisition Page athttp://newfrontiers.larc.nasa.gov/ as it becomes available. Questions may be addressed to Dr. Curt Niebur, New Frontiers Program Lead Scientist, Planetary Science Division, Science Mission Directorate, NASA, Washington, DC 20546; Tel.: (202) 358-0390; E-mail: [email protected].