The next New Frontiers mission will be selected during the decade 2013-2022. Based on their science value and projected costs, the 2013 Planetary Science Decadal Survey committee identified five candidate New Frontiers missions.[3]

Venus In Situ Explorer

The Venus In Situ Explorer would study the composition and surface properties of Venus. The primary science objectives of this mission would be to examine the physics and chemistry of Venus’s atmosphere and crust. The mission should attempt to characterize variables that cannot be measured from orbit, including the detailed composition of the lower atmosphere, and the elemental and mineralogical composition of surface materials. Had the proposed SAGE mission been selected, the Venus In Situ Explorer would have been removed from consideration.[3]

Although the exploration of the surface and lower atmosphere of Venus provides a major technical challenge, the scientific rewards are major. Venus is Earth’s sister planet, yet its tectonics, volcanism, surface-atmospheric processes, atmospheric dynamics and chemistry are all remarkably different from those on Earth, which has resulted in remarkably different end states for its surface crust and atmosphere. While returning physical samples of its surface and/or atmosphere may not be possible within the New Frontiers cost cap, innovative approaches might achieve the majority of the following objectives:

• Understand the physics and chemistry of Venus’ atmosphere through measurement of its composition, especially the abundances of its trace gases, light stable isotopes, and noble gas isotopes;
• Understand the physics and chemistry of Venus’ crust through analysis of near-IR descent images from below the clouds to the surface and through measurements of elemental abundances and mineralogy from a surface sample;
• Understand the properties of Venus’ atmosphere down to the surface through meteorological measurements and improve our understanding of Venus’ zonal cloud-level winds through temporal measurements over at least two Earth days; and
• 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.

Lunar South Pole-Aitken Basin Sample Return

The Lunar South Pole-Aitken Basin Sample Return) would return samples of the early Moon's deep crust. Had Moonrise been selected as the 3rd New Frontiers mission, Lunar South Pole-Aitken Basin Sample Return would have been removed from consideration.

The surface of the South Pole-Aitken basin, located on the Moon’s far side southern polar region, is likely to contain some fraction of the mineralogy of the Moon’s lower crust. Samples of these ancient materials that are not biased by nearside impact basin formation are highly desirable to further understand the history of Earth’s Moon. Therefore, a mission to return a sufficient sample of material from the heretofore-unsampled South Pole-Aitken basin terrain, including useful samples from the deep crust of the early Moon, should accomplish (following chemical, isotopic, and petrologic analysis of returned materials as well as radiometric age dating on Earth) the majority of following science objectives:

• Elucidate the nature of the Moon’s lower crust and 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 in order to understand lunar differentiation and thermal evolution; and
• Determine ages and compositions of far-side basalts to determine how mantle source regions on the far side of the Moon differ from regions sampled by Apollo and Luna basalts.[4]

Trojan Tour and Rendezvous

The Trojan Tour and Rendezvous mission would fly by two or more Jupiter Trojans, asteroids that orbit around the L4 and L5 Lagrange points at the same distance from the sun as Jupiter, and then settle into orbit around one of them - similar goals to the Dawn mission, though significantly further from the Sun.

Comet Surface Sample Return

A Comet Surface Sample Return mission would acquire and return to Earth a macroscopic sample from the surface of a comet nucleus using a sampling technique that preserves organic material in the sample.

Detailed study of comets promises the possibility of understanding the physical condition and constituents of the very early solar system, including the early history of water and the biogenic elements and the compounds containing them. Therefore, a mission that would sample and return the dust and organics from at least one if not several locations on the surface of a comet nucleus, including one in the vicinity of an active vent, is of prime interest in order to achieve the majority of the following science objectives:

• Understand the structure and composition of a comet through measurement of the chemical complexity of the sampled material, grain micro texture and its cohesive forces, age and composition of ices and organic and silicate grains;
• Understand the real time dynamics and evolution of a comet’s surface under the influence of sunlight by study of the diurnal conditions of its atmosphere and surface; and
• Investigate a comet’s overall physical structure in order to assess its internal heterogeneity.

Saturn Probe

A Saturn Probe mission would deploy a probe into Saturn’s atmosphere to determine the structure of the atmosphere as well as noble gas abundances and isotopic ratios of hydrogen, carbon, nitrogen, and oxygen. A carrier/relay craft with the probe would arrive at Saturn approximately seven years after launch. Thirty days or more before arrival, the probe separates from the carrier/relay craft. The probe would enter the atmosphere and begin measurements at 0.1 bars (a bar is the atmospheric pressure at sea level on Earth). At 1 bar, the probe would detach from its parachute for a more rapid descent to 5 bars and the end of the nominal mission after 55 minutes of data collection. The probe would be designed to survive to 10 bars, and the carrier/relay would continue to listen for as long as the entry site remains visible.

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