Characterization of cyclical spatial heterodyne spectrometers for astrophysical and planetary studies.

High-resolution spectroscopy can make key science measurements for a variety of astrophysics and planetary targets, including solar system planetary atmospheres, comets, solar wind charge exchange emission, and interstellar and interplanetary medium. With the ability to record adjacent spectral lines simultaneously key isotopic ratios such as D/H, C12/C13, O16/O18, etc., can be measured precisely. Traditional high spectral resolution spectrometers usually must couple to large optics to compensate for their low throughput, which prohibits achieving compactness, in particular in space and remote field applications. Also, the high cost of construction and maintenance limit their quantity and usage for the long duration temporal measurement of the sources. Spatial heterodyne spectrometers (SHS) are increasingly used in scientific observations and industry. To date, SHS instruments come in two major architectures: Michelson design and cyclical design. Cyclical SHS, also known as reflective SHS, can offer significant advantages over traditional spectrometers in obtaining high-resolution spectra in shorter wavelengths. Although cyclical SHSs have been introduced before, there has been no mathematical or performance characterization of their technique. This paper presents a comprehensive mathematical design and performance expectations of the cyclical tunable SHS technique to enable and expand its usage in a variety of platforms and applications, in the industry and astronomical observations from ground and space telescopes.

The NASA Roadmap to Ocean Worlds.

In this article, we summarize the work of the NASA Outer Planets Assessment Group (OPAG) Roadmaps to Ocean Worlds (ROW) group. The aim of this group is to assemble the scientific framework that will guide the exploration of ocean worlds, and to identify and prioritize science objectives for ocean worlds over the next several decades. The overarching goal of an Ocean Worlds exploration program as defined by ROW is to "identify ocean worlds, characterize their oceans, evaluate their habitability, search for life, and ultimately understand any life we find." The ROW team supports the creation of an exploration program that studies the full spectrum of ocean worlds, that is, not just the exploration of known ocean worlds such as Europa but candidate ocean worlds such as Triton as well. The ROW team finds that the confirmed ocean worlds Enceladus, Titan, and Europa are the highest priority bodies to target in the near term to address ROW goals. Triton is the highest priority candidate ocean world to target in the near term. A major finding of this study is that, to map out a coherent Ocean Worlds Program, significant input is required from studies here on Earth; rigorous Research and Analysis studies are called for to enable some future ocean worlds missions to be thoughtfully planned and undertaken. A second finding is that progress needs to be made in the area of collaborations between Earth ocean scientists and extraterrestrial ocean scientists.