Concept Study of a Full Stokes Spectropolarimeter with No Moving Parts for Investigations of Planetary Atmospheres and Icy Surfaces

1. Abstract

Future planetary exploration missions demand payloads that deliver high scientific return within strict engineering and operational constraints. Here, we present a concept study of a full-Stokes spectropolarimeter with a no-moving-part configuration for investigating planetary atmospheres and icy surfaces. The absence of moving parts reduces mechanical failure risks and calibration uncertainties, while simultaneous measurement of all Stokes parameters improves observational efficiency and reduces operational burden. The instrument can provide key information on atmospheric composition, aerosol and haze microphysics, and the physical properties of icy surfaces, making it a versatile payload for future planetary exploration missions.

2. Introduction

South Korea announced Korea’s Space Exploration Roadmap in November 2025, expanding its exploration objectives beyond the Earth–Moon system toward Mars and other deep-space planetary targets. Following this roadmap, Korean research institutes, universities, and industries have been carrying out conceptual studies and  needs assessments for future planetary exploration missions. Against this background, it is timely to examine scientific payload concepts that can provide high scientific return while remaining compatible with the technical and operational constraints of planetary exploration missions.

Planetary exploration missions require substantial investment, long development timelines, and operations constrained by limited launch windows. Because mission opportunities are rare, payloads should be designed to maximize the scientific value of the acquired data. Instruments that can obtain multiple types of information simultaneously are therefore particularly valuable, as they enhance observational efficiency and reduce operational burden.

Spectropolarimetry is one such approach, as it enables simultaneous retrieval of both compositional and scattering-related physical properties from fewer observations.

3. Scientific Motivation

Spectropolarimetry provides information beyond conventional spectroscopy by simultaneously constraining both compositional and physical properties of the observed medium. In planetary atmospheres, polarization signatures can reveal the microphysical properties of aerosols, clouds, and haze particles, including particle size, shape, and scattering behavior. These parameters are essential for understanding atmospheric radiative processes and improving radiative transfer modeling, and can reduce ambiguities in atmospheric retrievals. For icy bodies, spectropolarimetry can constrain surface physical properties such as grain size, texture, and roughness, which are important for characterizing icy materials and assessing surface conditions relevant to future landing or in situ exploration. A spectropolarimeter can therefore serve as a versatile payload for both atmospheric and surface investigations.

4. Instrument Concept

Moving parts are a major source of failure, performance degradation, and calibration uncertainty in planetary instruments, particularly under launch vibration, thermal cycling, and long-duration operation. A no-moving-part configuration helps preserve the initial optical alignment throughout the mission and minimizes mechanism-related risks, making it especially suitable for the harsh and unserviceable environments of planetary exploration.

In this study, we propose a full-Stokes spectropolarimeter with a no-moving-part configuration. The instrument measures all four Stokes parameters simultaneously using a fixed arrangement of optical elements, without any rotating or translating components. This enables temporally consistent polarization measurements that are less affected by target variability or spacecraft motion, while enhancing structural stability and operational simplicity.

5. Expected Scientific Applications

The proposed spectropolarimeter is applicable to a wide range of planetary targets. For Mars and the giant planets, it can constrain the microphysical properties of dust, aerosols, hazes, and clouds, thereby supporting improved atmospheric radiative transfer modeling. For icy bodies such as Europa and Enceladus, it can characterize surface grain size, texture, and roughness, providing information relevant to future landed and in situ exploration.

By combining atmospheric and surface diagnostic capabilities within a single, mechanically simple instrument, this concept represents a promising candidate payload for orbiter, flyby, and lander missions across the Solar System.

6. Conclusion

We present a concept study of a full-Stokes spectropolarimeter with a no-moving-part configuration for investigating planetary atmospheres and icy surfaces. By simultaneously measuring all four Stokes parameters without moving components, the proposed instrument concept provides enhanced optical stability, mechanical reliability, and observational efficiency. Its ability to probe both atmospheric microphysics and icy surface properties makes it a promising and versatile payload candidate for future planetary science missions.