Remote sensing of planetary space environment

Abstract

Planetary space, a critical region of mass and energy exchange between the planet and the interplanetary space, is an integral part of the planetary multi-layer coupling system. Atmospheres of different compositions and plasmas of different densities and energies exist in planetary space, where mass transportation at different temporal and spatial scales and various energy deposition and dissipation processes occur. These processes are driven by the changes in the solar wind and the internal driving forces of the planet. Knowledge pertaining to the global mass and energy transportation in planetary space is essential to investigate the mass escape from the planets. Understanding the forces and physical processes that drive changes in the planetary space environment is not only beneficial to protecting the life, technical systems, and infrastructures on the Earth, but is also helpful in understanding the past and future. In this regards, the systematic and overall view of planetary space environments is necessary for planetary science. Optical remote sensing implies a measurement made by indirect or “remote” means, which relies upon either emitted, reflected, or scattered optical radiation. There are three main types of optical remote sensing technologies, namely imaging (photography), spectrograph, and spectrographic imaging. Scientific application of optical remote sensing dates back to 1906 when G. Galilei constructed the first astronomical telescope, using which he discovered the four Galilean satellites of Jupiter and the phase variation of Venus. Since then, several discoveries in planetary science have been made by means of optical remote sensing, such as the discovery of new planets and their moons, the discovery of the primary compositions of planetary atmospheres, global convection of cold plasma in Earth’s space, the discovery of planetary aurora (Earth, Mars, Jupiter, Saturn) and volcanic activity on Io, and water eruption on Enceladus. The optical remote sensing method overcomes the difficulties of capturing global views and distinguishing spatial and temporal variations in in-situ particle and field detections. Furthermore, through an overview of the history of planetary optical remote sensing, we propose a development strategy for planetary optical remote sensing, in China, based on the national deep-space exploration plan. A “Quaternity” planetary optical detection system that integrates ground-based, balloon-borne, space-based, and moon-based optical remote sensing is proposed. For example, the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS) is planning to construct a ground-based optical telescope with an aperture of ~1.5 m in Northwest China to monitor the volcanic activity on Io and to conduct other planetary observations. As the first planetary optical remote sensing project in China, the balloon-borne planetary optical remote sensing for the Scientific Experiment System in Near Space (SENSE) Program is introduced in detail. The SENSE Program is a five-year Strategic Priority Research Program of the Chinese Academy of Sciences, which began in 2018. A balloon-borne Planetary Atmospheric Spectroscopic Telescope (PAST) with an aperture of 0.8 m will be launched into the stratosphere at the height of 35–40 km to image the planetary atmosphere and plasma in the ultraviolet and visible range. The main scientific target of PAST is to comparatively study the diversity of the planetary space environment and their different drivers. Test and scientific flights are scheduled in 2021 and 2022 in Northwest China and potentially in polar regions. By using the data from PAST and in combination with other data (such as Jupiter’s auroral images from the Hubble Space Telescope, Mars’ space environment data from Mars Atmosphere and Volatile Evolution mission, and Jupiter’s space environment data from Juno mission), the couplings between planetary atmosphere and plasma will be investigated to characterize the diversity of the evolution of the planetary space environment.