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Article

The Lower Ionosphere of Mars: Modeling and Effect of Dust  

Varun Sheel

The study of planetary ionospheres helps us to understand the composition, losses, and electrical properties of the atmosphere. The structure of the ionosphere depends on the neutral gas composition as well. Models based on fundamental equations have been able to simulate the neutral and ion structure of the Martian atmosphere. These models couple chemical, physical, radiative, and dynamical processes at various levels of complexities. The lower ionosphere (below 80 km) and its composition have not been observed and studied as comprehensively as the upper ionosphere. Most of our current understanding of the plasma environment in the lower atmosphere is based on theoretical models. Models indicate that Mars contains a D region, similar to that in the Earth’s ionosphere, produced primarily due to high-energy galactic cosmic rays that can penetrate to the lower altitudes. The D layer has been simulated to lie in the altitude range of ~25 to 35 km on the dayside ionosphere of Mars. A one-dimensional model, used to calculate the densities of 35 positive and negative ions, predicts hydrated ions to be dominant in the troposphere of Mars. Due to the variability of water vapor, these cluster ions show seasonal variability and can be measured by future experiments on Mars landers. Dust is an important component of the climate of Mars, wherein dust storms are known to affect the temperatures and winds of the lower atmosphere. The inclusion of ion–dust interactions in the model for the Martian ionosphere has yielded important effects of dust storms on the ionosphere. It has been found that during dust storms, the ion densities can significantly diminish, reducing the total ion conductivity in the troposphere by an order of magnitude. Also, large electric fields could be generated due to the charging of dust in the ionosphere, leading to electric discharges and, possibly, lightning.

Article

Planetary Spectroscopy  

Alian Wang

Planetary spectroscopy uses physical methods to study the chemical properties of the geological materials on the planetary bodies in our solar system. This article will present twelve types of spectroscopy frequently used in planetary explorations. Their energy (or wavelength) varies from γ-ray (keV) to far-infrared (μm), which involves the transitions of nuclei, atoms, ions, and molecules in planetary materials. The article will cover the basic concept of the transition for each of the twelve types of spectroscopy, along with their legendary science discoveries made during the past planetary exploration missions by the international planetary science and engineering community. The broad application of spectroscopy in planetary exploration is built upon the fact that only limited extraterrestrial materials were collected (meteorites, cosmic dust, and the returned samples by missions) that enabled the detailed investigations of their properties in laboratories, while spectroscopic measurements can be made on the objects of our solar system remotely and robotically, such as during the flyby, orbiting, lander, and rover missions. In this sense, the knowledge obtained by planetary spectroscopy has contributed to a major portion of planetary sciences. In the coming era of space explorations, more powerful spacecraft will be sent out by mankind, go to deep space, and explore exotic places. Generations of new planetary science payloads, including planetary spectrometers, will be created and will fly. New sciences will be revealed.