Thermosphere Of Mars Research Articles

The Mars thermosphere-ionosphere: Predictions for the arrival of Planet-B

The primary science objective of the Planet-B mission to Mars is to study the Martian upper atmosphere-ionosphere system and its interaction with the solar wind. An improved knowledge of the Martian magnetic field (whether it is induced or intrinsic) is needed, and will be provided by Planet-B. In addition, a proper characterization of the neutral thermosphere structure is essential to place the various plasma observations in context. The Neutral Mass Spectrometer (NMS) onboard Planet-B will provide the required neutral density information over the altitude range of 150–500 km. Much can be learned in advance of Planet-B data taking as multi-dimensional thermosphere-ionosphere and MHD models are exercised to predict the Mars near-space environment that might be expected during the solar maximum conditions of Cycle 23 (1999–2001). Global model simulations of the Mars thermosphere-ionosphere system are presented and analyzed in this paper. These Mars predictions pertain to the time of Planet-B arrival in October 1999 (F10.7∼200; Ls∼220). In particular, the National Center for Atmospheric Research (NCAR) Mars Thermosphere General Circulation Model (MTGCM) is exercised to calculate thermospheric neutral densities (CO2, CO, N2, O, Ar, O2), photochemical ions (CO+2, O+2, O+ below 200 km), neutral temperatures, and 3-components winds over 70–300 km. Cases are run with and without dust loading of the lower atmosphere in order to examine the potential impacts of dust storms on the thermosphere-ionosphere structure. Significant dust-driven impacts are predicted in the lower thermosphere (100–120 km), but are less pronounced above 150 km. The ionospheric peak height changes greatly with the passage of a Mars global dust storm event. In addition, Martian dayside exobase temperatures are generally warmer during dusty periods, in accord with Mariner 9 UVS data (Stewart et al., 1972). During the Planet-B mission, the NMS team intends to use the MTGCM as a facility tool whose simulated output can be utilized to aid various investigations.

Comparative thermospheres: Venus and Mars

The thermospheres of Venus and Mars are compared using Venera, Pioneer Venus, Mariner and Viking data. These measurements provide constraints for modeling efforts which probe thermospheric processes, balances, and responses to various forcings and input parameters. In particular, the National Center for Atmospheric Research (NCAR) non-LTE CO 2 radiative transfer model and the Thermospheric General Circulation Model (TGCM) have been adapted to the thermospheres of Venus and Mars for standard solar flux conditions. The better constraied Venus TGCM serves as a valuable precursor to the subsequent Mars TGCM, since both planets share many radiative and chemical processes peculiar to CO 2 atmospheres. Results indicate that planetary rotation significantly modifies thermospheric structure and winds; no nightside “cryosphere” of the type observed for Venus is predicted for Mars. Atomic O is greatly depleted on Mars compared to Venus. Resulting dayside heat balances suggest that CO 2 15-μm cooling strongly regulates Venus temperatures, while the Mars circulation is more effective as a thermostat. Fundamental planetary parameters are shown to be responsible for many of these differences in Venus and Mars thermospheric features.

The Mars thermosphere: 2. General circulation with coupled dynamics and composition

The National Center for Atmospheric Research thermospheric general circulation model (TGCM) for the Earth's thermosphere has been modified to examine the three‐dimensional structure and circulation of the upper mesosphere and thermosphere of Mars (MTGCM). The computational framework and major processes unique to a CO2 thermosphere are similar to those utilized in a recent Venus TGCM. Solar EUV, UV, and IR heating alone combine to drive the Martian winds above ∼100 km. An equinox version of the code is used to examine the Mars global dynamics and structure for two specific observational periods spanning a range of solar activity: Viking 1 (July 1976) and Mariner 6–7 (August–September 1969). The MTGCM is then modified to predict the state of the Mars thermosphere for various combinations of solar and orbital conditions. Calculations show that no nightside cryosphere of the type observed on Venus is obtained on the Mars nightside. Instead, planetary rotation significantly modifies the winds and the day‐to‐night contrast in densities and temperatures, giving a diurnal behavior similar to the Earth under quiet solar conditions. Maximum exospheric temperatures are calculated near 1500 LT (≤305 K), with minimum values at 0500 LT (≤175 K). The global temperature distribution is strongly modified by nightside adiabatic heating (subsidence) and day side cooling (upwelling). The global winds also affect vertical density distributions; vertical eddy diffusion much weaker than used in previous one‐dimensional models is required to maintain observed Viking profiles. A solar cycle variation in dayside exospheric temperatures of ∼195–305 K is simulated by our Viking and Mariner runs. The dayside heat budget responsible consists of a balance of EUV heating, adiabatic cooling, and molecular thermal conduction, with CO2 cooling having little influence. Solar heating is probably not the only driving mechanism of the Mars upper atmosphere; gravity wave and tidal influence from below will also likely be significant, especially during dust storm periods.

Mars thermospheric general circulation model: Calculations for the arrival of Phobos at Mars

The NCAR thermospheric general circulation model (TGCM) for the Earth's thermosphere has been modified to examine the three‐dimensional structure and circulation of the upper mesosphere and thermosphere of Mars (MTGCM). The computational framework and major processes unique to a CO2 thermosphere are similar to those utilized in a recent Venus TGCM. Mean orbital, seasonal, and solar conditions are specified. An Equinox version of the MTGCM is used to predict the Mars solar driven global circulation and structure for a non‐dusty (quiet) lower atmosphere at the time of arrival of the two Phobos spacecraft.

Aeronomy of the inner planets

Recent progress concerning the thermospheres of Venus and Mars is reviewed in this report. A dramatic advance in our understanding of the upper atmosphere and ionosphere of Venus has occurred during the 1979–82 quadrennium, and was primarily due to the large amount of data generated by the Pioneer Venus mission. Progress on Mars has been rather modest and has stemmed from theoretical modeling efforts related to the 1976 Viking observations. This report covers the following topics: the thermosphere and ionosphere of Mars, the thermosphere of Venus, some aspects of the solar wind‐ionosphere interaction of Venus, the dayside ionosphere of Venus including both composition and energetics, and the nightside ionosphere of Venus.