Characterizing Atmospheric Escape from Mars Today and Through Time, with MAVEN

Abstract

International audienceTwo of the primary goals of the MAVEN mission are to determine how the rate of escape of Martian atmospheric gas to space at the current epoch depends upon solar influences and planetary parameters and to estimate the total mass of atmosphere lost to space over the history of the planet. Along with MAVEN’s suite of nine science instruments, a collection of complementary models of the neutral and plasma environments of Mars’ upper atmosphere and near-space environment are an indispensable part of the MAVEN toolkit, for three primary reasons. First, escaping neutrals will not be directly measured by MAVEN and so neutral escape rates must be derived, via models, from in situ measurements of plasma temperatures and neutral and plasma densities and by remote measurements of the extended exosphere. Second, although escaping ions will be directly measured, all MAVEN measurements are limited in spatial coverage, so global models are needed for intelligent interpolation over spherical surfaces to calculate global escape rates. Third, MAVEN measurements will lead to multidimensional parameterizations of global escape rates for a range of solar and planetary parameters, but further global models informed by MAVEN data will be required to extend these parameterizations to the more extreme conditions that likely prevailed in the early solar system, which is essential for determining total integrated atmospheric loss. We describe these modeling tools and the strategies for using them in concert with MAVEN measurements to greater constrain the history of atmospheric loss on Mars

The Mars Atmosphere and Volatile Evolution (MAVEN) Mission

“…The MAVEN strategy for characterizing the upper atmospheric reservoir (goal 1) and determining atmospheric escape rates today (goal 2) and through time (goal 3) are described in detail in companion papers by and Lillis et al (2014) respectively. Below we briefly summarize the global models that will inform physical interpretation of MAVEN data, as well as our science closure strategy.…”

“…In this way, a global picture of photochemical escape will be built up for different combinations of external conditions (e.g., a small range of EUV flux). 3-D global models of hot-atom escape (see Lillis et al 2014) will be used to interpolate across global escape maps to calculate global photochemical escape rates and how they vary with the controlling drivers. Coverage is shown in MSE coordinates, assuming each orbit segment occurred during a steady IMF clock angle direction drawn from the distribution of clock angle directions recorded during the Mars Global Surveyor mission and presented in Brain et al (2003) Sputtering Escape As MAVEN will not directly measure escaping neutrals and their energies, we plan to derive sputtering escape rates using two complementary indirect techniques.…”

“…The Michigan framework uses a global multi-fluid MHD model while the LMD framework uses a hybrid model where ions and electrons are treated kinetically and in the fluid regime, respectively. These models are described in detail in Lillis et al (2014).…”

MAVEN IUVS observation of the hot oxygen corona at Mars

“…The literature is replete with detailed models of the production and transport of nonthermal oxygen into the Martian exosphere and widely varying predictions for the escape rate (for a thorough review of the modeling state-of-the-art in preparation for interpreting MAVEN data, see Lillis et al [2015] difficult to obtain the conclusive observations of the tenuous corona needed to validate these models. Remote sensing measurements focus on resonant scattering of sunlight by the relatively strong O I 130.4 nm triplet, but even so, the expected brightness at altitudes > 700 km where the hot population dominates is on the order of 1-10 Rayleighs.…”

What characterizes planetary space weather?

“…At Earth, the subsequent increase of ionizing radiations at aircraft altitude, and in the space station, raises concern for human safety and leads to monitoring efforts (Mertens et al 2010). SEPs also affect Earth's upper atmosphere chemistry, producing NO that leads to ozone depletions at high latitudes (Jackman et al 2005a, b;López-Puertas et al 2005;Rohen et al 2005). The effect of SEP events has been also observed at Mars (Zeitlin et al 2004), but their description at other bodies than the Earth still mainly relies on numerical simulations (Sheel et al 2012).…”