The Cameron bands and the UV doublet are two of the most prominent emission systems in the UV in Mars dayside. Their altitude variation has been exploited in the past to derive thermospheric temperatures from measurements obtained by the Mariner 6, 7, and 9 missions, the SPICAM instrument on board Mars Express, and the IUVS instrument on board MAVEN. Here we identify and quantify possible biases in these temperature determinations. For this purpose, we use a global model able to simulate these two emission systems, and we compare the temperature derived from the simulated emission with that predicted by the model at the same location and time. We find that an exponential fit to the scale height of the UV doublet can be used to derive temperatures with an error less than 10 K at altitudes above about 170 km and for low and moderate values of the Solar Zenith Angle. The temperature derived from the Cameron bands is biased towards higher values due to the non-negligible contribution of CO to the emission. We find that, at 170 km, the difference between the temperature derived from the Cameron bands and the UV doublet can be related to the CO abundance. Our results have implications for previous temperature determinations from the Mariners, SPICAM/MEx and IUVS/MAVEN, some of them being biased by about 25 K.

We present a non-local thermodynamic equilibrium retrieval scheme for atmospheric composition and its application to Mars CO2 infrared limb emissions as measured by the OMEGA instrument on board Mars Express (MEx). These emissions are caused by CO2 fluorescence of solar radiation, and thus the retrieval scheme accounts for non-LTE processes. We analyzed the dayside limb observations from a selection of three OMEGA orbits or data qubes. Before the retrieval was applied, we performed a radiometric calibration, cleaned the spectra (including clustering techniques) and generated radiance vertical profiles for each dataset. We also present information on the inversion set up, results on the retrieved CO2 density profiles, as well as the temperature profiles derived from the CO2 densities by assuming hydrostatic equilibrium. An extensive sensitivity study of the retrieval scheme was carried out, including its application to the OMEGA spectra taken at different MEx orbital configurations, to conclude on its performance and to offer recommendations for its systematic use with MEx datasets. The uncertainty due to the instrumental Gain calibration and that caused by the retrieval noise error itself are of large importance for the inversion, but a comparable component of the total error comes from the uncertainties of the temperature provided by the GCM. We demonstrated that, between 120 and 160 km, CO2 profiles can be derived with a precision around 30% and a vertical resolution of about 15 km.

EPSC-DPS Joint Meeting 2019, held 15-20 September 2019 in Geneva, Switzerland, id. EPSC-DPS2019-181.-- © Author(s) 2019. CC Attribution 4.0 license. https://creativecommons.org/licenses/by/4.0/deed.es

EPSC-DPS Joint Meeting 2019, held 15-20 September 2019 in Geneva, Switzerland, id. EPSC-DPS2019-888-1.- ©Author(s) 2019. CC Attribution 4.0 license. https://creativecommons.org/licenses/by/4.0/deed.es

The Martian mesosphere and thermosphere, the region above about 60 km, is not the primary target of the ExoMars 2016 mission but its Trace Gas Orbiter (TGO) can explore it and address many interesting issues, either in-situ during the aerobraking period or remotely during the regular mission. In the aerobraking phase TGO peeks into thermospheric densities and temperatures, in a broad range of latitudes and during a long continuous period. TGO carries two instruments designed for the detection of trace species, NOMAD and ACS, which will use the solar occultation technique. Their regular sounding at the terminator up to very high altitudes in many different molecular bands will represent the first time that an extensive and precise dataset of densities and hopefully temperatures are obtained at those altitudes and local times on Mars. But there are additional capabilities in TGO for studying the upper atmosphere of Mars, and we review them briefly. Our simulations suggest that airglow emissions from the UV to the IR might be observed outside the terminator. If eventually confirmed from orbit, they would supply new information about atmospheric dynamics and variability. However, their optimal exploitation requires a special spacecraft pointing, currently not considered in the regular operations but feasible in our opinion. We discuss the synergy between the TGO instruments, specially the wide spectral range achieved by combining them. We also encourage coordinated operations with other Mars-observing missions capable of supplying simultaneous measurements of its upper atmosphere.

Introduction The two European missions to Mars and Venus, Mars Express and Venus Express, have provided a unique set of infrared observations of their upper atmospheres in a limb geometry [1] [2]. These observations should allow for a first-time exploitation of the non-thermal CO2 emission in a terrestrial planet other than Earth, in at least the strongest system of ro-vibrational bands of this molecules, that in the 4.3 um spectral region. Although spectroscopically well characterized and theoretically well understood and modeled [3] [4] [5], the practical exploitation of these emissions is difficult for several reasons. Some of these are common to previous similar investigations and IR remote sounding on the Earth upper atmosphere and some of them specific to a CO2 atmosphere like the Martian case (and the Venusian one). One of the goals of the UPWARDS project [6] is the exploitation of these limb emissions as captured by OMEGA and PFS on Mars Express and the delivery of the major results obtained (densities and temperatures at thermospheric altitudes) to open repositories for its scientific dissemination. In this presentation we will describe the essential tools used (non-local thermodynamic models and retrieval suite) , the datasets selected, the major difficulties found in the retrieval process and a sample of the results obtained so far.

Introduction: The ExoMars orbiter will soon be finishing its aerobraking phase, and then, in summer 2018, it will start taking science measurements of the Martian atmosphere. From that point TGO will be making systematic solar occultation observations for the first time of the Martian atmosphere. This presents us with a unique opportunity to explore the atmospheric vertical structure (composition and temperature) at high spatial resolution, and hopefully in a wide range of altitudes extending into the upper thermosphere. Making good use of this data requires specialized tools, specifically a line-by-line radiative transfer model and an appropriate inversion scheme.

We report new radio interferometric observations of the quadruple pre-main-sequence (PMS) system ABD oradus. From these observations, combined with existing VLT near-infrared relative astrometry, we have refined the estimates of the dynamical masses of the system. In particular, we find component masses of 0.86 ± 0.09M⊙ and 0.090 ± 0.003M⊙ for ABD or A and ABD or C, respectively. These dynamical masses, coupled with temperatures and luminosities, allow for comparison with theoretical stellar models. The case of ABDorC, in terms of calibration of evolutionary models of low-mass young stars has been widely reported in previous studies. In this contribution, we compare the measured properties of ABDorA with several solar-composition models for PMS stars. The models used in this comparison predict the dynamical mass to within the quoted uncertainties.

M. A. López-Valverde (valverde@iaa.es), A. Cala-Hurtado, S. Jimenez-Monferrer, F. González-Galindo, Instituto de Astrofı̀sica de Andalucı́a-CSIC, Granada, Spain, L. Montabone, Space Science Institute, Boulder, USA, and Laboratoire de Météorologie Dynamique-IPSL, Paris, France, E. Millour, T. Navarro, F. Forget, Laboratoire de Météorologie Dynamique-IPSL, Paris, France, G. Marzo, ENEA, C.R.Casaccia, Rome, Italy, S. Fonti, Universitá del Salento, Lecce, Italy.

Several instruments on board Mars Express (MEx) have observed daytime atmospheric emissions in the IR, although the data at high altitudes and in a limb geometry have not been sufficiently exploited so far ([1], [9], [12]). Sounding in a limb geometry is a real challenge because this geometry favours optically thick conditions, difficult to handle. In addition, the emissions of the atmospheric species at the low pressures at these altitudes are no longer in LTE (local thermodynamic equilibrium), i.e. they cannot be described by the local kinetic temperature. This is normally a limitation compared to a classical (LTE) inversion scheme where the temperature is already known, and therefore the state populations. In the UPWARDS project (http://www.upwards-mars.eu) we aim at the retrieval of atmospheric densities of the carbon species (CO2 and CO) and of temperature in the middle and upper atmosphere of Mars (50-160 km), from the daytime limb observations between 2.7 and 4.7 μm, carried out by two instruments on board MEx, OMEGA and PFS. Both CO2 and CO have strong ro-vibrational bands that produce intense atmospheric IR emissions during daytime due to well-known non-LTE pumping by solar excitation (also called solar fluorescence). Although these emissions have been studied before ([3], [9], [12]), they have not been used to retrieve density or temperature in the Martian atmosphere so far. Non-LTE retrievals of CO and CO2 from IR emissions at high altitude are common nowadays in the Earth upper atmosphere [7], and have recently been performed also in Venus ([4], [11]). However, these Venus retrievals were performed under the approximation of optically thin conditions (CO retrievals from VIRTIS/Venus Express [4]) or from a nadir down-looking geometry, with a fixed and well-known emission layer (in the case of CO2, at 4.3 μm from VIRTIS [11]). The application of a non-LTE retrieval in a limb geometry which addresses optically thin and thick conditions and from the dominant species of the atmosphere is an entirely new challenge in planetary atmospheres, including the Earth. For this investigation we need, first of all, to combine state-of-the-art non-LTE models and line-by-line retrieval techniques in order to simulate these emissions correctly (forward model), and then retrieve the abundances of the emitting species from the measurements. This work in progress describes the design and test of a retrieval scheme suitable for the Mars non-LTE observations, and the preliminary results obtained from synthetic limb radiances and from actual OMEGA measurements.

We are carrying out a simulation study to characterise the advantages of VLBI with multiple beams, which will be a feature of the next generation of instruments. We will focus on VLBI astrometric measurements at lower frequencies (1.4 GHz and below). For our simulations, we have selected a network consisting of ASKAP, the Australian SKA precursor, plus existing Australian antennas from the LBA (Long Baseline Array) and the new antenna in New Zealand (figure 1a). We have used different models to represent the ionospheric turbulences and frequencies. The preliminary results show an improvement of an order of magnitude in the astrometric precision achieved using multiple calibrators with angular separations of a few degrees around the target, with respect to a single nearby (1 away) calibrator. Such astrometric precision is comparable to using in-beam phase referencing with a calibrator some arcminutes away. We plan to expand our simulations to include other networks with multi-beam capability, and ultimately SKA-like configurations.

We present the results of a Monte Carlo study of the astrometric precision and sensitivity of a realization of the SKA in wide-field observations.We consider several effects from the turbulent atmosphere (i.e., ionosphere and wet component of the troposphere) and also from the antenna receivers.We study the changes in dynamic range and astrometric precision as a function of observing frequency and source separation from the image center.We find that, for frequencies between 1 and 10 GHz, it is possible to obtain images with high fidelity, although the atmosphere strongly limits the sensitivity of the instrument compared to the case with no atmosphere.Outside this frequency window, the dynamic range of the images and the accuracy of the source positions decrease.We find that, even if a good a propri model of the atmospheric turbulences (with an accuracy of ∼ 1%) is used in the imaging, residual effects from the turbulences can still limit the dynamic ranges of deep, high-contrast (10 5 -10 6 ), images.