Methods for the analysis of data from the Planetary Fourier Spectrometer on the Mars Express Mission

This work presents an algorithm for the scientific analysis of individual calibrated measurements from the Planetary Fourier spectrometer (PFS).The instrument, included in the scientific payload of the ESA Mars Express mission to Mars, acquires spectra in the range between 250 and 8200 cm⁻¹, with a sampling step of ∼1 cm⁻¹ and an effective resolution of ∼2 cm⁻¹. The observed radiance depends on several parameters of the atmosphere and surface of Mars as described by the radiative transfer equation. Adopting the very general formalism of Bayesian analysis, we determined which quantities are actually retrievable from individual measurements. Namely, they are: the surface temperature, the column density of dust and water ice aerosols in the atmosphere, the air temperature as a function of altitude (in the indicative range 5-45 km above the surface), the surface pressure, and the column density of water vapor and carbon monoxide. These evaluations are carried out taking into account the noise equivalent radiance (NER) of the instrument and the natural variabilities of the investigated parameters in the Martian environment, as estimated from the expectations of the European Martian Climate Dataset v3.1 (EMCD). Other parameters included in the radiative transfer equation shall be assumed as known, because they are not retrievable from individual measurements due to the instrumental NER or an underconstrained inverse problem: the surface emissivity in the thermal infrared, the optical properties of suspended dust and the analytical shape of dust concentration vs. altitude.During the development of the algorithm devoted to these studies, different approaches were evaluated on the basis of formal, computational and scientific considerations, with the aim to develop the general design of an integrated software package.The resulting code was extensively tested on a wide set of simulated PFS spectra. These spectra were computed from the atmospheric and surface conditions extracted from the EMCD, assumed to be representative of the Martian environment for different values of latitude, local time and season. Their comparison with the retrievals from simulated observations allowed us to evaluate the systematic and random errors affecting the procedures with respect to the different quantities involved. The code evaluates the surface temperature with an error in the order of 1 K, while the vertical air temperature profile is computed with an uncertainty less than 2 K from in the region between 5 and 20 km above the surface, increasing up to 7 K at 50 km. The column opacity of dust, measured in terms of integrated optical thickness at 1100 cm⁻¹, is computed with an error of around 0.13. The surface pressure determination is carried out with a typical uncertainty of 0.2-0.3 millibar. Several auxiliary tests allowed us to study the correlations between the different retrieval errors and the possible causes of incorrect PFS data interpretation. The choice of a suitable model for the dust optical properties is demonstrated to be particularly critical.This paper also presents the first discussion about application of the procedure to actual PFS Martian data. Despite the calibration issues still affecting the determination of absolute radiance in the near-infrared, the algorithm is able to achieve a satisfactory modeling of observations in a wide range of situations.     

The origin of the CN radical in comets: A review from observations and models

The origin of CN radicals in comets is not completely understood so far. We present a study of CN and HCN production rates and CN Haser scale lengths showing that: (1) at heliocentric distances larger than 3 AU, CN radicals could be entirely produced by HCN photolysis; (2) closer to the Sun, for a fraction of comets CN production rates are higher than HCN ones whereas (3) in the others, CN distribution cannot be explained by the HCN photolysis although CN and HCN production rates seem to be similar. Thus, when the comets are closer than 3 AU to the Sun, an additional process to the HCN photolysis seems to be required to explain the CN density in some comets.The photolysis of HC₃N or C₂N₂ could explain the CN origin. But the HC₃N production rate is probably too low to reproduce CN density profile, even if uncertainties on its photolysis leave the place for all possible conclusions. The presence of C₂N₂ in comets is a reliable hypothesis to explain the CN origin; thus, its detection is a challenging issue. Since C₂N₂ is very difficult to detect from ground-based observations, only in situ measurements or space observations could determine the contribution of this compound in the CN origin.Another hypothesis is a direct production of CN radicals by the photo- or thermal degradation of complex refractory organic compounds present on cometary grains. This process could explain the spatial profile of CN inside jets and the discrepancy noted in the isotopic ratio ¹⁴N/¹⁵N between CN and HCN. Laboratory studies of the thermal and UV-induced degradation of solid nitrogenated compounds are required to model and validate this hypothesis.     

The Dergaon (H5) chondrite: Fall,classification, petrological and chemical characteristics,cosmogenic effects,and noble gas records

Abstract— A multiple fall of a stony meteorite occurred near the town of Dergaon in Assam, India, on March 2, 2001. Several fragments weighing <2 kg and a single large fragment weighing ～10 kg were recovered from the strewn field, which extended over several tens of square kilometers. Chemical, petrographic, and oxygen isotopic studies indicate it to be, in most aspects, a typical H5 chondrite, except the unusually low K content of ～340 ppm. A cosmic ray exposure of 9.7 Ma is inferred from the cosmogenic noble gas records. Activities of eleven cosmogenic radionuclides were measured. ²⁶Al and ²²Na activities as well as the ²²Na/²⁶Al activity ratio are close to the values expected on the basis of solar modulation of galactic cosmic rays. The low ⁶⁰Co activity (<1 dpm/kg) is indicative of a small preatmospheric size of the meteorite. Cosmic ray heavy nuclei track densities in olivine grains range from ～106 cm^?2 in samples from the largest fragment to approximately (4–9) × 105 cm^?2 in one of the smaller fragments. The combined track, radionuclide, and noble gas data suggest a preatmospheric radius of ～20 cm for the Dergaon meteorite.     

The Meteoritical Bulletin,No. 100, 2014 June

Meteoritical Bulletin 100 contains 1943 meteorites including 8 falls (Boumdeid [2011], Huaxi, Ko?ice, Silistra, So?tmany, Sutter's Mill, Thika, Tissint), with 1575 ordinary chondrites, 139 carbonaceous chondrites, 96 HED achondrites, 25 ureilites, 18 primitive achondrites, 17 iron meteorites, 15 enstatite chondrites, 11 lunar meteorites, 10 mesosiderites, 10 ungrouped achondrites, 8 pallasites, 8 Martian meteorites, 6 Rumuruti chondrites, 3 enstatite achondrites, and 2 angrites, and with 937 from Antarctica, 592 from Africa, 230 from Asia, 95 from South America, 44 from North America, 36 from Oceania, 6 from Europe, and 1 from an unknown location. This will be the last Bulletin published in the current format. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available online at http://www.lpi.usra.edu/meteor/     

Results from the Whole Earth Telescope — Indian contributions

The Indian team at ISRO has been part of the Whole Earth Telescope (WET) team since 1988 when we first participated in the campaign on V471 Tau. We have been part of many other observing campaigns over the last decade. This presentation traces the circumstances leading to our joining the WET team and how useful the coverage from the Indian longitude has been. The results of several pulsators from the WET runs during which we participated are also described. These include PG1159-035 the prototype of the GW Vir type of stars, RE J 0751+14 a cataclysmic variable, PG 1336-018 a binary with an sdB pulsator and finally HR 1217 a roAp star. The paper concludes with what the limitations are in our observations and how we can overcome them in the future.     

Canonical Modelling of Relative Spacecraft Motion Via Epicyclic Orbital Elements

This paper presents a Hamiltonian approach to modelling spacecraft motion relative to a circular reference orbit based on a derivation of canonical coordinates for the relative state-space dynamics. The Hamiltonian formulation facilitates the modelling of high-order terms and orbital perturbations within the context of the Clohessy–Wiltshire solution. First, the Hamiltonian is partitioned into a linear term and a high-order term. The Hamilton–Jacobi equations are solved for the linear part by separation, and new constants for the relative motions are obtained, called epicyclic elements. The influence of higher order terms and perturbations, such as Earth’s oblateness, are incorporated into the analysis by a variation of parameters procedure. As an example, closed-form solutions for J₂-invariant orbits are obtained.     

A New Analysis of the Spectra Obtained by the <Emphasis Type="Italic">Venera</Emphasis> Missions in the Venusian Atmosphere. I. The Analysis of the Data Received from the <Emphasis Type="Italic">Venera-11</Emphasis> Probe at Altitudes Below 37 km in the 0.44–0.66 µm Wavelength Range

The processes of the solar radiation extinction in deep layers of the Venus atmosphere in a wavelength range from 0.44 to 0.66 µm have been considered. The spectra of the solar radiation scattered in the atmosphere of Venus at various altitudes above the planetary surface measured by the Venera-11 entry probe in December 1978 are used as observational data. The problem of the data analysis is solved by selecting an atmospheric model; the discrete-ordinate method is applied in calculations. For the altitude interval from 2–10 km to 36 km, the altitude and spectral dependencies of the volume coefficient of true absorption have been obtained. At altitudes of 3–19 km, the spectral dependence is close to the wavelength dependence of the absorption cross section of S₃ molecules, whence it follows that the mixing ratio of this sulfur allotrope increases with altitude from 0.03 to 0.1 ppbv.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 4, 2005, pp. 304–320.Original Russian Text Copyright © 2005 by Maiorov, Ignat’ev, Moroz, Zasova, Moshkin, Khatuntsev, Ekonomov.     

Analysis of photoelectric light curves of V448 CYG taking the Roche geometry into account

Three-color photoelectric UBV light curves of the close binary system V448 Cyg obtained at the Abastumani Astrophysical Observatory are analyzed using a new code by Djurasevi. A new value for the ratio of the masses of the components, which is the fundamental parameter for determining the absolute elements of the system, has recently been published. The parameters obtained in our analysis differ substantially from those published previously because the new mass ratio has been employed. The location of the components of V448 Cyg on a mass-logg plot shows that this system, similarly to XZ Cep and V382 Cyg, is in a phase subsequent to a rapid transfer of mass.Translated from Astrofizika, Vol. 48, No. 1, pp. 59–68 (February 2005).     

Small-scale magnetic field diagnostics outside sunspots: Comparison of different methods

We analyse different observational data related to the problem of intrinsic magnetic field strength in small-scale fluxtubes outside sunspots. We conclude that the kG range of fluxtube fields follows from not only classical line ratio method, but also from other old and new techniques. For the quiet regions on the Sun, the most probable mode of such fields has a magnetic field strength of 1.2–1.5 kG assuming the rectangular field profile. To best interpret the observations, a weak background field between fluxtubes should be assumed, and its magnetic field strength is expected to increase with the filling factor of fluxtubes. The alternative point of view about subkilogauss fluxtube fields is critically examined, and possible sources of different conclusions are presented.     

Structure of solar-wind streams at the maximum of solar cycle 23

We study the formation of solar-wind streams in the years of maximum solar activity 2000–2002. We use observations of the scattering of radio emission by solar-wind streams at distances of ～4–60R_S from the Sun, data on the magnetic field structure and strength in the source region (R ～ 2.5R_S), and observations with the LASCO coronagraph onboard the SOHO spacecraft. Analysis of these data allowed us to investigate the changes in the structure of circumsolar plasma streams during the solar maximum. We constructed radio maps of the solar-wind transition, transonic region in which the heliolatitudinal stream structure is compared with the structure of the white-light corona. We show that the heliolatitudinal structure of the white-light corona largely determines the structure of the solar-wind transition region. We analyze the correlation between the location of the inner boundary of the transition region R_in and the magnetic field strength on the source surface |B_R|. We discuss the peculiarities of the R_in = F(|B_R|) correlation diagrams that distinguish them from similar diagrams at previous phases of the solar cycle.