Evolution of water production of 67P/Churyumov-Gerasimenko: An empirical model and a multi-instrument study

We examine the evolution of the water production of comet 67P/Churyumov–Gerasimenko during the Rosetta mission (2014 June–2016 May) based on in situ and remote sensing measurements made by Rosetta instruments, Earth-based telescopes and through the development of an empirical coma model. The derivation of the empirical model is described and the model is then applied to detrend spacecraft position effects from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) data. The inter-comparison of the instrument data sets shows a high level of consistency and provides insights into the water and dust production. We examine different phases of the orbit, including the early mission (beyond 3.5 au) where the ROSINA water production does not show the expected increase with decreasing heliocentric distance. A second important phase is the period around the inbound equinox, where the peak water production makes a dramatic transition from northern to southern latitudes. During this transition, the water distribution is complex, but is driven by rotation and active areas in the north and south. Finally, we consider the perihelion period, where there may be evidence of time dependence in the water production rate. The peak water production, as measured by ROSINA, occurs 18–22 d after perihelion at 3.5 ± 0.5 × 1028 water molecules s-1. We show that the water production is highly correlated with ground-based dust measurements, possibly indicating that several dust parameters are constant during the observed period. Using estimates of the dust/gas ratio, we use our measured water production rate to calculate a uniform surface loss of 2–4 m during the current perihelion passage

Excitonic Spectra of Cd1−x\text{}_{1-x}Fex\text{}_{x}Te Crystals

Strong modification of the optical spectra near the band-gap edge is observed in Cd$\text{}_{1-x}$Fe$\text{}_{x}$Te crystals as compared to the spectra of a pure compound. The evolution of the luminescence spectra at the increase in Fe concentration is represented by the change of radiative recombination channels from dominantly (A$\text{}^{0}$, x) acceptor bound exciton emission in undoped CdTe to the free exciton luminescence in Cd$\text{}_{1-x}$Fe$\text{}_{x}$Te solid solutions

Energy States of Ni in Zn1−x\text{}_{1-x}Mnx\text{}_{x}Se:Ni Solid Solutions

Absorption and reflectivity measurements were carried out on Zn$\text{}_{1-x}$Mn$\text{}_{x}$Se:Ni solid solutions. The spectra demonstrate the radical change of the structure of internal Ni$\text{}^{2+}$(3d$\text{}^{8}$) transitions at the presence of the Mn ions and strong dependence on Mn concentration. The threshold energy ħω$\text{}_{th}$ for the process of Ni photoionization to the valence band Ni$\text{}^{2+}$(3d$\text{}^{8}$) + ħω$\text{}_{th}$ → Ni$\text{}^{1+}$(3d$\text{}^{9}$) + h is shifted to the lower energy by 30 meV, but hardly depends on x despite the essential increase in the energy gap

Free Exciton Luminescence in ZnCdSe Solid Solutions, ZnSe Epitaxial Films and ZnSe1−x\text{}_{1-x}Sx\text{}_{x}/ZnSe1−y\text{}_{1-y}Sy\text{}_{y} Superlattices

We studied the luminescence of bulk Zn$\text{}_{1-x}$Cd$\text{}_{x}$Se solid solutions, epitaxial ZnSe films and ZnSe$\text{}_{1-x}$S$\text{}_{x}$/ZnSe$\text{}_{1-y}$S$\text{}_{y}$ superlattices at T=2-80 K. The analysis of the bands of exciton radiative annihilation with simultaneous emission of 1 or 2 LO phonons shows that the excitons in the studied samples can be considered as free particles with thermalized distribution of kinetic energies. In ZnSe$\text{}_{1-x}$S$\text{}_{x}$/ZnSe$\text{}_{1-y}$S$\text{}_{y}$ superlattices a three-dimensional character of exciton motion was established. The periodic potential of superlattice perturbs the exciton wave vector and induces additional elastic scattering of excitons

Analysis of the dust jet imaged by Rosetta VIRTIS-M in the coma of comet 67P/Churyumov-Gerasimenko on 2015 April 12

This work is a part of a more global effort aimed at understanding and interpreting in situ and remote sensing data acquired by instruments on board Rosetta. This study aims at deriving the dust mass source rate and the location of the dust jet source observed by Rosetta VIRTIS-M on 2015 April 12. The analysis is performed by means of the coupled kinetic modelling of gas and dust in the coma of comet 67P/Churyumov-Gerasimenko, which were used for calculating the coma brightness as it would be seen from the Rosetta spacecraft. The dust mass production rate and a possible location of the jet origin needed to explain the Rosetta VIRTIS-M dust brightness image were inferred by comparing the calculated brightness with VIRTIS-M data. Our analysis suggests that the dust mass production rate needed to maintain the observed jet is about 1.9 kg s(-1). According to our analysis, the location of the observed jet surface footprint is outside of the nucleus area characterized by the highest gas production rate, which suggests that gas and dust source rates are not necessarily proportional to each other across the entire nucleus surface. The inferred location of the possible jet origin is consistent with that of the observed active pits. In this paper, we show that the jet intensity is variable in time, and has a lifetime of at least 10 h.US Rosetta [1266313, 1266314]; NASA Planetary Atmospheres [NNX14AG84G]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]