Refinements in the data analysis of VIRTIS-M-IR Venus nightside spectra

The successful long-duration radiation measurements performed by the VIRTIS instrument aboard ESA’s Venus Express spacecraft have provided an excellent collection of atmospheric and surface data that stand out due to their high temporal and spatial coverage of the planet and due to a high diversity of measurement and environmental conditions.     

The Lunar Gravity Ranging System for the Gravity Recovery and Interior Laboratory (GRAIL) Mission

The Lunar Gravity Ranging System (LGRS) flying on NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission measures fluctuations in the separation between the two GRAIL orbiters with sensitivity below 0.6 microns/Hz^1/2. GRAIL adapts the mission design and instrumentation from the Gravity Recovery and Climate Experiment (GRACE) to a make a precise gravitational map of Earth’s Moon. Phase measurements of Ka-band carrier signals transmitted between spacecraft with line-of-sight separations between 50 km to 225 km provide the primary observable. Measurements of time offsets between the orbiters, frequency calibrations, and precise orbit determination provided by the Global Positioning System on GRACE are replaced by an S-band time-transfer cross link and Deep Space Network Doppler tracking of an X-band radioscience beacon and the spacecraft telecommunications link. Lack of an atmosphere at the Moon allows use of a single-frequency link and elimination of the accelerometer compared to the GRACE instrumentation. This paper describes the implementation, testing and performance of the instrument complement flown on the two GRAIL orbiters.     

Atmospheric Ions and Aerosol Formation

This paper discusses atmospheric ions and their role in aerosol formation. Emphasis is placed upon the upper troposphere where very low temperatures tend to facilitate new particle formation by nucleation. New measurements addressed include: Laboratory measurements of cluster ions, aircraft measurements of ambient atmospheric ions, atmospheric measurements of the powerful nucleating gas H₂SO₄ and its gaseous precursor SO₂. The paper also discusses model simulations of aerosol formation and growth. It is concluded that in the upper troposphere new aerosol formation via ions is a frequent process with relatively large rates. However new particle formation by homogeneous nucleation which does not involve ions also seems to be efficient. The bottleneck in the formation of upper troposphere aerosol particles with sizes sufficiently large to be climate relevant is mostly not nucleation but sufficient growth of new and still very small particles. Our recent upper troposphere SO₂ measurements suggest that particle growth by gaseous sulphuric acid condensation can be efficient in certain circumstances. If so, cosmic ray mediated formation of CCN sized particles should at least occasionally be operative in the upper troposphere.     

Infrared spectrometer PFS for the Mars 94 orbiter

Thin films containing a mixture of aliphatic (glycine) and aromatic (tryptophan or tyrosine) amino acids were exposed to a vacuum ultraviolet radiation (VUV) with wavelenghts 100–200 nm. Dipeptides (glycyl-tryptophan and glycyl-tyrosine) were synthesized in these conditions. We compared the actions of VUV and γ-radiation. Polymerization is an essential step in prebiological evolution and we have shown that this stage probably occured over an early Solar system history.     

Order out of Randomness: Self-Organization Processes in Astrophysics

Self-organization is a property of dissipative nonlinear processes that are governed by a global driving force and a local positive feedback mechanism, which creates regular geometric and/or temporal patterns, and decreases the entropy locally, in contrast to random processes. Here we investigate for the first time a comprehensive number of (17) self-organization processes that operate in planetary physics, solar physics, stellar physics, galactic physics, and cosmology. Self-organizing systems create spontaneous “order out of randomness”, during the evolution from an initially disordered system to an ordered quasi-stationary system, mostly by quasi-periodic limit-cycle dynamics, but also by harmonic (mechanical or gyromagnetic) resonances. The global driving force can be due to gravity, electromagnetic forces, mechanical forces (e.g., rotation or differential rotation), thermal pressure, or acceleration of nonthermal particles, while the positive feedback mechanism is often an instability, such as the magneto-rotational (Balbus-Hawley) instability, the convective (Rayleigh-Bénard) instability, turbulence, vortex attraction, magnetic reconnection, plasma condensation, or a loss-cone instability. Physical models of astrophysical self-organization processes require hydrodynamic, magneto-hydrodynamic (MHD), plasma, or N-body simulations. Analytical formulations of self-organizing systems generally involve coupled differential equations with limit-cycle solutions of the Lotka-Volterra or Hopf-bifurcation type.     

Amplification of the influence of solar flux variations on the winter stratosphere by planetary waves

Recent observational evidence has suggested that variations in solar activity may affect winter stratospheric polar ozone and temperature levels. The paucity of direct sunlight available during this season points strongly to a dynamical mechanism. We have carried out several large ensemble experiments within the middle atmosphere and the coupled middle atmosphere and lower thermosphere to simulate the radiative/dynamical coupling via planetary waves for a range of solar fluxes. In the former case, the model response in the winter stratosphere was linear and of the order of the summer stratopause forcing, whilst in the latter, the level of correlation in the winter stratosphere remained high, but was diluted over a wider volume. The inclusion of the upper atmosphere enhanced the winter polar stratospheric response by a factor of three.     

The longwave radiation estimated from NOAA polar orbiting satellites: An update and comparison with Nimbus-7 ERB results

The planetary outgoing longwave radiation has been estimated since 1974 from two different series of NOAA operational polar spacecraft. The first series provided data from June 1974 through February 1978 and was designated “SR” for the scaning radiometers used at that time. This data set has been used in a variety of radiation budget and climate studies, such as that by Ohring and Gruber, 1983. The second satellite system is the currently operational TIROS-N series of satellites. Data from this series began in January 1979 and are continuing. In both systems, estimates of the outgoing longwave radiation are obtained from narrow spectral interval (10–12 μm) window radiances. A comparison is made of the estimates from the two different series of satellites in order to arrive at an assessment of their compatibility. This is important since the SR observations were taken at approximately 0900 and 2100 local times, while the TIROS-N data alternate between 0730-1930 and 0300-1500 local times. In addition, there is a period of overlap between the TIROS-N data and the broad band (5–50 μm) Nimbus 7 EArth radiation budget data. A comparison of those two data sets indiciate excellent agreement generally within about 1–2 Wm^?2 on the monthly means on global and hemispherical scales. Comparisons of zonal averages indicate maximum differences as large as 9 Wm^?2.Evidence is presented to suggest that observations taken at different local observing times may be biased by the diurnal variation of emitted flux, even on global scales.     

Meteoric Layers in Planetary Atmospheres

Metallic ions coming from the ablation of extraterrestrial dust, play a significant role in the distribution of ions in the Earth’s ionosphere. Ions of magnesium and iron, and to a lesser extent, sodium, aluminium, calcium and nickel, are a permanent feature of the lower E-region. The presence of interplanetary dust at long distances from the Sun has been confirmed by the measurements obtained by several spacecrafts. As on Earth, the flux of interplanetary meteoroids can affect the ionospheric structure of other planets. The electron density of many planets show multiple narrow layers below the main ionospheric peak which are similar, in magnitude, to the upper ones. These layers could be due to long-lived metallic ions supplied by interplanetary dust and/or their satellites. In the case of Mars, the presence of a non-permanent ionospheric layer at altitudes ranging from 65 to 110 km has been confirmed and the ion Mg⁺?CO₂ identified. Here we present a review of the present status of observed low ionospheric layers in Venus, Mars, Jupiter, Saturn and Neptune together with meteoroid based models to explain the observations. Meteoroids could also affect the ionospheric structure of Titan, the largest Saturnian moon, and produce an ionospheric layer at around 700 km that could be investigated by Cassini.     

Sesame – An Experiment of the Rosetta Lander Philae: Objectives and General Design

SESAME is an instrument complex built in international co-operation and carried by the Rosetta lander Philae intended to land on comet 67P/Churyumov-Gerasimenko in 2014. The main goals of this instrument suite are to measure mechanical and electrical properties of the cometary surface and the shallow subsurface as well as of the particles emitted from the cometary surface. Most of the sensors are mounted within the six soles of the landing gear feet in order to provide good contact with or proximity to the cometary surface. The measuring principles, instrument designs, technical layout, operational concepts and the results from the first in-flight measurements are described. We conclude with comments on the consequences of the last minute change of the target comet and how to improve and to preserve the knowledge during the long-duration Rosetta mission.