Gaia is a cornerstone mission in the science programme of the EuropeanSpace Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page.

The Gaia mission

http://www.astro.sunysb.edu/metchev/PHY688/Pollack_etal96_core_accretion.pdf

Formation of the Giant Planets by Concurrent Accretion of Solids and Gas

We construct size distributions for carbonaceous and silicate grain populations in different regions of the Milky Way, LMC, and SMC. The size distributions include sufficient very small carbonaceous grains (including polycyclic aromatic hydrocarbon molecules) to account for the observed infrared and microwave emission from the diffuse interstellar medium. Our distributions reproduce the observed extinction of starlight, which varies depending on the interstellar environment through which the light travels. As shown by Cardelli, Clayton, and Mathis in 1989, these variations can be roughly parameterized by the ratio of visual extinction to reddening, RV. We adopt a fairly simple functional form for the size distribution, characterized by several parameters. We tabulate these parameters for various combinations of values for RV and bC, the C abundance in very small grains. We also find size distributions for the line of sight to HD 210121 and for sight lines in the LMC and SMC. For several size distributions, we evaluate the albedo and scattering asymmetry parameter and present model extinction curves extending beyond the Lyman limit.

https://iopscience.iop.org/article/10.1086/318651/pdf

Dust Grain-Size Distributions and Extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud

▪ Abstract This review surveys the observed properties of interstellar dust grains: the wavelength-dependent extinction of starlight, including absorption features, from UV to infrared; optical lum...

https://www.ifa.hawaii.edu/users/reipurth/reviews/draine.pdf

Interstellar dust grains

Dust -acoustic waves in dusty plasmas

We investigated the electrostatic charging behavior of submillimeter-sized dust particles located in Saturn's magnetosphere. The charging effects we considered included electron/ion capture from the magnetospheric plasma, electron/ion capture from the solar-wind plasma, the photoelectric effect from solar radiation, and secondary electron emission from energetic electrons. In our results, we show charging times and equilibrium potentials for particles located in different regions of Saturn's magnetosphere. We find that charging in Saturn's magnetosphere is not particularly sensitive to the dust particle's material properties. The equipotential ranges from $\sim$-2 V at 3.5 R$_S$, decreasing to $\sim$-5 V at 6 R$_S$, and then increasing to $\sim$-1.5 V at 10 R$_S$. The charging time for micron-sized particles is a few minutes, and for 0.01 micron-sized particles the charging time is 6 hours (or more). The latter is a significant fraction of Saturn's rotation period.

Charging processes for dust particles in Saturn's magnetosphere

Solar system dust is finely divided particulate matter that exists between the planets. These cosmic dust particles are also often called micrometeoroids and range in size from assemblages of a few molecules to tenth-millimeter-sized grains, above which size they are called meteoroids. Sources of this dust are larger meteoroids, comets, asteroids, the planets, and their moons and rings; there is interstellar dust sweeping through the solar system. Because of their small sizes, forces additional to solar and planetary gravity affect their trajectories. Radiation pressure and the interactions with ubiquitous magnetic fields disperse dust particles in space away from their sources. In this way, micrometeoroids become messengers of their parent bodies in distant regions of the solar system. A tablespoon of finely dispersed micrometer-sized dust grains scatters about 10 million times more light than a single meteoroid of the same mass. Therefore, a tiny amount of dust becomes recognizable, while the parent body from which it derived may remain undetected.

Dust in the Solar System

The Max-Planck-Institut fur Kernphysik in Heidelberg owns a dust accelerator, whichis able to provide micron and submicron sized particles with speeds between 1 and 80 km s −1 . The type of dust materials and the speed and mass range of the accelerated particles is dependent on the design of the dust reservoir at the front end of the accelerator beam line. In order to improve the capabilities of this reservoir, a new dust source was developed. A simplification in the source design allows a more efficient particle extraction. Also new sorts of dust can now be accelerated at the Heidelberg facilities: Iron, silver, copper, carbon and latex. This paper describes the dust source and the properties of the first accelerated dust samples. The experiments were performed at both, the 20 kV test bench and the 2 MV accelerator.

A new dust source for the Heidelberg dust accelerator

Dust was observed in the Jovian magnetosphere with the dust detector onboard the Galileo spacecraft. Measurements have been obtained inside a distance of about 100Rj from Jupiter’s center (Jupiter radius, RJ = 71,492 km) during a period of 20 days covering Galileo’s closest approach to Ganymede on September 6, 1996, 18:59 UTC. At least three types of dust particles have been detected: (1) submicrometer-sized particles found throughout the Jovian system with high and variable impact rates, implying that the particles’ trajectories are strongly affected by the interaction with the Jovian magnetic field; (2) concentrations of small dust impacts at the time of Ganymede closest approach, which could be secondary ejecta particles generated upon impact of other particles onto Ganymede’s surface; and (3) micrometer-sized dust particles, which could be on bound orbits about Jupiter, and which are concentrated in the inner Jovian system inside about 20RJ from Jupiter.

Dust measurements from galileo's second orbit about jupiter

The data gathered by the Cosmic Dust Analyser (CDA) on board Cassini close to 1 AU are investigated To compare the measured flux with models, the sensitivity of the targets is derived from calibration data The interplanetary model by Staubach [1] underestimates the measured flux by more than one order of magnitude Our attempt to classify the measured events as impacts on the large and the small target, indiates that there are impacts on the side walls which lead to measurable signals on the targets This brings the measured flux closer to the model, but cannot explain the large discrepancy It is shown that interstellar particles could fill the gap between the interplanetary flux model and the measured impact rate

Eberhard Grün

Papers

Charging processes for dust particles in Saturn's magnetosphere

Dust in the Solar System

A new dust source for the Heidelberg dust accelerator

Dust measurements from galileo's second orbit about jupiter

CDA cruise science: Comparison of measured dust flux at 1 AU with models