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

Galactic interstellar dust (ISD) is the major ingredient in planetary formation. However, information on this important material has been extremely limited. Recently the Ulysses dust detector has identified and measured interstellar dust outside 1.8~AU from the Sun at ecliptic latitudes above $50^{\circ}$. Inside this distance it could not reliably distinguish interstellar from interplanetary dust. Modeling the Ulysses data suggests that up to 30 % of dust flux with masses above $10^{-16}\rm kg$ at 1~AU is of interstellar origin. From the Hiten satellite in high eccentric orbit about the Earth there are indications that ISD indeed reaches the Earth's orbit. Two new missions carrying dust detectors, Cassini and Stardust, will greatly increase our observational knowledge. In this paper we briefly review instruments used on these missions and compare their capabilities. The Stardust mission [{\em Brownlee et al.}, 1996] will analyze the local interstellar dust population by an in-situ chemical analyzer and collect ISD between 2 and 3~AU from the Sun. The dust analyzer on the Cassini mission will determine the interstellar dust flux outside Venus' orbit and will provide also some compositional information. Techniques to identify the ISD flux levels at 1~AU are described that can quantify the interstellar dust flux in high-Earth orbit (outside the debris belts) and provide chemical composition information of galactic dust.

http://arxiv.org/pdf/astro-ph/9908022.pdf

Techniques for Galactic Dust Measurements in the Heliosphere

A linear time-of-flight mass spectrometer is developed for the detection and chemical analysis of nanometer-sized particles originating near the Sun. Nano-dust particles are thought to be produced by mutual collisions between interplanetary dust particles slowly spiraling toward the Sun and are accelerated outward to high velocities by interaction with the solar wind plasma. The WAVES instruments on the two STEREO spacecraft reported the detection, strong temporal variation, and potentially high flux of these particles. Here we report on the optimization and the results from the detailed characterization of the instrument's performance using submicrometer sized dust particles accelerated to 8–60 km/s. The Nano Dust Analyzer (NDA) concept is derived from previously developed detectors. It has a 200 cm2 effective target area and a mass resolution of approximately m/Δm = 50. The NDA instrument is designed to reliably detect and analyze nanometer-sized dust particles while being pointed close to the Sun's direction, from where they are expected to arrive. Measurements by such an instrument will determine the size-dependent flux of the nano-dust particles and its variations, it will characterize the composition of the nano-dust and, ultimately, it may determine their source. The flight version of the NDA instrument is estimated to be <5 kg and requires <10 W for operation.

Development of the nano-dust analyzer (NDA) for detection and compositional analysis of nanometer-size dust particles originating in the inner heliosphere

Solar System Dust

Measurements and analysis results from the GORID impact detector for the period April 1997 to end of 2000 are presented. The GORID detector was in a geostationary location at 80 Eastern longitude until June 2000 and has then be moved to 103 East. The average number of events with the highest classification (where all signals agree with pre launch calibration values for true impacts) is 2.4 per day. The daily number of impacts varied between 0 to more than 40. In addition, many impacts occur clustered in time and sometimes reappear at about the same time for one or more days after their first appearance. The most likely source of these clusters are exhaust particles from solid rocket motor firings. The large majority of the impacts occurred during local night times. At local night times GORID points to some extend into the Earth apex direction and this will result in increased fluxes from natural meteoroids. Between May and July increased event numbers are recorded during the local morning hours. At these times during the summer a portion of GORID’s detecting surfaces faces the sun indicating that these impacts could be from beta particles arriving from the sun direction. So far no conclusive impacts from meteor stream particles have been registered. Some observations are not yet well understood. These include a certain percentage of impacting particles with apparently a high negative charge and a large percentage of impacts with a long signal rise time which normally indicates a relatively low impact velocity. The data analysis is complicated by potentially disturbing effects like impacts on the detector baffle and noise induced by the surrounding space environment and the spacecraft itself.

/pdf/measurements-of-cosmic-dust-and-micro-debris-with-the-gorid-pja41rafma.pdf

Measurements of cosmic dust and micro-debris with the GORID impact detector in GEO

A self-triggered dust trajectory sensor not only determines the trajectories of charged dust particles but also acts as a highly sensitive dust detector. The objective of a dust trajectory sensor (DTS) is to measure charges Q ≥100 aC and trajectories of submicron-sized grains with accuracies of ∼1° in direction and ∼1% in speed in the range v =1–100 km/s. It determines the trajectories from the signals induced in an array of wire electrodes. Most signals are weak and distorted by amplifier noise. Transient recorders continuously store them until a trigger signal indicates the presence of a dust particle. A trigger signal was previously available only after the particle had passed through the DTS and was detected externally by impact ionization. In certain important applications, however, an external trigger is not available or too late. In this paper we discuss a method of generating a trigger from noisy DTS signals before the dust grain exits the sensor. Specifically, we use seven parallel, double-triangle-shaped velocity filters on each sensor electrode to cover the velocity range v =1–128 km/s. Each velocity filter feeds into four parallel amplitude filters, two for single large signals and two for pairs of smaller but coincident signals from adjacent wires. We demonstrate by computer simulation that the probability of generating at least one trigger is high, typically p t ≥0.99 at v =20 km/s, charge-to-noise ratio QNR ≥6.25, and angle of incidence from 0° to 27°. The minimum QNR required to derive a trigger varies with dust velocity as ∼v 1/2 . The false event rate, caused by amplifier noise, is estimated to be on the order of one per year.

Eberhard Grün

Papers

Techniques for Galactic Dust Measurements in the Heliosphere

Development of the nano-dust analyzer (NDA) for detection and compositional analysis of nanometer-size dust particles originating in the inner heliosphere

Solar System Dust

Measurements of cosmic dust and micro-debris with the GORID impact detector in GEO

A self-triggered dust trajectory sensor