M. Herranz

Dust measurements in the coma of comet 67P/Churyumov-Gerasimenko inbound to the Sun

Critical measurements for understanding accretion and the dust/gas ratio in the solar nebula, where planets were forming 4.5 billion years ago, are being obtained by the GIADA (Grain Impact Analyser and Dust Accumulator) experiment on the European Space Agency’s Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko. Between 3.6 and 3.4 astronomical units inbound, GIADA and OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) detected 35 outflowing grains of mass 10−10 to 10−7 kilograms, and 48 grains of mass 10−5 to 10−2 kilograms, respectively. Combined with gas data from the MIRO (Microwave Instrument for the Rosetta Orbiter) and ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instruments, we find a dust/gas mass ratio of 4 ± 2 averaged over the sunlit nucleus surface. A cloud of larger grains also encircles the nucleus in bound orbits from the previous perihelion. The largest orbiting clumps are meter-sized, confirming the dust/gas ratio of 3 inferred at perihelion from models of dust comae and trails.

DENSITY AND CHARGE of PRISTINE FLUFFY PARTICLES FROM COMET 67P/CHURYUMOV-GERASIMENKO

The Grain Impact Analyzer and Dust Accumulator (GIADA) instrument on board ESA’s Rosetta mission is constraining the origin of the dust particles detected within the coma of comet 67 P/Churyumov–Gerasimenko (67P). The collected particles belong to two families: (i) compact particles (ranging in size from 0.03 to 1 mm), witnessing the presence of materials that underwent processing within the solar nebula and (ii) fluffy aggregates (ranging in size from 0.2 to 2.5 mm) of sub-micron grains that may be a record of a primitive component, probably linked to interstellar dust. The dynamics of the fluffy aggregates constrain their equivalent bulk density to <1 kg m-3. These aggregates are charged, fragmented, and decelerated by the spacecraft negative potential and enter GIADA in showers of fragments at speeds <1 m s-1. The density of such optically thick aggregates is consistent with the low bulk density of the nucleus. The mass contribution of the fluffy aggregates to the refractory component of the nucleus is negligible and their coma brightness contribution is less than 15%.

GIADA: shining a light on the monitoring of the comet dust production from the nucleus of 67P/Churyumov-Gerasimenko

During the period between 15 September 2014 and 4 February 2015, the Rosetta spacecraft accomplished the circular orbit phase around the nucleus of comet 67P/Churyumov-Gerasimenko (67P). The Grain Impact Analyzer and Dust Accumulator (GIADA) onboard Rosetta moni- tored the 67P coma dust environment for the entire period. Aims. We aim to describe the dust spatial distribution in the coma of comet 67P by means of in situ measurements. We determine dynamical and physical properties of cometary dust particles to support the study of the production process and dust environment modification. Methods. We analyzed GIADA data with respect to the observation geometry and heliocentric distance to describe the coma dust spatial distribu- tion of 67P, to monitor its activity, and to retrieve information on active areas present on its nucleus. We combined GIADA detection information with calibration activity to distinguish different types of particles that populate the coma of 67P: compact particles and fluffy porous aggregates. By means of particle dynamical parameters measured by GIADA, we studied the dust acceleration region. Results. GIADA was able to distinguish different types of particles populating the coma of 67P: compact particles and fluffy porous aggregates. Most of the compact particle detections occurred at latitudes and longitudes where the spacecraft was in view of the comet’s neck region of the nucleus, the so-called Hapi region. This resulted in an oscillation of the compact particle abundance with respect to the spacecraft position and a global increase as the comet moved from 3.36 to 2.43 AU heliocentric distance. The speed of these particles, having masses from 10−10 to 10−7 kg, ranged from 0.3 to 12.2 m s−1 . The variation of particle mass and speed distribution with respect to the distance from the nucleus gave indications of the dust acceleration region. The influence of solar radiation pressure on micron and submicron particles was studied. The integrated dust mass flux collected from the Sun direction, that is, particles reflected by solar radiation pressure, was three times higher than the flux coming directly from the comet nucleus. The awakening 67P comet shows a strong dust flux anisotropy, confirming what was suggested by on-ground dust coma observations performed in 2008.

GIADA: ITS STATUS AFTER THE ROSETTA CRUISE PHASE AND ON-GROUND ACTIVITY IN SUPPORT OF THE ENCOUNTER WITH COMET 67P/CHURYUMOV-GERASIMENKO

GIADA (Grain Impact Analyser and Dust Accumulator) on-board the Rosetta mission to comet 67P/Churyumov-Gerasimenko was designed to study the physical and dynamical properties of dust particles ejected by the comet during the encounter. In this paper we report the results of the analysis of data collected by GIADA during the past seven years of the cruise phase. During this period the GIADA detection subsystems were switched on for periodic in-flight payload checkouts to monitor their state-of-health including potential changes in its performance that could affect its data collection. Only slight variations in sensitivity and dynamical range were identified that will not affect the GIADA measurement capability during the Rosetta comet encounter and rendezvous phase. The GIADA microbalance system detected the presence of low-volatility material over a period of about 169 days when the GIADA cover remained partially opened. It is highly probable that this material originated from the spacecraft itself, as a spacecrafts outgassing was observed by the ROSINA mass spectrometer (on-board Rosetta) during the cruise phase. The identification of the low-volatility mass deposited on the microbalances as self-contamination will allow us to evaluate the mass rate background to be subtracted from the GIADA science data. These results obtained from GIADA cruise data analysis coupled with laboratory calibration data obtained from measurements using the GIADA spare model for selected cometary dust analogs will be the basis for the interpretation of the GIADA scientific data.

The imaging magnetograph eXperiment for the SUNRISE balloon Antarctica project

The SUNRISE balloon project is a high-resolution mission to study solar magnetic fields able to resolve the critical scale of 100 km in the solar photosphere, or about one photon mean free path. The Imaging Magnetograph eXperiment (IMaX) is one of the three instruments that will fly in the balloon and will receive light from the 1m aperture telescope of the mission. IMaX should take advantage of the 15 days of uninterrupted solar observations and the exceptional resolution to help clarifying our understanding of the small-scale magnetic concentrations that pervade the solar surface. For this, IMaX should act as a diffraction limited imager able to carry out spectroscopic analysis with resolutions in the 50.000-100.000 range and capable to perform polarization measurements. The solutions adopted by the project to achieve all these three demanding goals are explained in this article. They include the use of Liquid Crystal Variable Retarders for the polarization modulation, one LiNbO3 etalon in double pass and two modern CCD detectors that allow for the application of phase diversity techniques by slightly changing the focus of one of the CCDs.

The GIADA experiment for ROSETTA mission to comet 46P/Wirtanen: Design and performances

Abstract Rosetta is one of the most ambitious missions planned by ESA for the beginning of the next millennium. It will explore from very close a comet nucleus along its trajectory up to perihelion. In the instrument complex forming the scientific payload, the GIADA (Grain Impact Analyser and Dust Accumulator) experiment is devoted to study the cometary dust flux evolution and grain dynamic properties. To achieve the required performances and the expected scientific return, GIADA has been designed as a multi-sensor instrument. It is able to detect grain passage by laser light scattering measurement, particle momentum through piezoelectric transducers and mass flux by means of quartz crystal microbalances. In this paper we describe the technical solutions and performances which have been reached on the development models of GIADA.

The Giada Experiment for the Rosetta Mission

The Grain Impact Analyser and Dust Accumulator (GIADA) instrument, on board the ESA Rosetta mission, shall analyse the physical and dynamical properties of grains ejected by the target comet and monitor the coma evolution in terms of dust flux and spatial distribution vs. time. The mission, formerly planned to visit comet 46P/Wirtanen, is now targeted to a rendezvous with comet 67P/Churyumov-Gerasimenko. The present operative mission plan foresees that Rosetta will follow the comet from about 4 AU pre-perihelion to about 2 AU post-perihelion. This will allow us to study, for the first time, the onset and evolution of activity of a comet nucleus and its environment. GIADA is composed by different sub-systems designed to measure mass, momentum and speed of single grains larger than about 30 μm in size and to monitor the cumulative flux of smaller grains coming from different directions. GIADA technical characteristics and scientific performances will guarantee a full monitoring of the dust environment and the achievement of unprecedented scientific results about cometary dust physics.

Detailed design of the imaging magnetograph experiment (IMaX): a visible imager magnetograph for the Sunrise mission

In this work, it is described the Imaging Magnetograph eXperiment, IMaX, one of the three postfocal instruments of the Sunrise mission. The Sunrise project consists on a stratospheric balloon with a 1 m aperture telescope, which will fly from the Antarctica within the NASA Long Duration Balloon Program. IMaX will provide vector magnetograms of the solar surface with a spatial resolution of 70 m. This data is relevant for understanding how the magnetic fields emerge in the solar surface, how they couple the photospheric base with the million degrees of temperature of the solar corona and which are the processes that are responsible of the generation of such an immense temperatures. To meet this goal IMaX should work as a high sensitivity polarimeter, high resolution spectrometer and a near diffraction limited imager. Liquid Crystal Variable Retarders will be used as polarization modulators taking advantage of the optical retardation induced by application of low electric fields and avoiding mechanical mechanisms. Therefore, the interest of these devices for aerospace applications is envisaged. The spectral resolution required will be achieved by using a LiNbO3 Fabry-Perot etalon in double pass configuration as spectral filter before the two CCDs detectors. As well phase-diversity techniques will be implemented in order to improve the image quality. Nowadays, IMaX project is in the detailed design phase before fabrication, integration, assembly and verification. This paper briefly describes the current status of the instrument and the technical solutions developed to fulfil the scientific requirements.

The JANUS camera onboard JUICE mission for Jupiter system optical imaging

JANUS (Jovis, Amorum ac Natorum Undique Scrutator) is the visible camera selected for the ESA JUICE mission to the Jupiter system. Resources constraints, S/C characteristics, mission design, environment and the great variability of observing conditions for several targets put stringent constraints on instrument architecture. In addition to the usual requirements for a planetary mission, the problem of mass and power consumption is particularly stringent due to the long-lasting cruising and operations at large distance from the Sun. JANUS design shall cope with a wide range of targets, from Jupiter atmosphere, to solid satellite surfaces, exosphere, rings, and lightning, all to be observed in several color and narrow-band filters. All targets shall be tracked during the mission and in some specific cases the DTM will be derived from stereo imaging. Mission design allows a quite long time range for observations in Jupiter system, with orbits around Jupiter and multiple fly-bys of satellites for 2.5 years, followed by about 6 months in orbit around Ganymede, at surface distances variable from 104 to few hundreds km. Our concept was based on a single optical channel, which was fine-tuned to cover all scientific objectives based on low to high-resolution imaging. A catoptric telescope with excellent optical quality is coupled with a rectangular detector, avoiding any scanning mechanism. In this paper the present JANUS design and its foreseen scientific capabilities are discussed.

New control system for the 1.5m and 0.9m telescopes at Sierra Nevada Observatory

The Sierra Nevada Observatory (Granada, Spain) has a number of telescopes. Our study will focus on two Nasmyth telescopes with apertures of 1.5m and 0.9m and an equatorial mount. The system currently installed to control these telescopes is a 1995 centralized VME module. However, given the problems which have arisen due to the number of wires and other complications, we have decided to change this control module. We will control each telescope with a distributed control philosophy, using a serial linear communication bus between independent nodes, although all system capabilities are accessible from a central unit anywhere and at any time via internet. We have divided the tasks and have one node for alpha control, another for delta control, one for the dome, one for the focus and the central unit to interface with a pc. The nodes for alpha, delta and the dome will be used by means of FPGAs in order to efficiently sample the encoders and the control algorithms, and to generate the output for the motors and the servo. The focus will have a microcontroller, and the system is easy to expand in the event of the inclusion of more nodes. After having studied several fieldbus systems, we have opted for the CAN bus, because of its reliability and broadcasting possibilities. In this way, all the important information will be on the bus, and every node will be able to access the information at any time. This document explains the new design made in the IAA for the new consoles of control whose basic characteristics are, the distributed control, the hardware simplify, the cable remove, the safety and maintenance improve and facilitating the observation improving the interface with the user, and finally to prepare the system for the remote observation.