2002 Kuiper prize lecture: Dust Astronomy

Dust particles, like photons, carry information from remote sites in space and time. From knowledge of the dust particles' birthplace and their bulk properties, we can learn about the remote environment out of which the particles were formed. This approach is called “Dust Astronomy” which is carried out by means of a dust telescope on a Dust Observatory in space. Targets for a dust telescope are the local interstellar medium and nearby star forming regions, as well as comets and asteroids. Dust from interstellar and interplanetary sources is distinguished by accurately sensing their trajectories. Trajectory sensors may use the electric charge signals that are induced when charged grains fly through the detector. Modern in-situ dust impact detectors are capable of providing mass, speed, physical and chemical information of dust grains in space. A Dust Observatory mission is feasible with state-of-the-art technology. It will (1) provide the distinction between interstellar dust and interplanetary dust of cometary and asteroidal origin, (2) determine the elemental composition of impacting dust particles, and (3) monitor the fluxes of various dust components as a function of direction and particle masses.     

The fossil phase in the life of a galaxy group

We investigate the origin and evolution of fossil groups in a concordance ΛCDM cosmological simulation. We consider haloes with masses between  1 × 10¹³  and  5 × 10¹³  h ⁻¹ M_⊙  , and study the physical mechanisms that lead to the formation of the large gap in magnitude between the brightest and the second most bright group member, which is typical for these fossil systems. Fossil groups are found to have high dark matter concentrations, which we can relate to their early formation time. The large magnitude gaps arise after the groups have built up half of their final mass, due to merging of massive group members. We show that the existence of fossil systems is primarily driven by the relatively early infall of massive satellites, and that we do not find a strong environmental dependence for these systems. In addition, we find tentative evidence for fossil group satellites falling in on orbits with typically lower angular momentum, which might lead to a more efficient merger on to the host. We find a population of groups at higher redshifts that go through a 'fossil phase': a stage where they show a large magnitude gap, which is terminated by renewed infall from their environment.     

The role of the wind-transported dust in slope streaks activity: Evidence from the HRSC data

Slope streaks are gravity-driven albedo features observed on martian slopes since the Viking missions. The debated mechanism of formation could involve alternatively dry granular flow or wet mass wasting. A systematic mapping of slope streaks from the High Resolution Stereo Camera is presented in this paper. Two regions known for their slope streaks activity have been studied, the first one is located close to Cerberus lava flow, and the second one is inside the Olympus Mons Aureole. The statistics of slope streaks shapes measured from orthorectified images confirm previous results from Mars Orbiter Camera surveys. Preferential orientations of slope streaks are reported. Slope streaks occur preferentially on west facing slopes at latitudes lower than 30° N for Olympus and on south-west facing slopes for Cerberus. Wind directions derived from a General Circulation Model during the dusty season correlate with these orientations. Furthermore, west facing slopes at Olympus have a thicker dust cover. These observations indicate that slope streaks are dust avalanches controlled by the preferential accumulation of dust in the downstream side of the wind flow. The paucity of slope streaks at high latitudes and their preferential orientation on south-facing slopes have been presented as an evidence for a potential role of H₂O phase transition in triggering or flow. The potential role of H₂O cannot be ruled out from our observations but the dust avalanche model together with the atmospheric circulation could potentially explain all observations. The role of H₂O might be limited to a stabilizing effect of dust deposits on northward facing slopes at intermediate latitudes (30° N-33° N) and on all slopes further north.     

Possible long-term decline in impact rates: 1. Martian geological data

Quantin et al. [Quantin, C., Allemand, P., Mangold, N., Delacourt, C., 2004a. Icarus 172, 555-572] tabulated crater count data for 56 landslides along the walls of Valles Marineris. Under the assumption of a constant cratering rate after about 3 Gyr ago, as used in the 1999-2005 iterations of the crater chronology isochron system of Hartmann, and in the Hartmann and Neukum system, these data indicate a regularly increasing rate of landslides, which would be difficult to explain. We suggest that these data may support a decline in inner Solar System cratering rates by about a factor of 3 since 3 Gyr ago, not unlike predictions based on asteroid belt collision models. Such a decline is also supported by our review of data on lunar impact melts and glass spherules in a companion paper [Hartmann, W.K., Quantin, C., Mangold, N., 2007. Icarus 186, 11-23]. Such models produce not only a more uniform rate of landslides over the last 3 Gyr, but also a more uniform rate of resurfacing processes which also had an apparent increase under the assumption of a constant cratering rate.     

Travel times of seepage water through multilayered covering systems for hazardous waste sites

In a field experiment station near Frankfurt am Main, West Germany, a three-layer covering system was constructed in order to evaluate the amount of seepage water through clay barrier systems and their long-term effectiveness. The test area is equipped with two large-scale lysimeters, excess tubes for neutron-moisture and gamma-gamma-density measurements, tensiometers, surface runoff and drain discharge recorders as well as with meteorological instruments.The results of the three-year observation period give a complete impression of the infiltration and seepage processes within the different covering layers. With the help of hydrochemical and isotopical analyses as well as with tracer experiments the velocity of the soil water was determined. Three major waterpaths were found in the vadose zone of the vegetation support layer as well as in the saturated zone of the barrier layer. Very low velocities follow the matrix porosity of the soil. High velocities occur along preferential waterpaths which follow inhomogenities within the soil. Minor parts of the lysimeter outflow react directly to the precipitation inflow and therefore reveal, that unretarded flowpaths exist as well.These results lead to the conclusion that a heterogeneous flow is predominant in clay liners even under distinctive conditions. This has consequences on the applicability of hydraulic equations, as well as on the prediction of tightening effects of clay barriers.     

Effects of area under‐estimations of sloped mountain terrain on simulated hydrological behaviour: a case study using the ACRU model

Sloped areas calculated from a GIS raster file, such as a digital elevation model, are smaller than the true surface area, because they are projected to a planimetric plane. In mountainous regions this sloped area under‐estimation (SAUE) can have significant consequences on hydrological calculations. A sensitivity analysis is conducted, using the ACRU agro‐hydrological modelling system in a small watershed in Glacier National Park, Montana, USA, to investigate the sensitivity of the SAUE on key elements of the hydrological cycle, including precipitation depth, April snow depth, August soil moisture deficit, actual evapotranspiration depth, and runoff depth. The sensitivity analysis is based on 224 unique combinations of slope, soil and land cover types, elevation with associated precipitation depths, and north and south facing radiation regimes. Results revealed an increasing influence of the SAUE on all hydrological processes with increasing slope steepness. Distinct differences and magnitudes between different land cover types, different elevations, and, in particular, different exposition were quantified. Actual evapotranspiration increases with SAUE, while runoff decreases. April soil water is simulated to decrease with an increase in SAUE. Finally, a comparison of a streamflow simulation of a small and steep alpine watershed with and without consideration of the SAUE is carried out. The sloped area of the small watershed is under‐estimated by 20·9%, and the difference in simulated runoff is 12·3%. When the SAUE was not considered, runoff was simulated to be higher, the associated coefficient of determination was slightly lower, and the slope of the regression line was flatter. Copyright © 2010 John Wiley & Sons, Ltd.     

Artisanal fishers' perceptions regarding coastal co-management policies in Chile and their potentials to scale-up marine biodiversity conservation

No-take Marine Protected Areas (Nt-MPAs) constitute an indispensable tool for biodiversity conservation. Nevertheless, there are other instruments such as marine coastal co-management policy frameworks which may be also considered as tools for conservation or as ancillary conservation instruments. Using focus groups, semi-structured interviews and survey questionnaires we analysed small-scale artisanal fishers' perceptions towards a coastal co-management regime in Chile and the potential to generate capacities and a social setting to scale-up marine conservation. Empirical evidence from the study shows artisanal fishers have indeed been empowered through the coastal co-management experience; however, there exist heterogeneity in their willingness to participate in the creation of Nt-MPAs, mainly determined by occupational mobility. Chilean artisanal fishers strongly support a bottom-up process in the conservation of marine biodiversity, though the need for top-down steering and guidance is also stressed, especially regarding enforcement.     

Tidal exchange between a freshwater tidal marsh and an impacted estuary: the Scheldt estuary, Belgium

Tidal marsh exchange studies are relatively simple tools to investigate the interaction between tidal marshes and estuaries. They have mostly been confined to only a few elements and to saltwater or brackish systems. This study presents mass-balance results of an integrated one year campaign in a freshwater tidal marsh along the Scheldt estuary (Belgium), covering oxygen, nutrients (N, P and Si), carbon, chlorophyll, suspended matter, chloride and sulfate. The role of seepage from the marsh was also investigated. A ranking between the parameters revealed that oxygenation was the strongest effect of the marsh on the estuarine water. Particulate parameters showed overall import. Export of dissolved silica (DSi) was more important than exchange of any other nutrient form. Export of DSi and import of total dissolved nitrogen (DIN) nevertheless contributed about equally to the increase of the Si:N ratio in the seepage water. The marsh had a counteracting effect on the long term trend of nutrient ratios in the estuary.