scholarly journals In Situ Measurements of Interstellar Dust

1997 ◽  
Vol 166 ◽  
pp. 381-384 ◽  
Author(s):  
M. Landgraf ◽  
E. Grün
Keyword(s):  
Mass Distribution ◽  
Interstellar Dust ◽  
Interstellar Cloud ◽  
In Situ Measurements ◽  
Mass Ratio ◽  
Interstellar Grains ◽  
Local Interstellar Cloud ◽  
Size Interval

AbstractWe present the mass distribution of interstellar grains measured in situ by the Galileo and Ulysses space probes as cumulative flux. The derived in situ mass distribution per logarithmic size interval is compared to the distribution determined by fitting extinction measurements. Large grains measured in situ contribute significantly to the overall mass of dust in the local interstellar cloud. The problem of a dust-to-gas mass ratio that contradicts cosmic abundances is discussed.

The Philae Lander reveals the presence of low strength primitive ice inside cometary boulders

2021 ◽  
Author(s):  
Laurence O'Rourke ◽  
Keyword(s):  
Compressive Strength ◽  
In Situ Measurements ◽  
Mass Ratio ◽  
Water Ice ◽  
Low Strength ◽  
Rich Material ◽  
Local Dust ◽  
Comet 67P ◽  
Deep Impression

<p>On the 12 November 2014, the Philae lander descended towards comet 67P/Churyumov–Gerasimenko, bounced twice off the surface, finally arriving under an overhanging cliff in the Abydos region. In this study (published in Nature on 28th Oct 2020), we present the results of our investigation of a previously undiscovered site of the second touchdown, where Philae spent almost two minutes of its cross-comet journey, producing four distinct surface contacts on two adjoining cometary boulders. It exposed primitive water ice —that is, water ice from the time of the comet’s formation 4.5 billion years ago — in their interiors while travelling through a crevice between the boulders. Our multi-instrument observations made 19 months later found that this water ice, mixed with ubiquitous dark organic-rich material, has a local dust/ice mass ratio of 2.3 +0.2/−0.16 : 1 , matching values previously observed in freshly exposed water ice from outbursts and water ice in shadow. At the end of the crevice, Philae fell forward and left a 0.25-metre-deep impression in the boulder ice, providing in situ measurements confirming that primitive ice has a very low compressive strength (less than 12 pascals, softer than freshly fallen light snow) and allowing a key estimation to be made of the porosity (75 ± 7 per cent) of the boulders’ icy interiors. Our results provide constraints for cometary landers that seek to access a volatile-rich ice sample. </p>

In situ measurements of interstellar dust with the Ulysses and Galileo spaceprobes

1996 ◽  
Vol 78 (1-2) ◽  
pp. 165-172 ◽  
Author(s):  
Michael Baguhl ◽  
Eberhard Gr�n ◽  
Markus Landgraf
Keyword(s):  
Interstellar Dust ◽  
In Situ Measurements

The Carbon:²³⁴Thorium ratios of sinking particles in the California Current Ecosystem 2: Examination of a thorium sorption, desorption, and particle transport model

2019 ◽  
Author(s):  
Michael Stukel ◽  
Thomas Kelly
Keyword(s):  
Organic Carbon ◽  
Water Column ◽  
Particulate Organic Carbon ◽  
Transport Model ◽  
California Current ◽  
In Situ Measurements ◽  
Power Law Distribution ◽  
Sinking Particles ◽  
Organic Carbon Concentration

Thorium-234 (234Th) is a powerful tracer of particle dynamics and the biological pump in the surface ocean; however, variability in carbon:thorium ratios of sinking particles adds substantial uncertainty to estimates of organic carbon export. We coupled a mechanistic thorium sorption and desorption model to a one-dimensional particle sinking model that uses realistic particle settling velocity spectra. The model generates estimates of 238U-234Th disequilibrium, particulate organic carbon concentration, and the C:234Th ratio of sinking particles, which are then compared to in situ measurements from quasi-Lagrangian studies conducted on six cruises in the California Current Ecosystem. Broad patterns observed in in situ measurements, including decreasing C:234Th ratios with depth and a strong correlation between sinking C:234Th and the ratio of vertically-integrated particulate organic carbon (POC) to vertically-integrated total water column 234Th, were accurately recovered by models assuming either a power law distribution of sinking speeds or a double log normal distribution of sinking speeds. Simulations suggested that the observed decrease in C:234Th with depth may be driven by preferential remineralization of carbon by particle-attached microbes. However, an alternate model structure featuring complete consumption and/or disaggregation of particles by mesozooplankton (e.g. no preferential remineralization of carbon) was also able to simulate decreasing C:234Th with depth (although the decrease was weaker), driven by 234Th adsorption onto slowly sinking particles. Model results also suggest that during bloom decays C:234Th ratios of sinking particles should be higher than expected (based on contemporaneous water column POC), because high settling velocities minimize carbon remineralization during sinking.

Evaluation of reanalysis and satellite-based sea surface winds using in situ measurements from Chinese Antarctic Expeditions

2013 ◽  
Vol 24 (3) ◽  
pp. 147
Author(s):  
Ming LI ◽  
Qinghua YANG ◽  
Jiechen ZHAO ◽  
Lin ZHANG ◽  
Chunhua LI ◽  
...  
Keyword(s):  
In Situ Measurements ◽  
Sea Surface ◽  
Surface Winds ◽  
Sea Surface Winds
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