Low velocity impacts into dust: results from the COLLIDE-2 microgravity experiment     

Joshua E. Colwell 《Icarus》2003,164(1):188-196

We present the results of the second flight of the Collisions Into Dust Experiment (COLLIDE-2), a space shuttle payload that performs six impact experiments into simulated planetary regolith at speeds between 1 and 100 cm/s. COLLIDE-2 flew on the STS-108 mission in December 2001 following an initial flight in April 1998. The experiment was modified since the first flight to provide higher quality data, and the impact parameters were varied. Spherical quartz projectiles of 1-cm radius were launched into quartz sand and JSC-1 lunar regolith simulant targets 2-cm deep. At impact speeds below ∼20 cm/s the projectile embedded itself in the target material and did not rebound. Some ejecta were produced at ∼10 cm/s. At speeds >25 cm/s the projectile rebounded and significant ejecta was produced. We present coefficients of restitution, ejecta velocities, and limits on ejecta masses. Ejecta velocities are typically less than 10% of the impact velocity, and the fraction of impact kinetic energy partitioned into ejecta kinetic energy is also less than 10%. Taken together with a proposed aerodynamic planetesimal growth mechanism, these results support planetesimal growth at impact speeds above the nominal observed threshold of about 20 cm/s.  相似文献   

Magnetic aggregation: II. Laboratory and microgravity experiments     

Henrik Nübold  Torsten Poppe  Carsten Dominik 《Icarus》2003,165(1):195-214

In a previous publication (Dominik and Nübold, 2002, Icarus 157, 173-186), we presented analytical expressions and theoretical considerations concerning preplanetary dust aggregation with magnetized grains in the solar nebula. The present work is dedicated to the experimental study of magnetic aggregation in a ground-based laboratory as well as under microgravity conditions on parabolic flights. We conducted aggregation experiments with dust analogues in order to study the temporal evolution and the structural outcome of grain growth processes dominated by or comprising exclusively magnetic grains. Within aggregation times ranging from a couple of seconds to a few minutes only, formation of huge chain-like and/or web-like dust aggregates was observed. After aggregate retrieval we were able to study the sizes and structures of the aggregates in great detail. We established the fractal dimension of the aggregates as D_fs=1.20±0.05 for single chains and D_fc=1.50±0.21 for inter-connected web-like structures. This is considerably lower than for non-magnetic grain growth. The dynamic exponent z for the mass increase with time according to t^z was found to be z=2.7 from in-situ video images of the microgravity aggregation runs. The results are compared with the theoretical considerations presented earlier as well as with previous experimental work on the same and on related topics, respectively.  相似文献   

Two Different Dust Storms in Northeast China:the Sources and Influences in East Asia     

Ke Hu  Yuying Liu  Zhen Cao 《东北亚地学研究》2003,(1)

Dust storms in Northeast China become more se-rious in recent years due to the global warming and local land use and cover change (LUCC) around the sand lands in western and northwestern Jilin Province. Field investigations and urban testing re-vealed that the amount of dusts brought by dust storm reaches a higher level in the past two years. According to an experiment on the “mud-snow”in April, 2000 and an observation in March, 2002, the dusts coming from the western Jilin and fall…  相似文献   

Properties of simulated cosmic matters after gamma-ray and neutron irradiation     

K. Koike  M. Nakagawa  H. Chihara  M. Okada  T. Awata  J. Takada 《Planetary and Space Science》2006,54(4):325-330

Interstellar and circumstellar matter is known to be strongly irradiated by cosmic radiation and several types of cosmic ray particles. The effects of irradiation on simulated interstellar and circumstellar matter such as CaCO₃, MgCO₃, SiO₂ and Al₂O₃ are investigated. Especially, thermoluminescence (TL) spectra after γ-ray and neutron irradiation are compared carefully. It is shown that the thermoluminescence after neutron irradiation appears significantly in the wavelength of blue region. On the reflectance in infrared region, the irradiation effect appears scarcely.  相似文献   

Influence of plasma on formation of crystalline Fe₂SiO₄ grains     

T. Sato  M. Kurumada  O. Kido  M. Shintaku  Y. Saito 《Planetary and Space Science》2006,54(6):612-616

The production of Fe₂SiO₄ (fayalite) crystalline grains was performed by two processes, namely, grain formation in a plasma field by evaporating a mixture powder of Fe and SiO and heat treatment of the product collected on the radio-frequency (RF) electrode side. Fe grains <20 nm in size covered with an amorphous SiO layer selectively formed Fe₂SiO₄ grains by heating at 800 °C. By heating at 600 °C, in addition to the formation of Fe₂SiO₄ crystal grains, the FeO phase appeared. The doping effect of excited oxygen in a plasma field into the Fe small grains may be the trigger on the formation of fayalite through the FeO phase formation. The present experimental result suggests that the probability of Fe₂SiO₄ grain formation in space is low.  相似文献   

A miniature laser anemometer for measurement of wind speed and dust suspension on Mars     

J.P. Merrison  H.P. Gunnlaugsson  J. Jensen  K. Kinch  P. Nørnberg  K.R. Rasmussen 《Planetary and Space Science》2004,52(13):1177-1186

Suspended dust is a dominant component of the Martian environment. It has a major influence on atmospheric circulation and it is deposited widely over the planetary surface causing a serious hazard to instrumentation. In order to study dust transport, quantification of the wind flow and dust concentration are vital. A simple laser-based anemometer system is presented that is able to measure suspended dust grain velocity and turbulence from a landed spacecraft. This system has advantages over other techniques of wind speed determination in being insensitive to contamination or atmospheric conditions such as temperature, pressure or composition. For the first time it would allow direct measurement of the suspended dust concentration on Mars. A prototype instrument has been constructed and successfully tested in a wind tunnel facility under simulated Martian conditions. The optics are simple in design, light weight and the instrument has low power consumption. It is also robust and the output signal is easily interpreted, producing only a small data volume. Future improvements will be discussed, specifically modification to measure wind direction, the possibility of obtaining information about dust grain size and the construction of a flight model.  相似文献   

A review on East Asian dust storm climate, modelling and monitoring   总被引：8，自引：1，他引：7  

Y. Shao  C.H. Dong 《Global and Planetary Change》2006,52(1-4):1

In arid and semi-arid area of Asia, dust storms occur frequently. Asian dust storms have a major impact on the air quality of the densely populated areas of China, Korea and Japan, and are important to the global dust cycle. In extreme cases, they result in the loss of human lives and disruptions of social and economic activities. In recent years, systematic research on Asian dust storms has been carried out. Much progress has been made in the development of integrated dust storm monitoring and modeling systems by making use of advanced numerical models, satellite remote sensing and GIS data. In this paper, we summarize the recent achievements in Asian dust storm research with an emphasis on dust climatology, modeling and satellite monitoring. The concept of integrated dust storm monitoring and modeling system is described and a summary of the developments in key research areas is given, including new dust models and techniques in satellite remote sensing and system integration. We then discuss the current research frontiers and the challenges for future studies.  相似文献   

Correlations Between Biogenic Components and Dust Input and Their Change Mechanism on Hess Rise,Central North Pacific,During the Late Quaternary*     

Defang You  Rujian Wang  Wenshen Xiao 《地球科学进展》2018,33(11):1203-1214

The study of marine export production is helpful to trace the changes of oceanic and global carbon reservoirs. Dust input is an important factor inspiring marine export production. Measurements of carbonate, Opal, TOC and C_org/N were performed on Core SO202-37-2, which was retrieved from Hess Rise, central North Pacific during the German SO202-INOPEX Expedition, for reconstructing variations of the local export production and dust input. The core age model is constructed via morphologically correlating its foraminifer oxygen isotope record with those of Core H3571 and the LR04 stack. XRF-Ti/Ca can be used as a proxy for dust input and its distribution pattern is consistent with that of Opal content, possibly indicating that dust input may have affected the local export production, i.e. the local export production increased (decreased) with enhancing (declining) dust input during interglacial (glacial) periods. Fluctuations in dust input might be due to southward/northward migration of the Westerly Jet over the dust source regions during interglacial and glacial periods. Although global dust output increased during glacial periods, meridional migration of the Westerly Jet in this area made the distribution pattern of the dust deposition in the study area different from that of other areas.  相似文献   

Observational limits on intergalactic matter     

Bogdan Wszolek 《Astrophysics and Space Science》1995,227(1-2):151-155

Intergalactic gas and dust are very difficult to detect. Several methods to detect intergalactic gas have been developed. The results of these methods have provided qualitative arguments and quantitative limits on the amount of intergalactic matter in the intergalactic environment. We present here arguments as to why the density of intergalactic matter is higher than previously thought possible.  相似文献   

塔里木盆地沙尘暴卫星云图特征分析   总被引：5，自引：0，他引：5  

徐希慧 《干旱气象》1997,(2)

利用美国ＮＯＡＡ－Ｎ系列卫星１９７８—１９８７年的云图资料和近几年的遥感图像资料，对塔里木盆地沙尘暴的卫星云图特征进行分析，对沙漠沙尘暴的时空分布特征进行探讨。  相似文献