The rubble-pile asteroid Itokawa as observed by Hayabusa

During the interval from September through early December 2005, the Hayabusa spacecraft was in close proximity to near-Earth asteroid 25143 Itokawa, and a variety of data were taken on its shape, mass, and surface topography as well as its mineralogic and elemental abundances. The asteroid's orthogonal axes are 535, 294, and 209 meters, the mass is 3.51 x 10(10) kilograms, and the estimated bulk density is 1.9 +/- 0.13 grams per cubic centimeter. The correspondence between the smooth areas on the surface (Muses Sea and Sagamihara) and the gravitationally low regions suggests mass movement and an effective resurfacing process by impact jolting. Itokawa is considered to be a rubble-pile body because of its low bulk density, high porosity, boulder-rich appearance, and shape. The existence of very large boulders and pillars suggests an early collisional breakup of a preexisting parent asteroid followed by a re-agglomeration into a rubble-pile object.     

Detailed images of asteroid 25143 Itokawa from Hayabusa

Rendezvous of the Japanese spacecraft Hayabusa with the near-Earth asteroid 25143 Itokawa took place during the interval September through November 2005. The onboard camera imaged the solid surface of this tiny asteroid (535 meters by 294 meters by 209 meters) with a spatial resolution of 70 centimeters per pixel, revealing diverse surface morphologies. Unlike previously explored asteroids, the surface of Itokawa reveals both rough and smooth terrains. Craters generally show unclear morphologies. Numerous boulders on Itokawa's surface suggest a rubble-pile structure.     

Near-infrared spectral results of asteroid Itokawa from the Hayabusa spacecraft

The near-infrared spectrometer on board the Japanese Hayabusa spacecraft found a variation of more than 10% in albedo and absorption band depth in the surface reflectance of asteroid 25143 Itokawa. Spectral shape over the 1-micrometer absorption band indicates that the surface of this body has an olivine-rich mineral assemblage potentially similar to that of LL5 or LL6 chondrites. Diversity in the physical condition of Itokawa's surface appears to be larger than for other S-type asteroids previously explored by spacecraft, such as 433 Eros.     

Mass and local topography measurements of Itokawa by Hayabusa

The ranging instrument aboard the Hayabusa spacecraft measured the surface topography of asteroid 25143 Itokawa and its mass. A typical rough area is similar in roughness to debris located on the interior wall of a large crater on asteroid 433 Eros, which suggests a surface structure on Itokawa similar to crater ejecta on Eros. The mass of Itokawa was estimated as (3.58 +/- 0.18) x 10(10) kilograms, implying a bulk density of (1.95 +/- 0.14) grams per cubic centimeter for a volume of (1.84 +/- 0.09) x 10(7) cubic meters and a bulk porosity of approximately 40%, which is similar to that of angular sands, when assuming an LL (low iron chondritic) meteorite composition. Combined with surface observations, these data indicate that Itokawa is the first subkilometer-sized small asteroid showing a rubble-pile body rather than a solid monolithic asteroid.     

Oxygen isotopic compositions of asteroidal materials returned from Itokawa by the Hayabusa mission

Meteorite studies suggest that each solar system object has a unique oxygen isotopic composition. Chondrites, the most primitive of meteorites, have been believed to be derived from asteroids, but oxygen isotopic compositions of asteroids themselves have not been established. We measured, using secondary ion mass spectrometry, oxygen isotopic compositions of rock particles from asteroid 25143 Itokawa returned by the Hayabusa spacecraft. Compositions of the particles are depleted in (16)O relative to terrestrial materials and indicate that Itokawa, an S-type asteroid, is one of the sources of the LL or L group of equilibrated ordinary chondrites. This is a direct oxygen-isotope link between chondrites and their parent asteroid.     

Touchdown of the Hayabusa spacecraft at the Muses Sea on Itokawa

After global observations of asteroid 25143 Itokawa by the Hayabusa spacecraft, we selected the smooth terrain of the Muses Sea for two touchdowns carried out on 19 and 25 November 2005 UTC for the first asteroid sample collection with an impact sampling mechanism. Here, we report initial findings about geological features, surface condition, regolith grain size, compositional variation, and constraints on the physical properties of this site by using both scientific and housekeeping data during the descent sequence of the first touchdown. Close-up images revealed the first touchdown site as a regolith field densely filled with size-sorted, millimeter- to centimeter-sized grains.     

Regolith migration and sorting on asteroid Itokawa

High-resolution images of the surface of asteroid Itokawa from the Hayabusa mission reveal it to be covered with unconsolidated millimeter-sized and larger gravels. Locations and morphologic characteristics of this gravel indicate that Itokawa has experienced considerable vibrations, which have triggered global-scale granular processes in its dry, vacuum, microgravity environment. These processes likely include granular convection, landslide-like granular migrations, and particle sorting, resulting in the segregation of the fine gravels into areas of potential lows. Granular processes become major resurfacing processes because of Itokawa's small size, implying that they can occur on other small asteroids should those have regolith.     

Three-dimensional structure of Hayabusa samples: origin and evolution of Itokawa regolith

Regolith particles on the asteroid Itokawa were recovered by the Hayabusa mission. Their three-dimensional (3D) structure and other properties, revealed by x-ray microtomography, provide information on regolith formation. Modal abundances of minerals, bulk density (3.4 grams per cubic centimeter), and the 3D textures indicate that the particles represent a mixture of equilibrated and less-equilibrated LL chondrite materials. Evidence for melting was not seen on any of the particles. Some particles have rounded edges. Overall, the particles' size and shape are different from those seen in particles from the lunar regolith. These features suggest that meteoroid impacts on the asteroid surface primarily form much of the regolith particle, and that seismic-induced grain motion in the smooth terrain abrades them over time.     

Neutron activation analysis of a particle returned from asteroid Itokawa

A single grain (~3 micrograms) returned by the Hayabusa spacecraft was analyzed by neutron activation analysis. This grain is mainly composed of olivine with minor amounts of plagioclase, troilite, and metal. Our results establish that the Itokawa sample has similar chemical characteristics (iron/scandium and nickel/cobalt ratios) to chondrites, confirming that this grain is extraterrestrial in origin and has primitive chemical compositions. Estimated iridium/nickel and iridium/cobalt ratios for metal in the Itokawa samples are about five times lower than CI carbonaceous chondrite values. A similar depletion of iridium was observed in chondrule metals of ordinary chondrites. These metals must have condensed from the nebular where refractory siderophile elements already condensed and were segregated.     

Irradiation history of Itokawa regolith material deduced from noble gases in the Hayabusa samples

Noble gas isotopes were measured in three rocky grains from asteroid Itokawa to elucidate a history of irradiation from cosmic rays and solar wind on its surface. Large amounts of solar helium (He), neon (Ne), and argon (Ar) trapped in various depths in the grains were observed, which can be explained by multiple implantations of solar wind particles into the grains, combined with preferential He loss caused by frictional wear of space-weathered rims on the grains. Short residence time of less than 8 million years was implied for the grains by an estimate on cosmic-ray-produced (21)Ne. Our results suggest that Itokawa is continuously losing its surface materials into space at a rate of tens of centimeters per million years. The lifetime of Itokawa should be much shorter than the age of our solar system.     

分子荧光法对水中氨氮含量的测定

采用分子荧光法对水中氨氮含量进行了测定,在硼酸缓冲液作用下,邻苯二甲醛(OPA)与氨氮反应,生成具有荧光性的物质,在一定的pH、反应温度和静置时间条件下,以362 nm为激发波长,在425 nm发射波长处测定荧光物质的荧光强度,探究了四硼酸钠、亚硫酸钠和OPA混合溶液配比、反应温度、静置时间对衍生物荧光值的影响。结果表明,在一定浓度范围内,衍生物的量与荧光强度有良好的线性关系,该方法灵敏度高,适用于氨氮浓度较低水样的测定,对于高浓度水样也可进行简单稀释后测定。     

原子荧光光谱法测定土壤中Hg含量

介绍应用AFS－220双道原子荧光光谱法测定土壤中Hg的方法，样品经王水消解后，以0．7％KBH4为还原剂，测定Hg的含量，其最低检出限为：0．09ng/ml。     

饲料中硒的测定-氢化物发生原子荧光光谱法

采用原子荧光光谱法测定饲料中的硒。结果表明,用硝酸和高氯酸对试样进行消化,用6mol·L-1的盐酸对试样进行还原,通过氢化物发生原子荧光光谱法对饲料中的硒进行测定,样品、质控样、添加回收测得值准确可靠。在0~50μg·L-1的浓度下,硒的浓度和荧光强度呈良好的线性关系,相关系数达到0.9999,测得数据结果RSD小于5.08%,加标回收率处于96.0%~109.0%之间,方法线性范围宽,稳定性好,灵敏度高。     

X-ray fluorescence analysis in biology

Our efforts to understand the important biological roles of many "minor" elements are limited by the capabilities of the existing instruments. X-ray fluorescence analysis is not the most sensitive method for the assay of minor elements, but it is the instrumental technique of choice both for certain clinical studies and for certain research problems. The technique will be more widely used as it becomes more widely known (25).     

微波萃取-原子荧光光谱法测定稻米中砷化学形态

采用微波萃取、高效液相色谱-氢化物发生-原子荧光光谱法联用技术建立了稻米中了三价砷As(Ⅲ)、五价砷As(V)、一甲基砷酸(MMA)、二甲基砷酸(DMA)等4种形态砷的分析方法。结果表明,稻米中4种形态砷的加标回收率为80%～110%,批内及批间相对标准偏差为0.3%～4.8%,方法检出限为1.6~4.0μg/kg。将该方法应用于实际样品的测定,分析结果显示,稻米样品中含有一定量的三价砷As(Ⅲ)和少量的二甲基砷酸(DMA),其形态之和已接近我国国标中关于稻米产品中砷限量标准的规定。     

The elemental composition of asteroid 433 eros: results of the NEAR-shoemaker X-ray spectrometer

We report major element composition ratios for regions of the asteroid 433 Eros imaged during two solar flares and quiet sun conditions during the period of May to July 2000. Low aluminum abundances for all regions argue against global differentiation of Eros. Magnesium/silicon, aluminum/silicon, calcium/silicon, and iron/silicon ratios are best interpreted as a relatively primitive, chondritic composition. Marked depletions in sulfur and possible aluminum and calcium depletions, relative to ordinary chondrites, may represent signatures of limited partial melting or impact volatilization.     

土壤中汞的检测-氢化物发生原子荧光法

采用盐酸—硝酸消化—原子荧光光谱法检测土壤样品中汞的含量,选择了仪器工作参数;研究了载气流速、硼氢化钾浓度等测试条件对检测的影响;分析了土壤标准样。结果表明:原子荧光法具有数据准确、精密度高、简便、高效、适用性强的特点,可用于土壤中微量汞的检测。     

氢化物发生-原子荧光光谱法测定水产饲料中的痕量砷

探讨氢化物发生-原子荧光光谱法测定水产饲料中痕量砷的方法,此法的检出限为0．01 mg·kg-1,相对标准偏差为2．9％,线性范围为0-100 μg·L-1,相关系数为0．999 9．回收率90．5％-104．0％。     

Pole and global shape of 25143 Itokawa

The locations of the pole and rotation axis of asteroid 25143 Itokawa were derived from Asteroid Multiband Imaging Camera data on the Hayabusa spacecraft. The retrograde pole orientation had a right ascension of 90.53 degrees and a declination of -66.30 degrees (52000 equinox) or equivalently 128.5 degrees and -89.66 degrees in ecliptic coordinates with a 3.9 degrees margin of error. The surface area is 0.393 square kilometers, the volume is 0.018378 cubic kilometers with a 5% margin of error, and the three axis lengths are 535 meters by 294 meters by 209 meters. The global Itokawa revealed a boomerang-shaped appearance composed of two distinct parts with partly faceted regions and a constricted ring structure.