NEAR's flyby of 253 mathilde: images of a C asteroid

On 27 June 1997, the Near Earth Asteroid Rendezvous (NEAR) spacecraft flew within 1212 kilometers of asteroid 253 Mathilde. Mathilde is an irregular, heavily cratered body measuring 66 kilometers by 48 kilometers by 46 kilometers. The asteroid's surface is dark (estimated albedo between 0.035 and 0.050) and similar in color to some CM carbonaceous chondrites. No albedo or color variations were detected. The volume derived from the images and the mass from Doppler tracking of the spacecraft yield a mean density of 1.3 +/- 0.2 grams per cubic centimeter, about half that of CM chondrites, indicating a porous interior structure.     

Radio science results during the NEAR-shoemaker spacecraft rendezvous with eros

We determined the mass of asteroid 433 Eros, its lower order gravitational harmonics, and rotation state, using ground-based Doppler and range tracking of the Near Earth Asteroid Rendezvous (NEAR)-Shoemaker spacecraft and images of the asteroid's surface landmarks. The mass of Eros is (6.687 +/- 0.003) x 10(18) grams, which, coupled with our volume estimate, implies a bulk density of 2. 67 +/- 0.03 grams per cubic centimeter. The asteroid appears to have a uniform density distribution. The right ascension and declination of the rotation pole are 11.37 +/- 0.05 and 17.22 +/- 0.05 degrees, respectively, and at least over the short term, the rotation state of Eros is stable with no measurable free precession of the spin pole. Escape velocities on the surface vary from 3.1 to 17.2 meters per second. The dynamical environment of Eros suggests that it is covered with regolith and that one might expect material transport toward the deepest potential wells in the saddle and 5.5-kilometer crater regions.     

PLANETARY SCIENCE: Most-Common Meteorites Find a Home Among the Asteroids

Meteoriticists have long been puzzled by the fact that the most common meteorites, so-called ordinary chondrites, don't appear to have come from the most common asteroids, the S-types. Last week, however, a group of researchers attending the spring meeting of the American Geophysical Union here announced that the 31-kilometer-long S-type asteroid Eros now being orbited by the NEAR Shoemaker spacecraft is made of the same stuff as ordinary chondrites. That conclusion comes from NEAR Shoemaker's first-ever analysis of the elemental composition of an asteroid.     

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.     

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.     

Images of asteroid 21 Lutetia: a remnant planetesimal from the early Solar System

Images obtained by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) cameras onboard the Rosetta spacecraft reveal that asteroid 21 Lutetia has a complex geology and one of the highest asteroid densities measured so far, 3.4 ± 0.3 grams per cubic centimeter. The north pole region is covered by a thick layer of regolith, which is seen to flow in major landslides associated with albedo variation. Its geologically complex surface, ancient surface age, and high density suggest that Lutetia is most likely a primordial planetesimal. This contrasts with smaller asteroids visited by previous spacecraft, which are probably shattered bodies, fragments of larger parents, or reaccumulated rubble piles.     

Imaging of small-scale features on 433 Eros from NEAR: evidence for a complex regolith

On 25 October 2000, the Near Earth Asteroid Rendevous (NEAR)-Shoemaker spacecraft executed a low-altitude flyover of asteroid 433 Eros, making it possible to image the surface at a resolution of about 1 meter per pixel. The images reveal an evolved surface distinguished by an abundance of ejecta blocks, a dearth of small craters, and smooth material infilling some topographic lows. The subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter-sized blocks.     

Lunar surface material: spacecraft measurements of density and strength

The relation of the density of the lunar surface layer to depth is probably best determined from spacecraft measurements of the bearing capacity as a function of depth. A comparison of these values with laboratory measurements of the bearing capacity of low-cohesion particulate materials as a function of the percentage of solid indicates that the bulk density at the lunar surface is about 1.1 grams per cubic centimeter and that it increases nearly linearly to about 1.6 grams per cubic centimeter at a depth of 5 centimeters.     

A direct measurement of the terrestrial mass accretion rate of cosmic dust

The mass of extraterrestrial material accreted by the Earth as submillimeter particles has not previously been measured with a single direct and precise technique that samples the particle sizes representing most of that mass. The flux of meteoroids in the mass range 10(-9) to 10(-4) grams has now been determined from an examination of hypervelocity impact craters on the space-facing end of the Long Duration Exposure Facility satellite. The meteoroid mass distribution peaks near 1.5 x 10(-5) grams (200 micrometers in diameter), and the small particle mass accretion rate is (40 +/- 20) x 106 kilograms per year, higher than previous estimates but in good agreement with total terrestrial mass accretion rates found by geochemical methods. This mass input is comparable with or greater than the average contribution from extraterrestrial bodies in the 1-centimeter to 10-kilometer size range.     

The shape of 433 eros from the NEAR-shoemaker laser rangefinder

Measurements from the Near Earth Asteroid Rendezvous (NEAR)-Shoemaker Laser Rangefinder (NLR) indicate that asteroid 433 Eros is a consolidated body with a complex shape dominated by collisions. The offset between the asteroid's center of mass and center of figure indicates a small deviation from a homogeneous internal structure that is most simply explained by variations in mechanical structure. Regional-scale relief and slope distributions show evidence for control of topography by a competent substrate. Impact crater morphology is influenced by both gravity and structural control. Small-scale topography reveals ridges and grooves that may be generated by impact-related fracturing.     

Eccentric ringlet in the maxwell gap at 1.45 saturn radii: multi-instrument voyager observations

The Voyager spacecraft observed a narrow, eccentric ringlet in the Maxwell gap (1.45 Saturn radii) in Saturn's rings. Intercomparison of the Voyager imaging, photopolarimeter, ultraviolet spectrometer, and radio science observations yields results not available from individual observations. The width of the ringlet varies from about 30 to about 100 kilometers, its edges are sharp on a radial scale < 1 kilometer, and its opacity exhibits a double peak near the center. The shape and width of the ringlet are consistent with a set of uniformly precessing, confocal ellipses with foci at Saturn's center of mass. The ringlet precesses as a unit at a rate consistent with the known dynamical oblateness of Saturn; the lack of differential precession across the ringlet yields a ringlet mass of about 5 x 10(18) grams. The ratio of surface mass density to particle cross-sectional area is about five times smaller than values obtained elsewhere in the Saturn ring system, indicating a relatively larger fraction of small particles. Also, comparison of the measured transmission of the ringlet at radio, visible, and ultraviolet wavelengths indicates that about half of the total extinction is due to particles smaller than 1 centimeter in radius, in contrast even with nearby regions of the C ring. However, the color and brightness of the ringlet material are not measurably different from those of nearby C ring particles. We find this ringlet is similar to several of the rings of Uranus.     

Asteroid 21 Lutetia: low mass, high density

Asteroid 21 Lutetia was approached by the Rosetta spacecraft on 10 July 2010. The additional Doppler shift of the spacecraft radio signals imposed by 21 Lutetia's gravitational perturbation on the flyby trajectory were used to determine the mass of the asteroid. Calibrating and correcting for all Doppler contributions not associated with Lutetia, a least-squares fit to the residual frequency observations from 4 hours before to 6 hours after closest approach yields a mass of (1.700 ± 0.017) × 10(18) kilograms. Using the volume model of Lutetia determined by the Rosetta Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) camera, the bulk density, an important parameter for clues to its composition and interior, is (3.4 ± 0.3) × 10(3) kilograms per cubic meter.     

Laser altimetry of small-scale features on 433 Eros from NEAR-Shoemaker

During the Near Earth Asteroid Rendezvous (NEAR)-Shoemaker's low-altitude flyover of asteroid 433 Eros, observations by the NEAR Laser Rangefinder (NLR) have helped to characterize small-scale surface features. On scales from meters to hundreds of meters, the surface has a fractal structure with roughness dominated by blocks, structural features, and walls of small craters. This fractal structure suggests that a single process, possibly impacts, dominates surface morphology on these scales.     

Gravitational parameters of the jupiter system from the Doppler tracking of pioneer 10

Preliminary analyses of Doppler data from Pioneer 10 during its encounter with Jupiter indicate that the mass of Io is about 20 percent greater than previously thought and that Io's mean density is about 3.5 grams per cubic centimeter. A determination of the dynamical flattening of Jupiter (a - b)/a (where a is the semimajor axis and b is the semiminor axis) is found to lie in the neighborhood of 0.065, which agrees with the value determined from satellite perturbations.     

Pioneer saturn celestial mechanics experiment

During the Pioneer Saturn encounter, a continuous round-trip radio link at S band ( approximately 2.2 gigahertz) was maintained between stations of the Deep Space Network and the spacecraft. From an analysis of the Doppler shift in the radio carrier frequency, it was possible to determine a number of gravitational effects on the trajectory. Gravitational moments ( J(2) and J(4)) for Saturn have been determined from preliminary analysis, and preliminary mass values have been determined for the Saturn satellites Rhea, Iapetus, and Titan. For all three satellites the densities are low, consistent with the compositions of ices. The rings have not been detected in the Doppler data, and hence the best preliminary estimate of their total mass is zero with a standard error of 3 x 10(-6) Saturn mass. New theoretical calculations for the Saturn interior are described which use the latest observational data, including Pioneer Saturn, and state-of-the-art physics for the internal composition. Probably liquid H(2)O and possibly NH(3) and CH(4) are primarily confined in Saturn to the vicinity of a core of approximately 15 to 20 Earth masses. There is a slight indication that helium may likewise be fractionated to the central regions.     

Meteoroid storms detected on the moon

Seismometers on the moon have detected several brief periods of enhanc ed meteoroid-impact activity, believed to represent encounters of the moon with "c louds" of objec ts in the kilogram range. The latest and most active encounter, in June 1975, is interpreted as a meteoroid c(loud of diameter 0.1 astronomical unit and total mass 10(l3) to 10(14) grams.     

Discovery of mass anomalies on Ganymede

We present the discovery of mass anomalies on Ganymede, Jupiter's third and largest Galilean satellite. This discovery is surprising for such a large icy satellite. We used the radio Doppler data generated with the Galileo spacecraft during its second encounter with Ganymede on 6 September 1996 to model the mass anomalies. Two surface mass anomalies, one a positive mass at high latitude and the other a negative mass at low latitude, can explain the data. There are no obvious geological features that can be identified with the anomalies.     

Tropical forests and the global carbon cycle

New data on the three major determinants of the carbon release from tropical forest clearing are used in a computer model that simulates land use change and its effects on the carbon content of vegetation and soil in order to calculate the net flux of carbon dioxide between tropical ecosystems and the atmosphere. The model also permits testing the sensitivity of the calculated flux to uncertainties in these data. The tropics were a net source of at least 0.4 x 10(15) grams but not more than 1.6 x 10(15) grams of carbon in 1980, considerably less than previous estimates. Decreases in soil organic matter were responsible for 0.1 x 10(15) to 0.3 x 10(15) grams of the release, while the burning and decay of cleared vegetation accounted for 0.3 x 10(15) to 1.3 x 10(15) grams. These estimates are lower than many previous ones because lower biomass estimates and slightly lower land clearing rates were used and because ecosystem recovery processes were included. These new estimates of the biotic release allow for the possibility of a balanced global budget given the large remaining uncertainties in the marine, terrestrial, and fossil fuel components of the carbon cycle.     

Mars gravity: high-resolution results from viking orbiter 2

Doppler radio-tracking data have provided detailed measurements for a martian gravity map extending from 30 degrees S to 65 degrees N in latitude and through 360 degrees of longitude. The feature resolution is approximately 500 kilometers, revealing a huge anomaly associated with Olympus Mons, a mascon in Isidis Planitia, and other anomalies correlated with volcanic structure. Olympus Mons has been modeled with a 600-kilometer surface disk having a mass of 8.7 x 1021grams.     

HEAVY GLASSWARE IN THE LABORATORY

(1) Estimations of the phosphorus content of diets reported to produce caries in rats indicate that rations containing 0.4802 grams of phosphorus per 100 grams of diet, or less than 0.4802 grams of phosphorus per 100 grams of diet, tend to induce dental caries in rats if Ca intake is 0.3424 per cent. (2) Estimations of the phosphorus content of diets reported to produce rats immune to dental caries indicate that such diets contain 0.5282 or more grams of phosphorus per 100 grams of diet and 0.4012 or less grams of calcium per 100 grams of diet. (3) Experimental evidence is presented which indicates that the level of phosphorus in the diet is an important factor in producing caries-susceptibility and caries-immunity in rats. (4) We have also found that a relation exists between blood composition (phosphorus) and the incidence of dental caries in rats. Caries arises in rats whose blood phosphorus falls below a critical level (about 10.5 +/- .5 mg(6) of phosphorus per 100 grams of serum), while those rats whose blood phosphorus concentration is 10.5 +/- .5 or above are immune from dental caries. (5) It is indicated that this blood figure is dependent upon the level of phosphorus, calcium and vitamin ingested in the diet. In a forthcoming paper we shall present the results of an extensive review of the recorded observations of our own and other laboratories on the relation between diet and susceptibility to dental caries in the rat and our conclusions from examining these data in the light of the working hypothesis (blood phosphorus critical level) here presented.