Photometric mapping of Asteroid (4) Vesta’s southern hemisphere with Hubble Space Telescope

We present the surface mapping of the southern hemisphere of Asteroid (4) Vesta obtained from Hubble Space Telescope (HST). From 105 images of Vesta through four filters in the wavelengths best to characterize the 1-μm pyroxene band, we constructed albedo and color-ratio maps of Vesta. These new maps cover latitudes −50° to +20°. The southern hemisphere of Vesta displays more diverse albedo and color features than the northern hemisphere, with about 15 new albedo and color features identified. The overall longitudinal albedo and color variations in the southern hemisphere are comparable with that of the northern hemisphere, with a range of about ±20% and ±10%, respectively. The eastern hemisphere is brighter and displays more diogenitic minerals than the western hemisphere. Correlations between 1-μm band depth and band width, as well as between 1-μm band depth and albedo, are present on a global scale, attributed to pyroxene composition variations. The lack of correlations between albedo and the spectral slope indicates the absence of globalized space weathering. The lack of a global correlation between 1-μm band depth and topography suggests that the surface composition of Vesta is not completely controlled by a single impact. The distribution of compositional variation on Vesta suggests a possible large impact basin. Evidence of space weathering is found in regions, including the bright rim of the south-pole crater where the steepest gravitational slope on Vesta is, and a dark area near a gravitationally flat area. We propose to divide the surface of Vesta into six geological units different from the background according to their 1-μm absorption features and spectral slopes, including two eucrite-rich units, a low-Ca eucrite unit, a diogenite-rich unit, a space weathered unit, and a freshly exposed unit. No evidence of olivine-rich area is present in these data.     

Simultaneous mapping of SO2, SO, NaCl in Io’s atmosphere with the Submillimeter Array

Many of the key properties of Io’s atmosphere, such as its spatial distribution, temperature, column density and composition, are still not fully assessed despite decades of extensive observations. The contribution of the possible gas sources to the atmospheric replenishment are then still unclear.This paper presents disk-resolved observations performed with the Submillimeter Array (SMA) at 345 GHz of atmospheric rotational lines of the main atmospheric species SO₂, and, for the first time, of the minor species SO and NaCl. All these species appear concentrated on the anti-jovian hemisphere, but do not share the same spatial distribution. The obtained maps and line-averaged fluxes are compared to realistic models simulating gas sources including volcanic plume outgassing, SO₂ frost sublimation and photolysis. Arguments in favor of each sources are examined and compared to observations, putting constraints on their relative roles for each species.While sublimation clearly appears as the favored major source for SO₂, SO₂ photolysis may account for most of the production of SO. Using constraints on the volcanic plumes distribution from Galileo results, we find that direct volcanic input can only contribute for a minor fraction of atmospheric SO₂, but represent a more significant source for SO atmosphere, and is likely to be the only source for NaCl. Temperature and column densities findings are also presented for SO₂, and compare well to previously published observations and atmospheric models.     

A spectroscopic comparison of HED meteorites and V-type asteroids in the inner Main Belt

V-type asteroids in the inner Main Belt (a < 2.5 AU) and the HED meteorites are thought to be genetically related to one another as collisional fragments from the surface of the large basaltic Asteroid 4 Vesta. We investigate this relationship by comparing the near-infrared (0.7-2.5 μm) spectra of 39 V-type asteroids to laboratory spectra of HED meteorites. The central wavelengths and areas spanned by the 1 and 2 μm pyroxene-olivine absorption bands that are characteristic of planetary basalts are measured for both the asteroidal and meteoritic data. The band centers are shown to be well correlated, however the ratio of areas spanned by the 1 and 2 μm absorption bands are much larger for the asteroids than for the meteorites. We argue that this offset in band area ratio is consistent with our currently limited understanding of the effects of space weathering, however we cannot rule out the possibility that this offset is due to compositional differences. Several other possible causes of this offset are discussed.Amongst these inner Main Belt asteroids we do not find evidence for non-Vestoid mineralogies. Instead, these asteroids seem to represent a continuum of compositions, consistent with an origin from a single differentiated parent body. In addition, our analysis shows that V-type asteroids with low inclinations (i < 6°) tend to have band centers slightly shifted towards long wavelengths. This may imply that more than one collision on Vesta’s surface was responsible for producing the observed population of inner belt V-type asteroids. Finally, we offer several predictions that can be tested when the Dawn spacecraft enters into orbit around Vesta in the summer of 2011.     

Penetrometry of granular and moist planetary surface materials: Application to the Huygens landing site on Titan

The Huygens probe landed on the then unknown surface of Titan in January 2005. A small, protruding penetrometer, part of the Surface Science Package (SSP), was pushed into the surface material measuring the mechanical resistance of the ground as the probe impacted the landing site. We present laboratory penetrometry into room temperature surface analogue materials using a replica penetrometer to investigate further the nature of Titan’s surface and examine the sensor’s capabilities. The results are then compared to the flight instrument’s signature and suggest the Titan surface substrate material consists of sand-sized particles with a mean grain size ～2 mm. A possible thin 7 mm coating with mechanical properties similar to terrestrial snow may overlie this substrate, although due to the limited data we are unable to detect any further layering or grading within the near-surface material. The unusual weakening with depth of the signature returned from Titan has, to date, only been reproduced using a damp sand target that becomes progressively wetter with depth, and supports the suggestion that the surface may consist of a damp and cohesive material with interstitial liquid contained between its grains. Comparison with terrestrial analogues highlights the unusual nature of the landing site material.     

In Situ Biological Contamination Studies of the Moon: Implications for Planetary Protection and Life Detection Missions

NASA and ESA have outlined visions for solar system exploration that will include a series of lunar robotic precursor missions to prepare for, and support a human return to the Moon, and future human exploration of Mars and other destinations, including possibly asteroids. One of the guiding principles for exploration is to pursue compelling scientific questions about the origin and evolution of life. The search for life on objects such as Mars will require careful operations, and that all systems be sufficiently cleaned and sterilized prior to launch to ensure that the scientific integrity of extraterrestrial samples is not jeopardized by terrestrial organic contamination. Under the Committee on Space Research’s (COSPAR’s) current planetary protection policy for the Moon, no sterilization procedures are required for outbound lunar spacecraft, nor is there a different planetary protection category for human missions, although preliminary COSPAR policy guidelines for human missions to Mars have been developed. Future in situ investigations of a variety of locations on the Moon by highly sensitive instruments designed to search for biologically derived organic compounds would help assess the contamination of the Moon by lunar spacecraft. These studies could also provide valuable “ground truth” data for Mars sample return missions and help define planetary protection requirements for future Mars bound spacecraft carrying life detection experiments. In addition, studies of the impact of terrestrial contamination of the lunar surface by the Apollo astronauts could provide valuable data to help refine future Mars surface exploration plans for a human mission to Mars.     

剪断翼龙的翅膀：对于翼展估计和多样性的评论

Giant azhdarchids are perhaps the most spectacular pterosaurs known and, although they lack the elaborate headcrests or striking dentition that adorn other charismatic pterosaurs, the sheer enormity of their proportions has drawn a wealth of popular and scientific interest. Their remains, however, are so fragmentary that only limited interpretations of their anatomy and taxonomy can be made with certainty. Here, we report on recent investigations into giant azhdarchid taxonomy and size estimates that suggest both may be over-inflated.     

Radial Dupuit interface flow to assess the aquifer storage and recovery potential of saltwater aquifers

A new accurate numerical solution is presented for aquifer storage and recovery (ASR) systems in coastal aquifers; flow is approximated as radial Dupuit interface flow. The radial velocities of points on the interface are a function of time, the vertical coordinate, and the dimensionless parameter D (the discharge of the well divided by the product of the hydraulic conductivity, the square of the aquifer thickness, and the dimensionless density difference). The recovery efficiency of an ASR system (the ratio of the recovered volume of water divided by the injected volume of water) is determined by D and by the relative lengths of the injection, storage and recovery periods. Graphs are produced for the recovery efficiency as a function of parameter D for ASR operations with and without storage periods and for multiple cycles. The presented solutions and graphs are to be used as screening tools to assess the feasibility of specific injection, storage and recovery scenarios of planned ASR systems in saltwater aquifers without having to run complicated flow and transport models. When the screening tool indicates that recovery efficiencies are acceptable, the consideration of other features such as mixing and chemistry is warranted.     

Uncertainty and risk in climate projections for the 21st century: comparing mitigation to non-intervention scenarios

Probabilistic climate projections based on two SRES scenarios, an IMAGE reference scenario and five IMAGE mitigation scenarios (all of them multi-gas scenarios) using the Bern2.5D climate model are calculated. Probability distributions of climate model parameters that are constrained by observations are employed as input for the climate model. The sensitivity of the resulting distributions with respect to prior assumptions on climate sensitivity is then assessed. Due to system inertia, prior assumptions on climate sensitivity play a minor role in the case of temperature projections for the first half of the 21st century, but these assumptions have a considerable influence on the distributions of the projected temperature increase in the year 2100. Upper and lower probabilities for exceeding 2°C by the year 2100 are calculated for the different scenarios. Only the most stringent mitigation measures lead to low probabilities for exceeding the 2°C threshold. This finding is robust with respect to our prior assumptions on climate sensitivity. Further, probability distributions of total present-value damages over the period 2000–2100 for the different scenarios are calculated assuming a wide range of damage cost functions, and the sensitivity of these distributions with respect to the assumed discount rate is investigated. Absolute values of damage costs depend heavily on the chosen damage cost function and discount rate. Nevertheless, some robust conclusions are possible.     

Warming of an elevated layer over the Caribbean

Air temperatures in the trade wind inversion (~850 hPa) over the Caribbean have been rising much faster than sea temperatures. This is associated with an accelerated Hadley circulation, with sinking motions over the Caribbean corresponding with increasing rising motion over the Amazon. The sinking motions induce a faster rate of warming and drying in the trade wind inversion than at other levels. Much of the trend in Caribbean climate is attributable to physical mechanisms; changes in atmospheric composition play a secondary role. Smoke and dust plumes from Africa, drifting westward across the Atlantic, enhance the greenhouse effect in an elevated (1–3 km) layer. A stabilized lower atmosphere across the Caribbean has contributed to warming and drying trends over the twentieth century which are projected to continue. The atmosphere is warming faster than the ocean, causing a decline in sensible heat fluxes that fuel tropical cyclones.     

Spatiotemporal change in China’s climatic growing season: 1955–2000

The timing, length, and thermal intensity of the climatic growing season in China show statistically significant changes over the period of 1955 to 2000. Nationally, the average start of the growing season has shifted 4.6–5.5 days earlier while the average end has moved 1.8–3.7 days later, increasing the length of the growing season by 6.9–8.7 days depending on the base temperature chosen. The thermal intensity of the growing season has increased by 74.9–196.8 growing degree-days, depending on the base temperature selected. The spatial characteristics of the change in the timing and length of the growing season differ from the geographical pattern of change in temperatures over this period; but the spatial characteristics of change in growing degree-days does resemble the pattern for temperatures, with higher rates in northern regions. Nationally, two distinct regimes are evident over time: an initial period where growing season indicators fluctuate near a base period average, and a second period of rapidly increasing growing season length and thermal intensity. Growing degree-days are highly correlated with March-to-November mean air temperatures in all climatic regions of China; the length of the growing season is likewise highly correlated with March-to-November mean air temperatures except in east, southeast and southwest China at base temperature of 0°C and southeast China at base temperature of 5°C. The growing season start date appears to have the greater influence on the length of the growing season. In China, warmer growing seasons are also likely to be longer growing seasons.