Spacecraft sample collection and subsurface excavation of asteroid (101955) Bennu.

Carbonaceous asteroids, such as (101955) Bennu, preserve material from the early Solar System, including volatile compounds and organic molecules. We report spacecraft imaging and spectral data collected during and after retrieval of a sample from Bennu's surface. The sampling event mobilized rocks and dust into a debris plume, excavating a 9-meter-long elliptical crater. This exposed material is darker, spectrally redder, and more abundant in fine particulates than the original surface. The bulk density of the displaced subsurface material was 500 to 700 kilograms per cubic meter, which is about half that of the whole asteroid. Particulates that landed on instrument optics spectrally resemble aqueously altered carbonaceous meteorites. The spacecraft stored 250 ± 101 grams of material, which will be delivered to Earth in 2023.

Thermal Fatigue as a Driving Mechanism for Activity on Asteroid Bennu.

Many boulders on (101955) Bennu, a near-Earth rubble pile asteroid, show signs of in situ disaggregation and exfoliation, indicating that thermal fatigue plays an important role in its landscape evolution. Observations of particle ejections from its surface also show it to be an active asteroid, though the driving mechanism of these events is yet to be determined. Exfoliation has been shown to mobilize disaggregated particles in terrestrial environments, suggesting that it may be capable of ejecting material from Bennu's surface. We investigate the nature of thermal fatigue on the asteroid, and the efficacy of fatigue-driven exfoliation as a mechanism for generating asteroid activity, by performing finite element modeling of stress fields induced in boulders from diurnal cycling. We develop a model to predict the spacing of exfoliation fractures and the number and speed of particles that may be ejected during exfoliation events. We find that crack spacing ranges from ~1 mm to 10 cm and disaggregated particles have ejection speeds up to ~2 m/s. Exfoliation events are most likely to occur in the late afternoon. These predictions are consistent with observed ejection events at Bennu and indicate that thermal fatigue is a viable mechanism for driving asteroid activity. Crack propagation rates and ejection speeds are greatest at perihelion when the diurnal temperature variation is largest, suggesting that events should be more energetic and more frequent when closer to the Sun. Annual thermal stresses that arise in large boulders may influence the spacing of exfoliation cracks or frequency of ejection events.

Bright carbonate veins on asteroid (101955) Bennu: Implications for aqueous alteration history.

The composition of asteroids and their connection to meteorites provide insight into geologic processes that occurred in the early Solar System. We present spectra of the Nightingale crater region on near-Earth asteroid Bennu with a distinct infrared absorption around 3.4 micrometers. Corresponding images of boulders show centimeters-thick, roughly meter-long bright veins. We interpret the veins as being composed of carbonates, similar to those found in aqueously altered carbonaceous chondrite meteorites. If the veins on Bennu are carbonates, fluid flow and hydrothermal deposition on Bennu's parent body would have occurred on kilometer scales for thousands to millions of years. This suggests large-scale, open-system hydrothermal alteration of carbonaceous asteroids in the early Solar System.

Variations in color and reflectance on the surface of asteroid (101955) Bennu.

Visible-wavelength color and reflectance provide information about the geologic history of planetary surfaces. Here we present multispectral images (0.44 to 0.89 micrometers) of near-Earth asteroid (101955) Bennu. The surface has variable colors overlain on a moderately blue global terrain. Two primary boulder types are distinguishable by their reflectance and texture. Space weathering of Bennu surface materials does not simply progress from red to blue (or vice versa). Instead, freshly exposed, redder surfaces initially brighten in the near-ultraviolet region (i.e., become bluer at shorter wavelengths), then brighten in the visible to near-infrared region, leading to Bennu's moderately blue average color. Craters indicate that the time scale of these color changes is ~105 years. We attribute the reflectance and color variation to a combination of primordial heterogeneity and varying exposure ages.

In situ evidence of thermally induced rock breakdown widespread on Bennu's surface.

Rock breakdown due to diurnal thermal cycling has been hypothesized to drive boulder degradation and regolith production on airless bodies. Numerous studies have invoked its importance in driving landscape evolution, yet morphological features produced by thermal fracture processes have never been definitively observed on an airless body, or any surface where other weathering mechanisms may be ruled out. The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission provides an opportunity to search for evidence of thermal breakdown and assess its significance on asteroid surfaces. Here we show boulder morphologies observed on Bennu that are consistent with terrestrial observations and models of fatigue-driven exfoliation and demonstrate how crack propagation via thermal stress can lead to their development. The rate and expression of this process will vary with asteroid composition and location, influencing how different bodies evolve and their apparent relative surface ages from space weathering and cratering records.

Episodes of particle ejection from the surface of the active asteroid (101955) Bennu.

Active asteroids are those that show evidence of ongoing mass loss. We report repeated instances of particle ejection from the surface of (101955) Bennu, demonstrating that it is an active asteroid. The ejection events were imaged by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) spacecraft. For the three largest observed events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. We also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the Bennu environment. We consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteoroid impacts, thermal stress fracturing, and secondary impacts.

The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations.

During its approach to asteroid (101955) Bennu, NASA's Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed Bennu's immediate environment, photometric properties, and rotation state. Discovery of a dusty environment, a natural satellite, or unexpected asteroid characteristics would have had consequences for the mission's safety and observation strategy. Here we show that spacecraft observations during this period were highly sensitive to satellites (sub-meter scale) but reveal none, although later navigational images indicate that further investigation is needed. We constrain average dust production in September 2018 from Bennu's surface to an upper limit of 150 g s-1 averaged over 34 min. Bennu's disk-integrated photometric phase function validates measurements from the pre-encounter astronomical campaign. We demonstrate that Bennu's rotation rate is accelerating continuously at 3.63 ± 0.52 × 10-6 degrees day-2, likely due to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, with evolutionary implications.

The unexpected surface of asteroid (101955) Bennu.

NASA'S Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer (OSIRIS-REx) spacecraft recently arrived at the near-Earth asteroid (101955) Bennu, a primitive body that represents the objects that may have brought prebiotic molecules and volatiles such as water to Earth1. Bennu is a low-albedo B-type asteroid2 that has been linked to organic-rich hydrated carbonaceous chondrites3. Such meteorites are altered by ejection from their parent body and contaminated by atmospheric entry and terrestrial microbes. Therefore, the primary mission objective is to return a sample of Bennu to Earth that is pristine-that is, not affected by these processes4. The OSIRIS-REx spacecraft carries a sophisticated suite of instruments to characterize Bennu's global properties, support the selection of a sampling site and document that site at a sub-centimetre scale5-11. Here we consider early OSIRIS-REx observations of Bennu to understand how the asteroid's properties compare to pre-encounter expectations and to assess the prospects for sample return. The bulk composition of Bennu appears to be hydrated and volatile-rich, as expected. However, in contrast to pre-encounter modelling of Bennu's thermal inertia12 and radar polarization ratios13-which indicated a generally smooth surface covered by centimetre-scale particles-resolved imaging reveals an unexpected surficial diversity. The albedo, texture, particle size and roughness are beyond the spacecraft design specifications. On the basis of our pre-encounter knowledge, we developed a sampling strategy to target 50-metre-diameter patches of loose regolith with grain sizes smaller than two centimetres4. We observe only a small number of apparently hazard-free regions, of the order of 5 to 20 metres in extent, the sampling of which poses a substantial challenge to mission success.

Deep Impact: observations from a worldwide Earth-based campaign.

On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics.

Detection of the 2165 inverse centimeter (4.619 micron) XCN band in the spectrum of L1551 IRS 5.

We report the detection of a broad absorption band at 2165 cm-1 (4.619 microns) in the spectrum of L1551 IRS 5. New laboratory results over the 2200-2100 cm-1 wavenumber interval (4.55-4.76 microns), performed with realistic interstellar ice analogs, suggest that this feature is due to a CN-containing compound. We will refer to this compound as XCN. We also confirm the presence of frozen CO (both in nonpolar and polar matrices) through absorption bands at 2140 cm-1 (4.67 microns) and 2135 cm-1 (4.68 microns). The relative abundance of solid-state CO to frozen H2O is approximately 0.13 while the abundance of XCN seems comparable to that of frozen CO.

Surface discharges on natural dielectrics in the solar system.

When Earth-orbiting spacecraft are exposed to large fluxes of energetic charged particles, electric discharges occur on circuit boards, solar panels, and other dielectric surfaces. Large fluxes of energetic partides can produce such discharges on natural materials in the solar system. Surface discharges will occur under a variety of conditions, but particularly favorable environments are expected to occur within the magnetospheres of the giant planets; an example is the surface of Io.

Airborne and groundbased spectrophotometry of comet P/Halley from 5-13 micrometers.

Spectrophotometry from 5-10 micrometers (delta lambda/lambda approximately 0.02) of comet Halley was obtained from the Kuiper Airborne Observatory on 1985 December 12.1 and 1986 April 8.6 and 10.5, UT. 8-13 micrometers data were obtained on 17.2 December 1985 from the Nickel Telescope at Lick Observatory. The spectra show a strong broad emission band at 10 micrometers and a weak feature at 6.8 micrometers. We do not confirm the strong 7.5 micrometers emission feature observed by the Vega 1 spacecraft. The 10 micrometers band, identified with silicate materials, has substructure indicative of crystalline material. The band can be fitted by combining spectra data from a sample of interplanetary dust particles. The primary component of the silicate emission is due to olivine. The 6.8 micrometers emission feature can be due either to carbonates or the C-H deformation mode in organic molecules. The lack of other emission bands is used to place limits on the types of organic molecules responsible for the emission observed by others at 3.4 micrometers. Color temperatures significantly higher than the equilibrium blackbody temperature indicate that small particles are abundant in the coma. Significant spatial and temporal variations in the spectrum have been observed and show trends similar to those observed by the spacecraft and from the ground. Temporal variability of the silicate emission relative to the 5-8 micrometers continuum suggests that there are at least two physically separated components of the dust.

Micosis profundas en pacientes con radiologia pulmonar anormal. / Deep mycoses in patients with abnormal pulmonary radiology

Este trabajo describe un estudio realizado en 510 pacientes del Hospital Vargas de Caracas, Venezuela, que presentaban una radiologia toracica anormal. Los resultados obtenidos indican que las pruebas serologicas para la histoplasmosis y la paracoccidioidomicosis pueden contribuir de manera importante al diagnostico de estas enfermedades

Demonstration and quantification oomycosis.

Using a radioimmunoassay technique, we have determined the total IgE concentration and specific IgE antibody level against Paracoccidioides brasiliensis in the sera of patients with mycologically confirmed active paracoccidioidcosis. Patients with aspergilloma, or individuals with antibodies against Cadida albicans, and sera of apparently healthy individuals from the endemic area were also examined. The level of total IgE was significantly elevated in 9 out of 10 cases of paracoccidioidomycosis. The mean level of specific IgE against P. brasiliensis was significantly higher in the serum of the patients in comparison with control individuals. The percentage of specific IgE relative to the total varied from 0.38 to 2.28%. The differences between IgE levels in pare other mycoses were statistically significant. Our results suggest a possible involvement of specific IgE antibodies against P. brasiliensis in the immune response of patients with paracoccidioidomycosis. The hyperimmunoglobulinemia E may be related to the T-cell defect that characterizes the severe forms of the disease.

[Cryptococcosis in Venezuela. Comments on a clinical case with unusual location]. / Cryptococcosis en Venezuela. Comentarios a un caso con localización excepcional.

A tumor like case of Cryptococcosis with a rare location in the abdomen of a young healthy woman is commented. It gave the opportunity to refer to the pathogeny of the disease, making in that way a brief review of the cases known in Venezuela and some not still published from which we got information. That review showed that generally doctors found more frequently organic lesions within the fields they are specially working for. It is obvious that mycosis must be considered in the diagnosis of nearly every patient in many countries and that laboratories must get appropriate equipment and personnel to help in that diagnosis.