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

Science ◽  
2019 ◽  
Vol 366 (6470) ◽  
pp. eaay3544 ◽  
Author(s):  
D. S. Lauretta ◽  
C. W. Hergenrother ◽  
S. R. Chesley ◽  
J. M. Leonard ◽  
J. Y. Pelgrift ◽  
...  
Keyword(s):  
Thermal Stress ◽  
Source Regions ◽  
Multiple Hypotheses ◽  
Spectral Interpretation ◽  
Show Evidence ◽  
Resource Identification ◽  
Event Times ◽  
Particle Velocities ◽  
Particle Ejection ◽  
Ice Sublimation

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.

scholarly journals PHOTOGRAMMETRIC PROCESSING OF OSIRIS-REX IMAGES OF ASTEROID (101955) BENNU

2020 ◽  
Vol V-3-2020 ◽  
pp. 587-594
Author(s):  
K. L. Edmundson ◽  
K. J. Becker ◽  
T. L. Becker ◽  
C. A. Bennett ◽  
D. N. DellaGiustina ◽  
...  
Keyword(s):  
Control Process ◽  
Laser Altimeter ◽  
Shape Models ◽  
Spectral Interpretation ◽  
Global Mapping ◽  
Resource Identification ◽  
Imaging Sensors ◽  
Future Work ◽  
Selection Of ◽  
Reconnaissance Surveys

Abstract. The principal objective of the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission is to retrieve a sample of the asteroid (101955) Bennu and return it to Earth. OSIRIS-REx arrived at Bennu in December 2018. Images of the asteroid by the OSIRIS-REx Camera Suite (OCAMS) were photogrammetrically controlled to produce a global basemap and site-specific image mosaics essential to the selection of a primary and backup sample site, which were announced in December 2019. In the control process, OCAMS images were registered to shape models created from OSIRIS-REx Laser Altimeter (OLA) data and from the process of stereophotoclinometry. This paper summarizes the photogrammetric control to date of images collected at Bennu. We briefly review the mission and the OCAMS imaging sensors. We then describe the photogrammetric control process for the global mapping campaign and targeted reconnaissance surveys of candidate sample sites. Finally, we discuss ongoing and future work.

scholarly journals Particle Size-Frequency Distributions of the OSIRIS-REx Candidate Sample Sites on Asteroid (101955) Bennu

2021 ◽  
Vol 13 (7) ◽  
pp. 1315
Author(s):  
Keara N. Burke ◽  
Daniella N. DellaGiustina ◽  
Carina A. Bennett ◽  
Kevin J. Walsh ◽  
Maurizio Pajola ◽  
...  
Keyword(s):  
Particle Size ◽  
Particle Packing ◽  
Sample Collection ◽  
Frequency Distributions ◽  
Global Survey ◽  
Size Frequency ◽  
Spectral Interpretation ◽  
Resource Identification ◽  
Sample Return Mission ◽  
Pixel Scale

We manually mapped particles ranging in longest axis from 0.3 cm to 95 m on (101955) Bennu for the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) asteroid sample return mission. This enabled the mission to identify candidate sample collection sites and shed light on the processes that have shaped the surface of this rubble-pile asteroid. Building on a global survey of particles, we used higher-resolution data from regional observations to calculate particle size-frequency distributions (PSFDs) and assess the viability of four candidate sites for sample collection (presence of unobstructed particles ≤ 2 cm). The four candidate sites have common characteristics: each is situated within a crater with a relative abundance of sampleable material. Their PSFDs, however, indicate that each site has experienced different geologic processing. The PSFD power-law slopes range from −3.0 ± 0.2 to −2.3 ± 0.1 across the four sites, based on images with a 0.01-m pixel scale. These values are consistent with, or shallower than, the global survey measurements. At one site, Osprey, the particle packing density appears to reach geometric saturation. We evaluate the uncertainty in these measurements and discuss their implications for other remotely sensed and mapped particles, and their importance to OSIRIS-REx sampling operations.

scholarly journals Aircraft measurements of High Arctic springtime aerosol show evidence for vertically varying sources, transport and composition

2018 ◽  
Author(s):  
Megan D. Willis ◽  
Heiko Bozem ◽  
Daniel Kunkel ◽  
Alex K. Y. Lee ◽  
Hannes Schulz ◽  
...  
Keyword(s):  
Potential Temperature ◽  
High Arctic ◽  
The Arctic ◽  
Chemical Transformations ◽  
Aerosol Composition ◽  
Source Regions ◽  
Arctic Regions ◽  
Arctic Aerosol ◽  
Show Evidence ◽  
Climate Interactions

Abstract. The sources, chemical transformations and removal mechanisms of aerosol transported to the Arctic are key factors that control Arctic aerosol-climate interactions. Our understanding of sources and processes is limited by a lack of vertically resolved observations in remote Arctic regions. We present vertically resolved observations of trace gases and aerosol composition in High Arctic springtime, made largely north of 80° N, during the NETCARE campaign. Trace gas gradients observed on these flights defined the polar dome as north of 66–68.5° N and below potential temperatures of 283.5–287.5 K (Bozem et al., 2018). In the polar dome, we observe evidence for vertically varying source regions and chemical processing. These vertical changes in sources and chemistry lead to systematic variation in aerosol composition as a function of potential temperature. We show evidence for sources of aerosol with higher organic aerosol (OA), ammonium (NH4) and refractory black carbon (rBC) content in the upper polar dome. Based on FLEXPART-ECMWF calculations, air masses sampled at all levels inside the polar dome (i.e., potential temperature

scholarly journals In-Flight Calibration and Performance of the OSIRIS-REx Visible and IR Spectrometer (OVIRS)

2018 ◽  
Vol 10 (9) ◽  
pp. 1486 ◽  
Author(s):  
Amy Simon ◽  
Dennis Reuter ◽  
Nicolas Gorius ◽  
Allen Lunsford ◽  
Richard Cosentino ◽  
...  
Keyword(s):  
Radiometric Calibration ◽  
Atmospheric Models ◽  
Ground Testing ◽  
Spectral Interpretation ◽  
Resource Identification ◽  
Infrared Spectrometer ◽  
Visible Wavelengths ◽  
And Performance ◽  
One Year ◽  
Better Than

Performance of the Origins, Spectral Interpretation, Resource Identification, Security–Regolith Explorer (OSIRIS-REx) Visible and InfraRed Spectrometer (OVIRS) instrument was validated, showing that it met all science requirements during extensive thermal vacuum ground testing. Preliminary instrument radiometric calibration coefficients and wavelength mapping were also determined before instrument delivery and launch using NIST-traceable sources. One year after launch, Earth flyby data were used to refine the wavelength map by comparing OVIRS spectra with atmospheric models. Near-simultaneous data from other Earth-orbiting satellites were used to cross-calibrate the OVIRS absolute radiometric response, particularly at visible wavelengths. Trending data from internal calibration sources and the Sun show that instrument radiometric performance has been stable to better than 1% in the 18 months since launch.

scholarly journals Weak spectral features on (101995) Bennu from the OSIRIS-REx Visible and InfraRed Spectrometer

2020 ◽  
Vol 644 ◽  
pp. A148 ◽  
Author(s):  
A. A. Simon ◽  
H. H. Kaplan ◽  
E. Cloutis ◽  
V. E. Hamilton ◽  
C. Lantz ◽  
...  
Keyword(s):  
Iron Oxides ◽  
Surface Shape ◽  
Spectral Features ◽  
Absorption Bands ◽  
Weak Absorption ◽  
Spectral Interpretation ◽  
Average Spectrum ◽  
Resource Identification ◽  
Infrared Spectrometer ◽  
Compositional Variations

Context. The NASA Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission has obtained thousands of spectra of asteroid (101955) Bennu with the OSIRIS-REx Visible and InfraRed Spectrometer. Aims. We present a spectral search for minor absorption bands and determine compositional variations on the surface of Bennu. Methods. Reflectance spectra with low and high spatial resolutions were analyzed for evidence of weak absorption bands. Spectra were also divided by a global average spectrum to isolate unique spectral features, and variations in the strongest band depths were mapped on a surface shape model. The global visible to near-IR spectrum of Bennu shows evidence of several weak absorption bands with depths of a few percent. Results. Several observed bands are consistent with phyllosilicates, and their distribution correlates with the stronger 2.74-μm hydration band. A 0.55-μm band is consistent with iron oxides and is deepest in the spectrally reddest areas on Bennu. The presence of hydrated phyllosilicates and iron oxides indicates substantial aqueous alteration in Bennu’s past. Conclusions. Bennu’s spectra are not identical to a limited set of carbonaceous chondrite spectra, possibly due to compositional properties and spatial scale differences; however, returned samples should contain a mixture of common chondrite materials.

Covering of cometary nucleus by refractory crust and its evolution into asteroid-like body

1999 ◽  
Vol 173 ◽  
pp. 365-370
Author(s):  
Kh.I. Ibadinov
Keyword(s):  
Laboratory Experiments ◽  
Cometary Nucleus ◽  
Sublimation Rate ◽  
Cometary Nuclei ◽  
Short Period Comet ◽  
Short Period ◽  
Brightness Decrease ◽  
Crust Thickness ◽  
Ice Sublimation ◽  
Period Comet

AbstractFrom the established dependence of the brightness decrease of a short-period comet dependence on the perihelion distance of its orbit it follows that part of the surface of these cometary nuclei gradually covers by a refractory crust. The results of cometary nucleus simulation show that at constant insolation energy the crust thickness is proportional to the square root of the insolation time and the ice sublimation rate is inversely proportional to the crust thickness. From laboratory experiments resulted the thermal regime, the gas productivity of the nucleus, covering of the nucleus by the crust, and the tempo of evolution of a short-period comet into the asteroid-like body studied.

The Cellular Origin in Atheromatous Lesion

1970 ◽  
Vol 28 ◽  
pp. 202-203
Author(s):  
T. M. Murad ◽  
H. A. I. Newman ◽  
K. F. Kern
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Rabbit Aorta ◽  
Mixed Population ◽  
The Other ◽  
Cellular Origin ◽  
Ultrastructural Studies ◽  
Atherosclerotic Lesions ◽  
Show Evidence ◽  
Early Lesion

The origin of lipid containing cells in atheromatous lesion has been disputed. Geer in his study on atheromatous lesions of rabbit aorta, suggested that the early lesion is composed mainly of lipid-laden macrophages and the later lesion has a mixed population of macrophages and smooth muscle cells. Parker on the other hand, was able to show evidence that the rabbit lesion is primarily composed of lipid-laden cells of smooth muscle origin. The above studies and many others were done on an intact lesion without any attempt of cellular isolation previous to their ultrastructural studies. Cell isolation procedures have been established for atherosclerotic lesions through collagenase and elastase digestion Therefore this procedure can be utilized to identify the cells involved in rabbit atheroma.

The Stability of the WHO Reference Thromboplastin NIBS & C 67/40

1979 ◽  
Vol 42 (04) ◽  
pp. 1135-1140 ◽  
Author(s):  
G I C Ingram
Keyword(s):  
Human Brain ◽  
Collaborative Study ◽  
Calibration Constant ◽  
Long Term Stability ◽  
Freeze Dried ◽  
Show Evidence ◽  
Human Material ◽  
Reference Preparation ◽  
The Stability

SummaryThe International Reference Preparation of human brain thromboplastin coded 67/40 has been thought to show evidence of instability. The evidence is discussed and is not thought to be strong; but it is suggested that it would be wise to replace 67/40 with a new preparation of human brain, both for this reason and because 67/40 is in a form (like Thrombotest) in which few workers seem to use human brain. A �plain� preparation would be more appropriate; and a freeze-dried sample of BCT is recommended as the successor preparation. The opportunity should be taken also to replace the corresponding ox and rabbit preparations. In the collaborative study which would be required it would then be desirable to test in parallel the three old and the three new preparations. The relative sensitivities of the old preparations could be compared with those found in earlier studies to obtain further evidence on the stability of 67/40; if stability were confirmed, the new preparations should be calibrated against it, but if not, the new human material should receive a calibration constant of 1.0 and the new ox and rabbit materials calibrated against that.The types of evidence available for monitoring the long-term stability of a thromboplastin are discussed.

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