18 research outputs found
Integrated heterodyne array receivers for submillimeter astronomy
The advent of large format (~100 pixel) spectroscopic imaging cameras at submillimeter wavelengths would fundamentally change the way in which astronomy is performed in this important wavelength regime. While the possibility of such instruments has been discussed for more than two decades, only recently have advances in mixer technology, device fabrication, micromachining, digital signal processing, and telescope design made the construction of such an instrument possible and economical. In our paper, we will present the design concept for a 10Ă10 heterodyne camera
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 x 10(-6) degrees day(-2), likely due to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, with evolutionary implications.This material is based upon work supported by NASA under Contract NNM10AA11C
issued through the New Frontiers Program. This work made use of sbpy (http://sbpy.
org), a community-driven Python package for small-body planetary astronomy supported by NASA PDART Grant No. 80NSSC18K0987. A portion of this research was
carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a
contract with the National Aeronautics and Space Administration. M.A.B. and S.F.
acknowledge financial support from CNES
Integrated heterodyne array receivers for submillimeter astronomy
The advent of large format (~100 pixel) spectroscopic imaging cameras at submillimeter wavelengths would fundamentally change the way in which astronomy is performed in this important wavelength regime. While the possibility of such instruments has been discussed for more than two decades, only recently have advances in mixer technology, device fabrication, micromachining, digital signal processing, and telescope design made the construction of such an instrument possible and economical. In our paper, we will present the design concept for a 10Ă10 heterodyne camera
Recommended from our members
Regional Photometric Modeling of Asteroid (101955) Bennu
We present a regional photometric analysis of asteroid (101955) Bennu, using image data from the MapCam color imager of the OSIRIS-REx Camera Suite (OCAMS). This analysis follows the previously reported global photometric analysis of Bennu, which found that Bennuâs roughness was difficult to photometrically model owing to unresolved surface variation. Here we find that, even with a high-resolution shape model (20 cm per facet) and automatic image registration (<1 pixel error), Bennu remains a challenging surface to photometrically model: neither a suite of empirical photometric models nor the physically motivated Hapke model were able to eliminate the scatter in the data due to pixel-scale variations. Nonetheless, the models improved on the global analysis by identifying regional variations in Bennuâs photometric response. A linear empirical model, when compared with independent measures of surface roughness and albedo, revealed correlations between those characteristics and phase slope. A regional Hapke analysis showed the same structure in its single-scattering albedo and asymmetry factors; although the Hapke parameters were loosely constrained, complicating interpretation of their spatial variation, the regional variation in relative parameter sensitivity also correlated with shallower phase slope, higher albedo, and less macroscopic roughness
Recommended from our members
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. We present multispectral images (0.44 to 0.89 microns) 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 (become bluer at shorter wavelengths), then brighten in the visible to near-infrared, leading to Bennuâs moderately blue average color. Craters indicate that the timescale of these color changes is ~105 years. We attribute the reflectance and color variation to a combination of primordial heterogeneity and varying exposure ages
Shape of (101955) Bennu indicative of a rubble pile with internal stiffness
International audienceThe shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the Solar System. Prior to the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and SecurityâRegolith Explorer) mission, Earth-based radar imaging gave an overview of (101955) Bennuâs shape. Here we construct a high-resolution shape model from OSIRIS-REx images. We find that Bennuâs top-like shape, considerable macroporosity and prominent surface boulders suggest that it is a rubble pile. High-standing, northâsouth ridges that extend from pole to pole, many long grooves and surface mass wasting indicate some low levels of internal friction and/or cohesion. Our shape model indicates that, similar to other top-shaped asteroids, Bennu formed by reaccumulation and underwent past periods of fast spin, which led to its current shape. Today, Bennu might follow a different evolutionary pathway, with an interior stiffness that permits surface cracking and mass wasting
Properties of Rubble-Pile Asteroid (101955) Bennu from OSIRIS-REx Imaging and Thermal Analysis
Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA's Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennu's surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennu's moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennu's surface particles span from the disruption of the asteroid's parent body (boulders) to recent in situ production (micrometre-scale particles)
Cross-Instrument Comparison of MapCam and OVIRS on OSIRIS-REx
Two of the instruments onboard the OSIRIS-REx spacecraft, the MapCam color imager and the OVIRS visible and infrared spectrometer, observed the surface of asteroid (101955) Bennu in partially overlapping wavelengths. Significant scientific advances have been enabled by using data from these two instruments in tandem, but a robust statistical understanding of their relationship is needed for future analyses to cross-compare their data as accurately and sensitively as possible. Here we present a cross-instrument comparison of data acquired by MapCam and OVIRS, including methods and results for all global and site-specific observation campaigns in which both instruments were active. In our analysis, we consider both the absolute radiometric offset and the relative (normalized) variation between the two instruments; we find that both depend strongly on the photometric and instrumental conditions during the observation. The two instruments have a large absolute offset (>15%) due to their independent radiometric calibrations. However, they are very consistent (relative offset as low as 1%) when each instrumentâs response is normalized at a single wavelength, particularly at low phase angles where shadows on Bennuâs rough surface are minimized. We recommend using the global datasets acquired at 12:30 pm local solar time for cross-comparisons; data acquired at higher phase angles have larger uncertainties.National Aeronautics and Space AdministrationOpen access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis
© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASAâs Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennuâs surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennuâs moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennuâs surface particles span from the disruption of the asteroidâs parent body (boulders) to recent in situ production (micrometre-scale particles)
The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations
© 2019, The Author(s). During its approach to asteroid (101955) Bennu, NASAâs Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed Bennuâs 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 missionâs 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 Bennuâs surface to an upper limit of 150 g sâ1 averaged over 34 min. Bennuâs disk-integrated photometric phase function validates measurements from the pre-encounter astronomical campaign. We demonstrate that Bennuâs rotation rate is accelerating continuously at 3.63 ± 0.52 Ă 10â6 degrees dayâ2, likely due to the YarkovskyâOâKeefeâRadzievskiiâPaddack (YORP) effect, with evolutionary implications