A. Mainzer

California Institute of Technology, Pasadena, California, United States

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Publications (349)321.55 Total impact

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    ABSTRACT: We present revised near-infrared albedo fits of 2835 Main Belt asteroids observed by WISE/NEOWISE over the course of its fully cryogenic survey in 2010. These fits are derived from reflected-light near-infrared images taken simultaneously with thermal emission measurements, allowing for more accurate measurements of the near-infrared albedos than is possible for visible albedo measurements. As our sample requires reflected light measurements, it undersamples small, low albedo asteroids, as well as those with blue spectral slopes across the wavelengths investigated. We find that the Main Belt separates into three distinct groups of 6%, 16%, and 40% reflectance at 3.4 um. Conversely, the 4.6 um albedo distribution spans the full range of possible values with no clear grouping. Asteroid families show a narrow distribution of 3.4 um albedos within each family that map to one of the three observed groupings, with the (221) Eos family being the sole family associated with the 16% reflectance 3.4 um albedo group. We show that near-infrared albedos derived from simultaneous thermal emission and reflected light measurements are an important indicator of asteroid taxonomy and can identify interesting targets for spectroscopic followup.
    The Astrophysical Journal 06/2014; 791(2). · 6.73 Impact Factor
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    ABSTRACT: NASA's Wide-field Infrared Survey Explorer (WISE) spacecraft has been brought out of hibernation and has resumed surveying the sky at 3.4 and 4.6 um. The scientific objectives of the NEOWISE reactivation mission are to detect, track, and characterize near-Earth asteroids and comets. The search for minor planets resumed on December 23, 2013, and the first new near-Earth object (NEO) was discovered six days later. As an infrared survey, NEOWISE detects asteroids based on their thermal emission and is equally sensitive to high and low albedo objects; consequently, NEOWISE-discovered NEOs tend to be large and dark. Over the course of its three-year mission, NEOWISE will determine radiometrically-derived diameters and albedos for approximately 2000 NEOs and tens of thousands of Main Belt asteroids. The 32 months of hibernation have had no significant effect on the mission's performance. Image quality, sensitivity, photometric and astrometric accuracy, completeness, and the rate of minor planet detections are all essentially unchanged from the prime mission's post-cryogenic phase.
    06/2014;
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    ABSTRACT: The Wide-field Infrared Survey Explorer (WISE) spacecraft has been reactivated as NEOWISE-R to characterize and search for Near Earth Objects. The brown dwarf WISE J085510.83-071442.5 has now been reobserved by NEOWISE-R, and we confirm the results of Luhman (2014b), who found a very low effective temperature, a very high proper motion, and a large parallax. The large proper motion has separated the brown dwarf from the background sources that influenced the 2010 WISE data, allowing a measurement of a very red WISE color of W1-W2 > 3.9. A re-analysis of the 2010 WISE astrometry using only the W2 band, combined with the new NEOWISE-R 2014 position, gives an improved parallax of 448 +/- 32 mas and proper motion of 8.072 +/- 0.026 arcsec/yr. These are all consistent with Luhman (2014b).
    05/2014;
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    ABSTRACT: Comet 17P/Holmes underwent a massive outburst in 2007 October, brightening by a factor of almost a million in under 48 hr. We used infrared images taken by the Wide-Field Infrared Survey Explorer mission to characterize the comet as it appeared at a heliocentric distance of 5.1 AU almost 3 yr after the outburst. The comet appeared to be active with a coma and dust trail along the orbital plane. We constrained the diameter, albedo, and beaming parameter of the nucleus to 4.135 ± 0.610 km, 0.03 ± 0.01, and 1.03 ± 0.21, respectively. The properties of the nucleus are consistent with those of other Jupiter family comets. The best-fit temperature of the coma was 134 ± 11 K, slightly higher than the blackbody temperature at that heliocentric distance. Using Finson-Probstein modeling, we found that the morphology of the trail was consistent with ejection during the 2007 outburst and was made up of dust grains between 250 μm and a few cm in radius. The trail mass was ~1.2-5.3 × 1010 kg.
    The Astrophysical Journal 05/2014; 787(2):116. · 6.73 Impact Factor
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    ABSTRACT: Comet 17P/Holmes underwent a massive outburst in 2007 Oct., brightening by a factor of almost a million in under 48 hours. We used infrared images taken by the Wide-Field Survey Explorer mission to characterize the comet as it appeared at a heliocentric distance of 5.1 AU almost 3 years after the outburst. The comet appeared to be active with a coma and dust trail along the orbital plane. We constrained the diameter, albedo, and beaming parameter of the nucleus to 4.135 $\pm$ 0.610 km, 0.03 $\pm$ 0.01 and 1.03 $\pm$ 0.21, respectively. The properties of the nucleus are consistent with those of other Jupiter Family comets. The best-fit temperature of the coma was 134 $\pm$ 11 K, slightly higher than the blackbody temperature at that heliocentric distance. Using Finson-Probstein modeling we found that the morphology of the trail was consistent with ejection during the 2007 outburst and was made up of dust grains between 250 $\mu$m and a few cm in radius. The trail mass was $\sim$ 1.2 - 5.3 $\times$ 10$^{10}$ kg.
    04/2014;
  • Article: 2014 HJ129
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    ABSTRACT: Abstract available on the publisher website.
    03/2014;
  • Article: 2014 HQ124
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    ABSTRACT: Abstract available on the publisher website.
    03/2014;
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    ABSTRACT: The results of taxonomical classification of the large primitive asteroids from the outer main belt to the giant planets based on NEOWISE data.
    02/2014;
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    ABSTRACT: The NEOWISE project has recently resumed its survey for asteroids and comets at 3.4 and 4.6 µm.
    02/2014;
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    ABSTRACT: Abstract available on the publisher website.
    01/2014;
  • Edward L. Wright, A. Mainzer
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    ABSTRACT: Thermophysical models have many parameters that cannot be determined using infrared observations at a single epoch. But by varying these parameters using a Monte Carlo Markov chain with reasonable prior distributions one can determine the uncertainties in the radiometric diameters introduced by the poorly known parameters: typically the rotation pole and the dimensionless thermal inertia parameter. This MCMC approach has been applied to several asteroids observed by WISE: 2010 AB78, a NEO observed by WISE in 3 epochs, has a well determined rotation pole and a diameter 1.28 +/- 0.03 km with 3 percent precision; 2010 CK9, an MBA observed by WISE in one epoch, has a diameter of 3.46 +/- 0.21 km with 6 percent precision; and 2010 MU112, a very hazardous asteroid with a MOID of 0.0011 AU, C3 = 869 km^2/sec^2, a diameter of 611 +/- 84 meters for 14 percent precision from one WISE epoch at phase angle 62 degrees. The proposed NEOcam mission will achieve a long lifetime using passive cooling and obtain many epochs of IR data on most NEOs, allowing the determination of rotation poles, thermal inertias, and diameters with good precision.
    01/2014;
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    ABSTRACT: The solar system science component of NASA’s Wide-field Infrared Survey Explorer (WISE), known as NEOWISE, extracted detections of more than 158,000 asteroids and comets, including 34,000 new discoveries. These objects were detected through a search algorithm that actively rejected inertially fixed sources such as stars and galaxies and selected candidate moving objects through the construction of position-time pairs known as tracklets. A minimum of five detections were required in order to construct a tracklet; this system enabled the discovery of new minor planets as well as detection of previously known objects. However, many more asteroids are potentially recoverable in the NEOWISE data, such as objects that failed to appear in five or more images. Stacking of objects with well-known ephemerides at the observational epoch has allowed for the recovery of many objects that fell below the single-frame detection threshold. Additional objects were recovered by searching the NEOWISE source lists for objects that appeared fewer than five times in single frames. We present the results of a pilot study that has allowed for the recovery of minor planets from the NEOWISE data using both techniques, resulting in the derivation of diameters and albedos for the sample. This pilot study will be extended to the entire catalog of known minor planets by the NEOWISE project in the near future.
    01/2014;
  • Article: 2013 YP139
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    ABSTRACT: Abstract available on the publisher website.
    12/2013;
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    ABSTRACT: Only a very small fraction of the asteroid population at size scales comparable to the object that exploded over Chelyabinsk, Russia has been discovered to date, and physical properties are poorly characterized. We present previously unreported detections of 106 close approaching near-Earth objects (NEOs) by the Wide-field Infrared Survey Explorer mission's NEOWISE project. These infrared observations constrain physical properties such as diameter and albedo for these objects, many of which are found to be smaller than 100 m. Because these objects are intrinsically faint, they were detected by WISE during very close approaches to the Earth, often at large apparent on-sky velocities. We observe a trend of increasing albedo with decreasing size, but as this sample of NEOs was discovered by visible light surveys, it is likely that selection biases against finding small, dark NEOs influence this finding.
    The Astrophysical Journal 10/2013; 784(2). · 6.73 Impact Factor
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    ABSTRACT: Asteroid families are the signatures of massive collisions between asteroids and represent an important source of small objects in the Main Belt. Using the Hierarchical Clustering Method to identify asteroid families, and the physical properties measured by the NEOWISE survey of Main Belt asteroids to discriminate between broad albedo classes, we refine family membership lists and identify new Main Belt families. This technique allows for improved family associations, especially for more dispersed families in crowded regions. We find 76 high confidence families representing over one-third of the total Main Belt population, of which 28 were previously unknown. We present here our results, focusing on both broad physical properties and specific interesting families. This work is the critical first step in determining the ages of asteroid families through numerical simulation of orbital evolution.
    10/2013;
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    ABSTRACT: Using the data from the WISE/NEOWISE mission we have derived albedo and size distribution of more than ~1200 Cybeles, ~1000 Hildas, ~1700 Jovian Trojans and a dozen irregular satellites of Jupiter and Saturn. This dataset increases by an order of magnitude our knowledge of the makeup of the small body populations between the Main Belt and Saturn. We find that all these populations are dominated by low albedo objects, with only the Cybele and Hilda populations having a small (less than 10% among the Cybeles and less than 1% among the Hildas, Trojans and irregular satellites) fraction of objects with albedos higher than 15%. Using the near-infrared albedos (in the 3.4 and 4.6 micron bands) we were also able to derive the taxonomic classifications of the largest objects in each populations, showing that they are dominated by C-, P- and D-type surfaces. The dominance of these dark bodies indicate two possible formation scenarios. The small body populations may have been formed in situ beyond the snow line, potentially serving as primitive bodies that can provide significant insight into the composition of the early Solar Nebula in the region of the Giant Planets. Alternatively, they may be captured bodies that were perturbed from the region outside the Giant Planets as the planets migrated during the early stages of Solar System formation. This allows for insight into the composition of the Trans-Neptunian population by study of populations that are closer, brighter and more accessible. The low percentages of the more stony objects common in the Main Asteroid Belt indicates that few of these objects were embedded in the populations, imposing significant constraints on the migration of Jupiter inside its current orbit.
    10/2013;
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    ABSTRACT: NEOWISE, the NASA planetary-funded extension of the Wide-field Infrared Survey Explorer (WISE) mission, observed over 150,000 minor planets over four infrared wavelength bands (Mainzer et al. 2011). Many of these observed asteroids have associated shapes and spin states derived by the radar community (see current list maintained by L. Benner at http://echo.jpl.nasa.gov lance/shapes/asteroid_shapes.html). Combined, these resources represent a valuable dataset for thermophysical modeling, a technique that combines shape models and infrared observations to determine the thermal inertia of an asteroid, which can indicate composition. However, the large number of objects within this dataset, as well as the detail of the radar shape models (which can be composed of thousands of surface facets), presented a computational challenge. In response, we employ advanced thermal modeling software which allows for full three-dimensional heat conduction, self-heating (via Monte Carlo ray tracing), and surfaces with variable reflective properties. We present thermophysical models using this software, and compare these results to more traditional thermophysical modeling techniques used in the asteroid community.
    10/2013;
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    ABSTRACT: The Wide-field Infrared Survey Explorer (WISE) observed 52 Centaurs and Scattered Disk Objects in the thermal infrared, including the 15 discoveries that were new. We present analyses of these observations to estimate sizes and mean optical albedos. We find mean albedos of 0.08 +/- 0.04 for the entire data set. Thermal fits yield average beaming parameters of 0.9 +/- 0.2 that are similar for both SDO and Centaur sub-classes. Biased cumulative size distributions yield size-frequency distribution power law indices ~ -1.7 +/- 0.3. The data also reveal a relation between albedo and color at the 3-sigma level. No significant relation between diameter and albedos is found.
    06/2013;
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    ABSTRACT: Using albedos from WISE/NEOWISE to separate distinct albedo groups within the Main Belt asteroids, we apply the Hierarchical Clustering Method to these subpopulations and identify dynamically associated clusters of asteroids. While this survey is limited to the ~35% of known Main Belt asteroids that were detected by NEOWISE, we present the families linked from these objects as higher confidence associations than can be obtained from dynamical linking alone. We find that over one-third of the observed population of the Main Belt is represented in the high-confidence cores of dynamical families. The albedo distribution of family members differs significantly from the albedo distribution of background objects in the same region of the Main Belt, however interpretation of this effect is complicated by the incomplete identification of lower-confidence family members. In total we link 38,298 asteroids into 76 distinct families. This work represents a critical step necessary to debias the albedo and size distributions of asteroids in the Main Belt and understand the formation and history of small bodies in our Solar system.
    The Astrophysical Journal 05/2013; 770(1). · 6.73 Impact Factor
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    ABSTRACT: We have carried out the Warm Spitzer Near Earth Object (NEO) Characterization survey (ExploreNEOs). We observed some 600 NEOs at 3.6 and 4.5 microns during the period 2009—2012. For each object we derive, through thermal modeling, diameter and albedo. Our results have been presented in a series of papers. To date, we have released almost all of our data and diameter and albedo solutions (Trilling et al. 2010, 2013). We compared the fidelity of our model solutions to “ground truth” data from other sources (Harris et al. 2011). We calculated statistical temperature histories for low delta-V objects (Mueller et al. 2011). We calculated the density of binary objects in our sample (Kistler et al. 2013). We derived the mean albedo for different taxonomic asteroid types (Thomas et al. 2011). We have carried out an extensive ground-based observing campaign and derived new absolute magnitudes for 100 NEOs, and derived an empirical correction from JPL/Horizons values that can be applied to all NEOs (Hagen et al. 2013). We have measured the fraction of NEOs that are likely of cometary origin (Mommert et al. 2013). Forthcoming papers will present additional ancillary ground-based data; a discussion of the probable source regions of NEOs, and the implications thereof; and results for a number of targets that were observed multiple times to understand the impact of phase angle and rotational variation on our model solutions. Together, these results help us constrain the global properties of NEOs and the evolution of the material in near-Earth space.
    04/2013;

Publication Stats

589 Citations
321.55 Total Impact Points

Institutions

  • 2006–2013
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States
  • 2003–2008
    • University of California, Los Angeles
      • Department of Physics and Astronomy
      Los Angeles, CA, United States
  • 2005
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States