The near-Earth object (NEO) population, which mainly consists of fragments from collisions between asteroids in the main asteroid belt, is thought to include contributions from short-period comets as ...well. One of the most promising NEO candidates for a cometary origin is near-Earth asteroid (3552) Don Quixote, which has never been reported to show activity. Here we present the discovery of cometary activity in Don Quixote based on thermal-infrared observations made with the Spitzer Space Telescope in its 3.6 and 4.5 mu m bands. Our observations clearly show the presence of a coma and a tail in the 4.5 mu m but not in the 3.6 mu m band, which is consistent with molecular band emission from CO sub(2). Thermal modeling of the combined photometric data on Don Quixote reveals a diameter of 18.4 super(+0.3) sub(-0.4) km and an albedo of 0.03 super(+0.02) sub(-0.01) which confirms Don Quixote to be the third-largest known NEO. We derive an upper limit on the dust production rate of 1.9 kg s super(-1) and derive a CO sub(2) gas production rate of (1.1 + or - 0.1) x 10 super(26) molecules s super(-1). Spitzer Infrared Spectrograph spectroscopic observations indicate the presence of fine-grained silicates, perhaps pyroxene rich, on the surface of Don Quixote. Our discovery suggests that CO sub(2) can be present in near-Earth space over a long time. The presence of CO sub(2) might also explain that Don Quixote's cometary nature remained hidden for nearly three decades.
Abstract We present the Citizen Science program Active Asteroids and describe discoveries stemming from our ongoing project. Our NASA Partner program is hosted on the Zooniverse online platform and ...launched on 2021 August 31, with the goal of engaging the community in the search for active asteroids—asteroids with comet-like tails or comae. We also set out to identify other unusual active solar system objects, such as active Centaurs, active quasi-Hilda asteroids (QHAs), and Jupiter-family comets (JFCs). Active objects are rare in large part because they are difficult to identify, so we ask volunteers to assist us in searching for active bodies in our collection of millions of images of known minor planets. We produced these cutout images with our project pipeline that makes use of publicly available Dark Energy Camera data. Since the project launch, roughly 8300 volunteers have scrutinized some 430,000 images to great effect, which we describe in this work. In total, we have identified previously unknown activity on 15 asteroids, plus one Centaur, that were thought to be asteroidal (i.e., inactive). Of the asteroids, we classify four as active QHAs, seven as JFCs, and four as active asteroids, consisting of one main-belt comet (MBC) and three MBC candidates. We also include our findings concerning known active objects that our program facilitated, an unanticipated avenue of scientific discovery. These include discovering activity occurring during an orbital epoch for which objects were not known to be active, and the reclassification of objects based on our dynamical analyses.
ABSTRACT Near-Earth objects (NEOs) are small solar system bodies whose orbits bring them close to the Earth's orbit. We are carrying out a Warm Spitzer Cycle 11 Exploration Science program entitled ...NEOSurvey-a fast and efficient flux-limited survey of 597 known NEOs in which we derive a diameter and albedo for each target. The vast majority of our targets are too faint to be observed by NEOWISE, though a small sample has been or will be observed by both observatories, which allows for a cross-check of our mutual results. Our primary goal is to create a large and uniform catalog of NEO properties. We present here the first results from this new program: fluxes and derived diameters and albedos for 80 NEOs, together with a description of the overall program and approach, including several updates to our thermal model. The largest source of error in our diameter and albedo solutions, which derive from our single-band thermal emission measurements, is uncertainty in , the beaming parameter used in our thermal modeling; for albedos, improvements in solar system absolute magnitudes would also help significantly. All data and derived diameters and albedos from this entire program are being posted on a publicly accessible Web page at nearearthobjects.nau.edu.
Biological soil crusts (biocrusts) are critical components of dryland and other ecosystems worldwide, and are increasingly recognized as novel model ecosystems from which more general principles of ...ecology can be elucidated. Biocrusts are often diverse communities, comprised of both eukaryotic and prokaryotic organisms with a range of metabolic lifestyles that enable the fixation of atmospheric carbon and nitrogen. However, how the function of these biocrust communities varies with succession is incompletely characterized, especially in comparison to more familiar terrestrial ecosystem types such as forests. We conducted a greenhouse experiment to investigate how community composition and soil-atmosphere trace gas fluxes of CO
2
, CH
4
, and N
2
O varied from early-successional light cyanobacterial biocrusts to mid-successional dark cyanobacteria biocrusts and late-successional moss-lichen biocrusts and as biocrusts of each successional stage matured. Cover type richness increased as biocrusts developed, and richness was generally highest in the late-successional moss-lichen biocrusts. Microbial community composition varied in relation to successional stage, but microbial diversity did not differ significantly among stages. Net photosynthetic uptake of CO
2
by each biocrust type also increased as biocrusts developed but tended to be moderately greater (by up to ≈25%) for the mid-successional dark cyanobacteria biocrusts than the light cyanobacterial biocrusts or the moss-lichen biocrusts. Rates of soil C accumulation were highest for the dark cyanobacteria biocrusts and light cyanobacteria biocrusts, and lowest for the moss-lichen biocrusts and bare soil controls. Biocrust CH
4
and N
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O fluxes were not consistently distinguishable from the same fluxes measured from bare soil controls; the measured rates were also substantially lower than have been reported in previous biocrust studies. Our experiment, which uniquely used greenhouse-grown biocrusts to manipulate community composition and accelerate biocrust development, shows how biocrust function varies along a dynamic gradient of biocrust successional stages.
•We find no correlation between band parameters and ExploreNEOs albedos and diameters.•There is no universal phase angle–Band Area Ratio correlation.•For NIR spectra, the Bus–DeMeo system identifies ...an excess of Q-types.•Our proportions of H, L, and LL chondrites differ from previous work on OC-like NEOs.
Near-infrared spectroscopy of Near-Earth Objects (NEOs) connects diagnostic spectral features to specific surface mineralogies. The combination of spectroscopy with albedos and diameters derived from thermal infrared observations can increase the scientific return beyond that of the individual datasets. For instance, some taxonomic classes can be separated into distinct compositional groupings with albedo and different mineralogies with similar albedos can be distinguished with spectroscopy. To that end, we have completed a spectroscopic observing campaign to complement the ExploreNEOs Warm Spitzer program that obtained albedos and diameters of nearly 600 NEOs (Trilling, D.E. et al. 2010. Astron. J. 140, 770–784. http://dx.doi.org/10.1088/0004-6256/140/3/770). The spectroscopy campaign included visible and near-infrared observations of ExploreNEOs targets from various observatories. Here we present the results of observations using the low-resolution prism mode (∼0.7–2.5μm) of the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We also include near-infrared observations of ExploreNEOs targets from the MIT-UH-IRTF Joint Campaign for Spectral Reconnaissance. Our dataset includes near-infrared spectra of 187 ExploreNEOs targets (125 observations of 92 objects from our survey and 213 observations of 154 objects from the MIT survey). We identify a taxonomic class for each spectrum and use band parameter analysis to investigate the mineralogies for the S-, Q-, and V-complex objects. Our analysis suggests that for spectra that contain near-infrared data but lack the visible wavelength region, the Bus–DeMeo system misidentifies some S-types as Q-types. We find no correlation between spectral band parameters and ExploreNEOs albedos and diameters. We investigate the correlations of phase angle with Band Area Ratio and near-infrared spectral slope. We find slightly negative Band Area Ratio (BAR) correlations with phase angle for Eros and Ivar, but a positive BAR correlation with phase angle for Ganymed. The results of our phase angle study are consistent with those of (Sanchez, J.A., Reddy, V., Nathues, A., Cloutis, E.A., Mann, P., Hiesinger, H. 2012. Icarus 220, 36–50. http://dx.doi.org/10.1016/j.icarus.2012.04.008, arXiv:1205.0248). We find evidence for spectral phase reddening for Eros, Ganymed, and Ivar. We identify the likely ordinary chondrite type analog for an appropriate subset of our sample. Our resulting proportions of H, L, and LL ordinary chondrites differ from those calculated for meteorite falls and in previous studies of ordinary chondrite-like NEOs.
► Fitted phase curves for about half a million asteroids using re-calibrated MPC data. ► Computed probabilities of belonging to C, S, and X for the half a million asteroids. ► Predicted taxonomic ...preponderance in asteroid families.
We explore the correlation between an asteroid’s taxonomy and photometric phase curve using the H, G12 photometric phase function, with the shape of the phase function described by the single parameter G12. We explore the usability of G12 in taxonomic classification for individual objects, asteroid families, and dynamical groups. We conclude that the mean values of G12 for the considered taxonomic complexes are statistically different, and also discuss the overall shape of the G12 distribution for each taxonomic complex. Based on the values of G12 for about half a million asteroids, we compute the probabilities of C, S, and X complex membership for each asteroid. For an individual asteroid, these probabilities are rather evenly distributed over all of the complexes, thus preventing meaningful classification. We then present and discuss the G12 distributions for asteroid families, and predict the taxonomic complex preponderance for asteroid families given the distribution of G12 in each family. For certain asteroid families, the probabilistic prediction of taxonomic complex preponderance can clearly be made. In particular, the C complex preponderant families are the easiest to detect, the Dora and Themis families being prime examples of such families. We continue by presenting the G12-based distribution of taxonomic complexes throughout the main asteroid belt in the proper element phase space. The Nysa–Polana family shows two distinct regions in the proper element space with different G12 values dominating in each region. We conclude that the G12-based probabilistic distribution of taxonomic complexes through the main belt agrees with the general view of C complex asteroid proportion increasing towards the outer belt. We conclude that the G12 photometric parameter cannot be used in determining taxonomic complex for individual asteroids, but it can be utilized in the statistical treatment of asteroid families and different regions of the main asteroid belt.
Spitzer Albedos of Near-Earth Objects Gustafsson, Annika; Trilling, David E.; Mommert, Michael ...
The Astronomical journal,
08/2019, Letnik:
158, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Thermal infrared observations are the most effective way to measure asteroid diameter and albedo for a large number of near-Earth objects (NEOs). Major surveys like NEOWISE, NEOSurvey, ExploreNEOs, ...and NEOLegacy find a small fraction of high albedo objects that do not have clear analogs in the current meteorite population. About 8% of Spitzer-observed NEOs have nominal albedo solutions greater than 0.5. This may be a result of light-curve variability leading to an incorrect estimate of diameter or inaccurate absolute visual magnitudes. For a sample of 23 high-albedo NEOs we do not find that their shapes are significantly different from the McNeill et al. NEO shape distribution. We performed a Monte Carlo analysis on 1505 NEOs observed by Spitzer, sampling the visible and thermal fluxes of all targets to determine the likelihood of obtaining a high albedo erroneously. Implementing the McNeill shape distribution for NEOs, we provide an upper limit on the geometric albedo of 0.5 0.1 for the near-Earth population.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) We use Spitzer Space Telescope 24 mu m data to search for debris disks among 122 AFGKM stars from the ~670 Myr clusters Hyades, Coma ...Ber, and Praesepe, utilizing a number of advances in data reduction and determining the intrinsic colors of main-sequence stars. For our sample, the 1sigma dispersion about the main-sequence V-KS, KS-24 locus is approximately 3.1%. We identify seven debris disks at 10% or more (> or =, slanted3sigma confidence level) above the expected KS-24 for purely photospheric emission. The incidence of excesses of 10% or greater in our sample at this age is ...%. Combining with results from the literature, the rate is ...% for early-type (B9-F4) stars and ...% for solar-like (F5-K9) stars. Our primary sample has strict criteria for inclusion to allow comparison with other work; when we relax these criteria, three additional debris disks are detected. They are all around stars of solar-like type and hence reinforce our conclusion that disks around such stars are still relatively common at 670 Myr and are similar to the rate around early-type stars. The apparently small difference in decay rates between early-type and solar-like stars is inconsistent with the first-order theoretical predictions that the later type stellar disks would decay an order of magnitude more quickly than the earlier type ones.
Extreme Asteroids in the Pan-STARRS 1 Survey McNeill, Andrew; Fitzsimmons, Alan; Jedicke, Robert ...
The Astronomical journal,
12/2018, Letnik:
156, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Using the first 18 months of the Pan-STARRS 1 survey, we have identified 33 candidate high-amplitude objects for follow-up observations and carried out observations of 22 asteroids. Four of the ...observed objects were found to have observed amplitude Aobs ≥ 1.0 mag. We find that these high-amplitude objects are most simply explained by single rubble-pile objects with some density-dependent internal strength, allowing them to resist mass shedding even at their highly elongated shapes. Three further objects, although below the cutoff for "high amplitude," had a combination of elongation and rotation period which also may require internal cohesive strength, depending on the density of the body. We find that none of the "high-amplitude asteroids" identified here require any unusual cohesive strengths to resist rotational fission. Three asteroids were sufficiently observed to allow for shape and spin-pole models to be determined through light curve inversion. Asteroid 45864 was determined to have retrograde rotation with spin-pole axes λ = 218° 10°, β = −82° 5° and asteroid 206167 was found to have best-fit spin-pole axes λ = 57° 5°, β = −67° 5°. An additional object not initially measured with Aobs > 1.0 mag, 49257, was determined to have a shape model that does suggest a high-amplitude object. Its spin-pole axes were best fit for values λ = 112° 6°, β = 6° 5°. In the course of this project, to date no large superfast rotators (Prot < 2.2 hr) have been identified.
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