Thermophysical models allow for improved constraints on the physical and thermal surface properties of asteroids beyond what can be inferred from more simple thermal modeling, provided that a ...sufficient number of observations is available. We present thermophysical modeling results of observations from the Near-Earth Object WISE (NEOWISE) mission for two near-Earth asteroids which are the targets of the DESTINY+ flyby mission: (3200) Phaethon and (155140) 2005 UD. Our model assumes a rotating, cratered, spherical surface, and employs a Monte Carlo Markov Chain to explore the multidimensional parameter space of the fit. We find an effective spherical diameter for Phaethon of km, a geometric albedo of pV = 0.16 0.02, and a thermal inertia Γ = 880 , using five epochs of NEOWISE observations. The best model fit for (155140) 2005 UD was less well constrained due to only having two NEOWISE observation epochs, giving a diameter of 1.2 0.4 km and a geometric albedo of pV = 0.14 0.09.
Abstract
We present space-based thermal infrared observations of the presumably Geminid-associated asteroids: (3200) Phaethon, 2005 UD, and 1999 YC using Wide-field Infrared Survey ...Explorer/Near-Earth Object WISE. The images were taken at the four wavelength bands 3.4
μ
m (W1), 4.6
μ
m (W2), 12
μ
m (W3), and 22
μ
m (W4). We find no evidence of lasting mass loss in the asteroids over the decadal multiepoch data sets. We set an upper limit to the mass-loss rate in dust of
Q
dust
≲ 2 kg s
−1
for Phaethon and ≲0.1 kg s
−1
for both 2005 UD and 1999 YC, respectively, with little dependency over the observed heliocentric distances of
R
h
= 1.0–2.3 au. For Phaethon, even if the maximum mass loss was sustained over the 1000(s) yr dynamical age of the Geminid stream, it is more than two orders of magnitude too small to supply the reported stream mass (10
13–14
kg). The Phaethon-associated dust trail (Geminid stream) is not detected at
R
h
= 2.3 au, corresponding to an upper limit on the optical depth of
τ
< 7 × 10
−9
. Additionally, no comoving asteroids with radii
r
e
< 650 m were found. The DESTINY
+
dust analyzer would be capable of detecting several of the 10
μ
m sized interplanetary dust particles when at far distances (≳50,000 km) from Phaethon. From 2005 UD, if the mass-loss rate lasted over the 10,000 yr dynamical age of the Daytime Sextantid meteoroid stream, the mass of the stream would be ∼10
10
kg. The 1999 YC images showed neither the related dust trail (the optical depth
τ
< 2 × 10
−8
) nor comoving objects with radii
r
e
< 170 m at
R
h
= 1.6 au. Estimated physical parameters from these limits do not explain the production mechanism of the Geminid meteoroid stream. Lastly, to explore the origin of the Geminids, we discuss the implications for our data in relation to the possibly sodium-driven perihelion activity of Phaethon.
Abstract Hyperactive comet activity typically becomes evident beyond the frost line (∼3–4 au) where it becomes too cold for water-ice to sublimate. If carbon monoxide (CO) and carbon dioxide (CO 2 ) ...are the species that drive activity at sufficiently large distances, then detailed studies on the production rates of these species are extremely valuable to examine the formation of the solar system because these two species (beyond water) are next culpable for driving cometary activity. The NEOWISE reactivated mission operates at two imaging bandpasses, W 1 and W 2 at 3.4 μ m and 4.6 μ m, respectively, with the W 2 channel being fully capable of detecting CO and CO 2 at 4.67 μ m and 4.23 μ m in the same bandpass. It is extremely difficult to study CO 2 from the ground due to contamination in Earth’s atmosphere. We present our W 1 and W 2 photometry, dust measurements, and findings for comets C/2014 B1 (Schwartz), C/2017 K2 (Pan-STARRS), and C/2010 U3 (Boattini), hereafter, B1, K2, and U3, respectively. Our results assess CO and CO 2 gas production rates observed by NEOWISE. We have determined: (1) comets B1 and K2 have CO 2 and CO gas production rates of ∼10 27 and ∼10 29 molecules s −1 , respectively, if one assumes the excess emission is attributed to either all CO or all CO 2; (2) B1 and K2 are considered hyperactive in that their measured Af ρ dust production values are on the order of ≳10 3 cm; and (3) the CO and CO 2 production rates do not always follow the expected convention of increasing with decreased heliocentric distance, while B1 and K2 exhibit noticeable dust activity on their inbound leg orbits.
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. Because 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 mu m. Conversely, the 4.6 mu m albedo distribution spans the full range of possible values with no clear grouping. Asteroid families show a narrow distribution of 3.4 mu m 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 mu m albedo group. We show that near-infrared albedos derived from simultaneous thermal emission and reflected light measurements are important indicators of asteroid taxonomy and can identify interesting targets for spectroscopic follow-up.
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.
We present initial results from the Wide-field Infrared Survey Explorer (WISE), a four-band all-sky thermal infrared survey that produces data well suited for measuring the physical properties of ...asteroids, and the NEOWISE enhancement to the WISE mission allowing for detailed study of solar system objects. Using a NEATM thermal model fitting routine, we compute diameters for over 100,000 Main Belt asteroids from their IR thermal flux, with errors better than 10%. We then incorporate literature values of visible measurements (in the form of the H absolute magnitude) to determine albedos. Using these data we investigate the albedo and diameter distributions of the Main Belt. As observed previously, we find a change in the average albedo when comparing the inner, middle, and outer portions of the Main Belt. We also confirm that the albedo distribution of each region is strongly bimodal. We observe groupings of objects with similar albedos in regions of the Main Belt associated with dynamical breakup families. Asteroid families typically show a characteristic albedo for all members, but there are notable exceptions to this. This paper is the first look at the Main Belt asteroids in the WISE data, and only represents the preliminary, observed raw size, and albedo distributions for the populations considered. These distributions are subject to survey biases inherent to the NEOWISE data set and cannot yet be interpreted as describing the true populations; the debiased size and albedo distributions will be the subject of the next paper in this series.
Abstract
Probing small main-belt asteroids provides insight into their formation and evolution through multiple dynamical and collisional processes. These asteroids also overlap in size with the ...potentially hazardous near-Earth object population and supply the majority of these objects. The Lucy mission will perform a flyby of the small main-belt asteroid, (152830) Dinkinesh, on 2023 November 1, in preparation for its mission to the Jupiter Trojan asteroids. In this Letter, we present data to support the planning of Lucy’s imminent encounter of Dinkinesh. We employed aperture photometry on stacked frames of Dinkinesh obtained by the Wide-field Infrared Survey Explorer and performed thermal modeling on a detection at 12
μ
m to compute diameter and albedo values. Through this method, we determined Dinkinesh has an effective spherical diameter of
0.76
−
0.21
+
0.11
km and a visual geometric albedo of
0.27
−
0.06
+
0.25
at the 16th and 84th percentiles. This albedo is consistent with typical stony (S-type) asteroids. These measurements will enable the Lucy team to optimize planning for the flyby of Dinkinesh, including refinement of exposure times and flyby geometry. The data obtained from this mission will, in turn, allow us to better understand the calibration of our thermal models by providing ground truth data. The Lucy flyby presents a rare opportunity to study the smallest main-belt asteroid ever observed in situ.
Quantifying the accuracy with which physical properties of asteroids can be determined from thermal modeling is critical to measuring the impact of infrared data on our understanding of asteroids. ...Previous work has used independently derived diameters (from asteroid radar, occultations, and spacecraft visits) to test the accuracy of the NEOWISE diameter determinations. Here, we present a new and different method for bounding the actual NEOWISE diameter errors in the Main Belt based on our knowledge of the albedos of asteroid families. We show the 1 relative diameter error for the Main Belt population must be less than 17.5% for the vast majority of objects. For a typical uncertainty on H magnitude of 0.2 mag, the relative error on diameter for the population would be ∼10%.
The Wide-field Infrared Survey Explorer (WISE) observed 52 Centaurs and scattered disk objects (SDOs) in the thermal infrared, including 15 new discoveries. We present analyses of these observations ...to estimate sizes and mean optical albedos. We find mean albedos of 0.08 + or - 0.04 for the entire data set. Thermal fits yield average beaming parameters of 0.9 + or - 0.2 that are similar for both SDO and Centaur sub-classes. Biased cumulative size distributions yield size-frequency distribution power law indices of ~-1.7 + or - 0.3. The data also reveal a relation between albedo and color at the 3sigma level. No significant relation between diameter and albedos is found.
Abstract
We present new thermophysical model fits of 1847 asteroids, deriving thermal inertia, diameter, and Bond and visible geometric albedo. We use thermal flux measurements obtained by the ...Wide-field Infrared Survey Explorer (WISE) during its fully cryogenic phase, when both the 12
μ
m (
W3
) and 22
μ
m (
W4
) bands were available. We take shape models and spin information from the Database of Asteroid Models from Inversion Techniques (DAMIT) and derive new shape models through lightcurve inversion and combining WISE photometry with existing DAMIT lightcurves. When we limit our sample to the asteroids with the most reliable shape models and thermal flux measurements, we find broadly consistent thermal inertia relations with recent studies. We apply fits to the diameters
D
(km) and thermal inertia Γ (J m
−2
s
−0.5
K
−1
) normalized to 1 au with a linear relation of the form
log
Γ
=
α
+
β
log
D
, where we find
α
= 2.667 ± 0.059 and
β
= −0.467 ± 0.044 for our sample alone and
α
= 2.509 ± 0.017 and
β
= −0.352 ± 0.012 when combined with other literature estimates. We find little evidence of any correlation between rotation period and thermal inertia, owing to the small number of slow rotators to consider in our sample. While the large uncertainties on the majority of our derived thermal inertia only allow us to identify broad trends between thermal inertia and other physical parameters, we can expect a significant increase in high-quality thermal flux measurements and asteroid shape models with upcoming infrared and wide-field surveys, enabling even more thermophysical modeling of higher precision in the future.
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