We have performed detailed thermophysical and dynamical modelling of the Jovian Trojan (1173) Anchises. Our results show that this is the most unusual object. By examining observational data of ...Anchises taken by IRAS, Akari and WISE at wavelengths between 11.5 and 60 μm, together with the variations in its optical light curve, we find that Anchises is most likely an elongated body, with an axis ratio, a/b, of around 1.4. This results in calculated best-fitting dimensions for Anchises of 170 × 121 × 121 km (or an equivalent diameter of 136 +18/−11 km). We find that the observations of Anchises are best fitted by the object having a retrograde sense of rotation, and an unusually high thermal inertia in the range 25-100 J m−2 s−0.5 K−1 (3σ confidence level). The geometric albedo of Anchises is found to be 0.027 (+0.006/−0.007). Anchises therefore has one of the highest published thermal inertias of any object larger than 100 km in diameter, at such large heliocentric distances, as well as being one of the lowest albedo objects ever observed. More observations (visual and thermal) are needed to see whether there is a link between the very shallow phase curve, with almost no opposition effect, and the derived thermal properties for this large Trojan asteroid. Our dynamical investigation of Anchises' orbit has revealed it to be dynamically unstable on time-scales of hundreds of millions of years, similar to the unstable Neptunian Trojans 2001 QR322 and 2008 LC18. Unlike those objects, however, we find that the dynamical stability of Anchises is not a function of its initial orbital elements, the result of the exceptional precision with which its orbit is known. Our results are the first to show that a Jovian Trojan is dynamically unstable, and add further weight to the idea that the planetary Trojans likely represent a significant ongoing contribution to the dynamically unstable Centaur population, the parents of the short-period comets. The observed instability (fully half of all clones of Anchises escape the Solar system within 350 Myr) does not rule out a primordial origin for Anchises, but, when taken in concert with the result of our thermophysical analysis, suggest that it would be a fascinating target for a future study.
CRISPR-based gene drives have the potential to spread within populations and are considered as promising vector control tools. A doublesex-targeting gene drive was able to suppress laboratory ...Anopheles mosquito populations in small and large cages, and it is considered for field application. Challenges related to the field-use of gene drives and the evolving regulatory framework suggest that systems able to modulate or revert the action of gene drives, could be part of post-release risk-mitigation plans. In this study, we challenge an AcrIIA4-based anti-drive to inhibit gene drive spread in age-structured Anopheles gambiae population under complex feeding and behavioural conditions. A stochastic model predicts the experimentally-observed genotype dynamics in age-structured populations in medium-sized cages and highlights the necessity of large-sized cage trials. These experiments and experimental-modelling framework demonstrate the effectiveness of the anti-drive in different scenarios, providing further corroboration for its use in controlling the spread of gene drive in Anopheles.
Recent stellar occultations have allowed accurate instantaneous size and apparent shape determinations of the large Kuiper belt object (50000) Quaoar and the detection of two rings with spatially ...variable optical depths. In this paper we present new visible range light curve data of Quaoar from the Kepler /K2 mission, and thermal light curves at 100 and 160 µm obtained with Herschel /PACS. The K2 data provide a single-peaked period of 8.88 h, very close to the previously determined 8.84 h, and it favours an asymmetric double-peaked light curve with a 17.76 h period. We clearly detected a thermal light curve with relative amplitudes of ~ 10% at 100 and at 160 µm. A detailed thermophysical modelling of the system shows that the measurements can be best fit with a triaxial ellipsoid shape, a volume-equivalent diameter of 1090 km, and axis ratios of a/b = 1.19 and b/c = 1.16. This shape matches the published occultation shape, as well as visual and thermal light curve data. The radiometric size uncertainty remains relatively large (±40 km) as the ring and satellite contributions to the system-integrated flux densities are unknown. In the less likely case of negligible ring or satellite contributions, Quaoar would have a size above 1100 km and a thermal inertia ≤ 10 J m −2 K −1 s −1/2 . A large and dark Weywot in combination with a possible ring contribution would lead to a size below 1080 km in combination with a thermal inertia ≳10 J m −2 K −1 s −1/2 , notably higher than that of smaller Kuiper belt objects with similar albedo and colours. We find that Quaoar’s density is in the range 1.67–1.77 g cm −3 , significantly lower than previous estimates. This density value closely matches the relationship observed between the size and density of the largest Kuiper belt objects.
The Bohemian Forest Ecosystem encompasses various wildlife management systems. Two large, contiguous national parks (one in Germany and one in the Czech Republic) form the centre of the area, are ...surrounded by private hunting grounds, and hunting regulations in each country differ. Here we aimed at unravelling the influence of management-related and environmental factors on the distribution of red deer (Cervus elaphus) and roe deer (Capreolus capreolus) in this ecosystem. We used the standing crop method based on counts of pellet groups, with point counts every 100 m along 218 randomly distributed transects. Our analysis, which accounted for overdispersion as well as zero inflation and spatial autocorrelation, corroborated the view that both human management and the physical and biological environment drive ungulate distribution in mountainous areas in Central Europe. In contrast to our expectations, protection by national parks was the least important variable for red deer and the third important out of four variables for roe deer; protection negatively influenced roe deer distribution in both parks and positively influenced red deer distribution in Germany. Country was the most influential variable for both red and roe deer, with higher counts of pellet groups in the Czech Republic than in Germany. Elevation, which indicates increasing environmental harshness, was the second most important variable for both species. Forest cover was the least important variable for roe deer and the third important variable for red deer; the relationship for roe deer was positive and linear, and optimal forest cover for red deer was about 70% within a 500 m radius. Our results have direct implications for the future conservation management of deer in protected areas in Central Europe and show in particular that large non-intervention zones may not cause agglomerations of deer that could lead to conflicts along the border of protected, mountainous areas.
Aims.
We aim to determine far-infrared fluxes at 70, 100, and 160
μ
m for the five major Uranus satellites, Titania, Oberon, Umbriel, Ariel, and Miranda. Our study is based on the available ...calibration observations at wavelengths taken with the PACS photometer aboard the
Herschel
Space Observatory.
Methods.
The bright image of Uranus was subtracted using a scaled Uranus point spread function (PSF) reference established from all maps of each wavelength in an iterative process removing the superimposed moons. The photometry of the satellites was performed using PSF photometry. Thermophysical models of the icy moons were fitted to the photometry of each measurement epoch and auxiliary data at shorter wavelengths.
Results.
The best-fit thermophysical models provide constraints for important properties of the moons, such as surface roughness and thermal inertia. We present the first thermal infrared radiometry longward of 50
μ
m for the four largest Uranian moons, Titania, Oberon, Umbriel, and Ariel, at epochs with equator-on illumination. Due to this inclination geometry, heat transport took place to the night side so that thermal inertia played a role, allowing us to constrain that parameter. Also, we found some indication for differences in the thermal properties of leading and trailing hemispheres. The total combined flux contribution of the four major moons relative to Uranus is 5.7 × 10
−3
, 4.8 × 10
−3
, and 3.4 × 10
−3
at 70, 100, and 160
μ
m, respectively. We therefore precisely specify the systematic error of the Uranus flux by its moons when Uranus is used as a far-infrared prime flux calibrator. Miranda is considerably fainter and always close to Uranus, impeding reliable photometry.
Conclusions.
We successfully demonstrate an image processing technique for PACS photometer data that allows us to remove a bright central source and reconstruct point source fluxes on the order of 10
−3
of the central source as close as ≈3 × the half width at half maximum of the PSF. We established improved thermophysical models of the five major Uranus satellites. Our derived thermal inertia values resemble those of trans-neptunian object (TNO) dwarf planets, Pluto and Haumea, more than those of smaller TNOs and Centaurs at heliocentric distances of about 30 AU.
Infrared measurements of asteroids are crucial for the determination of physical and thermal properties of individual objects, and for understanding the small-body populations in the solar system as ...a whole. However, standard radiometric methods can only be applied if the orbit of an object is known, hence its position at the time of the observation. With JWST-MIRI observations the situation will change and many unknown, often very small, solar system objects will be detected. Later orbit determinations are difficult due to the faintness of the objects and the lack of dedicated follow-up concepts. We present MIRI observations of the outer-belt asteroid (10920) 1998 BC1 and an unknown object, detected in all nine MIRI bands in close apparent proximity to (10920). We developed a new method called STM-ORBIT to interpret the multi-band measurements without knowing the object’s true location. The power of the new technique is that it determines the most-likely heliocentric and observer-centric distance and phase angle ranges, allowing us to make a radiometric size estimate. The application to the MIRI fluxes of (10920) was used to validate the method. It leads to a confirmation of the known radiometric size-albedo solution, and puts constraints on the asteroid’s location and orbit in agreement with its true orbit. To back up the validation of the method, we obtained additional ground-based light curve observations of (10920), combined with
Gaia
data, which indicate a very elongated object (
a/b ≥
1.5), with a spin-pole at (
λ
,
β
)
ecl
= (178°, +81°), with an estimated error of about 20°, and a rotation period of 4.861191 ± 0.000015 h. A thermophysical study of all available JWST-MIRI and WISE measurements leads to a size of 14.5–16.5 km (diameter of an equal-volume sphere), a geometric albedo
p
V
between 0.05 and 0.10, and a thermal inertia in the range 9–35 (best value 15) J m
−2
s
−0.5
K
−1
. For the newly discovered MIRI object, the STM-ORBIT method revealed a size of 100–230 m. The new asteroid must be on a low-inclination orbit (0.7° <
i <
2.0°) and it was located in the inner main-belt region during JWST observations. A beaming parameter
η
larger than 1.0 would push the size even below 100 meters, a main-belt regime that has escaped IR detections so far. This kind of MIRI observations can therefore contribute to formation and evolution studies via classical size-frequency studies, which are currently limited to objects larger than about one kilometer in size. We estimate that MIRI frames with pointings close to the ecliptic and short integration times of only a few seconds will always include a few asteroids; most of them will be unknown objects.
ABSTRACT
The Hilda asteroids are among the least studied populations in the asteroid belt, despite their potential importance as markers of Jupiter’s migration in the early Solar system. We present ...new mid-infrared observations of two notable Hildas, (1162) Larissa, and (1911) Schubart, obtained using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST), and use these to characterize their thermal inertia and physical properties. For (1162) Larissa, we obtain an effective diameter of 46.5$^{+2.3}_{-1.7}$ km, an albedo of 0.12 ± 0.02, and a thermal inertia of 15$^{+10}_{-8}$ Jm−2 s1/2 K−1. In addition, our Larissa thermal measurements are well matched with an ellipsoidal shape with an axial ratio a/b = 1.2 for the most-likely spin properties. Our modelling of (1911) Schubart is not as refined, but the thermal data point towards a high-obliquity spin-pole, with a best fit a/b = 1.3 ellipsoidal shape. This spin-shape solution is yielding a diameter of 72$^{+3}_{-4}$ km, an albedo of 0.039± 0.02, and a thermal inertia below 30 Jm−2 s1/2 K−1 (or 10$^{+20}_{-5}$ Jm−2 s1/2 K−1). As with (1162) Larissa, our results suggest that (1911) Schubart is aspherical, and likely elongated in shape. Detailed dynamical simulations of the two Hildas reveal that both exhibit strong dynamical stability, behaviour that suggests that they are primordial, rather than captured objects. The differences in their albedos, along with their divergent taxonomical classification, suggests that despite their common origin, the two have experienced markedly different histories.
Abstract
Asteroids (24) Themis and (65) Cybele have an absorption feature at 3.1
μ
m reported to be directly linked to surface water ice. We searched for water vapor escaping from these asteroids ...with the Herschel Space Observatory Heterodyne Instrument for the Far Infrared. While no H
2
O line emission was detected, we obtain sensitive 3
σ
water production rate upper limits of
Q
(H
2
O) < 4.1 × 10
26
molecules s
−1
for Themis and
Q
(H
2
O) < 7.6 × 10
26
molecules s
−1
for Cybele. Using a thermophysical model, we merge data from the Subaru/Cooled Mid-Infrared Camera and Spectrometer and the Herschel/Spectral and Photometric Imaging Receiver with the contents of a multi-observatory database to derive new radiometric properties for these two asteroids. For Themis, we find a thermal inertia
J m
−2
s
−1/2
K
−1
, a diameter
km, and a geometric
V
-band albedo
p
V
= 0.07 ± 0.01. For Cybele, we obtain a thermal inertia
J m
−2
s
−1/2
K
−1
, a diameter 282 ± 9 km, and an albedo
p
V
= 0.042 ± 0.005. Using all inputs, we estimate that water ice intimately mixed with the asteroids’ dark surface material would cover <0.0017% (for Themis) and <0.0033% (for Cybele) of their surfaces, while an areal mixture with very clean ice (Bond albedo 0.8 for Themis and 0.7 for Cybele) would cover <2.2% (for Themis) and <1.5% (for Cybele) of their surfaces. While surface (and subsurface) water ice may exist in small localized amounts on both asteroids, it is not the reason for the observed 3.1
μ
m absorption feature.
Aims. Our aims are to determine flux densities and their photometric accuracy for a set of seventeen stars that range in flux from intermediately bright (≲2.5 Jy) to faint (≳5 mJy) in the ...far-infrared (FIR). We also aim to derive signal-to-noise dependence with flux and time, and compare the results with predictions from the Herschel exposure-time calculation tool. Methods. We obtain aperture photometry from Herschel-PACS high-pass-filtered scan maps and chop/nod observations of the faint stars. The issues of detection limits and sky confusion noise are addressed by comparison of the field-of-view at different wavelengths, by multi-aperture photometry, by special processing of the maps to preserve extended emission, and with the help of large-scale absolute sky brightness maps from AKARI. This photometry is compared with flux-density predictions based on photospheric models for these stars. We obtain a robust noise estimate by fitting the flux distribution per map pixel histogram for the area around the stars, scaling it for the applied aperture size and correcting for noise correlation. Results. For 15 stars we obtain reliable photometry in at least one PACS filter, and for 11 stars we achieve this in all three PACS filters (70, 100, 160 μm). Faintest fluxes, for which the photometry still has good quality, are about 10–20 mJy with scan map photometry. The photometry of seven stars is consistent with models or flux predictions for pure photospheric emission, making them good primary standard candidates. Two stars exhibit source-intrinsic far-infrared excess: β Gem (Pollux), being the host star of a confirmed Jupiter-size exoplanet, due to emission of an associated dust disk, and η Dra due to dust emission in a binary system with a K1 dwarf. The investigation of the 160 μm sky background and environment of four sources reveals significant sky confusion prohibiting the determination of an accurate stellar flux at this wavelength. As a good model approximation, for nine stars we obtain scaling factors of the continuum flux models of four PACS fiducial standards with the same or quite similar spectral type. We can verify a linear dependence of signal-to-noise ratio (S/N) with flux and with square root of time over significant ranges. At 160 μm the latter relation is, however, affected by confusion noise. Conclusions. The PACS faint star sample has allowed a comprehensive sensitivity assessment of the PACS photometer. Accurate photometry allows us to establish a set of five FIR primary standard candidates, namely α Ari, ε Lep, ω Cap, HD 41047 and 42 Dra, which are 2–20 times fainter than the faintest PACS fiducial standard (γ Dra) with absolute accuracy of <6%. For three of these primary standard candidates, essential stellar parameters are known, meaning that a dedicated flux model code may be run.
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