ABSTRACT
67P/Churyumov–Gerasimenko is a Jupiter-family comet that was the target of the Rosetta mission, the first mission to successfully orbit and land a probe on a comet. This mission was ...accompanied by a large ground-based observing campaign. We have developed a pipeline to calibrate and measure photometry of comet 67P during its 2016 perihelion passage, making use of all visible wavelength broad-band imaging collected across a wide range of facilities. The pipeline calibrates the brightness of the comet to a common photometric system (Pan-STARRS 1) using background stars within the field allowing for compilation and comparison of multiple data sets. Results follow the predictions based on previous apparitions: 67P shows no obvious change in activity levels from orbit-to-orbit and coma colours remain constant throughout the apparition. We detected an outburst on 2015 August 22 of ∼0.14 mag. The brightness and estimated mass of this outburst puts it in line with the outbursts directly observed on the nucleus by Rosetta. An in situ outburst was observed at the same time as the one seen from the ground; however, linking these two events directly remains challenging.
Six Outbursts of Comet 46P/Wirtanen Kelley, Michael S. P.; Farnham, Tony L.; Li, Jian-Yang ...
The planetary science journal,
08/2021, Letnik:
2, Številka:
4
Journal Article
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Abstract
Cometary activity is a manifestation of sublimation-driven processes at the surface of nuclei. However, cometary outbursts may arise from other processes that are not necessarily driven by ...volatiles. In order to fully understand nuclear surfaces and their evolution, we must identify the causes of cometary outbursts. In that context, we present a study of mini-outbursts of comet 46P/Wirtanen. Six events are found in our long-term lightcurve of the comet around its perihelion passage in 2018. The apparent strengths range from −0.2 to −1.6 mag in a 5″ radius aperture and correspond to dust masses between ∼10
4
and 10
6
kg, but with large uncertainties due to the unknown grain size distributions. However, the nominal mass estimates are on the same order of magnitude as the mini-outbursts at comet 9P/Tempel 1 and 67P/Churyumov-Gerasimenko, events that were notably lacking at comet 103P/Hartley 2. We compare the frequency of outbursts at the four comets, and suggest that the surface of 46P has large-scale (∼10–100 m) roughness that is intermediate to that of 67P and 103P, if not similar to the latter. The strength of the outbursts appear to be correlated with time since the last event, but a physical interpretation with respect to solar insolation is lacking. We also examine Hubble Space Telescope images taken about two days following a near-perihelion outburst. No evidence for macroscopic ejecta was found in the image, with a limiting radius of about 2 m.
From the 389 OGLE-III 2002 observations of Galactic bulge microlensing events, we select 321 that are well described by a point-source point-lens light-curve model. From this sample we identify one ...event, 2002-BLG-055, that we regard as a strong planetary lensing candidate, and another, 2002-BLG-140, that is a possible candidate. If each of the 321 lens stars has one planet with a mass ratio q=m/M= 10-3 and orbit radius a=RE, the Einstein ring radius, analysis of detection efficiencies indicates that 14 planets should have been detectable with 2 > 25. Assuming our candidate is due to planetary lensing, then the abundance of planets with q= 10-3 and a=RE is np≈n/14 = 7 per cent. Conversion to physical units (Jupiter masses, MJup, and astronomical units, au) gives the abundance of ‘cool Jupiters’(m≈MJup, a≈ 4 au) per lens star as np≈n/5.5 = 18 per cent. The detection probability scales roughly with q and (2)-1/2, and drops off from a peak at a≈ 4 au like a Gaussian with a dispersion of 0.4 dex.
Aims.
The discovery of the first active interstellar object 2I/Borisov provides an unprecedented opportunity to study planetary formation processes in another planetary system. In particular, ...spectroscopic observations of 2I allow us to constrain the composition of its nuclear ices.
Methods.
We obtained optical spectra of 2I with the 4.2 m
William Herschel
and 2.5 m
Isaac Newton
telescopes between 2019 September 30 and October 13, when the comet was between 2.5 au and 2.4 au from the Sun. We also imaged the comet with broadband filters on 15 nights from September 11 to October 17, as well as with a CN narrow-band filter on October 18 and 20, with the TRAPPIST-North telescope.
Results.
Broadband imaging confirms that the dust coma colours (
B
−
V
= 0.82 ± 0.02,
V
−
R
= 0.46 ± 0.03,
R
−
I
= 0.44 ± 0.03,
B
−
R
= 1.28 ± 0.03) are the same as for Solar System comets. We detect CN emission in all spectra and in the TRAPPIST narrow-band images with production rates between 1.6 × 10
24
and 2.1 × 10
24
molec/s. No other species are detected. We determine three-sigma upper limits for C
2
, C
3
, and OH production rates of 6 × 10
23
molec/s, 2 × 10
23
molec/s and 2 × 10
27
molec/s, respectively, on October 02. There is no significant increase of the CN production rate or A(0)f
ρ
during our observing period. Finally, we place a three-sigma upper limit on the Q(C
2
)/Q(CN) ratio of 0.3 (on October 13). From this, we conclude that 2I is highly depleted in C
2
, and may have a composition similar to Solar System carbon-chain depleted comets.
Ganymede's surface exhibits great geological diversity, with old dark terrains, expressed through the surface composition, which is known to be dominated by two constituents: H2O-ice and an ...unidentified darkening agent. In this paper, new investigations of the composition of Ganymede's surface at global scale are presented. The analyses are derived from the linear spectral modeling of a high spectral resolution dataset, acquired with the near-infrared (1.40–2.50 μm) ground-based integral field spectrometer SINFONI (SINgle Faint Object Near-IR Investigation) of the Very Large Telescope (VLT hereafter) located in Chile. We show that, unlike the neighboring moon Europa, photometric corrections cannot be performed using a simple Lambertian model. However, we find that the Oren-Nayar (1994) model, generalizing the Lambert's law for rough surfaces, produces excellent results. Spectral modeling confirms that Ganymede's surface composition is dominated by H2O-ice, which is predominantly crystalline, as well as a darkening agent, but it also clearly highlights the necessity of secondary species to better fit the measurements: sulfuric acid hydrate and salts, likely sulfates and chlorinated. A latitudinal gradient and a hemispherical dichotomy are the strongest spatial patterns observed for the darkening agent, the H2O-ice, and the sulfuric acid: the darkening agent is by far the major compound at the equator and mid-latitudes (≤ ± 35°N), especially on the trailing hemisphere, while the H2O-ice and the sulfuric acid are mostly located at high latitudes and on the leading hemisphere. This anti-correlation is likely a consequence of the bombardment of the constituents in the Jovian magnetosphere which are much more intense at latitudes higher than ±35°N. Furthermore, the modeling confirms that polar caps are enriched in small, fresh, H2O-ice grains (i.e. ≤50 μm) while equatorial regions are mostly composed of larger grains (i.e. ≥200 μm, up to 1 mm). Finally, the spatial distribution of the salts is neither related to the Jovian magnetospheric bombardment nor the craters. These species are mostly detected on bright grooved terrains surrounding darker areas. Endogenous processes, such as freezing of upwelling fluids going through the ice shell, may explain this distribution. In addition, a small spectral residue that might be related to brines and/or hydrated silica-bearing minerals are located in the same areas.
•Near-infrared global mapping of Ganymede's surface from a ground-based telescope•Overall, an unidentified darkening agent is the major compound around the equator.•The water ice, mostly the crystalline form, is dominant at high latitudes (≥ ± 40°N).•Salts, very likely endogenic, improve spectral modeling for young geological regions.•A hemispherical dichotomy, due to Jupiter's magnetospheric bombardment, is observed.
A targeted search for Main Belt Comets Ferellec, Léa; Snodgrass, Colin; Fitzsimmons, Alan ...
Monthly notices of the Royal Astronomical Society,
01/2023, Letnik:
518, Številka:
2
Journal Article
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ABSTRACT
Main Belt Comets (MBCs) exhibit sublimation-driven activity while occupying asteroid-like orbits in the Main Asteroid Belt. MBCs and candidates show stronger clustering of their longitudes ...of perihelion around 15° than other objects from the Outer Main Belt (OMB). This potential property of MBCs could facilitate the discovery of new candidates by observing objects in similar orbits. We acquired deep r-band images of 534 targeted asteroids using the Isaac Newton Telescope/Wide Field Camera between 2018 and 2020. Our sample is comprised of OMB objects observed near perihelion, with longitudes of perihelion between 0 and 30° and orbital parameters similar to known MBCs. Our pipeline applied activity detection methods to 319 of these objects to look for tails or comae, and we visually inspected the remaining asteroids. Our activity detection pipeline highlighted a faint antisolar tail-like feature around 2001 NL19 (279870) observed on 2018 November 07, 6 months after perihelion. This is consistent with cometary activity; however, additional observations of this object will be needed during its next perihelion to investigate its potential MBC status. If it is active our survey yields a detection rate of ∼1:300, which is higher than previous similar surveys, supporting the idea of dynamical clustering of MBCs. If not, it is consistent with previously estimated abundance rates of MBCs in the OMB (<1:500).
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