Comet P/Tempel: Some highlights and conclusions from the 1988 apparition

From the brightness development and a sequence of imaging observations of the coma activity onset of comet P/Tempel 2 in 1988, it is concluded that there might have happened eruptive events of strong dust and gas outbursts during May and June 1988. A comparison of dust coma modeling calculations with CCD observations of the coma widely confirms Sekanina's nucleus model for the comet

The role of organic polymers in the structure of cometary dust

Several phenomena observed in P/Halley and other comets indicate additional fragmentation of dust particles or dust aggregates in cometary atmospheres. The disintegration of dust aggregates may be explained by sublimation of polymerized formaldehyde - POM - which play a role as binding material between submicron individual particles

Coma imaging of comet P/Brorsen-Metcalf at Calar Alto in late July to mid August 1989

Comet P/Brorsen-Metcalf was observed on 1989/07/28+30 and on 1989/08/04+12(+14) with the 3.5 m telescope and the 0.8 m Schmidt camera at Calar Alto/Spain. The images exhibit a narrow plasma tail pointing into anti-solar direction. On 1989/07/30 a triple tail was found which can be interpreted as tail ray event. The coma isophotes show prominent asymmetries with the nucleus located on the tailward side of the isophote foci and with a slightly higher brightness in the Northern Hemisphere of the coma. A strong curved jet feature was detected in the coma on 1989/07/30. The jet extended at least 30,000 km into the sunward coma hemisphere. The rotation period of about 1.3 days, estimated from the curvature of the coma jet, needs verification by other observations

Thermal Infrared and Optical Photometry of Asteroidal Comet C/2002 CE10_{10}

C/2002 CE$_{10}$ is an object in a retrograde elliptical orbit with Tisserand parameter $-0.853$ indicating a likely origin in the Oort Cloud. It appears to be a rather inactive comet since no coma and only a very weak tail was detected during the past perihelion passage. We present multi-color optical photometry, lightcurve and thermal mid-IR observations of the asteroidal comet. \textcolor{blue}{ With the photometric analysis in $BVRI$, the surface color is found to be redder than asteroids, corresponding to cometary nuclei and TNOs/Centaurs. The time-resolved differential photometry supports a rotation period of 8.19$\pm$0.05 h. The effective diameter and the geometric albedo are 17.9$\pm$0.9 km and 0.03$\pm$0.01, respectively, indicating a very dark reflectance of the surface. The dark and redder surface color of C/2002 CE$_{10}$ may be attribute to devolatilized material by surface aging suffered from the irradiation by cosmic rays or from impact by dust particles in the Oort Cloud. Alternatively, C/2002 CE$_{10}$ was formed of very dark refractory material originally like a rocky planetesimal. In both cases, this object lacks ices (on the surface at least). The dynamical and known physical characteristics of C/2002 CE$_{10}$ are best compatible with those of the Damocloids population in the Solar System, that appear to be exhaust cometary nucleus in Halley-type orbits. The study of physical properties of rocky Oort cloud objects may give us a key for the formation of the Oort cloud and the solar system.Comment: 9 pages, 4 figures accepted to Icaru

Spitzer Observations of Comet 67P/Churyumov-Gerasimenko at 5.5-4.3 AU From the Sun

We report Spitzer Space Telescope observations of comet 67P/Churyumov-Gerasimenko at 5.5 and 4.3 AU from the Sun, post-aphelion. Comet 67P is the primary target of the European Space Agency's Rosetta mission. The Rosetta spacecraft will rendezvous with the nucleus at heliocentric distances similar to our observations. Rotationally resolved observations at 8 and 24 microns (at a heliocentric distance, rh, of 4.8 AU) that sample the size and color-temperature of the nucleus are combined with aphelion R-band light curves observed at the Very Large Telescope (VLT) and yield a mean effective radius of 2.04 +/- 0.11 km, and an R-band geometric albedo of 0.054 +/- 0.006. The amplitudes of the R-band and mid-infrared light curves agree, which suggests that the variability is dominated by the shape of the nucleus. We also detect the dust trail of the comet at 4.8 and 5.5 AU, constrain the grain sizes to be less than or similar to 6 mm, and estimate the impact hazard to Rosetta. We find no evidence for recently ejected dust in our images. If the activity of 67P is consistent from orbit to orbit, then we may expect the Rosetta spacecraft will return images of an inactive or weakly active nucleus as it rendezvous with the comet at rh = 4 AU in 2014.Comment: 19 pages, 2 tables, 10 figures. Accepted for publication in the Astronomical Journa

Detecting and analysing geomorphological structures in images of comet 67P/Churyumov-Gerasimenko using Fourier transform

We present a method for automatised detection and analysis of quasi-periodic lineament structures from images at pixel-precision. The method exploits properties of the images' frequency domain found by using the Fourier transform. We developed this method with the goal of detecting lineament structures in an image of the Hathor cliff of comet 67P/Churyumov-Gerasimenko, which are caused by layerings and furrows in the nucleus material. Using our method, we determined the orientation and wavelength-range of these structures. The detected layering edges have similar orientations, spatial separations of 9-20 m, and are ubiquitous throughout the image. We suggest that the layerings are a global feature of the comet nucleus that provide information about formation and evolution of comet 67P. The furrows are non-uniformly distributed throughout the image. Their orientation is broadly parallel to the direction of the local gravity vector at the Hathor cliff, with spacings similar to that of the layering structures. The furrows are interpreted as signatures of local down-slope movement of cliff material. We demonstrate that the developed method is broadly applicable to the detection and analysis of various kinds of quasi-periodic structures like geological layering, folding and faulting, and texture analysis in general. In order to facilitate the application of our method, this paper is accompanied by a demo program written in Matlab

Mt. Wendelstein imaging of comet 41P/Tuttle-Giacobini-Kresak during the 2017 perihelion arc

Comet 41P/Tuttle-Giacobini-Kresak (41P), a Jupiter family comet with three discoveries over about 100 years, is in a short-periodic orbit around the Sun with the perihelion close to the Earth distance. The 2017 apparition of 41P offered a long-lasting visibility of the comet at a close distance to Earth. The four month-long imaging campaign with the 2 m telescope at the Mount Wendelstein Observatory was aimed at characterizing dust activity and nucleus properties of the comet. Using a new analysis method of the inner coma flux, we derived a small mean equivalent radius of about 600 m for the nucleus with an unusual body axes ratio that is higher than two. The nucleus rotation axis was determined from the geometric appearance of coma structures, which were enhanced in the images. A long-lasting coma fan was produced by an extended region at high latitudes on the slowly rotating nucleus, whereas isolated jets originated from narrow, low latitude active regions on the nucleus. The dust activity of 41P, despite being difficult to quantify exactly because of an unknown phase function correction for the comet, indicates a steep radial profile that falls off with an increasing distance from the Sun. Colors and flux profiles provide evidence for dust fragmentation in the inner coma of the comet. A singular outburst event created various dust structures in the coma. The outburst came from an extended region on the nucleus and was due to either a landslide on the nucleus or a sudden material release from a subsurface pocket of volatile ice.Comment: Published on 29 May 2020 in A&A, 25 pages, 12 figures, 9 table

ESO Large Programme on Trans-Neptunian Objects and Centaurs: Spectroscopic Investigation of Centaur 2001 BL41 and TNOs (26181) 1996 GQ21 and (26375) 1999 DE9*

Observational results that are part of an ESO Large Programme dedicated to the characterization of the physical properties of trans-Neptunian objects and Centaurs are presented. We report observations related to the Centaur 2001 BL41 and two trans-Neptunian objects, (26181) 1996 GQ21 and (26375) 1999 DE9. We present results from broadband photometry (JHK filters) and low-dispersion infrared spectroscopy performed with ISAAC at the Very Large Telescope, in Chile. None of the spectra show evidence of absorption features—in particular, water ice features. We use a radiative transfer model to investigate the surface composition of these icy and primitive outer solar system bodies. We suggest models composed of geographical mixtures of organic compounds and minerals

Analysis of layering-related linear features on comet 67P/Churyumov-Gerasimenko

We analysed layering-related linear features on the surface of comet 67P/Churyumov-Gerasimenko (67P) to determine the internal configuration of the layerings within the nucleus. We used high-resolution images from the OSIRIS Narrow Angle Camera onboard the Rosetta spacecraft, projected onto the SHAP7 shape model of the nucleus, to map 171 layering-related linear features which we believe to represent terrace margins and strata heads. From these curved lineaments, extending laterally to up to 1925 m, we extrapolated the subsurface layering planes and their normals. We furthermore fitted the lineaments with concentric ellipsoidal shells, which we compared to the established shell model based on planar terrace features. Our analysis confirms that the layerings on the comet's two lobes are independent from each other. Our data is not compatible with 67P's lobes representing fragments of a much larger layered body. The geometry we determined for the layerings on both lobes supports a concentrically layered, `onion-shell' inner structure of the nucleus. For the big lobe, our results are in close agreement with the established model of a largely undisturbed, regular, concentric inner structure following a generally ellipsoidal configuration. For the small lobe, the parameters of our ellipsoidal shells differ significantly from the established model, suggesting that the internal structure of the small lobe cannot be unambiguously modelled by regular, concentric ellipsoids and could have suffered deformational or evolutional influences. A more complex model is required to represent the actual geometry of the layerings in the small lobe