We observed the newly discovered hyperbolic minor planet 1I/'Oumuamua (2017 U1) on 2017 October 30 with Lowell Observatory's 4.3 m Discovery Channel Telescope. From these observations, we derived a ...partial lightcurve with a peak-to-trough amplitude of at least 1.2 mag. This lightcurve segment rules out rotation periods less than 3 hr and suggests that the period is at least 5 hr. On the assumption that the variability is due to a changing cross-section, the axial ratio is at least 3:1. We saw no evidence for a coma or tail in either individual images or in a stacked image having an equivalent exposure time of 9000 s.
•Presence of water ice grains in the innermost coma of 103P/Hartley 2.•1μm water ice particles, thermally and physically decoupled from the dust.•Water ice grains are likely aggregates.
On November ...4th, 2010, the Deep Impact eXtended Investigation (DIXI) successfully encountered comet 103P/Hartley 2, when it was at a heliocentric distance of 1.06AU. Spatially resolved near-IR spectra of comet Hartley 2 were acquired in the 1.05–4.83μm wavelength range using the HRI-IR spectrometer. We present spectral maps of the inner ∼10km of the coma collected 7min and 23min after closest approach. The extracted reflectance spectra include well-defined absorption bands near 1.5, 2.0, and 3.0μm consistent in position, bandwidth, and shape with the presence of water ice grains. Using Hapke’s radiative transfer model, we characterize the type of mixing (areal vs. intimate), relative abundance, grain size, and spatial distribution of water ice and refractories. Our modeling suggests that the dust, which dominates the innermost coma of Hartley 2 and is at a temperature of 300K, is thermally and physically decoupled from the fine-grained water ice particles, which are on the order of 1μm in size. The strong correlation between the water ice, dust, and CO2 spatial distribution supports the concept that CO2 gas drags the water ice and dust grains from the nucleus. Once in the coma, the water ice begins subliming while the dust is in a constant outflow. The derived water ice scale-length is compatible with the lifetimes expected for 1-μm pure water ice grains at 1AU, if velocities are near 0.5m/s. Such velocities, about three order of magnitudes lower than the expansion velocities expected for isolated 1-μm water ice particles (Hanner, 1981; Whipple, 1951), suggest that the observed water ice grains are likely aggregates.
Understanding the cosmogonic record encoded in the parent volatiles stored in cometary nuclei requires investigating whether evolution (thermal or otherwise) has modified the composition of ...short-period comets during successive perihelion passages. As the most volatile molecules systematically observed in comets, the abundances of CO, CH4, and C2H6 in short-period comets may serve to elucidate the interplay between natal conditions and post-formative evolution in setting present-day composition, yet secure measurements of CO and CH4 in Jupiter-family comets (JFCs) are especially sparse. The highly favorable 2018 apparition of JFC 21P/Giacobini-Zinner enabled a sensitive search for these "hypervolatiles" in a prototypical carbon-chain depleted comet. We observed 21P/Giacobini-Zinner with the iSHELL spectrograph at the NASA Infrared Telescope Facility on four pre-perihelion dates, two dates near-perihelion, and one post-perihelion date. We obtained detections of CO, CH4, and C2H6 simultaneously with H2O on multiple dates. We present rotational temperatures, production rates, and mixing ratios. Combined with previous work, our results may indicate that the hypervolatile coma composition of 21P/Giacobini-Zinner was variable across apparitions as well as within a particular perihelion passage, yet the spread in these measurements is a relatively small fraction of the variation in each molecule from comet to comet. We discuss the implications of our measured hypervolatile content of 21P/Giacobini-Zinner for the evolution of JFCs, and place our results in the context of findings from the Rosetta mission and ground-based studies of comets.
We have applied our asymmetric spherical adaptation of Coupled Escape Probability to the modeling of optically thick cometary comae. Expanding on our previously published work, here we present models ...including asymmetric comae. Near-nucleus observations from the Deep Impact mission have been modeled, including observed coma morphology features. We present results for two primary volatile species of interest, H2O and CO2, for comet 9P/Tempel 1. Production rates calculated using our best-fit models are notably greater than those derived from the Deep Impact data based on the assumption of optically thin conditions, both for H2O and CO2 but more so for CO2, and fall between the Deep Impact values and the global pre-impact production rates measured at other observatories and published by Schleicher et al. (2006), Mumma et al. (2005), and Mäkinen et al. (2007).
We used the new high spectral resolution cross-dispersed facility spectrograph, iSHELL, at the NASA Infrared Telescope Facility on Maunakea, HI, to observe Jupiter-family comet (JFC) ...45P/Honda-Mrkos-Pajdušáková. We report water production rates, as well as production rates and abundance ratios relative to H2O, for eight trace parent molecules (native ices), CO, CH4, H2CO, CH3OH, HCN, NH3, C2H2, and C2H6, on 2 days spanning UT 2017 January 6/7 and 7/8, shortly following perihelion. Trace species were measured simultaneously with H2O and/or OH prompt emission, a proxy for H2O production, thereby providing a robust and consistent means of establishing the native ice composition of 45P. Its favorable geocentric radial velocity (approximately −35 km s−1) permitted sensitive measures of the "hypervolatiles" CO and CH4, which are substantially undercharacterized in JFCs. Our results represent the most precise ground-based measures of CO and CH4 to date in a JFC, providing a foundation for building meaningful statistics regarding their abundances. The abundance ratio for CH4 in 45P (0.79% 0.06% relative to H2O) was consistent with its median value as measured among Oort Cloud comets, whereas CO (0.60% 0.04%) was strongly depleted. Compared with all measured comets, HCN (0.049% 0.012%) was strongly depleted, CH3OH (3.6% 0.3%) was enriched, and the remaining species were consistent with their respective median abundances. The volatile composition measured for 45P could indicate processing of ices prior to their incorporation into its nucleus. Spatial analysis of emissions suggests enhanced release of more volatile species into the sunward-facing hemisphere of the coma.
Aims. The Alice far-ultraviolet spectrograph onboard Rosetta is designed to observe emissions from various atomic and molecular species from within the coma of comet 67P/ Churyumov-Gerasimenko and to ...determine their spatial distribution and evolution with time and heliocentric distance. Methods. Following orbit insertion in August 2014, Alice made observations of the inner coma above the limbs of the nucleus of the comet from cometocentric distances varying between 10 and 80 km. Depending on the position and orientation of the slit relative to the nucleus, emissions of atomic hydrogen and oxygen were initially detected. These emissions are spatially localized close to the nucleus and spatially variable with a strong enhancement above the comet’s neck at northern latitudes. Weaker emission from atomic carbon and CO were subsequently detected. Results. Analysis of the relative line intensities suggests photoelectron impact dissociation of H2O vapor as the source of the observed H i and O i emissions. The electrons are produced by photoionization of H2O. The observed C i emissions are also attributed to electron impact dissociation, of CO2, and their relative brightness to H i reflects the variation of CO2 to H2O column abundance in the coma.
EPOXI at Comet Hartley 2 A'Hearn, Michael F.; Belton, Michael J. S.; Delamere, W. Alan ...
Science (American Association for the Advancement of Science),
06/2011, Letnik:
332, Številka:
6036
Journal Article
Recenzirano
Understanding how comets work—what drives their activity—is crucial to the use of comets in studying the early solar system. EPOXI (Extrasolar Planet Observation and Deep Impact Extended ...Investigation) flew past comet 103P/Hartley 2, one with an unusually small but very active nucleus, taking both images and spectra. Unlike large, relatively inactive nuclei, this nucleus is outgassing primarily because of CO 2 , which drags chunks of ice out of the nucleus. It also shows substantial differences in the relative abundance of volatiles from various parts of the nucleus.
We report on initial results from 20 days' worth of Transiting Exoplanet Survey Satellite spacecraft observations of comet 46P/Wirtanen. The long-duration, high-cadence measurements show a 2018 ...September 26 outburst that exhibited a two-phase, 0.5 mag brightening profile, and may be the best temporally characterized natural outburst ever recorded. Gas velocities from the outburst peaked at 800 , while dust expanded at only 10s of . Coadded images also revealed a previously unreported dust trail that extends beyond the 24° field of view.
The Alice ultraviolet spectrograph on the European Space Agency Rosetta spacecraft observed comet 67P/Churyumov-Gerasimenko in its orbit around the Sun for just over two years. Alice observations ...taken in 2015 October, two months after perihelion, show large increases in the comet's Lyβ, O i 1304, O i 1356, and C i 1657 atomic emission that initially appeared to indicate gaseous outbursts. However, the Rosetta Plasma Consortium instruments showed a coronal mass ejection (CME) impact at the comet coincident with the emission increases, suggesting that the CME impact may have been the cause of the increased emission. The presence of the semi-forbidden O i 1356 emission multiplet is indicative of a substantial increase in dissociative electron impact emission from the coma, suggesting a change in the electron population during the CME impact. The increase in dissociative electron impact could be a result of the interaction between the CME and the coma of 67P or an outburst coincident with the arrival of the CME. The observed dissociative electron impact emission during this period is used to characterize the O2 content of the coma at two peaks during the CME arrival. The mechanism that could cause the relationship between the CME and UV emission brightness is not well constrained, but we present several hypotheses to explain the correlation.
COMETARY VOLATILES AND THE ORIGIN OF COMETS A'HEARN, Michael F; FEAGA, Lori M; SUNSHINE, Jessica M ...
Astrophysical journal/The Astrophysical journal,
10/2012, Letnik:
758, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We describe recent results on the CO/CO sub(2)/H sub(2)O composition of comets together with a survey of older literature (primarily for CO/H sub(2)O) and compare these with models of the ...protoplanetary disk. Even with the currently small sample, there is a wide dispersion in abundance ratios and little if any systematic difference between Jupiter-family comets (JFCs) and long-period and Halley-type comets (LPCs and HTCs). We argue that the cometary observations require reactions on grain surfaces to convert CO to CO sub(2) and also require formation of all types of comets in largely, but not entirely, overlapping regions, probably between the CO and CO sub(2) snow lines. Any difference in the regions of formation is in the opposite direction from the classical picture with the JFCs having formed closer to the Sun than the LPCs. In the classical picture, the LPCs formed in the region of the giant planets and the JFCs formed in the Kuiper Belt. However, these data suggest, consistent with suggestions on dynamical grounds, that the JFCs and LPCs formed in largely overlapping regions where the giant planets are today and with JFCs on average forming slightly closer to the Sun than did the LPCs. Presumably at least the JFCs passed through the scattered disk on their way to their present dynamical family.
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