Cometary Objects Research Articles

Structural analysis of the comet 45P/Honda based on isophote modeling

The work focuses on using the isophote method to construct a 45P/Honda comet model. At the same time, important problems were solved for modeling the physical surface of a comet and studying the structure of the cometary nucleus. This is due to the fact that, on the basis of modern studies of meteoroids, complex internal processes and dynamic phenomena on their surface have been discovered. The study of comet nuclei is of great importance, since, according to the theory of their formation, they were formed from the matter of the protoplanetary disk. Thus, modeling and analysis of the structure of various comets make it possible to create a more accurate theory of their evolution. This made it possible to evaluate the structural parameters more accurately and reliably. This allowed for the evaluation of the structural parameters more accurately and reliably. Isophotes of the nucleus, coma and tail of comet 45P/Honda were determined. Depending on the point where the comet is located on the trajectory of its orbit, one can see structural changes in the comet’s brightness from the nucleus to the peripheral region. Near the cometary nucleus, the isophotes are circular in shape. If in the center of the model the isophotes have a shape close to narrow rings, then elongations in the direction of the cometary tail and thickening of their structure appear towards the peripheral regions. Large and small tail rays can be distinguished, and the nucleus is well marked. In the future, the author’s method for modeling isophotes, developed in this work, will allow studying the structure of various cometary objects, and, based on the results, determine the degree of comet activity. On the other hand, about the development of the theory of dynamic processes and the evolution of the Solar system, one can use the data on changes in cometary activity in the process of its movement around the Sun.

Oort cloud Ecology

Jan Hendrik Oort hypothesized the existence of a distant cloud of cometary objects that orbit the Sun based on a spike in the reciprocal orbital separation at 1∕a ≲ 10−4au−1. The Oort cloud is the source of long-period comets, but has not been observed directly, and its origin remains theoretical. Theories on its origin evoke a sequence of events that have been tested individually but never as a consistent chronology. We present a chronology of the formation and early evolution of the Oort cloud, and test the sequence of events by simulating the formation process in subsequent amalgamated steps. These simulations start with the Solar System being born with planets and asteroids in a stellar cluster orbiting the Galactic center. Upon ejection from its birth environment, we continue to follow the evolution of the Solar System while it navigates the Galaxy as an isolated planetary system. We conclude that the range in semi-major axis between ~100 au and several ~103au still bears the signatures of the Sun being born in a ≳1000M⊙pc−3star cluster, and that most of the outer Oort cloud formed after the Solar System was ejected. The ejection of the Solar System, we argue, happened between ~20 Myr and 50 Myr after its birth. Trailing and leading trails of asteroids and comets along the Sun’s orbit in the Galactic potential are the by-product of the formation of the Oort cloud. These arms are composed of material that became unbound from the Solar System when the Oort cloud formed. Today, the bulk of the material in the Oort cloud (~70%) originates from the region in the circumstellar disk that was located between ~15 au and ~35 au, near the current location of the ice giants and the Centaur family of asteroids. According to our simulations, this population is eradicated if the ice-giant planets are born in orbital resonance. Planet migration or chaotic orbital reorganization occurring while the Solar System is still a cluster member is, according to our model, inconsistent with the presence of the Oort cloud. About half the inner Oort cloud, between 100 and 104au, and a quarter of the material in the outer Oort cloud, ≳104au, could be non-native to the Solar System but was captured from free-floating debris in the cluster or from the circumstellar disks of other stars in the birth cluster. Characterizing this population will help us to reconstruct the history of the Solar System.

Swarm of fragments from the Tunguska event

ABSTRACTThe Tunguska event took place on 1908 June 30. It was accompanied by an abnormal effect on the Earth's atmosphere, manifesting itself through ‘white nights’. These nights were associated with a dispersion of cosmic matter and the formation of a field of noctilucent clouds with a uniquely large size of over 10 million km2. However, overall, the cosmic matter was scattered over a territory of around 18 million km2. The most likely cause of the Tunguska event was the flux of fragments from the broken-up cometary object. The destruction of the cosmic body over Siberia, according to local inhabitants, was marked by numerous sound phenomena. After analysing eyewitness accounts, we can conclude that there were at least two major objects at the Tunguska event. The largest object exploded over the Taiga and caused damage to the forest. In addition, there were several dozen fragments of around 10 m in size, as well as many fragments of a smaller size.

Some peculiarities of activity for comets with orbits on 2–5 AU

Periodic comets of different dynamical groups with orbits at 2–5 AU still occasionally active. The observed dust activity of such objects can be connected with the processes of water ice sublimation (MBCs) or crystallisation of amorphous water ice (QHCs) as well as with external causes. Despite the absence of connections between cometary flares and cyclic variations of solar activity indexes, some individual solar flares can affect the brightness of comets. Cometary objects in the main asteroid belt have lower statistic of flares than comets at orbits similar to quasi-Hilda objects.

Herschel/HIFI observations of ionised carbon in theβPictoris debris disk

Context: The dusty debris disk around the $\sim$20 Myr old main-sequence A-star {\beta} Pictoris is known to contain gas. Evidence points towards a secondary origin of the gas as opposed to being a direct remnant form the initial protoplanetary disk, although the dominant gas production mechanism is so far not identified. The origin of the observed overabundance of C and O compared to solar abundances of metallic elements, e.g. Na and Fe, is also unclear. Aims: Our goal is to constrain the spatial distribution of C in the disk, and thereby the gas origin and its abundance pattern. Methods: We used the HIFI instrument onboard Herschel to observe and spectrally resolve CII emission at 158 $\mu$m from the {\beta} Pic debris disk. Assuming Keplerian rotation, we use the spectrally resolved line profile to constrain the spatial distribution of the gas. Results: We show that most of the gas is located around $\sim$100 AU or beyond. We estimate a total C gas mass of $1.3\times10^{-2}$ M$_\oplus$. The data suggest that more gas is located on the southwest side of the disk than on the northeast side. The data are consistent with the hypothesis of a well-mixed gas (constant C/Fe ratio throughout the disk). Assuming instead a spatial profile expected from a simplified accretion disk model, we found it to give a significantly worse fit to the observations. Conclusions: Since the bulk of the gas is found outside 30 AU, we argue that the cometary objects known as "falling evaporating bodies" are unlikely to be the dominant source of gas; production from grain-grain collisions or photodesorption seems more likely. The incompatibility of the observations with a simplified accretion disk model could favour a preferential depletion explanation for the overabundance of C and O. More stringent constraints on the spatial distribution will be available from ALMA observations of CI at 609 $\mu$m.

Near-Earth objects: finding them before they find us

Illustrations vii Preface xi Acknowledgments xiii Chapter 1 Earth's Closest Neighbors 1 Chapter 2 The Solar System's Origin: The Classical View 15 Chapter 3 How and Where Do Near-Earth Objects Form? 29 Chapter 4 Near-Earth Objects as the Enablers and Destroyers of Life 47 Chapter 5 Discovering and Tracking Near-Earth Objects 57 Chapter 6 The Nature of Asteroids and Comets 79 Chapter 7 Nature's Natural Resources and the Human Exploration of Our Solar System 100 Chapter 8 Near-Earth Objects as Threats to Earth 109 Chapter 9 Predicting the Likelihood of an Earth Impact 125 Chapter 10 Deflecting an Earth-Threatening Near-Earth Object 140 References 155 Index of Asteroid and Cometary Objects 159 General Index 161

Polarimetry and photometry of the peculiar main-belt object 7968 = 133P/Elst-Pizarro

133P/Elst-Pizarro is an object that has been described as either an active asteroid or a cometary object in the main asteroid belt. Here we present a photometric and polarimetric study of this object in an attempt to infer additional information about its origin. With the FORS1 instrument of the ESO VLT, we have performed during the 2007 apparition of 133P/Elst-Pizarro quasi-simultaneous photometry and polarimetry of its nucleus at nine epochs in the phase angle range 0 - 20 deg. For each observing epoch, we also combined all available frames to obtain a deep image of the object, to seek signatures of weak cometary activity. Polarimetric data were analysed by means of a novel physical interference modelling. The object brightness was found to be highly variable over timescales <1h, a result fully consistent with previous studies. Using the albedo-polarization relationships for asteroids and our photometric results, we found for our target an albedo of about 0.06-0.07 and a mean radius of about 1.6 km. Throughout the observing epochs, our deep imaging of the comet detects a tail and an anti-tail. Their temporal variations are consistent with an activity profile starting around mid May 2007 of minimum duration of four months. Our images show marginal evidence of a coma around the nucleus. The overall light scattering behaviour (photometry and polarimetry) resembles most closely that of F-type asteroids.

Low-temperature magnetic properties of iron-bearing sulfides and their contribution to magnetism of cometary bodies

In this study we present a review of low-temperature magnetic properties of alabandite (Fe, Mn)S, daubreelite FeCr 2S 4, pyrrhotite Fe 1− x S and troilite FeS updated with new experimental data. The results indicate that besides FeNi alloys mainly daubreelite with its Curie temperature T C ∼ 150 K and strong induced and remanent magnetizations may be a significant magnetic mineral in cold environments and may complement that of FeNi or even dominate magnetic properties of sulfide rich bodies at temperatures below T C . Comets are known to contain iron-bearing sulfides within dusty fraction and their surfaces are subject to temperature variations in the range of 100–200 K down to the depth of several meters while the cometary interior is thermally stable at several tens of Kelvin which is within the temperature range where alabandite, daubreelite or troilite are “magnetic”. Thus not only FeNi alloys, but also sulfides have to be considered in the interpretation of magnetic data from cometary objects such as will be delivered by Rosetta mission. Modeling indicates that magnetic interactions between cometary nucleus containing iron-bearing sulfides and interplanetary magnetic field would be difficult, but not impossible, to detect from orbit. Rosetta’s Philae lander present on the surface would provide more reliable signal.

The distant activity of the Long Period Comets C/2003 O1 (LINEAR) and C/2004 K1 (Catalina)

Aims. We study the distant dust environment of two Long Period Comets: C/2003 O1 (LINEAR) (observed at r h = 7.39 AU) and C/2004 K1 (Catalina) (observed at r h = 3.43 AU). The case of C/2003 O1 is particularly interesting since the comet has a quite large perihelion heliocentric distance (r h = 6.85 AU).Methods. We analysed R -band images taken at the CAHA 2.2 m telescope to characterise the properties of the cometary dust coma. The images of both comets were also used as input into an inverse numerical model, to derive information about the dynamical parameters of coma dust grains until a time ~500 days before the observation.Results. Both the comets appeared to be active, and of similar shape and size despite the great difference in their heliocentric distance of observation. C/2003 O1 exhibited a tail extending to at least 3.7 105 km. It is a very active object, since its Af ρ is 552 ± 36 cm within the inner 5”. C/2004 K1 showed a similar long tail, extending to 2.6 105 km. Its Af ρ is 539 ± 35 cm within the inner 5”. An almost constant dust grain ejection velocity between 0.5 and 0.9 m/s at 1 cm dust size has been derived for C/2003 O1 and an increase from 0.5 to 2 m/s at 1 cm dust size for C/2004 K1, reflecting the different volatile dragging the dust environment (probably CO for C/2003 O1 and water for C/2004 K1). Model results allow some speculations about the comet nucleus size of C/2003 O1 (LINEAR) and its CO content: for a Q CO similar in value to those observed for other distant cometary objects, a comet radius R n from 13 to 17 km can be inferred.

Updated analysis of the dynamical relation between asteroid 2003 EH1 and comets C/1490 Y1 and C/1385 U1

Abstract The asteroid 2003 EH1, proposed as the parent body of the Quadrantid meteor shower, is thought to be the remnant of a past cometary object, tentatively identified with the historical comets C/1490 Y1 and C/1385 U1. In this work, we use recovery astrometry to extend the observed arc of 2003 EH1 from 10 months to about 5 years, enough to exclude the proposed direct relationship of the asteroid with both of the comets.

Comets in the near-Earth object population

Because the lifespan of near-Earth objects (NEOs) is shorter than the age of the Solar System, these objects originate elsewhere. Their most likely sources are the main asteroid belt and comets. Through physical observations we seek to identify potential dormant or extinct comets among “asteroids” catalogued as NEOs and thereby determine the fraction of “comet candidates” within the total NEO population. Both discovery statistics and dynamical models indicate that candidate cometary objects in near-Earth space are predominantly found among those having a jovian Tisserand parameter T j < 3 . Therefore, we seek to identify comet candidates among asteroid-like NEOs using three criteria: T j < 3 , spectral parameters (C, D, T, or P taxonomic types), and/or low (<0.075) albedos. We present new observations for 20 NEOs having T j < 3 , consisting of visible spectra, near-infrared spectra, and/or albedo measurements obtained using the NASA Infrared Telescope Facility, the Kitt Peak National Observatory 4 m, and the Magellan Observatory 6.5-m. Four of our “asteroid” targets have been subsequently confirmed as low activity comets. Thus our sample includes spectra of the nuclei of Comets 2002 EX12 = 169P (NEAT), 2001 WF2 = 182P (LONEOS), 2003 WY25 = D/1891 W1 (Blanplain), and Halley Family Comet 2006 HR30 = P/2006 HR30 (Siding Spring). From the available literature, we tabulate physical properties for 55 NEOs having T j < 3 , and after accounting for possible bias effects, we estimate that 54 ± 10 % of NEOs in T j < 3 orbits have “comet-like” spectra or albedos. Bias corrected discovery statistics [Stuart, J.S., Binzel, R.P., 2004. Icarus 170, 295–311] estimate 30 ± 5 % of the entire NEO population resides in orbits having T j < 3 . Combining these two factors suggests that 16 ± 5 % of the total discovered “asteroid-like” NEO population has “comet-like” dynamical and physical properties. Outer main-belt asteroids typically have similar taxonomic and albedo properties as our “comet candidates.” Using the model of Bottke et al. [Bottke, W.F., Morbidelli, A., Jedicke, R., Petit, J.M., Levison, H., Michel, P., Metcalfe, T.S., 2002. Icarus 156, 399–433] to evaluate source region probabilities, we conclude that 8 ± 5 % of the total asteroid-like NEO population have the requisite orbital properties, physical properties, and dynamical likelihood to have originated as comets from the outer Solar System.

Polarimetric Imager for Comets, PICO

We constructed an imaging polarimeter, PICO, that was optimized for comets and/or cometary objects. PICO has a field-of-view of 5$' \times$ 10$'$ and employs a fixed Wollaston prism as an analyzer. In the case of polarimeters using a double-beam prism, such as a Wollaston prism, lateral chromatic aberrations originating from the prism often degrade the image quality and measurement accuracy. However, PICO suffers little lateral chromatic aberration due to compensation provided by newly designed lens systems that generate opposite lateral colors. Owing to this design, PICO can obtain highly resolved and very accurate polarization images throughout the FOV (field-of-view). The total accuracy is estimated to be $\Delta P \simeq [(P/8{5})^2 + 0.3^2]^{1/2}\;$% in polarization degree and $\theta \leq$ 3$^{\circ}$ in position angle; these values are satisfactory for cometary studies.

Properties and environment of the molecular complex near Holmberg IX

This paper is aimed at providing new insight into the nature and origin of the molecular complex situated near the line of sight toward Holmberg IX in the M 81 group of galaxies. The first high resolution CO maps of the complex as well as single dish 13CO(1–0), 12CO(3–2) and millimeter continuum observations and the results of a survey of 12CO in the region are presented. These data together with the available HI, optical and X-ray observations are analyzed to study the properties and environment of the complex. We confirm there is no unobscured massive star formation inside the complex, and from the millimeter constraint on the extinction it must have a low star formation rate or be forming only low mass stars. According to the CO line ratios the abundances and physical conditions could be similar to that of cold gas in spirals. We find from its dynamics (no rotation) and its mass (2–6 million solar masses) that it resembles a massive GMC. Also, re-inspecting N-body simulations of the M 81 group and the H i data we find that it might be located inside the extreme outer disk of M 81 and be cospatial with the H i feature known as Concentration i. The negative result of the CO survey suggests that the complex is unique in this region and calls for a peculiar local formation process. We find that the distribution of the CO emission in the data cube is asymmetrical in a way similar to a cometary object. The optical observations of the nearby supershell MH9/10 suggest the existence of an outflow toward the complex. We consider the possibility that the molecular complex is related to this hypothetical outflow.

Migration Processes and Volatiles Delivery

Migration processes of comets and asteroids from the outer regions of the solar system, including the Edgeworth–Kuiper belt, are regarded as important mechanisms for the formation and evolution of the inner planets. These minor bodies may be responsible for the delivery of volatile matter to the inner planets and thus be responsible for the origin of life. We estimate that the cumulative mass of icy comets impacting on the Earth during the formation of the giant planets is similar to the mass of water in the Earth oceans, and that Mars acquired more water per unit planet mass than Earth. We find that these cometary objects mostly evolved from typical near-Earth orbits and Encke-type orbits with aphelia located inside the orbit of Jupiter, and played a greater role than those with Jupiter-crossing orbits. The relative importance of comets and chondrites in the delivery of volatiles is constrained by the observed fractionation patterns of atmospheric noble gas abundance.

From the Solar system comet cloud to near-Earth space

AbstractThe dynamical evolution of objects from different zones of the solar system comet cloud to near-Earth space has been investigated. The steady-state number of objects with perihelion distancesq&amp;lt; 1.5 AU and periodsP &amp;lt;20 yr, arising from the near-parabolic flux of comets with absolute magnitudes brighter thanH10= 7 is ∼ 200 − 1000. The corresponding number for Halley-type comets is hundreds of times larger than the number of known Halley-type comets. The flux of objects in the Centaurs zone, captured from the near-parabolic flux is 300 times as large as the flux of new comets. The total number of cometary objects with semi-major axesain the range 50 &amp;lt;a&amp;lt; 500 AU andq∼ 1 AU is ∼ 10 times as large as the number of active comets. The probability of the transfer of objects from the trans-Neptunian orbits with 35 &amp;lt;q&amp;lt; 50 AU anda∼ 600 AU into the Jupiter family is ∼ 0.0001. The calculations show that trans-Neptunian objects on high-eccentricity orbits can be a significant continuous source for both the replenishment of the Oort cloud and the capture to short-period orbits.

A computer model of the atmospheric entry of the Tunguska object

Mathematical models of the entry trajectory for various types of meteors have frequently been applied in an effort to determine the nature of the Tunguska object. This approach has been used to support both a stony asteroid and a cometary object as the most probable cause of the event. An accurate trajectory model must include an evaluation of both the mechanical fragmentation and the aerothermal ablation and must couple these two processes. Inaccuracies in the calculated ablation rate can lead to substantial errors in the predicted terminal altitude of a given entry body, this is particularly true for relatively weak, icy objects such as comets. The present study uses an analytical approximation of the mechanical fragmentation and radial spreading of the bolide and examines aerothermal ablation in some detail, including an evaluation of radiative cooling of the shock layer gases and the effect of radiation blockage by ablation products coming off the meteor's surface. Such calculations can be performed only in an approximate manner since the properties of high temperature gases are not well established at the extremc pressures and temperatures involved. It is found that the sudden release of energy approximately 8 km above the surface which was associated with the Tunguska event could have been produced by the disruption of either a comet or an asteroid, although a cometary origin would have required a very steep atmospheric entry angle. Therefore, although an asteroidal origin seems more likely, it is concluded that a trajectory analysis of this type cannot be used at the present time to exclude either type of object with absolute certainty.

Analysis of POSS Images of Comet–Asteroid Transition Object 107P/1949 W1 (Wilson–Harrington)

We have analyzed the only two known images taken of Comet 107P = Asteroid (4015) Wilson–Harrington while it was a distinctly cometary object. The images reside on two Palomar Observatory Sky Survey (POSS) photographic plates taken on 19 November 1949 UT and provide a unique way of studying the fading gasps of a dying comet. The comet appears as a streak, a tail is evident, but the coma is indistinguishable. A comparison of the profiles of the streaks and the stellar PSF yielded no coma, implying the coma's scale height is small (upper limit of a few hundred kilometers). Finson–Probstein modeling of the tail demonstrates that it is not a dust tail. If it were, the size of the particles would have to be tens to hundreds of micrometers in size (which contradicts the tail's blue color [vs. the Sun]) and they would have to have been released several weeks before the observations (which contradicts observers' reports that the tail dissipated in a few days). Instead, we are seeing CO+and H2O+fluorescence in a plasma tail. With this composition, the tail's blue hue and short lifetime are explained. The lag angle of the tail on the image is about 15°, larger than the “typical” for Type I tails, but the value is not implausible. We show that the deviation of the solar wind from radial need not have been atypical to explain it. We have calibrated the relevant portions of the photographic plates and, from the surface brightness of the tail and an estimate of its age, we have calculated a plausible maximum to the production rate of H2O and CO during Wilson–Harrington's outburst:QH2O≈QCO≈ 5 × 1027molecules sec−1. The measurements indicate that CO is roughly as abundant as H2O on the dormant comet's nucleus.

A new dynamical class of object in the outer Solar System

Some three dozen objects have now been discovered1,2,3,4,5 beyond the orbit of Neptune and classified as members of the Kuiper belt—a remnant population of icy planetesimals that failed to be incorporated into planets. At still greater distances is believed to lie the Oort cloud—a massive population of cometary objects distributed approximately in a sphere of characteristic dimension 50,000au(ref. 6). Here we report the discovery of an object, 1996TL66, that appears to be representative of a population of scattered bodies located between the Kuiper belt and the Oort cloud. 1996TL66has an orbital semimajor axis of 84au, and is in an extremely eccentric and highly inclined orbit (e = 0.58, i = 24°). With a red magnitude ∼20.9, it is the brightest trans-neptunian object yet found since Pluto and Charon. Its discovery suggests that the Kuiper belt extends substantially beyond the 30–50auregion sampled by previous surveys, and may contain much more mass than previously suspected.

Detailed data for 259 fireballs from the Canadian camera network and inferences concerning the influx of large meteoroids

Abstract— We present data for 259 meteoric fireballs observed with the Canadian camera network, including velocities, heights, orbits, luminosities along each trail, estimates of preatmospheric masses and surviving meteorites (if any) as well as membership in meteor showers. Some 213 of the events comprise an unbiased sample of the 754 fireballs observed in a total of 1.51 × 1010 km2 h of clear‐sky observations. The number of fireballs and the amount of clear sky in which they were recorded are given for each day of the year. We find at least 37% of the unbiased sample are members of some 15 recognized meteor showers. Preatmospheric masses, based on an assumed luminous efficiency of 0.04 for velocities &gt;10 km s−1, range from 1 g for some very fast fireballs up to hundreds of kilograms for the largest events. We present plots and equations for the flux, as a function of initial mass, for the entire group of fireballs and for some subgroups: meteorite‐dropping objects; meteor shower members; groups that appear to be mainly of asteroidal or cometary origin; and for very fast objects. For masses of a few kilograms, asteroidal objects outnumber cometary ones. Cometary objects attain greater peak brightness than asteroidal ones of equal mass largely due to higher velocity, but also because they fragment more severely. For 66 fireballs, we estimate the meteoroid density using photometric and dynamic masses. Presumed cometary objects have typical densities near 1.0, while asteroidal values show two groups that suggest meteoroids similar to carbonaceous and ordinary chondrites. Our basic data may be used by others for further studies or to reexamine our results using assumptions different from those employed in this paper.

Multiple impact event in the Paleozoic: Collision with a string of comets or asteroids?

Eight circular geologic structures ranging from ∼3 to 17 km in diameter, showing evidence of outward‐directed radial deformation and intensive brecciation, lie within a linear swath ∼15 km wide along a straight line stretching ∼700 km across the United States from southern Illinois through Missouri to eastern Kansas. Based on their similar geological characteristics and the presence of diagnostic and/or probable evidence of shock, these structures, once classified as ‘cryptovolcanic’ or ‘cryptoexplosion’ structures, are more confidently ascribed to hypervelocity impact. No other similar occurrence of aligned features is known, and we calculate the probability of a chance alignment to be &lt;10−9. The unusual alignment suggests that the features are coeval and related to a multiple impact event, with a best‐constrained late Mississippian‐early Pennsylvanian (∼330–310 Myr) age. Calculations suggest that the proposed impact‐crater chain is unlikely to have been formed by an incoming impactor disrupted by terrestrial or lunar tidal effects, and may have been the result of a string of asteroidal or cometary objects produced by breakup within the inner Solar System.