Asteroids In Cometary Orbits Research Articles

The dynamical evolution of escaped Jupiter Trojan asteroids, link to other minor body populations

The Jupiter Trojans constitute an important asteroidal population both in number and also in relation to their dynamical and physical properties. They are asteroids located around L4 and L5 Lagrangian points on relatively stable orbits, in 1: 1 mean motion resonance with Jupiter. However, not all of them lie in orbits that remain stable over the age of the Solar System. Unstable zones allow some Trojans to escape in time scales shorter than the Solar System age. This may contribute to populate other small body populations. In this paper, we study this process by performing long-term numerical simulations of the observed Trojans, focusing on the trajectories of those that leave the resonance. The orbits of current Trojan asteroids are taken as initial conditions and their evolution is followed under the gravitational action of the Sun and the planets. We built “occupancy maps” that represent the zones in the Solar System where escaped Trojans should be found. We find the rate of escape of Trojans from L5, ∼ 1.1 times greater than from L4. The majority of escaped Trojans have encounters with Jupiter although they have encounters with the other planets too. The median lifetime of escaped Trojans in the Solar System is ∼ 264, 000 years for L4 and ∼ 249, 000 years for L5. Almost all escaped Trojans reach the comet zone, ∼ 90% cross the Centaur zone and only L4 Trojans reach the transneptunian zone. Considering the real asymmetry between L4 and L5, we show that 18 L4 Trojans and 14 L5 Trojans with diameter D > 1 km are ejected from the resonance every Myr. The contribution of the escaped Trojans to other minor body populations would be negligible, being the contribution from L4 and L5 to Jupiter-family comets (JFCs) and no-JFCs almost the same, and the L4 contribution to Centaurs and TNOs, orders of magnitude greater than that of L5. Considering the collisional removal, besides the dynamical one, and assuming that Trojans that escape due to collisions follow the same dynamical behavior that the ones removed by dynamics, we would have a minor contribution of Trojans to comets and Centaurs. However, there would be some specific regions were escaped Trojans could be important such as Asteroids in Cometary Orbits (ACOs), Encke-type comets, Shoemaker-Levy 9-type impacts on Jupiter and Near-Earth objects (NEOs).

The visible and near-infrared spectra of asteroids in cometary orbits

Context. Dynamical and albedo properties suggest that asteroids in cometary orbits (ACOs) are dormant or extinct comets. Their study provides new insights for understanding the end-states of comets and the size of the comet population. Aims. We intend to study the visible and near-infrared (NIR) spectral properties of different ACO populations and compare them to the independently determined properties of comets. Methods. We select our ACOs sample based on published dynamical criteria and present our own observational results obtained using the 10.4 m Gran Telescopio Canarias (GTC), the 4.2 m William Herschel Telescope (WHT), the 3.56 m Telescopio Nazionale Galileo (TNG), and the 2.5 m Isaac Newton Telescope (INT), all located at the El Roque de los Muchachos Observatory (La Palma, Spain), and the 3.0 m NASA Infrared Telescope Facility (IRTF), located at the Mauna Kea Observatory, in Hawaii. We include in the analysis the spectra of ACOs obtained from the literature. We derive the spectral class and the visible and NIR spectral slopes. We also study the presence of hydrated minerals by studying the 0.7 μm band and the UV-drop below 0.5 μm associated with phyllosilicates. Results. We present new observations of 17 ACOs, 11 of them observed in the visible, 2 in the NIR and 4 in the visible and NIR. We also discuss the spectra of 12 ACOs obtained from the literature. All but two ACOs have a primitive-like class spectrum (X or D-type). Almost 100% of the ACOs in long-period cometary orbits (Damocloids) are D-types. Those in Jupiter family comet orbits (JFC-ACOs) are ∼60% D-types and ∼40% X-types. The mean spectral slope S′ of JFC-ACOs is 9.7 ± 4.6%/1000 Å and for the Damocloids this is 12.2 ± 2.0%/1000 Å. No evidence of hydration on the surface of ACOs is found from their visible spectra. The spectral slope and spectral class distribution of ACOs is similar to that of comets. Conclusions. The spectral taxonomical classification and the spectral slope distribution of ACOs, and the lack of spectral features indicative of the presence of hydrated minerals on their surface, strongly suggest that ACOs are likely dormant or extinct comets.

Monitoring of Asteroids in Cometary Orbits and Active Asteroids

Asteroids in Cometary Orbits (ACOs) are objects that behave dynamically like comets and have not shown any kind of activity in the past. Active Asteroids are objects that have typical asteroid orbits and have displayed gas and dust ejections. In this article, the results of the monitoring of 63 ACOs and four Active Asteroids are presented. ACOs were selected following a strict criterion based on their orbital parameters (Tancredi, 2014) so that they have a dynamical evolution similar to the periodic comets. Of the approximately 670000 asteroids discovered, a set of more than 600 objects classified as ACOs to this criterion was selected. The Active Asteroids were observed close to places in their orbit where activity had already been reported. Observations were made in 28 nights spread in different months during the years 2015, and 2016 at the Observatório Astronômico do Sertão de Itaparica (Itacuruba, Brazil) with the 1-m telescope of the IMPACTON project. The work consisted in the study of the surface brightness profile of the objects, in comparison with profiles of field stars, in search of a widening that would indicate the presence of cometary type activity. In addition, all the photometric data published in the Minor Planet Center database for the observed objects were extracted. The observed magnitudes were transformed to absolute magnitudes and compared with the available data, in order to search for possible unusual brightening. Surface brightness profiles were obtained for 42 of the 63 studied ACOs (approximately 6% of the initial sample) with no traces of activity in them, except for 2015 PD229 that is already cataloged as a comet (P/2015 PD229 ISON-Cameron), which showed a slight widening in its profile. Only one ACO exhibited significant variations of reduced magnitude: 174P/(60558) Echeclus, which is also already classified as asteroid and comet. A good profile for three Active Asteroids was obtained: 176P, 238P, and 288P. For the first two, there was no significant widening of the profile. Profiles with signs of activity were observed for 288P in three consecutive months (09-11/2016), close to the place in its orbit where activity had already been reported in 2011–2012. 238P was observed brighter than the mean reduced magnitude, two months before the first reports of activity, which would be an indicator that the activity was already present. It would be desirable to extend the list of observed ACOs and to continue monitoring the Active Asteroids to detect their potential reactivation. These observations are critical to address the different mechanisms to explain the activity of this set of objects.

Orbital Shapes of Asteroids in Cometary Orbits based on 0.7m Telescope Imaging

The study of orbital elements of Asteroids in Cometary Orbits (ACOs) is based on images taken by a 0.7-m telescope to find positions of asteroids and calculate their orbital elements. This work focuses on variation of positions and orbital shape of an asteroid, 1667Pels, which is obtained by analyzing orbital elements and minimum orbital intersection distances. Each observation, those parameters are affected by the gravity from Jupiter on ACOs. The accuracy of single site data was calibrated by comparing the result from this work to other observations in Minor Planet Center database.

Dormant comets among the near-Earth object population: a meteor-based survey

Dormant comets in the near-Earth object (NEO) population are thought to be involved in the terrestrial accretion of water and organic materials. Identification of dormant comets is difficult as they are observationally indistinguishable from their asteroidal counterparts, however they may have produced dust during their final active stages which potentially are detectable today as weak meteor showers at the Earth. Here we present the result of a reconnaissance survey looking for dormant comets using 13~567~542 meteor orbits measured by the Canadian Meteor Orbit Radar (CMOR). We simulate the dynamical evolution of the hypothetical meteoroid streams originated from 407 near-Earth asteroids in cometary orbits (NEACOs) that resemble orbital characteristics of Jupiter-family comets (JFCs). Out of the 44 hypothetical showers that are predicted to be detectable by CMOR, we identify 5 positive detections that are statistically unlikely to be chance associations, including 3 previously known associations. This translates to a lower limit to the dormant comet fraction of $2.0\pm1.7\%$ in the NEO population and a dormancy rate of $\sim 10^{-5}~\mathrm{yr^{-1}}$ per comet. The low dormancy rate confirms disruption and dynamical removal as the dominant end state for near-Earth JFCs. We also predict the existence of a significant number of meteoroid streams whose parents have already been disrupted or dynamically removed.

Size and albedo distributions of asteroids in cometary orbits using WISE data

We study the distributions of effective diameter ($D$), beaming parameter ($\eta$), and visible geometric albedo ($p_V$) of asteroids in cometry orbits (ACOs) populations, derived from NASA's Wide-field Infrared Explorer (WISE) observations, and compare these with the same, independently determined properties of the comets. The near-Earth asteroid thermal model (NEATM) is used to compute the $D$, $p_V$ and $\eta$. We obtained $D$ and $p_V$ for 49 ACOs in Jupiter family cometary orbits (JF-ACOs) and 16 ACOs in Halley-type orbits (Damocloids). We also obtained $\eta$ for 45 of them. All but three JF-ACOs (95% of the sample) present a low albedo compatible with a cometary origin. The $p_V$ and $\eta$ distributions of both ACO populations are very similar. For the entire sample of ACOs, the mean geometric albedo is $\bar{p_V} = 0.05 \pm 0.02$, ($\bar{p_V} = 0.05 \pm 0.01$ and $\bar{p_V} =0.05 \pm 0.02$ for JF-ACOs and Damocloids, respectively) compatible with a narrow albedo distribution similar to that of the Jupiter family comets (JFCs), with a $\bar{p_V} \sim 0.04$. The $\bar{\eta} =1.0 \pm 0.2$. We find no correlations between $D$, $p_V$ , or $\eta$. We compare the cumulative size distribution (CSD) of ACOs, Centaurs, and JFCs. Although the Centaur sample contains larger objects, the linear parts in their log-log plot of the CSDs presents a similar cumulative exponent ($\beta = 1.85 \pm 0.30$ and $1.76 \pm 0.35$, respectively). The CSD for Damocloids presents a much shallower exponent $\beta = 0.89 \pm 0.17$. The CSD for JF-ACOs is shallower and shifted towards larger diameters with respect to the CSD of active JFCs, which suggests that the mantling process has a size dependency whereby large comets tend to reach an inactive stage faster than small ones. Finally, the population of JF-ACOs is comparable in number that of JFCs, although there are more tens-km JF-ACOs than JFCs.

A criterion to classify asteroids and comets based on the orbital parameters

The classification criterion between asteroids and comets has evolved in recent decades, but the main distinction remains unchanged. Comets present gas and dust ejection from the surface at some point of their orbits, therefore, these objects are considered to be active. On the other hand, asteroids do not show any kind of large scale gas and dust ejection, they are inert. Nevertheless, this classification scheme is impractical when we have more than 500,000 asteroids already discovered. In addition, comets are not active all along their orbits. In order for a comet to display activity at present or in the recent past in the inner region of the Solar System (heliocentric distance <2AU), the cometary orbit must be unstable in the time scale on the order of ten thousands of years; otherwise, the object should have completely consumed its volatile component. Close encounters with the most massive planets is the only mechanism that could produce “macroscopic” instabilities on a short time scale. The macroscopic changes in the orbital elements can be detected in a numerical integration of the dynamical evolution of the object over a time scale of several thousand years. This procedure to identify asteroids in cometary-like orbits is also impractical because it would require months of computing time. Therefore, a classification scheme based on the orbital elements to identify the border cases between the asteroid and comet populations is urgently required.We present a criterion to classify asteroids and comets and to find the border case based on the Tisserand’s parameter, the Minimum Orbital Intersection Distance (MOID), and considering some information regarding the aphelion and perihelion distances. Objects in mean-motion are disregarded. After applying a filter to the sample of over half a million asteroids already discovered to select the precise orbits and to the sample of 487 short-period comets, we apply the proposed classification criterion. The resulting sample consists of ∼331 Asteroids in Cometary Orbits (ACOs). The ACOs are further classified in subclasses similar to the cometary classification. There are 436 Jupiter Family Comets and 203 ACOs of the Jupiter Family type. This new criterion is more strict that the criteria used by other authors to identify ACOs; nonetheless, with the new criterion we ensure that the ACOs have a chaotic dynamical evolution similar to the periodic comets. The discovered dormant or extinct comets seems, if they exist at all, to be a small fraction of the active comets.We also analyse the available photometric data of ACOs to identify possible large brightness variations. Among the sample of ACOs, there is only one object with brightness variations typical of an active comet: 174P/(60558) Echeclus. But this object has already been double classified as asteroid and comet.

SDSS photometry of asteroids in cometary orbits

Aiming at exploring the relationship between asteroids in cometary orbits and other minor body populations from the observational point of view, I explore the large photometric database of the Sloan Digital Sky Survey - Moving Objects Catalog. The sample of interest was carefully selected analyzing colors and orbital properties within the data in the catalog. I computed the spectral slope for each object and compared with published spectroscopic results of other Asteroids in Cometary Orbits, as well as with other populations of asteroids in the outer region of the Main belt and Trojans. Using this extended database I find that Asteroids in Cometary Orbits with Tisserand parameter below 2.9, and especially below 2.8, are most likely of primitive origin. The population of objects with Tisserand parameter larger than 2.9 is a mixture of populations ranging from the inner to the outer Main belt.

Physical and dynamical characterization of (5201) Ferraz-Mello, a possible extinct Jupiter family comet

Context. The subject of asteroids in cometary orbits (ACOs) has been of growing interest lately. These objects have the orbital characteristics typical of comets, but are asteroidal in appearance, i.e., show no signs of a coma at any part of their orbits. At least a fraction of these objects are thought to be comets that have either exhausted all their volatile content or developed a refractory crust that prevents sublimation. In particular, the asteroid (5201) Ferraz-Mello has, since its discovery, been suspected to be an extinct Jupiter family comet due to the peculiar nature of its orbit. Aims. The aim of this work is to put constraints on the possible origin of (5201) Ferraz-Mello by means of spectroscopic characterization and a study of the dynamics of this asteroid Methods. We used the SOAR Optical Imager (SOI) to obtain observations of (5201) Ferraz-Mello using four SDSS filters. These observations were compared to asteroids listed in the Sloan Moving objects catalog and also to photometry of cometary nuclei, Centaurs, and TNOs. The orbital evolution of (5201) Ferraz-Mello and of a sample of asteroids and comets that are close to that object in the a − e plane were simulated using a pure N-body code for 4 000 years forward and 4 000 years backward in time. Results. The reflectance spectrum obtained from its colors in the SDSS system is unusual, with a steep spectral gradient that is comparable to TNOs and Centaurs, but with an increase in the reflectance in the g band that is not common in those populations. A similar behavior is seen in cometary nuclei that were observed in the presence of a faint dust coma. The dynamical results confirm the very chaotic evolution found previously and its dynamical similarity to the chaotic evolution of some comets. The asteroid is situated in the very stochastic layer at the border of the 2/1 resonance, and it has a very short Lyapunov time (30–40) years. Together, the spectral characteristcs and the dynamical evolution suggest that (5201) Ferraz-Mello is a dormant or extinct comet.

Spectral properties of asteroids in cometary orbits

Spectral properties of asteroids in cometary orbits

Collisional activation of asteroids in cometary orbits

Aims. We study the time an asteroid in a cometary orbit must wait to receive a collision producing a crater depth enough to expose subsurface volatiles, aiming to analyze the possibility of collisional reactivation of these objects if they are dormant comets. Methods. We perform a numerical integration of the asteroids in cometary orbits and a population of projectiles to find the mean intrinsic collision probabilities and mean impact velocities of the targets. The projectile population was obtained as a sample with the same distribution of orbital elements as observed for main belt asteroids, and we also take into account that its size distribution changes for different size ranges. Only 206 asteroids in cometary orbits, that are not members of other asteroid groups, with a Tisserand parameter 2 ≤ TJ ≤ 2.9 and perihelion distance q > 1.3 AU were considered. Results. A large fraction of the objects in the sample receive at least 1 collision energetic enough to break the comet crust and allow a dormant comet to reach an active state in a period shorter than a Jupiter Family Comet dynamical lifetime. A large fraction of the objects in the sample with rt ≥ 8–9 km receive several collisions and could be active for more than 3 × 10 4 yr. We found an excess in the number of dormant comet candidates from the expected values which is indicative of the presence in the ACOs population of objects that are not comets in a dormant state. These objects could be asteroids with TJ < 3 that reach their present orbits by some dynamical mechanism that perturbs the original asteroidal orbit changing its Tisserand invariant.

Spectral properties of asteroids in cometary orbits

Aims. In this paper we analyze the spectra of a sample of asteroids in cometary orbits (ACOs) in order to understand the relationship between them, the Jupiter family comets (JFCs), and the outer main belt populations, such as Hilda, Trojan and Cybele asteroids. Methods. We obtained visible (0.55−0.90 µm) and/or near-infrared (0.8−2.3 µm) spectra of 24 ACOs using 3 telescopes at the Roque de los Muchachos Observatory (La Palma, Spain). Using this data, we derived the taxonomic classification of the asteroids. As most ACOs present featureless spectra (B-, C-, P-, D-type) we also derived their gradient (S � ). Considering also published spectra of ACOs we correlated Swith orbital and dynamical parameters and obtained the cumulative distribution of S � , and compare it with that of other related populations. Results. We present visible and/or near infrared spectra of 24 ACOs, most of them (21) presenting featureless spectra. After including the spectra of other ACOs already published, we analyzed a total of 41 objects, 34 of them having featureless spectra like the spectra of comet nuclei and outer main-belt asteroids. We also noticed a significant difference in the taxonomic distribution of the ACOs in Near-Earth orbits (q 1.3 AU), indicative of different source/transport mechanisms. About 35% of the ACOs in the NEO population analyzed have spectra that present the typical silicate absorption bands at 1 and 2 µ m( S- and V-type), while only 1 of the 24 ACOs in the non-NEO population (about 4%) is S-type and the other 23 have a featureless spectrum. Thus the NEO sub-population of ACOs is composed of a significant fraction of asteroids scattered from the inner main-belt. We didn't find any subtle features in the 0.5−2.0 µm region of featureless ACOs that can be used to discriminate wheather an ACO comes from a cometary or an asteroidal origin. The analysis of the gradient shows that ACOs present an interesting, and significant, anti-correlation between the Tisserand parameter and the spectral gradient, meaning that the reddest objects have the lower Tisserand parameter (i.e., higher chance of a cometary origin). Finally, we obtained the Scumulative distribution for ACOs. This distribution is bluer than that of comet nuclei, Damocloids and outer main-belt population of asteroids, indicative of a significant contamination of asteroids scattered from the inner main-belt.

The size distribution of asteroids in cometary orbits and related populations

Aims. In this work we study the cumulative size distribution of the population of asteroids in cometary orbits (ACOs), aiming to discriminate its cometary or asteroidal origin. Methods. The cumulative luminosity function was determined based on the absolute magnitudes of the ACOs. The cumulative size distribution was then derived and compared to that of possible sources of ACOs, such as the Trojans and Hilda asteroids and Jupiter family comets. The size distribution of the two sub-populations, NEOs and non-NEOs, identified by Licandro et al. (2005) were also analyzed. Results. The derived cumulative size distribution index of the ACO population is 2.55 ± 0.04. The two subpopulations have distinct indexes: −2.20 ± 0.04 and −2.45 ± 0.04 for the NEOs and non-NEOs, respectively. The first value is similar to that of the Trojans and Hilda asteroids and the second to the Jupiter family comets. The obtained values suggest that the non-NEO sub-population of ACOs can be composed of a significant fraction of dormant Jupiter family comets. On the other hand, the NEO sub-population is mostly formed by scattered objects from diverse sources, including main belt asteroids.

Multi-wavelength spectral study of asteroids in cometary orbits

We present a preliminary analysis of visible + infrared spectra (0.5–2.4 μm) of 17 asteroids in cometary orbits (ACOs), asteroidal objects with Tisserand parameter T < 3. These objects are part of a larger database of ACOs observed with the Italian 3.56 m “Telescopio Nazionale Galileo” and the 2.5 m “Nordic Optical Telescope” at the “El Roque de los Muchachos” Observatory (La Palma, Spain). The sample includes 3 near-Earth objects (NEOs), objects with q ⩽ 1.3 AU, and 14 objects non-NEO ACOs (objects with q > 1.3 AU). The spectra of the 14 non-NEO ACOs are featureless and no low-level differences are found with respect to normal D-type main belt asteroids. The slope distribution of these objects is also indistinguishable from that of Hilda and Trojan asteroids. Two of the three NEOs in cometary orbits present silicate features typical of S and Q-type asteroids. Considering also that a large fraction (∼30%) of the 16 NEOs in cometary orbits observed by Binzel, R., Rivkin, A. Stuart, J., Harris, A., Bus, S., Burbine, T. [Observed spectral properties of near-Earth objects: results for population distribution, source regions, and space weathering processes. Icarus, 170, 259–294, 2004] are S or Q-type, we conclude that this suggests a different origin of the two populations.

Asteroids in cometary orbits

Orbital integrations are presented for a total of 14 asteroids with perihelia inside 1.7 AU and with aphelion distances in excess of 4 AU, 10 of which were discovered in 1979–1984. The integrations were normally extended over approximately ±1000 years in a three-body model (Sun-Jupiter-asteroid). The effects of uncertainties of starting orbits are not treated in this work, and as far as the real asteroids are concerned, the results should be regarded mostly as preliminary indications. A wide variety of orbital evolutions is found, and some of them evidently belong to the cometary, chaotic type. Three such cases are identified with certainty (1983 SA, 1983 XF, and 1984 BC) and two or three more with various degrees of likelihood. An asteroidal motion is found for the well-observed object 1979 VA. A stable libration around the 2 1 resonance is found for 1981 FD, which obviously adds to the Griqua group. A long-lasting libration around the 5 3 resonance performed by 1982 YA is probably unstable. Temporary librations are also found for 1983 SA ( 4 3 resonance) and 1983 XF ( 2 1 resonance), but these objects appear to transit into irregular motions with close approaches to Jupiter (less than 0.01 AU for 1983 XF). A very rapid large-amplitude ω libration around 90° is found in the future motion of 1983 VA. If this will indeed occur for the real asteroid, the object will oscillate with a period of only 750 years between a main-belt orbit of very high inclination and a low-inclination Apollo-type orbit.