scholarly journals The discovery rate of new comets in the age of large surveys. Trends, statistics, and an updated evaluation of the comet flux

2009 ◽  
Vol 5 (S263) ◽  
pp. 76-80
Author(s):  
Julio A. Fernández
Keyword(s):  
Oort Cloud ◽  
Long Period ◽  
Orbital Energies ◽  
Tidal Forces ◽  
Two Samples ◽  
Total Magnitude ◽  
Inner Region

AbstractWe analyze a sample of 58 Oort cloud comets (OCCs) (original orbital energiesxin the range 0 <x< 100, in units of 10−6AU−1), plus 45 long-period comets with negative orbital energies or poorly determined or undeterminedx, discovered during the period 1999-2007. To analyze the degree of completeness of the sample, we use Everhart's (1967 Astr. J 72, 716) concept of “excess magnitude” (in magnitudes × days), defined as the integrated magnitude excess that a given comet presents over the time above a threshold magnitude for detection. This quantity is a measure of the likelihood that the comet will be finally detected. We define two sub-samples of OCCs: 1)new comets(orbital energies 0 <x< 30) as those whose perihelia can shift from outside to the inner planetary region in a single revolution; and 2)inner cloud comets(orbital energies 30 ≤x< 100), that come from the inner region of the Oort cloud, and for which external perturbers (essentially galactic tidal forces and passing stars) are not strong enough to allow them to overshoot the Jupiter-Saturn barrier. From the observed comet flux and making allowance for missed discoveries, we find a flux of OCCs brighter than absolute total magnitude 9 of ≃0.65 ± 0.18 per year within Earth's orbit. From this flux, about two-thirds corresponds to new comets and the rest to inner cloud comets. We find striking differences in theq-distribution of these two samples: while new comets appear to follow an uniformq-distribution, inner cloud comets show an increase in the rate of perihelion passages withq.

On the origin of the Kreutz family of sungrazing comets

2021 ◽  
Vol 508 (1) ◽  
pp. 789-802
Author(s):  
Julio A Fernández ◽  
Pablo Lemos ◽  
Tabaré Gallardo
Keyword(s):  
Semimajor Axis ◽  
Oort Cloud ◽  
Type Model ◽  
Natural Consequence ◽  
Mechanism Model ◽  
Long Period ◽  
Tidal Forces ◽  
Short Period ◽  
Wide Range ◽  
Sungrazing Comets

ABSTRACT We evaluate numerically three different models for the parent comet of the Kreutz family of sungrazers: (i) A Centaur on a highly inclined or retrograde orbit that diffuse to the inner planetary region where it became a sungrazer (Model 1). (ii) A parent comet injected from the Oort cloud straight into a near-parabolic, sungrazing orbit. Near perihelion the comet was disrupted by tidal forces from the Sun giving rise to a myriad of fragments that created the Kreutz family (Model 2). (iii) A two-step process by which an Oort cloud comet is first injected in a non-sungrazing, Earth-crossing orbit where its semimajor axis decreases from typical Oort cloud values (a ∼ 104 au) to around 102 au, and then it evolves to a sungrazing orbit by the Lidov–Kozai mechanism (Model 3). Model 1 fails to produce sungrazers of the Kreutz type. Model 2 produces some Kreutz sungrazers and has the appeal of being the most straightforward. Yet the impulses received by the fragments originated in the catastrophic disruption of the parent comet will tend to acquire a wide range of orbital energies or periods (from short-period to long-period orbits) that is in contradiction with the observations. Model 3 seems to be the most promising one since it leads to the generation of some sungrazers of the Kreutz type and, particularly, it reproduces the clustering of the argument of perihelion ω of the observed Kreutz family members around 60°–90°, as a natural consequence of the action of the Lidov–Kozai mechanism.

scholarly journals Dynamical evolution of Oort cloud comets to near-Earth space

2006 ◽  
Vol 2 (S236) ◽  
pp. 43-54 ◽  
Author(s):  
Olga A. Mazeeva
Keyword(s):  
Dynamical Evolution ◽  
Absolute Magnitude ◽  
Oort Cloud ◽  
Outer Solar System ◽  
Earth Space ◽  
Near Earth Space ◽  
Long Period ◽  
Order Of Magnitude ◽  
Orbital Periods ◽  
Stellar Perturbations

AbstractThe dynamical evolution of 2⋅105 hypothetical Oort cloud comets by the action of planetary, galactic and stellar perturbations during 2⋅109 years is studied numerically. The evolution of comet orbits from the outer (104 AU <a<5⋅104 AU, a is semimajor axes) and the inner Oort cloud (5⋅103 AU <a<104 AU) to near-Earth space is investigated separately. The distribution of the perihelion (q) passage frequency in the planetary region is obtained calculating the numbers of comets in every interval of Δ q per year. The flux of long-period (LP) comets (orbital periods P>200 yr) with perihelion distances q<1.5 AU brighter than visual absolute magnitude H10=7 is ∼ 1.5 comets per year, and ∼18 comets with H10<10.9. The ratio of all LP comets with q<1.5 AU to ‘new’ comets is ∼5. The frequency of passages of LP comets from the inner Oort cloud through region q<1.5 AU is ∼3.5⋅10−13 yr−1, that is roughly one order of magnitude less than frequency of passages of LP comets from the outer cloud (∼5.28⋅10−12 yr−1). We show that the flux of ‘new’ comets with 15<q<31 AU is higher than with q<15 AU, by a factor ∼1.7 for comets from the outer Oort cloud and, by a factor ∼7 for comets from the inner cloud. The perihelia of comets from the outer cloud previously passed through the planetary region are predominated in the Saturn-Uranus region. The majority of inner cloud comets come in the outer solar system (q>15 AU), and a small fraction (∼0.01) of them can reach orbits with q<1.5 AU. The frequency of transfer of comets from the inner cloud (a<104 AU) to the outer Oort cloud (a>104 AU), from where they are injected to the region q<1.5 AU, is ∼6⋅10−14 yr−1.

scholarly journals The influx rate of long-period comets in the Earth's neighborhood and their debris contribution to the interplanetary medium

2012 ◽  
Vol 10 (H16) ◽  
pp. 140-140
Author(s):  
Julio Angel Fernández
Keyword(s):  
Steady State ◽  
Interplanetary Medium ◽  
Interplanetary Dust ◽  
Large Contribution ◽  
Influx Rate ◽  
Long Period ◽  
Impact Rate ◽  
Total Magnitude ◽  
Dust Complex ◽  
The Impact

AbstractWe analyze the flux of new and evolved long-period comets (LPCs) reaching the Earth's neighborhood (perihelion distances q < 1.3 AU), their physical lifetimes, and their implications as regards to the amount of meteoritic matter that is being deposited in the near-Earth region. The flux of LPCs with q < 1.3 au is found to be of about 340 ± 40, brighter than absolute total magnitude 8.6 (radius R ~ 0.6 km) (Fernández and Sosa 2012). Bearing in mind that most of these comets disintegrate into meteoritic matter, this represents a large contribution to the interplanetary dust complex which requires an amount of matter of about 10 tons s−1 to keep it in steady state. These aspects, as well as the impact rate with Earth of meteoroids of LPC origin, will be discussed in this presentation.

scholarly journals The influence of high pressure on the properties of natural alumino-silicates

2002 ◽  
Vol 34 (2) ◽  
pp. 163-168
Author(s):  
N. Susic
Keyword(s):  
High Pressure ◽  
Thermal Behaviour ◽  
Amorphous Layer ◽  
New Materials ◽  
Crystalline Phases ◽  
Amorphous Phases ◽  
Long Period ◽  
Two Samples ◽  
Mineral Compositions

The effect of the application of high-pressure (up to 12 GPa) on natural alumino-silicates has been studied. Chemical and mineral compositions and thermal behaviour have been analyzed of two samples of alumino-silicates. Results obtained indicate that the application of high pressure causes notable changes. A particularly significant one is the formation of amorphous phases on account of crystalline phases. An amorphous layer formed on particle surfaces with its diverse physical, mechanical, chemical, and other properties, especially over a long period of time, can influence the processes provoking or activating land slides or soil settlements. This enables derivation of many new materials with entirely new properties important for use in the ceramic and brick industries.

Long-period Comets and the Oort Cloud

1997 ◽  
Vol 822 (1 Near-Earth Ob) ◽  
pp. 67-95 ◽  
Author(s):  
PAUL R. WEISSMAN
Keyword(s):  
Oort Cloud ◽  
Long Period

scholarly journals Statistical test of the distribution of perihelion points and its implication for cometary origin

1985 ◽  
Vol 83 ◽  
pp. 11-17
Author(s):  
S. Yabushita
Keyword(s):  
Selection Effect ◽  
Statistical Test ◽  
Oort Cloud ◽  
Long Period ◽  
The Asymmetry ◽  
South Asymmetry ◽  
Cometary Origin

AbstractThe distribution of perihelion points of long-period comets is known to cluster towards the solar apex, and some authors ascribe it to north-south asymmetry in the distribution of observers. Validity or otherwise of this alleged selection effect is tested by randomly picking up the same number of perihelia in the southern (δ < 0) as those in the northern (δ > 0) hemisphere. It is shown that the observed clustering cannot be ascribed to the asymmetry of observers. Further, 67 comets which are new in Oort’s sense are tested similary. The character of their distribution is similar to that of all the known comets. It appears difficult to interpret the clustering in terms of a recent stellar disturbance of the Oort cloud.

scholarly journals Non-gravitational effects change the original 1/a-distribution of near-parabolic comets

2020 ◽  
Vol 633 ◽  
pp. A80 ◽  
Author(s):  
Małgorzata Królikowska
Keyword(s):  
Semimajor Axis ◽  
Oort Cloud ◽  
Gravitational Acceleration ◽  
Gravitational Effects ◽  
Long Period ◽  
Dynamical Properties ◽  
The Individual ◽  
Almost All ◽  
Data Processing Methods

Context. The original 1∕a-distribution is the only observational basis for the origin of long-period comets (LPCs) and the dynamical properties of the Oort Cloud. Although they are very subtle in the motion of these comets, non-gravitational effects can cause major changes in the original semimajor axis, 1∕aori. Aims. We obtained reliable non-gravitational orbits for as many LPCs with small perihelion distances of q < 3.1 au as possible, and determined the corresponding shape of the Oort spike. Methods. We determined the osculating orbits of each comet using several data-processing methods, and selected the preferred orbit using a few specific criteria. The distribution of 1∕aori for the whole comet sample was constructed using the individual Gaussian distribution we obtained for the preferred solution of each comet. Results. The derived distribution of 1∕aori for almost all known small-perihelion Oort spike comets was based on 64% of the non-gravitational orbits. This was compared with the distribution based on purely gravitational orbits, as well as with 1∕aori constructed earlier for LPCs with q > 3.1 au. We present a statistical analysis of the magnitudes of the non-gravitational acceleration for about 100 LPCs. Conclusions. The 1∕aori-distribution, which is based mainly on the non-gravitational orbits of small-perihelion Oort spike comets, is shifted by about 10 × 10−6 au−1 to higher values of 1∕aori compared with the distribution that is obtained when the non-gravitational effects on comet motion are ignored. We show the differences in the 1∕aori-distributions between LPCs with q < 3.1 au and those with q > 3.1 au. These findings indicate the important role of non-gravitational acceleration in the motion and origin of LPCs and in the formation of the Oort Cloud.

scholarly journals The Oort Cloud and long-period comets

2013 ◽  
Vol 49 (1) ◽  
pp. 8-20 ◽  
Author(s):  
Hans Rickman
Keyword(s):  
Oort Cloud ◽  
Long Period

scholarly journals Dynamics and orbital evolution of Oort cloud comets

1996 ◽  
Vol 172 ◽  
pp. 209-212 ◽  
Author(s):  
J.Q. Zheng ◽  
M.J. Valtonen ◽  
S. Mikkola ◽  
H. Rickman
Keyword(s):  
Solar System ◽  
Orbital Evolution ◽  
Oort Cloud ◽  
Long Period ◽  
Gravitational Perturbations ◽  
Short Period ◽  
Orbital Periods

Investigators generally conjecture a steady flux of new comets from the Oort cloud through the inner Solar system. Due to gravitational perturbations by major planets these objects may escape, become long period comets (LPCs) if their orbital periods P are larger than 200yr or become short period comets (SPCs) when their period is less than 200yr. SPCs are further divided in two types: the Halley type comets (HT, for P > 20yr) and the Jupiter family comets (JF, for P < 20yr).

scholarly journals The “memory” of the Oort cloud

2018 ◽  
Vol 620 ◽  
pp. A45 ◽  
Author(s):  
Marc Fouchard ◽  
Arika Higuchi ◽  
Takashi Ito ◽  
Lucie Maquet
Keyword(s):  
Initial Distribution ◽  
Oort Cloud ◽  
Cloud Formation ◽  
Orbital Energy ◽  
Initial Population ◽  
Isotropic Model ◽  
Initial Shape ◽  
Long Period ◽  
Galactic Longitude

Aims. Our aim in this paper is to try to discover if we can find any record of the Oort cloud formation process in the orbital distribution of currently observable long-periodic comets. Methods. Long-term simulations of tens of millions of comets from two different kinds of proto-Oort clouds (isotropic and disk-like) were performed. In these simulations we considered the Galactic tides, stellar passage, and planetary perturbations. Results. In the case of an initially disk-like proto-Oort cloud, the final Oort cloud remains anisotroic inside of about 13 200 au. A record of the initial shape is preserved, here referred to as the “memory”, even on the final distribution of observable comets. This memory is measurable in particular for observable comets for which the previous perihelion was beyond 10 au and that were significantly affected by Uranus or Neptune at that moment (the so-called Kaib-Quinn jumpers observable class). Indeed, these comets are strongly concentrated along an extended scattered disk that is the remnant of the initial population 1 Gyr before the comets are observable. In addition, for this class of comets, the distributions of ecliptic inclination and Galactic longitude of the ascending node at the previous perihelion preceding the observable perihelion highlight characteristics that are not present in the isotropic model. Furthermore, the disk-like model produces four times more observable comets than the isotropic one, and its flux is independent of the initial distribution of orbital energy. Also for the disk-like model, the region beyond Neptune up to ~40 au gives the major contribution to the final flux of observable comets. Conclusions. The disk-like model sustains a flux of observable comets that are more consistent with the actually observed flux than using the isotropic model. However, further investigations are needed to reveal whether a fingerprint of the initial proto-Oort cloud, such as those highlighted in the present article, is present in the sample of known long-period comets.

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