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RE: Long-Period Comets
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Title: The Location of Oort Cloud Comets C/2011 L4 Panstarrs and C/2012 S1 ISON, on a Comets' Evolutionary Diagram
Authors: Ignacio Ferrin

(1) We reduced 9615 photometric observations of comets C/2011 L4 Panstarrs, C/2012 S1 ISON, C/1973 E1 Kohoutek, C/2002 O4 Honig and 1P/Halley, and we present their secular light curves (SLCs). (2) We measured the Slowdown Event (SDE) of C/2011 L4 Panstarrs, R(SDE)= -4.97±0.03 AU (or t(SDE)=20120414±3 d). (4) We measured the SDE of C/2012 S1 ISON, R(SDE)=-5.07±0.03 AU (or 20130117±3 d). Notice the coincidence with C/2011 L4 Panstarrs. For the absolute magnitude we find m(-1,1)= +12.7±0.1, an intrinsically faint comet. (5) Technically speaking, since January 17th±3 d, 2013, comet ISON has been on a standstill for more than ~132 d, within the same magnitude ±0.2 mag, a rather puzzling feat (Figure 8). Since the nucleus brightens like R+2, the comet is actually dimming. There is a significant probability that the comet may turn off as comet C/2002 Honig did, or alternatively, it may disintegrate at perihelion. (6) Comet ISON is depleted in water content by a factor of 9.2, approximately. (7) We locate the two comets in an evolutionary diagram. The diagram is forgiving, and the results are robust. (8) We present the SLC of comet C/1973 E1 Kohoutek, the famous comet that fizzled, and show reasons to conclude that it did not. We show the SLC of comet C/2002 O4 Honig, a comet that disintegrated. (10) We define the Jupiter Family Interval of Comets, as 1.24<R(SDE)<2.09 AU. This is a narrow Interval in which 5 comets from the Oort Cloud and 6 comets from the JF, have their SDEs. (11) We determine the Death Ages of several comets, DA(KO)=1.7E06 cy, DA(V1)=1.4E05, DA(L4)= 36000cy, DA(Ho)=6 cy. (12) Suffocating comets move upward in the RR versus ML-AGE diagram, and sublimating comets move downward. There must be an intermediate value where motion must be horizontal, a suffocation-sublimation-border. We estimate the border at RR(SB)=(6±5)E4.

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Oort Cloud Comets
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Title: Dynamics of Dust Particles Released from Oort Cloud Comets and Their Contribution to Radar Meteors
Authors: David Nesvorny, David Vokrouhlicky, Petr Pokorny, Diego Janches

The Oort Cloud Comets (OCCs), exemplified by the Great Comet of 1997 (Hale-Bopp), are occasional visitors from the heatless periphery of the solar system. Previous works hypothesized that a great majority of OCCs must physically disrupt after one or two passages through the inner solar system, where strong thermal gradients can cause phase transitions or volatile pressure buildup. Here we study the fate of small debris particles produced by OCC disruptions to determine whether the imprints of a hypothetical population of OCC meteoroids can be found in the existing meteor radar data. We find that OCC particles with diameters D<10 um are blown out from the solar system by radiation pressure, while those with D>1 um have a very low Earth-impact probability. The intermediate particle sizes, D=100 um, represent a sweet spot. About 1% of these particles orbitally evolve by Poynting-Robertson drag to reach orbits with semimajor axis a=1 AU. They are expected to produce meteors with radiants near the apex of the Earth's orbital motion. We find that the model distributions of their impact speeds and orbits provide a good match to radar observations of apex meteors, except for the eccentricity distribution, which is more skewed toward e=1 in our model. Finally, we propose an explanation for the long-standing problem in meteor science related to the relative strength of apex and helion/antihelion sources. As we show in detail, the observed trend, with the apex meteors being more prominent in observations of highly sensitive radars, can be related to orbital dynamics of particles released on the long-period orbits.

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The Sun Steals Comets from Other Stars

The next time you thrill at the sight of a comet blazing across the night sky, consider this: it's a stolen pleasure. You're enjoying the spectacle at the expense of a distant star.
Sophisticated computer simulations run by researchers at the Southwest Research Institute (SWRI) have exposed the crime.

"If the results are right, our Sun snatched comets from neighbouring stars' back yards" - SWRI scientist Hal Levison.

And he believes this kind of thievery accounts for most of the comets in the Oort Cloud at the edge of our solar system.

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Many comets originally formed in other solar systems

Many of the most well known comets in history, including Halley, Hale-Bopp and McNaught, may have been born in orbit around other stars and not the Sun, according to a new study by Queen's University astronomy professor Martin Duncan and an international team of astronomers.
The researchers used computer simulations to show that the Sun may have captured small icy bodies from its sibling stars while it was in its birth star cluster, and this created a reservoir for observed comets.

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Many famous comets could originate from other solar systems

For many comets, among the more famous are comets Halley, Hale-Bopp, and, more recently, Comet McNaught, could be born on paths orbiting around other stars and not around our Sun, according to a new theory developed by a team of international astronomers including a post-PhD student of the Côte d'Azur Observatory (INSU, Université de Sophia Antipolis). The results are published in Science Express 10 06 2010 online.

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Title: Reassessing the Source of Long-Period Comets
Authors: Nathan A. Kaib, Thomas Quinn

We present numerical simulations to model the production of observable long-period comets (LPCs) from the Oort Cloud, a vast reservoir of icy bodies surrounding the Sun. We show that inner Oort Cloud objects can penetrate Jupiter's orbit via a largely unexplored dynamical pathway, and they are an important, if not the dominant, source of known LPCs. We use this LPC production to place observationally motivated constraints on the population and mass of the inner Oort Cloud, which are consistent with giant planet formation theory. These constraints indicate that only one comet shower producing late Eocene bombardment levels has likely occurred since the Cambrian Explosion, making these phenomena an improbable cause of additional extinction events.

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