Cometary Activity beyond the Planets

Recent observations show activity in long-period comet C/2017 K2 at heliocentric distances beyond the orbit of Uranus. With this as motivation, we constructed a simple model that takes a detailed account of gas transport modes and simulates the time-dependent sublimation of supervolatile ice from beneath a porous mantle on an incoming cometary nucleus. The model reveals a localized increase in carbon monoxide (CO) sublimation close to heliocentric distance r H = 150 au (local blackbody temperature ∼23 K), followed by a plateau and then a slow increase in activity toward smaller distances. This localized increase occurs as heat transport in the nucleus transitions between two regimes characterized by the rising temperature of the CO front at larger distances and nearly isothermal CO at smaller distances. As this transition is a general property of sublimation through a porous mantle, we predict that future observations of sufficient sensitivity will show that inbound comets (and interstellar interlopers) will exhibit activity at distances far beyond the planetary region of the solar system.

A Sublime Opportunity: The Dynamics of Transitioning Cometary Bodies and the Feasibility of In Situ Observations of the Evolution of Their Activity

The compositional and morphological evolution of minor bodies in the solar system is primarily driven by the evolution of their heliocentric distances, as the level of incident solar radiation regulates cometary activity. We investigate the dynamical transfer of Centaurs into the inner solar system, facilitated by mean motion resonances with Jupiter and Saturn. The recently discovered object P/2019 LD2 will transition from the Centaur region to the inner solar system in 2063. In order to contextualize LD2, we perform N-body simulations of a population of Centaurs and Jupiter-family comets. Objects between Jupiter and Saturn with Tisserand parameter T J ∼ 3 are transferred onto orbits with perihelia q < 4 au within the next 1000 yr with notably high efficiency. Our simulations show that there may be additional LD2-like objects transitioning into the inner solar system in the near future, all of which have low ΔV with respect to Jupiter. We calculate the distribution of orbital elements resulting from a single Jovian encounter and show that objects with initial perihelia close to Jupiter are efficiently scattered to q < 4 au. Moreover, approximately 55% of the transitioning objects in our simulated population experience at least one Jovian encounter prior to reaching q < 4 au. We demonstrate that a spacecraft stationed near Jupiter would be well positioned to rendezvous, orbit-match, and accompany LD2 into the inner solar system, providing an opportunity to observe the onset of intense activity in a pristine comet in situ. Finally, we discuss the prospect of identifying additional targets for similar measurements with forthcoming observational facilities.

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.

FIRST FINDINGS ON COMETARY ACTIVITY FROM THE PTF COMET SAMPLE

We present preliminary results from the Palomar Transient Factory (PTF) uniform sample of short period comets (SPCs) and long period comets (LPCs), captured between September 2009 and March 2013. We study their dynamical and physical properties in relation to their activity for a better understanding of cometary evolution. This observing campaign was part of PTF in its intermediate phase (iPTF) at the California Institute of Technology (Caltech). The photometric sample comprises more than 180 comets, which makes it one of the largest samples studied to-date. We present a new approach to identifying active comets that compares subtracted aperture magnitudes of comets with the distribution of stars of similar brightness in each image. In this paper, we present initial findings on cometary activity in relationship to their perihelion distances. We show differences between the distributions of the SPCs and that of the LPCs. As others predicted, it seems that a larger fraction of LPCs are found to be active at larger perihelia than for the SPCs. We look at ratios of active comets in different perihelia brackets and compare those to previous works and results. We do not discuss the statistical significance of our findings as this is still work in progress.

The dust tail gap of C/2014 Q1 (PanSTARRS)

&lt;p&gt;A dust tail &amp;#8216;gap&amp;#8217; was discovered in amateur images of the dust tail of C/2014 Q1 (PanSTARRS), which appeared around the comet&amp;#8217;s most recent perihelion on 6&lt;sup&gt;th&lt;/sup&gt; July 2015. This gap presented itself as a wedge-shaped region devoid of dust, with the comet&amp;#8217;s dust tail appearing to be normal on either side of this dark zone.&lt;/p&gt; &lt;p&gt;The results of the C/2014 Q1 study, employing Finson-Probstein modelling of the dust tail, show that none of the dust lay along the comet&amp;#8217;s orbital path, confirming that both sections of dust were part of the dust tail and not a typical separation between dust tail and dust trail. A gap, devoid of dust, separates these two sections. The edges of this gap are bounded fairly accurately by lines of constant dust ejection time, corresponding to dust that should have been ejected between 6&lt;sup&gt;th&lt;/sup&gt; July and 12&lt;sup&gt;th&lt;/sup&gt; July. This suggests that cometary activity between these two dates was drastically reduced, although the cause of this is still unknown. The gap was visible throughout July and August 2015, and its shape and structure remained constant in the context of expected dust tail behaviour. &amp;#160;&lt;/p&gt; &lt;p&gt;The limited dataset for C/2014 Q1 meant that the formation mechanism of this gap could not be fully investigated. &amp;#160;However,&amp;#160;a&amp;#160;subsequent&amp;#160;survey of&amp;#160;amateur and professional comet&amp;#160;images revealed the presence of similar&amp;#160;gaps in the dust tails of several&amp;#160;other&amp;#160;comets. Analysis of these comets show many similarities with the results of the C/2014 Q1 study, including that these dust gaps observed all form during the comets&amp;#8217; perihelia. We present the results of individual analyses&amp;#160;and&amp;#160;cross-comparison of these&amp;#160;comets, and&amp;#160;summarize what we believe are the most likely scenarios for the formation of these perplexing features.&amp;#160;&lt;/p&gt;

Unusual polarimetric properties for interstellar comet 2I/Borisov

So far, only two interstellar objects have been observed within our Solar System. While the first one, 1I/‘Oumuamua, had asteroidal characteristics, the second one, 2I/Borisov, showed clear evidence of cometary activity. We performed polarimetric observations of comet 2I/Borisov using the European Southern Observatory Very Large Telescope to derive the physical characteristics of its coma dust particles. Here we show that the polarization of 2I/Borisov is higher than what is typically measured for Solar System comets. This feature distinguishes 2I/Borisov from dynamically evolved objects such as Jupiter-family and all short- and long-period comets in our Solar System. The only object with similar polarimetric properties as 2I/Borisov is comet C/1995 O1 (Hale-Bopp), an object that is believed to have approached the Sun only once before its apparition in 1997. Unlike Hale-Bopp and many other comets, though, comet 2I/Borisov shows a polarimetrically homogeneous coma, suggesting that it is an even more pristine object.