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Universe
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The Advances of Comets' Activity
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The Advances of Comets' Activity

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Solar and Stellar Physics".

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 10919

Special Issue Editor

Dr. Giovanna Rinaldi

E-Mail Website
Guest Editor
Istituto Nazionale Di Astrofisica, National Institute of Astrophysics (INAF), 00136 Rome, Italy
Interests: remote sensing and in situ data analysis; atmospheric planets; comets; radiative transfer tools for simulation of coma and atmospheric planets; scattering properties of dust and icy particles

Special Issue Information

Dear Colleagues,

Comets are made of volatile and refractory material and, orbiting around the Sun, experience various levels of sublimation. Cometary activity consists in the ejection from cometary nuclei of dust and gas molecules induced by ice sublimation. It is widely assumed that dust is accelerated by the gas drag, but the details of the physical process driving activity remain unknown, especially regarding the mechanisms by which dust is detached from the nucleus to then be accelerated by gas.

The cometary activity and dust displacement on the surface play a major role in nucleus topography modifications.

This Special Issue aims to collect state-of-the-art knowledge on cometary activity derived from recent observations and modeling, also driving possible future perspectives and developments.

Cross-communication between observers, modelers, and laboratory experimentalists will favor steps toward a more comprehensive understanding of cometary activity. Topics of interest to this Special Issue include but are most certainly not limited to works focusing on cometary activity by means of multiwavelength comet observations, coma dynamical simulations, thermophysical modeling, and laboratory experiments.

Dr. Giovanna Rinaldi
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • comets
  • activity
  • dynamical simulations
  • data analysis
  • observational–space vehicles
  • instruments—imaging spectroscopy and in situ measurements

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Published Papers (5 papers)

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Research

Jump to: Review

23 pages, 2018 KiB  
Article
Main Belt Comets and other “Interlopers” in the Solar System
by Vincenzo Orofino
Universe 2022, 8(10), 518; https://doi.org/10.3390/universe8100518 - 4 Oct 2022
Cited by 1 | Viewed by 1720
Abstract
According to traditional ideas about the formation of the Solar System starting from a protoplanetary disk of gas and dust, a well-defined distribution of planets and minor bodies is expected: (a) volatile-poor rocky bodies (terrestrial planets and asteroids) in the inner part of [...] Read more.
According to traditional ideas about the formation of the Solar System starting from a protoplanetary disk of gas and dust, a well-defined distribution of planets and minor bodies is expected: (a) volatile-poor rocky bodies (terrestrial planets and asteroids) in the inner part of the Solar System and (b) volatile-rich objects (gaseous giant planets, comets, Centaurs, and trans-Neptunian objects) in the outer part. All these bodies are expected to orbit near a plane (the ecliptic) coinciding with that of the protoplanetary disk. However, in the modern Solar System many bodies are present that do not respect this simplistic expectation. First of all, there are the so-called Main Belt Comets, apparently asteroidal objects that show an activity similar to that of comets. In addition, there is an object (and several others very probably exist), which, despite its S-type spectrum characteristic of rocky bodies, is found on a cometary orbit. Finally, there are many asteroids on very inclined orbits with respect to the ecliptic. These very interesting groups of objects, which, according to the traditional point of view, could be collectively seen as some sort of “interlopers” of the Solar System, will be discussed in this review, which offers descriptions of their properties and their likely origin. In this respect, the possibility is discussed that many active asteroids (such as those belonging to the Taurid Complex) are the result of the fragmentation of large comets that occurred in the relatively recent past. Full article
(This article belongs to the Special Issue The Advances of Comets' Activity)
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21 pages, 4677 KiB  
Article
Mechanical Properties of Cometary Surfaces
by Jens Biele, Jean-Baptiste Vincent and Jörg Knollenberg
Universe 2022, 8(9), 487; https://doi.org/10.3390/universe8090487 - 15 Sep 2022
Cited by 5 | Viewed by 1975
Abstract
Mechanical properties, in particular, strength (tensile, shear, compressive) and porosity, are important parameters for understanding the evolution and activity of comets. However, they are notoriously difficult to measure. Unfortunately, neither Deep Impact nor other comet observations prior to Rosetta provided firm data on [...] Read more.
Mechanical properties, in particular, strength (tensile, shear, compressive) and porosity, are important parameters for understanding the evolution and activity of comets. However, they are notoriously difficult to measure. Unfortunately, neither Deep Impact nor other comet observations prior to Rosetta provided firm data on the strength of cometary material. This changed with the Rosetta mission and its detailed close observation data and with the landing(s) of Philae in 2014. There are already many articles and reviews in the literature that derive or compile many different strength values from various Rosetta and Philae data. In this paper, we attempt to provide an overview of the available direct and indirect data; we focus on comet Churyumov–Gerasimenko/67P but include a discussion on the Deep Impact strength results. As a prerequisite, we start by giving precise definitions of ‘strength’, discuss soil mechanics based on the Mohr–Coulomb ‘law’ of micro-gravity, and discuss bulk density and porosity, sintering, and the physics of the strength of a cohesive granular medium. We proceed by discussing the scaling of strength with the size and strain rate, which is needed to understand the observational data. We show how measured elastic properties and thermal (conductivity) data can be correlated with strength. Finally, a singular very high strength value is reviewed as well as some particularly small-strength values inferred from the bouncing motion of Philae, data from its collisions with the surface of the comet, and scratch marks it left, allegedly, on the surface close to its final resting site. The synthesis is presented as an overview figure of the tensile and compressive strength of cometary matter as a function of the size scale; conclusions about the size dependence and apparent natural variability of strength are drawn. Full article
(This article belongs to the Special Issue The Advances of Comets' Activity)
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17 pages, 3187 KiB  
Article
Monte Carlo Models of Comet Dust Tails Observed from the Ground
by Fernando Moreno
Universe 2022, 8(7), 366; https://doi.org/10.3390/universe8070366 - 3 Jul 2022
Cited by 3 | Viewed by 2066
Abstract
Dust particles leaving the comet nucleus surface are entrained by the gas within the first few nuclear radius distances and are subjected to a complex hydrodynamical environment. From distances of about 20 nuclear radii outwards, the particles decouple from the accelerating gas and [...] Read more.
Dust particles leaving the comet nucleus surface are entrained by the gas within the first few nuclear radius distances and are subjected to a complex hydrodynamical environment. From distances of about 20 nuclear radii outwards, the particles decouple from the accelerating gas and are mainly affected by solar gravity and radiation pressure for small-sized nuclei. Their motion is then a function of their so-called β parameter, which is the ratio of the radiation pressure force to gravity force, and their velocity when the gas drag vanishes. At a given observation time, the position of those particles projected on the sky plane form the coma, tail and trail structures that can be observed from ground-based or space-borne instrumentation. Monte Carlo models, based on the computer simulation of the Keplerian trajectories of a large set of dust particles, provide the best possible approach to extract the dust environment parameters from the observed scattered solar light or thermal emission. In this paper, we describe the Monte Carlo code along with some successful applications of such technique to a number of targets. Full article
(This article belongs to the Special Issue The Advances of Comets' Activity)
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Review

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16 pages, 2872 KiB  
Review
Activity of Comets Constrains the Chemistry and Structure of the Protoplanetary Disk
by Marco Fulle
Universe 2022, 8(8), 417; https://doi.org/10.3390/universe8080417 - 10 Aug 2022
Cited by 1 | Viewed by 1658
Abstract
Recent data of molecular clouds and protoplanetary disks constrain the composition and structure of the disk and planetesimals. Laboratory experiments suggest that dust accretion in disks stops at pebble sizes. Sublimation and recondensation of water ice at the disk water-snow line suggest that [...] Read more.
Recent data of molecular clouds and protoplanetary disks constrain the composition and structure of the disk and planetesimals. Laboratory experiments suggest that dust accretion in disks stops at pebble sizes. Sublimation and recondensation of water ice at the disk water-snow line suggest that pebbles split into water-rich and water-poor ones. The same conclusion has been recently reached by models of cometary activity consistent with the structure of porous Interplanetary Dust Particles (IDPs) and of porous dust collected by the Stardust and Rosetta missions. The observation of crystalline water ice in protoplanetary disks by the Herschel satellite, the erosion of comets, and the seasonal evolution of the nucleus color require that the two pebble families have a water-ice mass fraction close to 33% and 2%, respectively. Here, we show that the diversity of comets is thus due to random mixtures with different area fractions Ap and Ar of water-poor and water-rich pebbles, predicting most of the data observed in comets: why the deuterium-to-hydrogen ratio in cometary water correlates to the ratio Ap/Ar, which pebbles dominate the activity of Dynamically New Comets (DNCs), what is the origin of cometary outbursts, why comets cannot be collisional products, and why the brightness evolution of DNCs during their first approach to the Sun is actually unpredictable. Full article
(This article belongs to the Special Issue The Advances of Comets' Activity)
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34 pages, 8846 KiB  
Review
Formation of Comets
by Jürgen Blum, Dorothea Bischoff and Bastian Gundlach
Universe 2022, 8(7), 381; https://doi.org/10.3390/universe8070381 - 15 Jul 2022
Cited by 22 | Viewed by 2510
Abstract
Questions regarding how primordial or pristine the comets of the solar system are have been an ongoing controversy. In this review, we describe comets’ physical evolution from dust and ice grains in the solar nebula to the contemporary small bodies in the outer [...] Read more.
Questions regarding how primordial or pristine the comets of the solar system are have been an ongoing controversy. In this review, we describe comets’ physical evolution from dust and ice grains in the solar nebula to the contemporary small bodies in the outer solar system. This includes the phases of dust agglomeration, the formation of planetesimals, their thermal evolution and the outcomes of collisional processes. We use empirical evidence about comets, in particular from the Rosetta Mission to comet 67P/Churyumov–Gerasimenko, to draw conclusions about the possible thermal and collisional evolution of comets. Full article
(This article belongs to the Special Issue The Advances of Comets' Activity)
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