Cometary masses derived from non-gravitational forces

Sosa, Andrea; Fernández, Julio A.

doi:10.1111/j.1365-2966.2008.14183.x

Cited by 43 publications

(44 citation statements)

References 77 publications

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“…Based on analysis of ejected material from comet tails, the aggregates (cometesimals) exist in structures up to several meters in diameter (29)(30)(31). The mass density of a range of comet nuclei (0.15 g·cm −3 ≤ ρ ≤ 0.7 g·cm −3 ) indicate that the comets described above are typical of other comets in the terrestrial solar system, and that the rigid aggregate packing model can likely be applied to other comets and porous bodies as well (11,29,(31)(32)(33).…”

Section: Significancementioning

confidence: 99%

Packing density of rigid aggregates is independent of scale

Zangmeister

Radney

Dockery

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Large planetary seedlings, comets, microscale pharmaceuticals, and nanoscale soot particles are made from rigid, aggregated subunits that are compacted under low compression into larger structures spanning over 10 orders of magnitude in dimensional space. Here, we demonstrate that the packing density (θ f ) of compacted rigid aggregates is independent of spatial scale for systems under weak compaction. The θ f of rigid aggregated structures across six orders of magnitude were measured using nanoscale spherical soot aerosol composed of aggregates with ∼17-nm monomeric subunits and aggregates made from uniform monomeric 6-mm spherical subunits at the macroscale. We find θ f = 0.36 ± 0.02 at both dimensions. These values are remarkably similar to θ f observed for comet nuclei and measured values of other rigid aggregated systems across a wide variety of spatial and formative conditions. We present a packing model that incorporates the aggregate morphology and show that θ f is independent of both monomer and aggregate size. These observations suggest that the θ f of rigid aggregates subject to weak compaction forces is independent of spatial dimension across varied formative conditions. M any systems are comprised of elementary subunits packed within a defined volume. The simplest 3D system consists of uniform spheres, and despite its apparent simplicity, a rigorous mathematical description eluded researchers for nearly four centuries dating back to Kepler's conjecture in 1611. In 2005, Hales provided a definitive mathematical proof confirming the observed experimental maximum packing density of 74% (1). Packing of more complex structures is far more mathematically challenging and instead relies on empirical studies (2-9). One of the most ubiquitous packing systems in the universe are rigid aggregates composed of a collection of monomeric units joined together into a fractal structure and subsequently densified through omnidirectional applied force, as shown in Fig. 1 (10).The formation and compaction mechanism of disordered aggregates is presumed to be independent of dimension, composition, and spatial scale, and has been observed in a diverse range of materials and conditions, such as the accretion of material in interstellar space and the formation and compaction of aerosol in the Earth's atmosphere. Many interstellar formations comprise nano-or microscale dust particles that begin as disordered monomeric subunits, which electrostatically aggregate to form fractal (lacey) agglomerates that serve as foundries for comets and planetary seedlings (10-16). Soot, ubiquitous in the Earth's troposphere, is also comprised of nanometer sized carbonaceous monomers aggregated in a disordered lacey structure. Compaction into spheres occurs after trace gas and/or liquid adsorption and evaporation. In both cases, the resulting structure is constrained by aggregate rigidity (17).The systems described above are similarly constructed from single-unit building blocks assembled into larger disordered structures. The final structure ...

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Section: Significancementioning

confidence: 99%

Packing density of rigid aggregates is independent of scale

Zangmeister

Radney

Dockery

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…(1) Sosa & Fernández (2009), (2) Davidsson & Gutiérrez (2004), (3) Farnham & Cochran (2002), (4) Rickman et al (1987), (5) this study.…”

Section: Mass Determinationmentioning

confidence: 99%

CONGO, model of cometary non-gravitational forces combining astrometric and production rate data

Maquet

Colas

Jordá

et al. 2012

A&A

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The gravitational orbit of a comet is affected by the sublimation of water molecules by the nucleus when the comet approaches perihelion. This outgassing triggers a non-gravitational force (NGF) that significantly modifies the orbit of the comet. Up to now, modelling of this effect is mostly based on an empirical model defined in the early 70s that uses a simplified outgassing model. Attempts have been made to use advanced anisotropic thermal models both to calculate the NGF taking several observational constraints into account and to retrieve the nucleus's mass and density, but (i) this approach is restricted to a handful of cometary nuclei that are sufficiently well known to allow this type of modelling, and (ii) the authors usually do not fit the astrometric measurements directly but rather non-gravitational parameters calculated with the above-mentioned empirical model. We present a new model for non-gravitational forces with the aim of revisiting the problem of NGF calculation and nucleus density determination. Our model is closer to the nucleus outgassing physics with only a few free parameters. The amplitude of the perturbation depends on several parameters describing the comet activity that can be constrained by visible, infrared, and radio observations of the coma and the nucleus of the comet. It also depends on the nucleus mass, which can in turn be determined by modelling the effect of the NGF on the orbit of a comet. The method is based on the decomposition of the surface of the nucleus in several elements located at different latitudes. The contribution of each surface element to the overall NGF is fitted from the astrometric measurements, together with the density of the nucleus. This method is the only one available so far to estimate the density of cometary nuclei from ground-based observations. This method is tested on the well-known comet 19P/Borrelly. The density found for these comet is between 150 and 600 kg m −3 .

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“…Similar approaches were presented later by Rickman et al (1991), and more recently by Szutowicz et al (2002aSzutowicz et al ( , 2002b, Farnham & Cochran (2002), Szutowicz & Rickman (2006), and Sosa & Fernández (2009).…”

Section: Introductionmentioning

confidence: 63%

“…As an educated guess, we chose < u > = (0.27 ± 0.1) km s −1 (see Sosa & Fernández 2009 for further details). At heliocentric distances r < 3 AU the cometary activity is governed by the sublimation of water ice, so we take m as the water molecular mass.…”

Section: The Methodsmentioning

confidence: 99%

Non-gravitational forces and masses of some long-period comets. The cases of Hale-Bopp and Hyakutake

Sosa

Fernández

2009

Proc. IAU

Self Cite

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Abstract. By means of a simple non-gravitational force model of the cometary nucleus, which relies on the observed light curves assumed to be a good representation of the water sublimation rate, we estimate the masses of a sample of long-period comets (LPCs).A critical issue of our method is the assumption of a correlation between visual heliocentric magnitudes and water production rates. This is a necessary assumption because of the sparse observational data of gas production rates (with the exception of very few comets like Hale-Bopp or Hyakutake). In this regard we present here a new correlation for LPCs. We also present the preliminary results for the masses of comets Hale-Bopp and Hyakutake.

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Cometary masses derived from non-gravitational forces

Cited by 43 publications

References 77 publications

Packing density of rigid aggregates is independent of scale

Packing density of rigid aggregates is independent of scale

CONGO, model of cometary non-gravitational forces combining astrometric and production rate data

Non-gravitational forces and masses of some long-period comets. The cases of Hale-Bopp and Hyakutake

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