Masses of long-period comets derived from non-gravitational effects - analysis of the computed results and the consistency and reliability of the non-gravitational parameters

Abstract

We estimate masses for a selected sample of long‐period comets (LPCs) (with orbital periods P > 1000 yr and perihelion distances q < 2 au), with good photometric visual light curves and known non‐gravitational parameters. We follow a procedure similar to that developed by Szutowicz et al. to estimate the masses of comets C/1995 O1 (Hale–Bopp) and C/1996 B2 (Hyakutake). The method also requires the knowledge of the water production rates Q, for which we find a new correlation between Q and the visual total heliocentric magnitude mh of LPCs, which can be expressed as log10Q= 30.53 − 0.234mh. The computed masses are in the range [0.5, 10]× 1012 kg. From these masses, and by assuming a cometary bulk density ρ of 0.4 g cm−3, we estimate the effective nuclear radii RN for the studied LPCs to be in the range [0.7, 1.8] km. From the computed values of RN, we find that the active surface areas are (in most cases) greater than the geometric ones (fractions f ranging from 0.8 to 2.4). We argue that this could be understood as a state of hyperactivity, which can be explained if a significant fraction of the sublimated water molecules come from the sublimation of icy grains in the coma. Hyperactivity would make LPC nuclei smaller (i.e. less massive) than expected from their coma brightness. Other effects, like extremely low densities or overestimated non‐gravitational parameters, might also contribute to the rather high computed value of f. For comet C/1995 O1 (Hale–Bopp), we find a seeming inconsistency between some size estimates and some computed non‐gravitational parameters. We analyse some alternatives to this apparent paradox. We also compute absolute total magnitudes and photometric indices for the studied sample of LPCs and find a new correlation between masses and absolute total visual magnitudes H. By assuming ρ= 0.4 g cm−3, we can convert masses to diameters D, leading to a relation log10D(km) = 1.5 − 0.13H.

Oort cloud and Scattered Disc formation during a late dynamical instability in the Solar System

“…Fernández et al, 1999). For LPCs, however, the active fraction is very large, and can 'exceed' 100% (Sosa & Fernández, 2011). Thus LPCs are brighter than JFCs of a comparable size at the same heliocentric distance.…”

“…For short-period comets ν is usually higher than 3. From a limited sample of LPCs Sosa & Fernández (2011) find ν ∼ 3. Using ν = 4 yields to the commonlyused value H 10 , which is close to Whipple's (1978) average for both LPCs and short-period comets.…”

“…Is there some way of comparing values of H T versus H? Sosa & Fernández (2011) use observational data of the water production of LPCs and the subsequent non-gravitational forces to derive a relation between the diameter of the nucleus of the LPC and its total absolute magnitude, which is given by log…”

How to link the relative abundances of gas species in coma of comets to their initial chemical composition?

“…18 shows the H 2 O molar production curves (mol m À2 s À1 ), per unit of cometary surface area and per second, of some short and long-period comets compared to amorphous models. Red (before perihelion passage) and blue (after perihelion passage) dots represent the observational data of Comets C/1995 O1 (Hale-Bopp), C/2002 V1 (NEAT), C/2002 T7 (LINEAR), C/2009 P1 (Garradd), 19P/Borrelly, 21P/Giacobini-Zinner, 67PC-G, and 96P/Machholz 1, for which estimations of nucleus sizes (Fernández 2000;Sosa and Fernández, 2011;Weiler et al, 2011;Combi et al, 2013) and H 2 O productions (Biver et al, 2002;Combi et al, 2009Combi et al, , 2011aCombi et al, , 2013 exist over a significant range of heliocentric distances. Lines represent the H 2 O production from the amorphous 'nominal', 'high inertia' and 'dust mantle' (5 cm and 10 cm thick) models.…”

“…of the nuclei: their sizes and fractions of active surface area were mainly computed from their estimated absolute nucleus magnitudes and their water production rates (Lamy et al, 2004;Tancredi et al, 2006;Snodgrass et al, 2011). Thus, the estimations of the size of nuclei can vary by factors of 2-3, such as for Hale-Bopp with a radius varying from 20 to 50 km following the methods used (Weaver and Lamy, 1997;Fernández et al,2000 ;McCarthy et al, 2007;Sosa and Fernández, 2011). In addition, the high values of H 2 O production for the long-period Comets C/2002 V1 (NEAT) and C/2009 P1 (Garradd) could be also due to the sublimation of icy materials not only from the surface of the nucleus, but also from grains ejected in the coma, producing an extended source of gas and generating an activity larger than expected for a 100% active surface nucleus (Combi et al, 2011b;Sosa and Fernández, 2011).…”