Further Investigation of Changes in Cometary Rotation (original) (raw)
Related papers
Rotation and activity of comets
Advances in Space Research, 2007
We explore how nuclear rotation and activity can be used as effective probes of the gross nuclear structure and therefore of the interior of comets. We present a model of nuclear activity and discuss that in the context of how activity and rotation can control the present day size distribution of active short period comets. We argue that there is a real paucity of sub-km comets when compared with what one expects based on the size distribution of the known Kuiper Belt Objects.
Implications of the small spin changes measured for large Jupiter-family comet nuclei
Monthly Notices of the Royal Astronomical Society, 2018
Rotational spin-up due to outgassing of comet nuclei has been identified as a possible mechanism for considerable mass-loss and splitting. We report a search for spin changes for three large Jupiter-family comets (JFCs): 14P/Wolf, 143P/Kowal-Mrkos, and 162P/Siding Spring. None of the three comets has detectable period changes, and we set conservative upper limits of 4.2 (14P), 6.6 (143P), and 25 (162P) min per orbit. Comparing these results with all eight other JFCs with measured rotational changes, we deduce that none of the observed large JFCs experiences significant spin changes. This suggests that large comet nuclei are less likely to undergo rotationally driven splitting, and therefore more likely to survive more perihelion passages than smaller nuclei. We find supporting evidence for this hypothesis in the cumulative size distributions of JFCs and dormant comets, as well as in recent numerical studies of cometary orbital dynamics. We added 143P to the sample of 13 other JFCs with known albedos and phase-function slopes. This sample shows a possible correlation of increasing phase-function slopes for larger geometric albedos. Partly based on findings from recent space missions to JFCs, we hypothesize that this correlation corresponds to an evolutionary trend for JFCs. We propose that newly activated JFCs have larger albedos and steeper phase functions, which gradually decrease due to sublimation-driven erosion. If confirmed, this could be used to analyse surface erosion from ground and to distinguish between dormant comets and asteroids.
The Astrophysical Journal, 2013
We introduce a parameter, X, to predict the changes in the rotational period of a comet in terms of the rotational period itself, the nuclear radius, and the orbital characteristics. We show that X should be a constant if the bulk densities and shapes of nuclei are nearly identical and the activity patterns are similar for all comets. For four nuclei for which rotational changes are well documented, despite the nearly factor 30 variation observed among the effective active fractions of these comets, X is constant to within a factor two. We present an analysis for the sungrazing comet C/2012 S1 (ISON) to explore what rotational changes it could undergo during the upcoming perihelion passage where its perihelion distance will be ~2.7 solar radii. When close to the sun, barring a catastrophic disruption of the nucleus, the activity of ISON will be sufficiently strong to put the nucleus into a non-principal-axis rotational state and observable changes to the rotational period should also occur. Additional causes for rotational state changes near perihelion for ISON are tidal torques caused by the sun and the significant mass loss due to a number of mechanisms resulting in alterations to the moments of inertia of the nucleus.
Rotation of Cometary Nuclei [and Discussion]
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1984
Asymmetric comas and repetitive appearances of structures in the heads and tails of comets are used to infer nuclei rotation periods. However, periodic behaviour of optically-thick expanding comas or of ion plasma production may contribute spurious results. The spin periods of comets are longer than those of asteroids, ranging generally over 10-100 h and above probable limits for gravitational escape. The periods show a flatter distribution, which may reflect an accretional rather than collisional fragmentation history. Arguments for spin-up with age due to sublimating gases are weak; the converse is possible and spin-down due to preferential escape of particles from equatorial regions appears likely.
The Evolution of Jupiter Family Comets over 2000 Years
Symposium - International Astronomical Union, 1992
The orbital evolution of the whole sample sample of short-period comets was computed by numerical integrations for a time interval of 2000 yr centered on the present epoch. This data base is intended to serve in various studies involving the statistics of orbital evolution and correlation with physical parameters or discovery circumstances. We present some results concerning the following aspects: the evolution of the orbital elements and their past-future asymmetry, statistics on the discovery of comets and on the encounters of comets with Jupiter.
Astronomy & Astrophysics, 2012
We study the dynamical evolution of the near-Earth Jupiter family comets (NEJFCs) that came close to or crossed the Earth's orbit at the epoch of their discovery (perihelion distances q disc < 1.3 AU). We found a minimum in the time evolution of the mean perihelion distanceq of the NEJFCs at the discovery time of each comet (taken as t = 0) and a past-future asymmetry ofq in an interval -1000 yr, +1000 yr centred on t = 0, confirming previous results. The asymmetry indicates that there are more comets with greater q in the past than in the future. For comparison purposes, we also analysed the population of near-Earth asteroids in cometary orbits (defined as those with aphelion distances Q > 4.5 AU) and with absolute magnitudes H < 18. We found some remarkable differences in the dynamical evolution of both populations that argue against a common origin. To further analyse the dynamical evolution of NEJFCs, we integrated in time a large sample of fictitious comets, cloned from the observed NEJFCs, over a 20 000 yr time interval and started the integration before the comet's discovery time, when it had a perihelion distance q > 2 AU. By assuming that NEJFCs are mostly discovered when they decrease their perihelion distances below a certain threshold q thre = 1.05 AU for the first time during their evolution, we were able to reproduce the main features of the observedq evolution in the interval [-1000, 1000] yr with respect to the discovery time. Our best fits indicate that ∼40% of the population of NEJFCs would be composed of young, fresh comets that entered the region q < 2 AU a few hundred years before decreasing their perihelion distances below q thre , while ∼60% would be composed of older, more evolved comets, discovered after spending at least ∼3000 yr in the q < 2 AU region before their perihelion distances drop below q thre . As a byproduct, we put some constraints on the physical lifetime τ phys of NEJFCs in the q < 2 AU region. We found a lower limit of a few hundreds of revolutions and an upper limit of about 10 000-12 000 yr, or about 1600-2000 revolutions, somewhat longer than some previous estimates. These constraints are consistent with other estimates of τ phys , based either on mass loss (sublimation, outbursts, splittings) or on the extinction rate of Jupiter family comets (JFCs).
The persistent activity of Jupiter-family comets at 3–7AU
Icarus, 2013
We present an analysis of comet activity based on the Spitzer Space Telescope component of the Survey of the Ensemble Physical Properties of Cometary Nuclei. We show that the survey is well suited to measuring the activity of Jupiter-family comets at 3-7 AU from the Sun. Dust was detected in 33 of 89 targets (37 ± 6%), and we conclude that 21 comets (24 ± 5%) have morphologies that suggest ongoing or recent cometary activity. Our dust detections are sensitivity limited, therefore our measured activity rate is necessarily a lower limit. All comets with small perihelion distances (q < 1.8 AU) are inactive in our survey, and the active comets in our sample are strongly biased to post-perihelion epochs. We introduce the quantity f ρ, intended to be a thermal emission counterpart to the often reported Af ρ, and find that the comets with large perihelion distances likely have greater dust production rates than other comets in our survey at 3-7 AU from the Sun, indicating a bias in the discovered Jupiter-family comet population. By examining the orbital history of our survey sample, we suggest that comets perturbed to smaller perihelion distances in the past 150 yr are more likely to be active, but more study on this effect is needed.
Evolution of Comet Nucleus Rotation
Icarus, 2002
The secular evolution of comet nucleus rotation states subject to outgassing torques is studied. The dynamical model assumes that the nucleus inertia ellipsoid is axially symmetric. The outgassing torques acting on the surface are modeled using standard cometary activity formulae. The general rotational equations of motion are derived and separately averaged over the fast rotational dynamics terms and the comet orbit. Special cases where the averaging assumptions cannot be applied are evaluated separately. The modification of the comet orbit due to comet outgassing is neglected. Resulting from this analysis is a system of secular differential equations that describes the dynamics of the comet nucleus angular momentum and rotation state. We find that the qualitative secular evolution of the rotation state is controlled by a single parameter that combines parameters related to the comet orbit and parameters related to the nucleus surface geometry and activity. From this solution, we find qualitatively different evolutionary paths for comet nuclei whose entire surface is active, as compared to nuclei with only a single active region. For surface activity models between these extremes, we show that certain evolutionary paths are more likely than others. Additionally, our solution indicates that a comet nucleus' rotational angular momentum will tend to increase over time, potentially contributing to the observed phenomenon of comet nucleus splitting. c 2002 Elsevier Science (USA)
First Results of the Integration of Motion of Short-Period Comets Over 800 Years
Astrophysics and Space Science Library, 1985
All the known short-period comets have been followed by numerical integration over a time span of 821 years, from 1585 to 2406. A preliminary survey of the results of these integrations has shown some interesting features, which become recognizable thanks to the length of the time interval covered, not negligible if compared with the typical evolutionary time scale of comets moving in short-period orbits. Interesting phenomena that have been recognized include: (1) captures from, or ejections into, very elongated ellipses, with perihelia of the parking orbits close to the orbit of Jupiter and aphelia within or beyond the region of outer planets; (2) passages of comets from the control of Saturn to that of Jupiter; (3) orbital evolutions controlled mainly by Saturn; (4) librations of comets around low-order resonances; (5) repeated close approaches of comets to Jupiter, often with the comet being captured as a temporary satellite; (6) an almost perfect coincidence of two comet orbits just before a close approach to Jupiter, suggesting their genetic relationship.
The Persistent Activity of Jupiter-Family Comets at 3 to 7 AU
2013
We present an analysis of comet activity based on the Spitzer Space Telescope component of the Survey of the Ensemble Physical Properties of Cometary Nuclei. We show that the survey is well suited to measuring the activity of Jupiter-family comets at 3-7 AU from the Sun. Dust was detected in 33 of 89 targets (37 +/- 6%), and we conclude that 21 comets (24 +/- 5%) have morphologies that suggest ongoing or recent cometary activity. Our dust detections are sensitivity limited, therefore our measured activity rate is necessarily a lower limit. All comets with small perihelion distances (q < 1.8 AU) are inactive in our survey, and the active comets in our sample are strongly biased to post-perihelion epochs. We introduce the quantity epsilon-f-rho, intended to be a thermal emission counterpart to the often reported A-f-rho, and find that the comets with large perihelion distances likely have greater dust production rates than other comets in our survey at 3-7 AU from the Sun, indicati...