We present analyses of Spitzer observations of 29P/Schwassmann-Wachmann 1 using 16 \(\mu\)m IRS "blue" peak-up (PU) and 24 \(\mu\)m and 70 \(\mu\)m MIPS images obtained on UT 2003 November 23 and 24 ...that characterize the Centaur's large-grain (10-100 \(\mu\)m) dust coma during a time of non-outbursting "quiescent" activity. Estimates of \(\epsilon f \rho\) for each band (16 \(\mu\)m (2600 \(\pm\) 43 cm), 24 \(\mu\)m (5800 \(\pm\) 63 cm), and 70 \(\mu\)m (1800 \(\pm\) 900 cm)) follow the trend between nucleus size vs. \(\epsilon f \rho\) that was observed for the WISE/NEOWISE comet ensemble. A coma model was used to derive a dust production rate in the range of 50-100 kg/s. For the first time, a color temperature map of SW1's coma was constructed using the 16 \(\mu\)m and 24 \(\mu\)m imaging data. With peaks at \(\sim\) 140K, this map implies that coma water ice grains should be slowly sublimating and producing water gas in the coma. We analyzed the persistent 24 \(\mu\)m "wing" (a curved southwestern coma) feature at 352,000 km (90\(''\)) from the nucleus attributed by Stansberry et al. (2004) to nucleus rotation and instead propose that it is largely created by solar radiation pressure and gravity acting on micron sized grains. We performed coma removal to the 16 \(\mu\)m PU image in order to refine the nucleus' emitted thermal flux. A new application of the Near Earth Asteroid Thermal Model (NEATM; Harris 1998) at five wavelengths (5.730 \(\mu\)m, 7.873 \(\mu\)m, 15.80 \(\mu\)m, 23.68 \(\mu\)m, and 71.42 \(\mu\)m) was then used to refine SW1's effective radius measurement to \(R = 32.3 \pm 3.1\) km and infrared beaming parameter to \(\eta = 1.1 \pm 0.2\), respectively.
The New Horizons spacecraft's flyby of Kuiper Belt Object (KBO) (486958) Arrokoth revealed a bilobed shape with highly flattened lobes both aligned to its equatorial plane, and a rotational axis ...almost aligned to the orbital plane (obliquity ~99 deg). Arrokoth belongs to the Cold Classical Kuiper Belt Object population that occupies dynamically undisturbed orbits around the Sun, and as such, is a primitive object that formed in situ. Therefore, whether its shape is primordial or evolutionary carries important implications for understanding the evolution of both KBOs and potentially their dynamically derived objects, Centaurs and Jupiter Family Comets (JFC). Applying our mass loss driven shape evolution model (MONET), here we suggest that the current shape of Arrokoth could be of evolutionary origin due to volatile outgassing in a timescale of about 1 to 100 Myr, while its spin state would not significantly affected. We further argue that such a process may be ubiquitous in the evolution of the shape of KBOs shortly after their formation. This shape changing process could also be reactivated when KBOs dynamically evolve to become Centaurs and then JFCs and receive dramatically increased solar heating.
Studying materials released from Jupiter-family comets (JFCs) -- as seen in
their inner com\ae, the envelope of gas and dust that forms as the comet
approaches the Sun -- improves the understanding ...of their origin and
evolutionary history. As part of a coordinated, multi-wavelength observing
campaign, we observed comet 45P/Honda-Mrkos-Pajdu\v{s}\'{a}kov\'{a} during its
close approach to Earth in February 2017. Narrowband observations were taken
using the Bok 90" telescope at Kitt Peak National Observatory on February 16
and 17 UT, revealing gas and dust structures. We observed different jet
directions for different volatile species, implying source region
heterogeneity, consistent with other ground-based and \textit{in situ}
observations of other comet nuclei. A repeating feature visible in CN and C$_2$
images on February 16 was also observed on February 17 with an interval of
$7.6\pm0.1$ hours, consistent with the rotation period of the comet derived
from Arecibo Observatory radar observations. The repeating feature's projected
gas velocity away from the nucleus is 0.8 km s$^{-1}$, with an expansion
velocity of 0.5 km s$^{-1}$. A bright compact spot adjacent to the nucleus
provides a lower limit of the amount of material released in one cycle of
$\sim$9.2 kg, depending on composition -- a quantity small enough to be
produced by repeated exposure of nucleus ices to sunlight. This repeating CN
jet, forming within 400 km of the nucleus, may be typical of inner coma
behavior in JFCs; however, similar features could be obscured by other
processes and daughter product species when viewed from distances further than
the scale length of CN molecules.
The outer Solar System object (29981) 1999 TD
10 was observed simultaneously in the
R, and
J and
H bands in September 2001, and in
B,
V,
R, and
I in October 2002. We derive
B
−
V
=
0.80
±
0.05
mag
...,
V
−
R
=
0.48
±
0.05
mag
,
R
−
I
=
0.44
±
0.05
mag
,
R
−
J
=
1.24
±
0.05
mag
, and
J
−
H
=
0.61
±
0.07
mag
. Combining our data with the data from Rousselot et al. (2003, Astron. Astrophys. 407, 1139) we derive a synodic period of
15.382
±
0.001
hr
in agreement with the period from Rousselot et al. Our observations at the same time, with better S/N and seeing, show no evidence of a coma, contrary to the claim by Choi et al. (2003, Icarus 165, 101).
We present the results of a global coma morphology campaign for comet C/2012 S1 (ISON), which was organized to involve both professional and amateur observers. In response to the campaign, many ...hundreds of images, from nearly two dozen groups were collected. Images were taken primarily in the continuum, which help to characterize the behavior of dust in the coma of comet ISON. The campaign received images from January 12 through November 22, 2013 (an interval over which the heliocentric distance decreased from 5.1 AU to 0.35 AU), allowing monitoring of the long-term evolution of coma morphology during the pre-perihelion leg of comet ISON. Data were contributed by observers spread around the world, resulting in particularly good temporal coverage during November when comet ISON was brightest but its visibility was limited from any one location due to the small solar elongation. We analyze the northwestern sunward continuum coma feature observed in comet ISON during the first half of 2013, finding that it was likely present from at least February through May and did not show variations on diurnal time scales. From these images we constrain the grain velocities to ~10 m/s, and we find that the grains spent 2-4 weeks in the sunward side prior to merging with the dust tail. We present a rationale for the lack of continuum coma features from September until mid-November 2013, determining that if the feature from the first half of 2013 was present, it was likely too small to be clearly detected. We also analyze the continuum coma morphology observed subsequent to the November 12 outburst, and constrain the first appearance of new features in the continuum to later than November 13.99 UT.
Samarasinha & Mueller (2013) related changes of cometary rotation to other physical parameters for four Jupiter family comets defining a parameter \(X\), which is approximately constant within a ...factor of two irrespective of the active fraction of a comet. Two additional comets are added to this sample in this paper and the claim of a nearly constant parameter \(X\) for these six comets is confirmed, albeit with a larger scatter. Taking the geometric mean of \(X\) for all the comets above excluding 2P/Encke (as \(X\) for each comet was determined with respect to that of 2P/Encke), the expected changes in the rotation periods for a sample of 24 periodic comets are derived. We identify comets from this sample that are most likely to show observationally detectable changes in their rotation periods. Using this sample and including the six comets used to determine \(X\), we find a correlation between the parameter \(\zeta\) (i.e. the total water production per unit surface area per orbit approximated by that inside of 4 au) and the perihelion distance \(q\); specifically we derive \(\zeta\) \(\propto\) \(q^{-0.8}\) and provide a theoretical basis for this in Appendix A. This relationship between \(\zeta\) and \(q\) enables ready comparisons of activity due to insolation between comets. Additionally, a relationship between the nuclear radius \(R\) and the rotation period \(P\) is found. Specifically, we find that on average smaller nuclei have smaller rotation periods compared to the rotation periods of larger nuclei. This is consistent with expectations for rotational evolution and spin-up of comet nuclei, providing strong observational evidence for sublimation-driven rotational changes in comets.
The final Deep Space 1 (DS1) mission target, comet 19P/Borrelly, was observedfrom July 28-August 1, 2000 at the CTIO-1.5 m telescope in the R filter. Theobserved lightcurve has a large peak to peak ...variation between 0.84 mag and1.0 mag. A period of 26.0 c 1 hr (assuming a double-peaked lightcurve)was found using all five nights. This is in good agreement with the period of25.02 c 0.5 hr quoted by Lamy et al. (1998) using only 6 points ofHST data and is also consistent with HST data taken around the DS1 encountertime by Weaver et al. (2002).Using the mean magnitude R = 20.8 mag and assuming a 4% albedo, we derivean effective nuclear radius of 2.6 km. The large lightcurve amplitude translates toa long to intermediate axial ratio a/b . 2.2, in excellent agreement with theHST result of a/b . 2.4 (Lamy et al., 1998) and with DS1 images (Soderblom et al., 2002).
We calculate the direction of the rotational angular momentum vector,M, of comet 19P/Borrelly based on rotational lightcurve data from 2000, groundbased imaging of the coma during the Deep Space ...1encounter, and the basic near-nucleus coma morphology as revealed by the Deep Space 1 spacecraft. For the most likely direction, we derivea family of solutions (with center at RA = 221°, Dec = -7°) if the direction of M is towards the sunward hemisphere during the Deep Space 1 encounter, whereas if the rotation is of opposite sense, the diametrically opposite family of solutions (with center at RA = 41°, Dec = 7°) would result. We argue that the coma morphology in September 2001 is consistent with the nucleus being a principal axis rotator or one observationally indistinguishable from it. Therefore, for all practical purposes, the direction of the rotational angular momentum vector coincides with the spin axis. We also discuss why the determination of the spin axis direction based on observations from the last apparition is in disagreement with the current result.
Studying materials released from Jupiter-family comets (JFCs) -- as seen in their inner com\ae, the envelope of gas and dust that forms as the comet approaches the Sun -- improves the understanding ...of their origin and evolutionary history. As part of a coordinated, multi-wavelength observing campaign, we observed comet 45P/Honda-Mrkos-Pajduš\'{a}kov\'{a} during its close approach to Earth in February 2017. Narrowband observations were taken using the Bok 90" telescope at Kitt Peak National Observatory on February 16 and 17 UT, revealing gas and dust structures. We observed different jet directions for different volatile species, implying source region heterogeneity, consistent with other ground-based and \textit{in situ} observations of other comet nuclei. A repeating feature visible in CN and C\(_2\) images on February 16 was also observed on February 17 with an interval of \(7.6\pm0.1\) hours, consistent with the rotation period of the comet derived from Arecibo Observatory radar observations. The repeating feature's projected gas velocity away from the nucleus is 0.8 km s\(^{-1}\), with an expansion velocity of 0.5 km s\(^{-1}\). A bright compact spot adjacent to the nucleus provides a lower limit of the amount of material released in one cycle of \(\sim\)9.2 kg, depending on composition -- a quantity small enough to be produced by repeated exposure of nucleus ices to sunlight. This repeating CN jet, forming within 400 km of the nucleus, may be typical of inner coma behavior in JFCs; however, similar features could be obscured by other processes and daughter product species when viewed from distances further than the scale length of CN molecules.
