Debiasing the NEOWISE Cryogenic Mission Comet Populations (original) (raw)

Measuring the size distribution of long period comets

2009

Very little is currently known about the size distribution of long period comet nuclei. The nuclei of long period comets are believed to be icy planetesimals, ejected from the protoplanetary disk during the assembly of the giant planets, and relatively unaltered since. As such, their size distribution would be an important clue to conditions in the protoplanetary disk. Unfortunately, nuclear sizes have only been measured for four long period comets. Existing estimates of the nuclear size distribution have thus had to make the untested assumption that the coma brightness is proportional to the surface area of the nucleus. Given this assumption, existing data suggest that the size distribution of cometary nuclei is much flatter than that predicted by most planetesimal models. In this thesis, the relationship between the coma brightness and nuclear size of long period comets is investigated. Seven long-period comets were observed, using the 2.3m telescope at Siding Spring Observatory, ...

Comet Size Distributions and Distant Activity

ESO ASTROPHYSICS SYMPOSIA, 2000

We present the results of observations of distant comet nuclei as observed with the Keck II telescope during 1997 December. Our sample included 17 SP Jupiterfamily comets, 3 Halley-family comets, and 1 dynamically new comet. The nucleus radii ranged between 0.6 and 12.7 km assuming a 4 albedo, the average near RN3 km showing that, in general, the comet nuclei are relatively small. This doubles the known sample of size estimates for the comet population. These data are compared to the size distributions for the Centaurs and the Edgeworth-Kuiper Belt objects.

Magnitude and size distribution of long-period comets in Earth-crossing or approaching orbits

Monthly Notices of the Royal Astronomical Society, 2012

We analyse the population of near-Earth long-period comets (LPCs; perihelion distances q < 1.3 au and orbital periods P > 10 3 yr). We have considered the sample of LPCs discovered during the period 1900-2009 and their estimated absolute total visual magnitudes H. For the period 1900-1970 we have relied upon historical estimates of absolute total magnitudes, while for the more recent period 1970-2009 we have made our own estimates of H based on Green's photometric data base and IAU Circulars. We have also used historical records for the sample of brightest comets (H < 4.5) covering the period: 1500-1899, based mainly on the Vsekhsvyatskii, Hasegawa and Kronk catalogues. We find that the cumulative distribution of H can be represented by a three-modal law of the form log 10 N <H = C + αH, where the C values are constants for the different legs, and α 0.28 ± 0.10 for H < 4.0, α 0.56 ± 0.10 for 4.0 ≤ H < 5.8, and α 0.20 ± 0.02 for 5.8 ≤ H < 8.6. The large increase of the slope of the second leg of the H-distribution might be at least partially attributed to splitting of comet nuclei, leading to the creation of two or more daughter comets. The cumulative H-distribution tends to flatten for comets fainter than H 8.6. LPCs fainter than H 12 (or diameters D 0.5 km) are extremely rare, despite several sky surveys of near-Earth objects implemented during the last couple of decades, suggesting a minimum size for an LPC to remain active. We also find that about 30 per cent of all LPCs with q < 1.3 au are new (original bound energies 0 < E or < 10 −4 au −1), and that among the new comets about half come from the outer Oort cloud (energies 0 E or 0.3 × 10 −4 au −1), and the other half from the inner Oort cloud (energies 0.3 × 10 −4 E or 10 −4 au −1).

Comet nucleus size distributions from HST and Keck telescopes

Icarus, 2004

The Wide Field Camera (WFC) on the Hubble Space Telescope and the Low Resolution Imaging Spectrograph (LRIS) on the Keck II telescope have been used to image 21 distant dynamically new, long-period (LP) and short-period (SP) Jupiter-family (JF) comet nuclei (near aphelion), as part of a long-term program to search for physical differences between short-period comets and Oort cloud comets. WFC data were obtained on Comets C/1987 H1 (Shoemaker) and C/1984 K1 (Shoemaker) during Cycle 5 (1995 December) and on C/1988 B1 (Shoemaker), C/1987 F1 (Torres), and C/1983 O1 (Černis) during Cycle 6 (1997 April, May, and June). The HST comets were at heliocentric distances 20.4 < r[AU] < 29.5. Each comet observation was allocated 7 orbits, for ≈ 3.6 hrs of integration. The most difficult part of the image reduction was the removal of cosmic rays. We present our scheme for cosmic ray removal. None of the HST comet nuclei was detected to the 3-σ level at m R ∼ 27. The inferred upper limits to the nucleus radii are 4.0 < R N [km] < 10.5. The SP comets range in radius between 0.34 < R N [km] < 15.4, with a median value of R N ∼ 1.61 km. The LP comets ranged in size between < 4.0-56 km. Over a range of radii between 1-10 km, the nuclei can be fit with a cumulative distribution N(> R N) ∝ R −α N with α = 1.45 ± 0.05, and for nuclei in the range 2-5 km, α = 1.91 ± 0.06. Statistical analysis and modeling shows that the slopes of the observed TNO and JF comet distributions are not compatible, suggesting that the intrinsic distribution of JF comet nuclei is a differential a −3.5 power law truncated at small nucleus radii between 0.3 and 2.0 km.

Nuclear magnitudes and the size distribution of Jupiter family comets

Icarus, 2006

We present a new catalog of absolute nuclear magnitudes of Jupiter family (JF) comets, which is an updated version of our previous catalog [Tancredi, G., Fernández, J.A., Rickman, H., Licandro, J., 2000. Astron. Astrophys. Suppl. Ser. 146, 73–90]. From the new catalog we find a linear cumulative luminosity function (CLF) of slope 0.54±0.050.54±0.05 for JF comets with q≲2.5 AUq≲2.5 AU. By considering this CLF combined with the few measured geometric albedos with their respective uncertainties, and assuming a canonical albedo of 0.035±0.0120.035±0.012 for those comets with undetermined albedos, we derive a cumulative size distribution that follows a power-law of index −2.7±0.3−2.7±0.3. The slope is similar to that derived from some theoretical collisional models and from some populations of Solar System bodies like the trans-neptunian objects. We also discuss and compare our size distribution with those by other authors that have recently appeared in the literature. Some striking differences in the computed slopes are explained in terms of biases in the studied samples, the different weights given to the brightest members of the samples, and discrepancies in the values of a few absolute nuclear magnitudes. We also compute sizes and fractions of active surface area of JF comets from their estimated absolute nuclear magnitudes and their water production rates. With the outgassing model that we use, about 60% of the computed fractions f of active surface area are found to be smaller than 0.2, with one case (28P/Neujmin 1) of no more than 0.001, which suggests that JF comets may transit through stages of very low activity, or even dormancy. There is an indication that JF comets with radii RN≳3 kmRN≳3 km have active fractions f≲0.01f≲0.01, which might be due to the rapid formation of insulating dust mantles on larger nuclei.

The population, magnitudes, and sizes of Jupiter family comets

Astronomy & Astrophysics, 1999

We analyze the sample of measured nuclear magnitudes of the observed Jupiter family (JF) comets (taken as those with orbital periods P < 20 years and Tisserand parameters T > 2). We find a tendency of the measured nuclear magnitudes to be fainter as JF comets are observed with CCD detectors attached to medium-and large-size telescopes (e.g. Spacewatch Telescope). However, a few JF comets observed very far from the Sun (4-7 AU) show a wide dispersion of their derived absolute nuclear magnitudes which suggests that either these JF comets keep active all along the orbit, so the reported unusually bright distant magnitudes were strongly contaminated by a coma, or some of the measured "nuclear magnitudes" were grossly overestimated (i.e. their brightness underestimated).

The Orbit and Size-Frequency Distribution of Long Period Comets Observed by Pan-STARRS1

Icarus

We introduce a new technique to estimate the comet nuclear size frequency distribution (SFD) that combines a cometary activity model with a survey simulation and apply it to 150 long period comets (LPC) detected by the Pan-STARRS1 near-Earth object survey. The debiased LPC size-frequency distribution is in agreement with previous estimates for large comets with nuclear diameter 1 km but we measure a significant drop in the SFD slope for small objects with diameters < 1 km and approaching only 100 m diameter. Large objects have a slope α big = 0.72 ± 0.09(stat.) ± 0.15(sys.) while small objects behave as α small = 0.07 ± 0.03(stat.) ± 0.09(sys.) where the SFD is ∝ 10 αH N and H N represents the cometary nuclear absolute magnitude. The total number of LPCs that are > 1 km diameter and have perihelia q < 10 au is 0.46 ± 0.15 × 10 9 while there are only 2.4 ± 0.5(stat.) ± 2(sys.) × 10 9 objects with diameters > 100 m due to the shallow slope of the SFD for diameters < 1 km. We estimate that the total number of 'potentially active' objects with diameters ≥ 1 km in the Oort cloud, objects that would be defined as LPCs if their perihelia evolved to < 10 au, is (1.5±1)×10 12 with a combined mass of 1.3±0.9 M ⊕. The debiased LPC orbit distribution is broadly in agreement with expectations from contemporary dynamical models but there are discrepancies that could point towards a future ability to disentangle the relative importance of stellar perturbations and galactic tides in producing the LPC population.

The Demographics of Long‐Period Comets

The Astrophysical Journal, 2005

The absolute magnitude and perihelion distributions of long-period comets are derived, using data from the Lincoln Near-Earth Asteroid Research (LINEAR) survey. The results are surprising in three ways. Firstly, the flux of comets through the inner solar system is much lower than some previous estimates. Secondly, the expected rise in comet numbers to larger perihelia is not seen. Thirdly, the number of comets per unit absolute magnitude does not significantly rise to fainter magnitudes. These results imply that the Oort cloud contains many fewer comets than some previous estimates, that small long-period comets collide with the Earth too infrequently to be a plausible source of Tunguska-style impacts, and that some physical process must have prevented small icy planetesmals from reaching the Oort cloud, or have rendered them unobservable. A tight limit is placed on the space density of interstellar comets, but the predicted space density is lower still. The number of long-period comets that will be discovered by telescopes such as SkyMapper, Pan-Starrs and LSST is predicted, and the optimum observing strategy discussed.

Re-Distribution of the Regions of 100 Comets Using a Statistical Method

Iraqi Journal of Science

In this study, the comets have distributions regarding their heliocentric distances where they appear in two regions, Kuiper belt (short period) and Oort cloud (long period). Details here give new information about the entire regions of these comets; the research shows that 54% of comets are nearby asteroid belt, but only 11% are in Kuiper belts and 35 % are from Oort cloud. The research focuses on comets with a nucleus's radius larger than 1 km. The comets with a nuclear radius of 1-10 km have high percentage 51%. From the results, the maximum comets' radius is found in comet 29P/Schwassmann -Wachmann as roughly 87 km, and also in comet C/2018 N2 (ASASSN) which has radius 88 km. All comets, that have been distributed concerning heliocentric, depend on statistical results to divide new comets' regions versus their radiuses. The results reveal new details of comets' distances from the sun. The distances of 100 comets are shown in Figure (2). The results...

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...