The Orbit and Size-Frequency Distribution of Long Period Comets Observed by Pan-STARRS1 (original) (raw)

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).

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.

Debiasing the NEOWISE Cryogenic Mission Comet Populations

The Astronomical Journal

We use NEOWISE data from the four-band and three-band cryogenic phases of the Wide-field Infrared Survey Explorer mission to constrain size distributions of the comet populations and debias measurements of the shortand long-period comet (LPC) populations. We find that the fit to the debiased LPC population yields a cumulative size−frequency distribution (SFD) power-law slope (β) of −1.0±0.1, while the debiased Jupiter-family comet (JFC) SFD has a steeper slope with β=−2.3±0.2. The JFCs in our debiased sample yielded a mean nucleus size of 1.3 km in diameter, while the LPCs' mean size is roughly twice as large, 2.1 km, yielding mean size ratios (á ñ á ñ D D LPC JFC) that differ by a factor of 1.6. Over the course of the 8 months of the survey, our results indicate that the number of LPCs passing within 1.5 au are a factor of several higher than previous estimates, while JFCs are within the previous range of estimates of a few thousand down to sizes near 1.3 km in diameter. Finally, we also observe evidence for structure in the orbital distribution of LPCs, with an overdensity of comets clustered near 110°inclination and perihelion near 2.9 au that is not attributable to observational bias.

Where do long-period comets come from? 26 comets from the non-gravitational Oort spike

Monthly Notices of the Royal Astronomical Society, 2010

Since 1950, when Oort published his hypothesis, several important new facts have been established in this field. At present, there are still questions surrounding the apparent source region (or regions) of long-period comets, the definition of dynamically new comets and the characteristics of the hypothetical Oort Cloud. Our aim in this investigation is to look for the apparent source of selected long-period comets and to refine the definition of dynamically new comets. Based on pure gravitational original orbits, all comets studied in this paper are widely called dynamically new. However, we show that the incorporation of non-gravitational forces into the orbit determination process significantly changes the situation. We have determined the precise non-gravitational orbits of all investigated comets. Then, we have followed numerically their past and future motions during one orbital period. Applying the ingenious method of Sitarski of creating swarms of virtual comets compatible with observations, we have been able to derive the uncertainties of original and future orbital elements, as well as the uncertainties of previous and next perihelion distances. We conclude that the past and future evolutions of cometary orbits under Galactic tide perturbations is the only way to find which comets are really dynamically new. In our sample, fewer than 30 per cent of comets are, in fact, dynamically new. Most of these have small previous perihelion distances. However, 60 per cent of these will be lost on hyperbolic orbits in the future. This evidence suggests that the investigation into the apparent source of longperiod comets is challenging. We have also shown that a significant percentage of long-period comets can visit the zone of visibility during at least two or three consecutive perihelion passages.

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, ...

Non-gravitational effects change the original 1/a-distribution of near-parabolic comets

Astronomy & Astrophysics

Context. The original 1∕a-distribution is the only observational basis for the origin of long-period comets (LPCs) and the dynamical properties of the Oort Cloud. Although they are very subtle in the motion of these comets, non-gravitational effects can cause major changes in the original semimajor axis, 1∕aori. Aims. We obtained reliable non-gravitational orbits for as many LPCs with small perihelion distances of q < 3.1 au as possible, and determined the corresponding shape of the Oort spike. Methods. We determined the osculating orbits of each comet using several data-processing methods, and selected the preferred orbit using a few specific criteria. The distribution of 1∕aori for the whole comet sample was constructed using the individual Gaussian distribution we obtained for the preferred solution of each comet. Results. The derived distribution of 1∕aori for almost all known small-perihelion Oort spike comets was based on 64% of the non-gravitational orbits. This was compar...

The Influence Of Individual Stars On The long-Term Dynamics Of Comets C/2014 UN271 And C/2017 K2

Astronomy & Astrophysics

Context. In June 2021, the discovery of an unusual comet C/2014 UN271 (Bernardinelli-Bernstein) was announced. Its cometary activity beyond the orbit of Uranus has also refreshed interest in similar objects, including C/2017 K2 (PANSTARRS). Another peculiarity of these objects is the long interval of positional data, taken at large heliocentric distances. Aims. These two comets are suitable candidates for a detailed investigation of their long-term motion outside the planetary zone. Using the carefully selected orbital solutions, we aim to estimate the orbital parameters of their orbits at the previous perihelion passage. This might allow us to discriminate between dynamically old and new comets. Methods. To follow the dynamical evolution of long-period comets far outside the planetary zone, it is necessary to take into account both the perturbation caused by the overall Galactic gravitational potential and the actions of individual stars appearing in the solar neighborhood. To this...

Small comet statistics and probability of detection in Ly-α

Advances in Space Research, 1991

The relationship between size-distributions of short-and long-period comets is discussed. The effect of losses on the number of small short-period comets is shown. The flux of comets moving in the vicinity of the Earth is calculated for different observation direction8. The estimated upper limit on the number of comets greater than 100 m that pass closer than 0.3 AU to the Earth is about 130 per year. The possible consequences for observing small comets in Ly-a are indicated.

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.

The main-belt comets: The Pan-STARRS1 perspective

Icarus, 2015

We analyze a set of 760 475 observations of 333 026 unique main-belt objects obtained by the Pan-STARRS1 (PS1) survey telescope between 2012 May 20 and 2013 November 9, a period during which PS1 discovered two main-belt comets, P/2012 T1 (PANSTARRS) and P/2013 R3 (Catalina-PANSTARRS). PS1 comet detection procedures currently consist of the comparison of the point spread functions (PSFs) of moving objects to those of reference stars, and the flagging of objects that show anomalously large radial PSF widths for human evaluation and possible observational follow-up. Based on the number of missed discovery opportunities among comets discovered by other observers, we estimate an upper limit comet discovery efficiency rate of ∼ 70% for PS1. Additional analyses that could improve comet discovery yields in future surveys include linear PSF analysis, modeling of trailed stellar PSFs for comparison to trailed moving object PSFs, searches for azimuthally localized activity, comparison of point-source-optimized photometry to extended-source-optimized photometry, searches for photometric excesses in objects with known absolute magnitudes, and crowd-sourcing. Analysis of the discovery statistics of the PS1 survey indicates an expected fraction of 59 MBCs per 10 6 outer main-belt asteroids (corresponding to a total expected population of ∼ 140 MBCs among the outer main-belt asteroid population with absolute magnitudes of 12 < H V < 19.5), and a 95% confidence upper limit of 96 MBCs per 10 6 outer main-belt asteroids (corresponding to a total of ∼230 MBCs), assuming a detection efficiency of 50%. We note however that significantly more sensitive future surveys (particularly those utilizing larger aperture telescopes) could detect many more MBCs than estimated here. Examination of the orbital element distribution of all known MBCs reveals an excess of high eccentricities (0.1 < e < 0.3) relative to the background asteroid population. Theoretical calculations show that, given these eccentricities, the sublimation rate for a typical MBC is orders of magnitude larger at perihelion than at aphelion, providing a plausible physical explanation for the observed behavior of MBCs peaking in observed activity strength near perihelion. These results indicate that the overall rate of mantle growth should be slow, consistent with observational evidence that MBC activity can be sustained over multiple orbit passages. [