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Some peculiarities of orbits of observed comets.
Irina Guseva
Pulkovo Observatory, St Petersburg State University


Main subject of investigation:
Spatial distribution of orbits of real (observed) comets

Data for analysis:
JPL catalogue of orbital parameters of observed comets

By September, 1, 2014 -

3 277 observed comets.


Solar system
Comet classification: Short-period (<200 yr) Long-period (>200 yr)

Image: NASA JPL-Caltech R. Hurt


Oort cloud:
doughnut-shaped inner Oort cloud ­ Hills cloud 2 ­ 20 AU (0.03 ­ 0.3 ly) spherical outer Oort cloud 20 ­ 50 (- 100) AU (0.3 ­ 0.8 ly)


JPL catalogue of orbital parameters of comets:
http://ssd.jpl.nasa.gov/dat/ELEMENTS.COMET By September, 1, 2014 3 277 observed comets.

Excluded from investigation:
a) "Very old comets" - 107 - observed before 1760 Their orbits were approximately reconstructed with eccentricity e = 1 b) Fragments of destroyed comets ­ the only object was taken into account from each group: 73P/ Schwassmann-Wachmann (66 objects), C/1882 R1 (Great September comet - 4 objects), D/1993 F2 (Shoemaker-Levy 9 ­ 21 objects). ) Small sungrazers (Kreutz, Meyer, Marsden, Kracht ­ 1478 objects) with e = 1, observed from the space only by SOHO, SMM, Solwind


Work with the JPL catalogue:
1604 comets were analyzed after exclusion of the aforecited objects. Comets were divided into 4 groups by eccentricity: e< 0.9 e= e> 0.9
Each group was analyzed separately.


Table 1. Distribution of comets by eccentricity

Eccentricity e < 0.9 0.9 < e < 1

Number of comets (short-p. - long-p.) 552 (548 + 4) 504 (64 + 440) 253 295

% of total amount 34.4 31.4

e=1 e>1

15.8 18.4


Comets with e < 0.9 (only 4 comets of 532 are the long-period ones, more than 200 yr)


All comets with e < 1


Evolution of the Oort cloud (simulation)

Alessandro Morbidelli (2005) Origin and dynamical evolution of comets and their reservoirs". arXiv:astro-ph/0512256 Dones L., Levison H.F., Duncan M.J., Weissman P.R., Simulations of the formation of the Oort Cloud the reference model. Icarus, 2005


Simulation and reality


Distribution of "anti-perihelia" of short-period comets with e < 0.9 (ecliptic coordinates)


Distribution of "anti-perihelia" of short-period comets with e < 0.9 (ecliptic coordinates)


Distribution of "anti-perihelia" of long-period comets with 0.9 < e < 1 (ecliptic coordinates)

­


Distribution of "anti-perihelia" of long-period comets with 0.9 < e < 1 (galactic coordinates)


Distribution of "anti-perihelia" of short-period comets with e < 0.9 (galactic coordinates)


Distribution of "anti-perihelia" of long-period comets with 0.9 < e < 1 (ecliptic coordinates)

­


Distribution of "anti-perihelia" of comets with e = 1 (ecliptic coordinates)


Distribution of "anti-perihelia" of comets with e > 1 (ecliptic coordinates)


Distribution of "anti-perihelia" of long-period comets with 0.9 < e < 1 (galactic coordinates)


Distribution of "anti-perihelia" of comets with e = 1 (galactic coordinates)


Distribution of "anti-perihelia" of comets with e > 1 (galactic coordinates)


Distribution of "anti-perihelia" of comets with e > 0.9 (ecliptic coordinates)


Distribution of "anti-perihelia" of comets with e > 0.9 (galactic coordinates)


Density of distribution by latitude bands (ecliptic coordinates)


Density of distribution by latitude bands (galactic coordinates)


Science Vol.329, 9 July 2010

"A substantial fraction of the Oort cloud comets, perhaps exceeding 90%, are from the protoplanetary disks of other stars"

"The Sun's Hill sphere has an unstable maximum boundary of 230,000 AU (1.1 parsecs (3.6 light-years))"


Nearest massive stars:
Cen - ~ 2 M
sun

(1.1 + 0.9) G2 / K1

Dist: 4.366 ly = 1.34 pc = 747 mas RV = -21.6 km/s Galactic: l = 315.734є b = -0.680є Dist: 8.60 ly = 2.64 pc = 379 mas RV = -7.6 km/s Galactic: l = 227.230є b = -8.890є

Equatorial coordinates: = 14h 39m 36.495s = 219.902 = -60є 50' 02.31" = -60.834 Sirius - ~ 3 M (2 + 1) A0/DA2

sun

Equatorial coordinates: = 06h 45m 08.917s = 101.287є = -16є 42' 58.02" = -16.716є



Main results:
1. Amount of short-period, long-period comets and sum of comets with parabolic and hyperbolic orbits is about equal. 2. Short-period comets have perihelia / aphelia near the ecliptic plane and show a weak concentration near the direction to the galactic center. 3. Long-period comets, comets with parabolic and hyperbolic orbits have very similar distributions of their "anti-perihelia", flattened to the galactic plane. It allows to suppose their common origin from the birth stars cluster. 4. These groups of comets have not evident concentration near the direction to the galactic center, that could be expected as a result of galactic tidal forces. 5. Probably, some revealed concentrations are connected with nearest massive stars.


Thanks !