EDP Sciences
Free Access
Volume 437, Number 3, July III 2005
Page(s) 1093 - 1108
Section Planets and planetary systems
DOI https://doi.org/10.1051/0004-6361:20042000

A&A 437, 1093-1108 (2005)
DOI: 10.1051/0004-6361:20042000

Some characteristics of the outer Oort cloud as inferred from observations of new comets

L. Neslusan and M. Jakubík

Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranská Lomnica, Slovakia
    e-mail: [ne;mjakubik]@ta3.sk

(Received 13 September 2004 / Accepted 10 March 2005)

We study the outer Oort cloud (OC) by numerical integration of 126 600 orbits of hypothetical comets representing this cometary reservoir. We determine the distribution of the semi-major axis a for $4.6 \loa \log\,(a) \loa 5$, and estimate its population and total mass, as well as some other characteristics. The distribution of the semi-major axis is found initially by assuming a constant $\log\,(a)$ distribution and then identifying the theoretically predicted $\log\,(a)$ distribution of new comets with their observed $\log\,(a)$ distribution. The semi-major axis of outer-OC comets ranges from $\log\,(a) \approx 4.35$ to typically $\log\,(a) \approx 5$ on the decadic-logarithm scale. The relative distribution of this element can, however, be roughly determined only for $\log\,(a) \goa 4.55$: d $N \propto a^{-s}\, {\rm d}a$, where $0.6 \loa s \loa 0.8$. The perihelion distribution of new comets with $\log\,(a) \loa 4.55$ is not constant in the zone of visibility (ZV) and a bias due to the observational selection cannot be eliminated. The lower limit of the outer OC population is $1\times 10^{11}$ to $2\times 10^{11}$. The currently available cometary data do not allow us to give a more exact lower estimate or an average estimate of the population. The OC has also been depleted by the combined Galactic-tide-planetary (GTP) perturbation with a local maximum rate at $\log\,(a) \approx 4.5$. The ratio of these comets that are lost from the outer OC and of new comets that enter into the ZV in the same time frame is $\approx$2.5. The distributions of the angular elements of new comets at their previous perihelion passage are used to evaluate the correctness of our model of the outer OC. Specifically, we calculated the root of mean squares between the corresponding theoretical and observed distributions of $\omega$, $\Omega$, and $\cos\,(i)$ resulting in $2{-}5\%$ unexplained residua.

Key words: comets: general -- Oort cloud -- planets and satellites: formation

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