C/1999 U4 Catalina-Skiff

Solar System
Dynamics &
Planetology
Group

General description

C/1999 U4 was discovered on 31 October 1999 by the Catalina Sky Survey, and, independently, on 1 November by B. A. Skiff under LONEOS Survey. At once, its cometary apperance was reported [IAUC 7298, 1999 November 1]. Later, pre-discovery detections from 18 September and 30 October 1999 were found.

This comet made its closest approach to Earth on 11 January 2002 (4.415 au), 2.5 months after perihelion.

Solution given below is based on data span over 4.6 yr in a range of heliocentric distances: 7.55 au – 4.915 au (perihelion) – 8.22 au.

Figure caption: Time distribution of positional observations with corresponding heliocentric (red curve) and geocentric (green curve) distance at which they were taken. The horizontal dotted line shows the perihelion distance for a given comet whereas vertical dotted line — the moment of perihelion passage.

SSDP Cometary Note C1999U4A2-001

Comet C/1999 U4 Catalina-Skiff

number of observations	911
number of residuals	1807
data interval	1999 Sep. 18 — 2004 Apr. 11
rms [arcsec]	0.78
orbit quality class	1a+

Osculating orbital elements (heliocentric; ecliptic J2000.0)

Epoch (TT)	20011018.0	= JD 2452200.5
time of perihelion passage (TT)	20011028.456827	± 0.000242
perihelion distance	4.91532891	± 0.00000132
eccentricity	1.00766217	± 0.00000263
argument of perihelion [deg]	77.511961	± 0.000024
longitude of the ascending node [deg]	32.288874	± 0.000011
inclination [deg]	51.926317	± 0.000009
inverse semimajor axis [10^-6 au^-1]	-1558.83	± 0.53

Note: Epoch is given in a format: yyyymmdd.d, time of perihelion passage in a format of yyyymmdd.dddddd.

Figure caption: Six 2D-projections of the 6D space of original swarm (5001 VCs) of C/1999 U4. Each density map is given in logarithmic scale presented on the right in the individual panel.
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Original orbital elements (barycentric; at 250 au from the Sun)

Epoch (TT)	16960618
time of perihelion passage (TT)	20011029.942046	± 0.000253
perihelion distance	4.88670740	± 0.00000124
eccentricity	0.99984462	± 0.00000257
argument of perihelion [deg]	77.829741	± 0.000025
longitude of the ascending node [deg]	32.387465	± 0.000011
inclination [deg]	52.060460	± 0.000010
inverse semimajor axis [10^-6 au^-1]	31.80	± 0.53

Note: Values of uncertainties of original/future orbital elements were derived using a swarm of 5001 osculating orbits of VCs (including the nominal osculating orbit given above) for original/future orbital evolution calclulations and then by fitting the distribution of a given orbital element of original/future swarm of VCs to Gaussian distribution.

Original barycentric positions and velocities of 5001 VCs at 250 au from the Sun are given here (data format), i.e. before entering the planetary zone.

Future orbital elements (barycentric; at 250 au from the Sun)

Epoch (TT)	23030529
time of perihelion passage (TT)	20011026.980430	± 0.000244
perihelion distance	4.90968719	± 0.00000136
eccentricity	1.00143976	± 0.00000263
argument of perihelion [deg]	77.397331	± 0.000024
longitude of the ascending node [deg]	32.273045	± 0.000011
inclination [deg]	51.997123	± 0.000009
inverse semimajor axis [10^-6 au^-1]	-293.25	± 0.54