Orbital History of P/1998 X1 (ODAS)

OCA-DLR Asteroid Survey (O.D.A.S.)

P/1998 X1

This short-period comet has been discovered on December 15, 1998.

It should be observable until spring 1999. For an ephemeris and the latest orbital elements use the MPC Ephemeris Service.

The investigations described below are based on observations covering an arc of four months.

Orbital elements: computed with FIND_ORB.

P/1998X1
   Perihelion 1998 Jul 20.981118 TT
Epoch 1999 Jan 22.0 TT = JDT 2451200.5
M  26.94855              (2000.0)            P               Q
n   0.14565298     Peri.   68.81538      0.38018300     -0.92491116
a   3.5775837      Node   358.83928      0.83959725      0.34533159
e   0.4480899      Incl.    1.35215      0.38799143      0.15901396
P   6.77           H   14.9           G   0.15      q 1.9745046
From 155 observations 1998 Dec. 15-1999 Apr. 14;   RMS error 0.938 arcseconds

The orbital evolution of this comet has been studied by numerical integration methods, taking into account the perturbations by all major planets (Mercury through Neptune, Earth and Moon were treated as a single body). The time interval from 1900 to 2100 was covered by this calculations. It has to be emphasized, though, that the current orbit is still rather uncertain, and its obvious chaotic nature, typical for a Jupiter-family comet makes this kind of investigations quite tentative.

This figure shows the distance between the comet and the Earth, revealing a typical pattern which reflects the geometry of the two orbits. It can be seen that the next favorable apparitions will be in 2005.

But more important for the understanding of the dynamical evolution of the comet is its relationship with Jupiter. The distance to the giant planet is shown here. The most significant event is the close approach in 1995, and a similar one in the future, i.e. 2042.

The orbital evolution is displayed in this figure. In the left panel the path of the comet is represented by the position of the body during the whole time interval, plotting a dot every 20 days, (or one every day when it is close to the planet(. Jupiters orbit is displayed in a similar way. Also shown is the line of the mutual nodes, i.e. the orbital intersection points. The ascending node is marked with a capital Omega. The line of apsides is drawn, marking the point of closest approach to the Sun, Perihelion with the letter q. - The orbital geometry is shown as the projection of the comet's orbit onto the plane of the planets. The coordinate system chosen is heliocentric and given in astronomical units (AU), i.e. the mean distance between the Earth and the Sun, equal to 150 Million kilometres.

The interesting thing with this admitedly rather messy figure is, that it shows that the comet's current orbit (i.e. the smallest ellipse) is only one of three different orbits it followed during the timeinterval. If we take our calculations at face value they indicate that the close approach in September 1995, to within 0.23 AU transfered the orbit from a larger ellipse. This event also lowered the perihelion distance to its current value of about 2 AU, which most likely led to its discovery, since it now can come closer to the Earth, and therefore should be brighter and more easily to detect. - The current orbit seems to be stable until that next close encounter with Jupiter. With the improved orbit as input the found orbital evolution did not change very much, indicating that it is reliable for that period before the encounter. More astrometric observations are still possible in this dark period and will serve to further improving the orbit determination.

On the right-hand side of the figure some orbital parameters are given, where a represents the semi-major axis, e the eccentricity, and i the inclination. The closest and farthest point in the asteroid's orbit, perihelion and aphelion, are designated by q and Q, respectively. These values refer to the current orbit. The orientation of the orbit is described by two angle: the longitude of the ascending node Omega and the argument of perihelion omega. For orbits which do not experience strong perturbations these angles do vary slowly with time, due the effects of the gravitational perturbations by the planets. For this orbit, and typical for most short-period comets, the perturbational effects of Jupiter can lead to dramatic changes, in particular during close approaches The range of the values covered during the time interval in consideration is therefore given.

Finally, close approaches with Jupiter are listed when they occur to within 150 Million kilometres, or 1 AU.

A total view of the orbits of the inner planets, Mercury, Venus, Earth and Mars together with the comet's path projected onto the ecliptic plane.

In this table all close approaches found to any major planets are summarized. The various columns contain the date and time of the closest approach, also given in Julian Date (JD), the distance from the Earth (Delta) and from the Sun (R), in AU. The encounter velocity relative to the planet (VP) and the Sun (VH), in km/sec. N

The evolution of the orbital elements during the 200 year period 1900 to 2100 can be seen in this series of plots