aesmael

    Or perhaps I should be more specific and say C/2006 P1, since Robert McNaught has apparently discovered a number of comets on the order of two dozen.


    I was searching to see if a more firm determination of the comet's orbit had been made so I could check when we might expect it to return and how far out its aphelion lay (I was under the impression this was Comet McNaught's first visit to the inner solar system; it must have been disturbed from its orbit decades ago [conservative amateur estimate] and been falling inward ever since). Well, possibly you can imagine my surprise, dear reader, when I checked the comet's Wikipedia entry and found its eccentricity listed as 1.00003006 (that its inclination of nearly 78 degrees places its orbit at something like right angles to what we traditionally think of as the 'solar system' is not unusual). Possibly you can not.

    In either case I am inclined to say that in astronomy eccentricity (e) is often described as a measure of how noncircular an orbit is. For a circular orbit e = 0. If the orbit is elliptical, as is the usual case, e is between 0 and 1. When e = 1 then the orbit is parabolic and if e > 1, as in this case, the orbit is said to be hyperbolic. I have also seen this described as 'open' - if the value quoted at Wikipedia is accurate then McNaught is never coming back and this was a one-shot show. Naturally, there are no values listed for period or aphelion distance.

    My first thought was that this must be an example of an interstellar comet, just passing through and otherwise unrelated to our old friend Sol, but as this article sensibly points out it may simply be the case that our comet picked up a bit of a boost from some interaction during its passage. I suspect if there were indications McNaught were of interstellar origin a bigger (or different) fuss would have been raised - but I am somewhat out of the noose so perhaps there was.and I did not realise.