PDA

View Full Version : Why is comet McNaught so bright?



ATKINS
2007-Jan-22, 09:23 PM
The photo of comet McNaught's staggered tail in today's APOD (http://antwrp.gsfc.nasa.gov/apod/ap070122.html)shows a phenomenon which has presumably never before been observed (or at least not on such a scale or with such brightness).

For us to be able to see the tail in this way as a sort of oriental fan (which we are viewing side-on to some extent given that the plane of the comet's trajectory is not at all perpendicular to our line of sight from Earth), with the sun as the pivotal point of the various strands, there must be a prodigious amount of released matter involved. Each visible strand must be several millions of kilometers in length (without mentioning the upward extension of each strand which is presumably much longer but which is invisible in the photo due to light polution from the sun) and the overall semi-circular display must run to several tens of millions of kilometres. That makes for a whole lot of water and dust, according to conventional wisdom.

My question is: do we know which of the various parameters of the comet and its trajectory is responsible for such a prodigious outpouring?

Is it the exceptional size of the comet's nucleus (has it been measured?), is it an extraordinarily high concentration of water-ice in the comet's nucleus (unlike the other comet nuclei which have actually been imaged and which show no trace of water-ice), is it the closeness of the comet's approach to the sun (inside the orbit of Mercury, as I understand) or might it have something to do with the parameters of the comet's trajectory? It can't be a very short-period comet, otherwise NASA would presumably already have known about it and have "seen it coming". They didn't. Has the precise orbit of the comet been calculated and might it have actually arrived directly from the Oort cloud?

Or might there be some other, so far unconsidered, parameter involved?

Peter Wilson
2007-Jan-22, 10:06 PM
I think its all of the above.

Kaptain K
2007-Jan-24, 07:02 PM
Has the precise orbit of the comet been calculated and might it have actually arrived directly from the Oort cloud?
Last I heard, the orbit is slightly hyperbolic. It may have come from interstellar space!

01101001
2007-Jan-24, 07:27 PM
I think its all of the above.

And, a side-effect of the particular orbit it now has, I believe, that this is its first (and probably only) trip near our Sun, so it has an adundance of near-surface volatiles to offer.

tony873004
2007-Jan-25, 05:10 AM
Last I heard, the orbit is slightly hyperbolic. It may have come from interstellar space!
It almost certainly did not come from interstellar space. The incoming eccentricity of its orbit, at 1.0001 is just barely hyperbolic. It is only a few meters / second faster than parabolic. The odds are slim that an interstellar visitor would have a barely hyperbolic orbit. Rather, it would be much more likely to have a velocity at infinity of several tens of kilometers per second, rather than just a few meters per second, giving it a high eccentricity of 1.437, or 1.927, etc.

It probably gained its hyperbolic speed from whatever event nudged it from the Oort cloud onto its nearly sun-grazing trajectory.

Kaptain K
2007-Jan-25, 10:22 AM
...this is its first (and probably only) trip near our Sun, so it has an adundance of near-surface volatiles to offer.
Kohotek was also a "first timer" and was anticipated to be very bright! The "comet of the century" turned out to be the "dud of the decade"!

Mister Earl
2007-Jan-25, 04:44 PM
Ugh.... still haven't been able to see this comet... curse my working hours!!
:(

peter eldergill
2007-Jan-25, 05:01 PM
Last I heard, the orbit is slightly hyperbolic. It may have come from interstellar space!

How can an orbit be "slightly" hyperbolic?

Pete

NEOWatcher
2007-Jan-25, 05:11 PM
How can an orbit be "slightly" hyperbolic?

Pete
It's the same as a little pregnant.

Seriously though; I'm sure it's a comment about the distance of the foci from the vertex. (the amount of "bend")

BigDon
2007-Jan-25, 05:14 PM
Is 011 saying that this may be its only trip around the Sun because its likely to be consumed or because its likely to be ejected out of the system?

NEOWatcher
2007-Jan-25, 05:22 PM
Is 011 saying that this may be its only trip around the Sun because its likely to be consumed or because its likely to be ejected out of the system?
I heard from somewhere that it is right around solar escape velocity.

01101001
2007-Jan-25, 05:31 PM
Is 011 saying that this may be its only trip around the Sun because its likely to be consumed or because its likely to be ejected out of the system?

Maybe. Or, more accurately, this may be its first trip in nearer the sun. It's probably been in distant orbit for... hundreds of years -- even billions.

Bad Astronomer Video Blog: Comet McNaught: daytime comet! (http://www.badastronomy.com/bablog/2007/01/14/comet-mcnaught-daytime-comet/)

There may be more accurate measurements of its orbit by now, but then, the BA speculated that it may not be coming back. He said a comment in the blog (probably on the earlier McNaught video blog when he said it would come back) indicated it was then suspected to be hyperbolic -- it would escape the solar system. (And, then the BA sorta mangled the math. Curse video that it is so hard to amend. The BA should produce his video blogs with CGI, a little animated BA with a synthesized voice. Then he could just type up new dialog and make another animation run -- like NASA did with Apollo!)

So, I'll wait for the numbers I haven't seen yet, or even looked for. Maybe. Maybe not. Maybe settled by now. Maybe not. Have I appeared to have sufficiently suspended judgment?

Squashed
2007-Jan-25, 06:09 PM
The photo of comet McNaught's staggered tail in today's APOD (http://antwrp.gsfc.nasa.gov/apod/ap070122.html)shows a phenomenon which has presumably never before been observed (or at least not on such a scale or with such brightness).

...

I know this is not a religious site but a lot of ancient writings are rooted in observations and such and so could this type of comet display (http://antwrp.gsfc.nasa.gov/apod/ap070122.html) be the root of the "Star of Bethlehem" that led the wise men to the baby Jesus?

I do not see how a star could be the case because the writings (http://www.biblegateway.com/passage/?search=Matthew%202:1-12;&version=31;) say the star led them to Bethlehem and then stopped.

Any non-religious thoughts on this matter?

Kaptain K
2007-Jan-26, 09:14 AM
How can an orbit be "slightly" hyperbolic?
The same way that an orbit can be slightly elliptical. Any eccentricity greater than one (parabolic) is hyperbolic. 1.0001 is slightly hyperbolic. Any eccentricity between zero (circle) and one is elliptical. 0.0001 is slightly elliptical. 0.9999 is very elliptical.