PDA

View Full Version : Comet Elenin May Be Disintegrating



Centaur
2011-Aug-30, 05:26 PM
Here's a link to an article in "Universe Today" regarding the possible disintegration of Comet Elenin: www.universetoday.com/88494/comet-elenin-could-be-disintigrating

And here's a link to my Comet Elenin graphics: www.CurtRenz.com/comets

Superluminal
2011-Aug-31, 01:12 AM
Just like 1999 S4 Linnear. Not a big surprise.

Noclevername
2011-Aug-31, 01:33 AM
Oh noes! Now what we blame our earthquakes on? Oh, right... on the EARTH :rolleyes:

mantiss
2011-Aug-31, 10:37 PM
One annoyance gone, of course the "enthusiasts" out there will blame it on USAF or NASA... grr...

I guess it's best to laugh at it, I quite enjoyed watching SW3 do the cookie crumble thing back in the day.

kheider
2011-Sep-10, 10:50 AM
Looks like we may see a greatly weakened Elenin with SOHO come Sept 23rd. I suspect the absolute magnitude of the comet has dropped from 10 to ~14 though.

The first radio observations of comet Elenin
http://spaceobs.org/en/2011/09/09/the-first-radio-observations-of-comet-elenin/

PS: Today (Sept 10) is perihelion.

-- Kevin Heider

Centaur
2011-Sep-10, 11:30 PM
PS: Today (Sept 10) is perihelion.



Indeed it was, Kevin, at 17:14 UT, and the comet's now headed back toward the outer portion of the solar system. It will pass north through the ecliptic plane (ascending node through the Earth’s orbital plane) on September 14. From our vantage point the comet will have its least angular separation from the Sun (1.9į north) on September 26. It will pass its closest to the Earth on October 16 at 0.234 AU, while in the constellation of Cancer which is well into the northern celestial hemisphere. Let's hope there will be something left to see.

Jeff Root
2011-Sep-11, 01:19 AM
Could perihelion really be determined to the minute? That seems
unbelievably precise for a small comet. Was it just a prediction?

-- Jeff, in Minneapolis

Centaur
2011-Sep-11, 01:34 AM
Could perihelion really be determined to the minute? That seems
unbelievably precise for a small comet. Was it just a prediction?

-- Jeff, in Minneapolis

You have a point, Jeff. It was a JPL prediction based on previous observations and then applying the laws of celestial mechanics. That results in an expected perihelion time that is a basis for predicting the comet’s positions. JPL’s September 9 orbital solution gives the Julian Date in Dynamical Time for the perihelion as 2455815.218553681725. That’s a precision of less than a ten-millionth of a second. That’s a bit more absurd than I was being. Okay, I’ll amend my statement to “about” 17:14 UT. Or perhaps “somewhere in the vicinity of” 17 hr UT would calm your sensibilities even more.

thoth II
2011-Sep-20, 07:41 PM
Centaur,

maybe you know? I heard info. from a source I don't really trust, Richard Hoagland, but he cited NASA ephermerides on Elenin. He stated that Elenin is the first comet in history discovered to have been in a hyperbolic orbit. What I find interesting about this is, and I have thought this out from celestial mechanics:

parabolic orbits, such as a long period comet originating in the Oort Cloud, would have a total orbital energy of zero.

hyperbolic orbits, such as Elenin, would have a total energy of greater than zero, thus would have to come from outside the solar system. I find that very interesting if it is true, and if so, where could it possibly have come from :think:

Centaur
2011-Sep-20, 08:12 PM
Centaur,

maybe you know? I heard info. from a source I don't really trust, Richard Hoagland, but he cited NASA ephermerides on Elenin. He stated that Elenin is the first comet in history discovered to have been in a hyperbolic orbit. What I find interesting about this is, and I have thought this out from celestial mechanics:

parabolic orbits, such as a long period comet originating in the Oort Cloud, would have a total orbital energy of zero.

hyperbolic orbits, such as Elenin, would have a total energy of greater than zero, thus would have to come from outside the solar system. I find that very interesting if it is true, and if so, where could it possibly have come from :think:

Hoagland has twisted the statistics. Whether he has intentionally done this to suit his agenda, or is simply ignorant, I do not know. I use NASA/JPL’s heliocentric osculating orbital elements to draw my Comet Elenin graphics. Those elements (and the derived ephemeris) only create the appearance of a hyperbolic orbit due to perturbations from solar system bodies. NASA/JPL also provides barycentric elements for the comet, and they indicate the orbit is elliptical with a semi-major axis of 518 AU and a period of 11,800 Years. The barycenter is the combined center of mass of all solar system bodies.

The heliocentric elements are more accurate and useful for when a comet is in the inner solar system. When a comet is outside of the planetary neighborhood, the barycentric elements paint the larger picture more properly.

Of course a perfectly parabolic orbit with an eccentricity of precisely one has a probability of zero. A truly hyperbolic (eccentricity permanently greater than one) orbit relative to the solar system barycenter would indicate an origin from outside the solar system. That is not the case with Comet Elenin.

thoth II
2011-Sep-20, 09:24 PM
Hoagland has twisted the statistics. Whether he has intentionally done this to suit his agenda, or is simply ignorant, I do not know. I use NASA/JPL’s heliocentric osculating orbital elements to draw my Comet Elenin graphics. Those elements (and the derived ephemeris) only create the appearance of a hyperbolic orbit due to perturbations from solar system bodies. NASA/JPL also provides barycentric elements for the comet, and they indicate the orbit is elliptical with a semi-major axis of 518 AU and a period of 11,800 Years. The barycenter is the combined center of mass of all solar system bodies.

The heliocentric elements are more accurate and useful for when a comet is in the inner solar system. When a comet is outside of the planetary neighborhood, the barycentric elements paint the larger picture more properly.

Of course a perfectly parabolic orbit with an eccentricity of precisely one has a probability of zero. A truly hyperbolic (eccentricity permanently greater than one) orbit relative to the solar system barycenter would indicate an origin from outside the solar system. That is not the case with Comet Elenin.

Thank you, that clear it up, and it seems very likely this comet is just another long period comet.

Jeff Root
2011-Sep-20, 09:47 PM
To clear it up more thoroughly ...

Is there any chance that Comet Elenin *was* on a hyperbolic
trajectory before interaction with the planets?

Have *any* comets been found to have hyperbolic trajectories?

Have comets been found with trajectories indistinguishable
from parabolic / hyperbolic?

And going beyond ...

If comets originate from asteroids being kicked out of the
inner Solar System by giant planets, interstellar space should
have an enormous population of comet nuclei created over
the last ten billion years or so. Why don't we see them?

-- Jeff, in Minneapolis

Centaur
2011-Sep-20, 10:56 PM
To clear it up more thoroughly ...

Is there any chance that Comet Elenin *was* on a hyperbolic
trajectory before interaction with the planets?

Have *any* comets been found to have hyperbolic trajectories?

Have comets been found with trajectories indistinguishable
from parabolic / hyperbolic?

And going beyond ...

If comets originate from asteroids being kicked out of the
inner Solar System by giant planets, interstellar space should
have an enormous population of comet nuclei created over
the last ten billion years or so. Why don't we see them?

-- Jeff, in Minneapolis


In the case of Comet Elenin, I suggest you ask Aldo Vitagliano to tackle the problem. He is the author of the Solex numerical integration program for celestial mechanics. His e-mail address can be found at the bottom of this webpage: http://main.chemistry.unina.it/~alvitagl/solex

Hundreds of known comets have heliocentric osculating orbits that are hyperbolic for the solutionís epoch. None have barycentric orbits that are significantly hyperbolic, i.e. no more than can be ascribed to the influence of Jupiter. Of course that does not make it impossible that some originated in interstellar space, but if one of that sort were to pass by it would likely have an eccentricity substantially greater than one.

Comets are thought to have originated from Centaurs and the Kuiper belt. The total mass of all primary belt asteroids is estimated to be about 4% that of the Moon. Of course it may have been much more in the past of the 4.6 billion year old solar system (not 10 billion). But it certainly would have been nowhere near the mass of Jupiter, whose gravity is suspected to have prevented them from coalescing into a major planet and may have ejected many of them from the solar system. Any reasonable amount of asteroid mass scattered over the vast volume of interstellar space would be awfully hard to detect. We canít even detect most of what is suspected to be in the solar systemís Kuiper belt and Oort cloud. Perhaps you would like to perform the search.

kheider
2011-Sep-21, 01:53 AM
Good answers Curt.

We know of ~381 comets with periods greater than 10,000 years.

We know of 4,329 comets (~1,500 are Kreutz Sungrazers)
http://www.johnstonsarchive.net/astro/sslist.html

Using http://ssd.jpl.nasa.gov/sbdb_query.cgi
Constraints: comets and [ period > 10000 (years) or e > 1 ]
381 matches (as of 2011-Sep-20)

C/1847 J1 (Colla) is the first comet to show e>1.

Even in 1987 we knew of 152 comets with original orbital periods greater than 10,000 years.
http://adsabs.harvard.edu/full/1987A%26A...187..913D

Using http://ssd.jpl.nasa.gov/sbdb_query.cgi with only e > 1, we see there are 260 comets known to be hyperbolic.

-- Kevin Heider

Jeff Root
2011-Sep-21, 04:16 AM
Centaur,

If it is true that giant planets frequently migrate sunward
due to ejection of asteroids, then the Milky Way should have
many quadrillions of asteroids zooming around. I'm saying
that they must exist in such enormous numbers that we
ought to see them pass close to the Sun fairly often.

I said "ten billion years or so" because that is how long giant
planets in other solar systems must have been throwing out
asteroids.

If comets originated from Centaurs and the Kuiper belt, but
not from closer in, then you are saying that Jupiter never
migrated inward by throwing out large numbers of asteroids
from closer in? Or were such closer asteroids thrown out of
the Solar System entirely, never to return?

-- Jeff, in Minneapolis

kheider
2011-Sep-21, 03:52 PM
Jupiter migrated inwards by ejecting objects from the Solar System while the wimpier planets Saturn, Neptune, and Uranus migrated outwards by scattering objects inwards. There use to be many orders more objects in the asteroid belt and Kuiper belt.

See: http://en.wikipedia.org/wiki/Nice_Model
-- Kevin Heider

Centaur
2011-Sep-21, 09:58 PM
Centaur,

If it is true that giant planets frequently migrate sunward
due to ejection of asteroids, then the Milky Way should have
many quadrillions of asteroids zooming around. I'm saying
that they must exist in such enormous numbers that we
ought to see them pass close to the Sun fairly often.

I said "ten billion years or so" because that is how long giant
planets in other solar systems must have been throwing out
asteroids.

If comets originated from Centaurs and the Kuiper belt, but
not from closer in, then you are saying that Jupiter never
migrated inward by throwing out large numbers of asteroids
from closer in? Or were such closer asteroids thrown out of
the Solar System entirely, never to return?

-- Jeff, in Minneapolis

Since no unquestionably interstellar comets have ever been detected, perhaps portions of your conjecture need to be reworked, particularly any thoughts invoking the words "should", "must" or "ought". See kheider's fine answer to your final question.

Jeff Root
2011-Sep-22, 01:17 AM
Since no unquestionably interstellar comets have ever
been detected, ...
That has been my understanding.



... perhaps portions of your conjecture need to be reworked,
particularly any thoughts invoking the words "should", "must"
or "ought".
Yes, but why? You are essentially saying that my questions
are well-placed: There is no evidence of interstellar comets,
so is the theory that giant planets moved inward by expelling
asteroids wrong? That's the way it appears. But the fact that
no unquestionably interstellar comets have ever been detected
was known perfectly well by the people who developed the
theory. So, what is going on?



See kheider's fine answer to your final question.
kheider says that Jupiter migrated inwards by ejecting objects
from the Solar System. If there is no population of extrasolar
objects, then that would appear to be impossible, unless
Jupiter's migration was an unusual occurrance.

-- Jeff, in Minneapolis

Centaur
2011-Sep-22, 05:02 AM
...unless
Jupiter's migration was an unusual occurrance.


Ah, now thereís a clue. Solar systems with material, organization and history similar to our own may be rarer than assumed. Also consider that the volume of space between stars is almost unimaginably immense.

Jeff Root
2011-Sep-22, 09:48 AM
Why would Jupiter's inward migration be unusual?
Especially considering all the "hot Jupiters" discovered?

Sure, the space between stars is immense, but it appears
that the majority of stars have companions (either planets
or other stars) large enough to kick asteroids completely
out of the system. I would expect each such system to kick
out millions or even billions of objects that would be large
enough for us to see if they passed within 1 AU of the Sun.

100 billion star systems in the Milky Way times 1 billion
objects kicked out of each would be 100 quintillion objects
flying around the galaxy. And that's just the big stuff.

-- Jeff, in Minneapolis

Centaur
2011-Sep-22, 04:09 PM
Why would Jupiter's inward migration be unusual?
Especially considering all the "hot Jupiters" discovered?

Sure, the space between stars is immense, but it appears
that the majority of stars have companions (either planets
or other stars) large enough to kick asteroids completely
out of the system. I would expect each such system to kick
out millions or even billions of objects that would be large
enough for us to see if they passed within 1 AU of the Sun.

100 billion star systems in the Milky Way times 1 billion
objects kicked out of each would be 100 quintillion objects
flying around the galaxy. And that's just the big stuff.

-- Jeff, in Minneapolis

First generation stars and the material surrounding them do not contain the heavy elements that produce rocky or icy objects. We are uncertain of the percentage of stars surrounded by asteroids or Jupiter sized planets. Some (perhaps many) ejected objects escape the galaxy or go into its halo. The spherical volume of space centered on the Sun and reaching out to the nearest star equals 8.84 x 10^16 cubic astronomical units or 2.96 x 10^41 cubic kilometers. The volume of space in the galaxy is roughly 2.6 x 10^28 cubic astronomical units or about 8.9 x 10^52 cubic kilometers. For the galactic halo it would be much more. Again, since we have not detected unquestionably interstellar comets, it may be wise to revisit certain assumptions.