Sedna

[ajtribick]

Doesn't the definition of a planet given there rule out the less massive planet of Mu Arae? Their orbits cross, so by the example they gave there, the less massive planet is disqualified, even though it is likely a gas giant...

[TERRIER]

Sorry to bring up the Pluto argument again but......
....OK, so there's always going to be a doubt in some minds as to whether Pluto should be really classed as a planet.

The fact that it is classed as a planet should surely be for a historic reason, and to honour the efforts of it's discoverer Clyde Tombaugh.
His painstaking work, manually scanning millions of points of light on many photographic plates of the nights sky, using only the 1930's technology of his fine-tooth comb ....
.......alright he had a blink comparator* ,deserves to be honoured.
I agree with the Evil Doctor, that had other large Kuiper Belt objects been discovered at the same time Tombaugh discovered Pluto, then its planet status may never have been accepted.

That's just my ?0 0/- 2d worth.

Thank you Evil Doctor G and Grant for quickly coming up with an .ssc for Sedna, and to Jestr for creating the planet texture.

regards
TERRIER

PS
*No disrespect to current astronomers whos painstaking work helps us gain an ever increasing knowledge of the universe. Its just that we have microchip technology now

[Guest]

I'm a newbie here. Is there a way to use that artist's conception, that was published with the news release, in Celestia for Sedna?

[Guest]

Thank you for this new addition to the universe, everyone!

[t00fri]

The Epoch in Celestia is given in Julian days, so that would be:

Oops. That would explain why Sedna appeared to be about 350 AU from Sol on its orbit then . I've corrected it now - thanks, Grant.

Here's a view from 4000 AU above Sol (I labelled Sedna as a planet here, to make it stand out more)... look at the size of that orbit!!!



(the blue circle is Pluto's orbit!)

After this object is only known since a very short while how can anybody know whether the above excentric, elliptical orbit is anywhere near correct??

Bye Fridger

[selden]

Fridger,

Many of the dim objects that have been discovered recently also are present in "prediscovery" photgraphs that were taken years ago. They just weren't noticed. Now those old pictures can be used for position measurements to produce better and better orbital parameters as older images are found.

[Evil Dr Ganymede]

They have been tracking Sedna for several months now too (it was discovered in 2003). You don't need too many observations to track an orbit, plus you can find it on earlier photos too.

[t00fri]

They have been tracking Sedna for several months now too (it was discovered in 2003). You don't need too many observations to track an orbit, plus you can find it on earlier photos too.

Selden, Evil Dr,
sure, this I am aware of, and I have also more or less followed the story so far. But even with months of observation they need a real lot of old data to make sure that the orbit is elliptical and not parabolic ( or hyperbolic) for example. In the questionable orbital region, furthest away from us, I am not sure how much has previously been seen of Sedna??

You sure know that a suitable ellipse can be very well fitted to the "front part" of a parabola...As to the interpretation of Sedna, a parabolic orbit would make quite a difference, I guess...


Bye Fridger

[Guest]

OK, now I'm confused. I installed the Sedna ssc file directly from the above posts, and am running it in 1.3.2pre7. The Sedna I get is associated with an elliptical orbit line, but the planet and its moon are not ON the orbit line as seen in orbit screenshots in prior posts above. In fact, as you zoom in, Sedna is ridiculously far away from its orbit line. Here is a screenshot. The red line is the Sedna orbit. Sedna itself and it small moon are off far to the right center.




How can Celestia create an orbit for an object, but not draw the object on the orbit line or even near it?

HELP

Frank

[maxim]

This is an old Celestia bug. You can see it with lot`s of asteroids and comets too. I think it has to do with precision.

maxim

[granthutchison]

In 1.3.2pre7, try increasing the variable OrbitPathSamplePoints in celestia.cfg. Celestia approximates orbits with straight-line segments, and what you're seeing is the inevitable point at the inner end of a big ellipse.

Grant

[t00fri]

Fridger,

Many of the dim objects that have been discovered recently also are present in "prediscovery" photgraphs that were taken years ago. They just weren't noticed. Now those old pictures can be used for position measurements to produce better and better orbital parameters as older images are found.

Selden,

here come some "second thoughts" and some "research" I did, concerning my own questions above.

The original scientific discovery paper is interesting to read
http://www.gps.caltech.edu/~mbrown/papers/ps/sedna.pdf

There is also reference to the orbit-determination software that was used. Notably a least square method that claims to make relatively little assumptions about the orbit:

http://www.projectpluto.com/find_orb.htm

This is a "one man" code project, though, not at all of the standards I am used to in particle physics. The error analysis so far incorporated is what I would call "primitive": It only allows to propagate a certain amount of Gaussian noise around the initial positions through the orbit program...Hmm...

From the actual discovery images together with 2 follow-up observations, the two methods used come indeed up with strongly different orbit parameters. Only if the successive "gamble" of believing the suggested identifications with very faint (and claimed unique) prediscovery images back to 2001 is added in, the ambiguities are significantly reduced.

The most remarkable results are the large Perihelion distance of 76+-4 AU, much larger than the typical 50 AU regime along with the high eccentricity of 0.84+-0.01. The semi-major axis comes out to 480+-40 AU. The quoted uncertainty is only ~10% which I may accept as a "fit" result but not a true physical uncertainty, given the level of error analysis available in the software.

Bye Fridger

[eburacum45]

I've added colour (by using Jen's Amalthea texture) and a rotational period of 40 days to my copy of this world;

cite for colour and rotation here http://www.gps.caltech.edu/~mbrown/sedna/

[eburacum45]

oops that is forty hours- back to the drawing board...


there- fixed.

[ANDREA]

Fridger,Many of the dim objects that have been discovered recently also are present in "prediscovery" photgraphs that were taken years ago. They just weren't noticed. Now those old pictures can be used for position measurements to produce better and better orbital parameters as older images are found.

The most remarkable results are the large Perihelion distance of 76+-4 AU, much larger than the typical 50 AU regime along with the high eccentricity of 0.84+-0.01. The semi-major axis comes out to 480+-40 AU. The quoted uncertainty is only ~10% which I may accept as a "fit" result but not a true physical uncertainty, given the level of error analysis available in the software. Bye Fridger

Selden and Fridger, I'm happy to bring my cent to this debate.
My SpaceGuard RHP group (Andrea Pelloni, myself- Roberto Haver- Prof. Giuseppe Forti of Arcetri Observatory) have found two new precoveries of 2003 VB12 Sedna, just published by MPC, so its known orbit now is 11 years longer, from Sep 1990 to Mar 2004, a total of 13.5 years.
Here are the new orbital elements after the insertion of these new positions:

Heliocentric Ecliptical Orbital Elements for TDB Epoch 2452178.467091144
a = 551.2039416 AU
e = 0.8615909
i = 11.92987 deg
w = 310.84807 deg
omega = 144.48101 deg
T = 2479107.299536146
M = 357.94906 deg
q = 76.291619448944 AU

Visual Magnitude Parameters
Absolute Magnitude H = 1.56
Slope Parameter G = 0.15
Estimated radius = 998.37 km.
Note: Estimated radius should be regarded only as an order-of-magnitude estimate.

SkyMorph Parameters
Epoch: 2452178.467091144
eccentricity e: 0.8615909399625944
Perihelion Distance q: 76.291619448944
Perihelion Date T: 2479107.299536146
Longitude of the Ascending Node omega: 144.48101619100063
Argument of Perihelion w: 310.84807180472313
Inclination i: 11.92987318282951
Absolute Magnitude H: 1.56

Now we know a bit more of this interesting and long debated object.
Hope this can be of any interest.
By

Andrea

[t00fri]

Fridger,Many of the dim objects that have been discovered recently also are present in "prediscovery" photgraphs that were taken years ago. They just weren't noticed. Now those old pictures can be used for position measurements to produce better and better orbital parameters as older images are found.

The most remarkable results are the large Perihelion distance of 76+-4 AU, much larger than the typical 50 AU regime along with the high eccentricity of 0.84+-0.01. The semi-major axis comes out to 480+-40 AU. The quoted uncertainty is only ~10% which I may accept as a "fit" result but not a true physical uncertainty, given the level of error analysis available in the software. Bye Fridger

Selden and Fridger, I'm happy to bring my cent to this debate.
My SpaceGuard RHP group (Andrea Pelloni, myself- Roberto Haver- Prof. Giuseppe Forti of Arcetri Observatory) have found two new precoveries of 2003 VB12 Sedna, just published by MPC, so its known orbit now is 11 years longer, from Sep 1990 to Mar 2004, a total of 13.5 years.
Here are the new orbital elements after the insertion of these new positions:

Heliocentric Ecliptical Orbital Elements for TDB Epoch 2452178.467091144
a = 551.2039416 AU
e = 0.8615909
i = 11.92987 deg
w = 310.84807 deg
omega = 144.48101 deg
T = 2479107.299536146
M = 357.94906 deg
q = 76.291619448944 AU

Visual Magnitude Parameters
Absolute Magnitude H = 1.56
Slope Parameter G = 0.15
Estimated radius = 998.37 km.
Note: Estimated radius should be regarded only as an order-of-magnitude estimate.

SkyMorph Parameters
Epoch: 2452178.467091144
eccentricity e: 0.8615909399625944
Perihelion Distance q: 76.291619448944
Perihelion Date T: 2479107.299536146
Longitude of the Ascending Node omega: 144.48101619100063
Argument of Perihelion w: 310.84807180472313
Inclination i: 11.92987318282951
Absolute Magnitude H: 1.56

Now we know a bit more of this interesting and long debated object.
Hope this can be of any interest.
By

Andrea

Hi Andrea,

very interesting, indeed. Notably, since your new prediscovery images are going as far back as 1990!

Yet as a (theoretical) physicist, I always ask quickly about inherent uncertainties/errors! Only a reliable error estimate can make the measured values significant!

None of your parameters above has an error assigned to it, but many many (insignificant) digits...

Going back as much as 14 years, the issue of unique identification for such a weak body, seems highly non-trivial to me. Over 14 years, the extrapolation uncertainties on the position of Sedna are much increased, given the short time window of present data, such that it would be miraculous if within the 1990 error ellipse there was only ONE single candidate?

How did you manage to exclude other weak light sources in that field??

As one can see, the originally quoted error on the major half-axis 480+-40 was underestimated (as I anticipated;-)), since your new result of around 550 AU is almost 2 sigma away from 480!

For me another "magic" aspect is that astronomers claim to "know" the orbit so accurately after having directly measured only about 1 per mille (!) of the orbit length or O(10 years) from a total revolution time of 10500 years or so!? This can only work, if from the onset, the shape of the orbit was required to be elliptical in the fit. If in principle "open" paths are admitted I doubt that these 10 years of "data" can exclude an "open", i.e. parabolic or hyperbolic trajectory...

Given the various speculations about the origin of Sedna, it seems clearly plausible to /assume/ that the orbit is "closed". But then this assumption should also be clearly stated.

Personally, I am convinced that such issues will not significantly affect the two main results: the surprisingly large perihelion distance of ~75 AU and the qualitatively high eccentriciy of Sedna's trajectory. But other aspects including Sedna's origin, could well be affected significantly.


Bye Fridger

[Guest]

Hi Andrea,very interesting, indeed. Notably, since your new prediscovery images are going as far back as 1990! Yet as a (theoretical) physicist, I always ask quickly about inherent uncertainties/errors! Only a reliable error estimate can make the measured values significant! None of your parameters above has an error assigned to it, but many many (insignificant) digits... Going back as much as 14 years, the issue of unique identification for such a weak body, seems highly non-trivial to me. Over 14 years, the extrapolation uncertainties on the position of Sedna are much increased, given the short time window of present data, such that it would be miraculous if within the 1990 error ellipse there was only ONE single candidate? How did you manage to exclude other weak light sources in that field?? As one can see, the originally quoted error on the major half-axis 480+-40 was underestimated (as I anticipated;-)), since your new result of around 550 AU is almost 2 sigma away from 480!
For me another "magic" aspect is that astronomers claim to "know" the orbit so accurately after having directly measured only about 1 per mille (!) of the orbit length or O(10 years) from a total revolution time of 10500 years or so!? This can only work, if from the onset, the shape of the orbit was required to be elliptical in the fit. If in principle "open" paths are admitted I doubt that these 10 years of "data" can exclude an "open", i.e. parabolic or hyperbolic trajectory...
Given the various speculations about the origin of Sedna, it seems clearly plausible to /assume/ that the orbit is "closed". But then this assumption should also be clearly stated. Personally, I am convinced that such issues will not significantly affect the two main results: the surprisingly large perihelion distance of ~75 AU and the qualitatively high eccentriciy of Sedna's trajectory. But other aspects including Sedna's origin, could well be affected significantly. Bye Fridger

Hello Fridger, first of all I agree on the excessive number of output digits, but this is the output of CODES, the software we use for Minor Planets Astrometry, and that as a physicist probably could be interesting for you, so please give a look at this address:
http://home.earthlink.net/~jimbaer1/
There you'll find all the physics/mathematics that can give answers to your doubts.
I'm sending you by private e-mail the complete output file of CODES for our Sedna's astrometric measurements, where you'll find many more information on the matter, and if you'll need more information, Jim Baer is a very kind man that will give you all the answers.
But about your doubt on the "magic" knowledge of orbits, the Minor Planet Center (MPC), and CODES too, normally is able to give useful orbital elements for Main Belt Asteroids after only 2 days of astrometric reports, and I think this is sufficiently compatible with the 13.5 years of known orbit for a so distant object.
The MPCs wrong assuntions are negligible on the mass of data.
Probably the number of objects this size/distance is higher that supposed, mainly because the number of images of the same region repeated at 1 day interval (this is the minimum needed to recognize as asteroid an object that moves so slowly) is very small, so it is very difficult to find these couples, and even more difficult or impossible if the object is close to their aphelion distance.
Hope to have been clear, sorry for my English.
By

Andrea

[ANDREA]

[Hope to have been clear, sorry for my English. By Andrea

Sorry, previous post was mine.
By

Andrea

[t00fri]

[Hope to have been clear, sorry for my English. By Andrea

Sorry, previous post was mine.
By

Andrea

Hi Andrea & other Sedna fans ,

thanks for your detailed data, Andrea, they are very useful for me to forming my own opinion about the significance of the results.


Altogether the discovery story of Sedna, the extraction of its orbit parameters and the quest for its origin is really a beautiful showcase of possible excitement in this field!

Let me also point out that the Sedna discovery also represents a great example for own --most educational -- experimentation.

Meanwhile, we know the two main software programs that were used to extract the orbit parameters from the existing data:

-- A least square method that claims to make relatively little assumptions about the orbit:

http://www.projectpluto.com/find_orb.htm

-- and the program CODES that Andrea and friends were using for their interesting work:

http://home.earthlink.net/~jimbaer1/

The code exists for Windows and UNIX/Linux and interested people could right away start playing themselves. Simulating orbit measurements with Celestia as input to these professional programs would provide most instructive information about what amount of data is needed to sustain the claims presently made! One could also investigate what effects a distortion of the input data would have on the output parameters etc.


Bye Fridger

[ANDREA]

Hi Andrea & other Sedna fans ,thanks for your detailed data, Andrea, they are very useful for me to forming my own opinion about the significance of the results. Bye Fridger

Hello Fridger, you are welcome!
Just to add a bit of information on the matter, in the last 3 years our RHP Group obtained precoveries for other 30 objects, all published with our names in the MPECs , and exactly 2 Centaurs, 2 COMETS, 2 KBOs, 18 NEAs and 5 UNUSuals, and this is the reason why I and Roberto, though being amateur astronomers, have our place in the SpaceGuard group, that performs this research, among a crowd of professional astronomers.
Just for this, probably, in my speech there is a bit of proud.
But our discoveries are free of charge for the professional community, so....let me feel proud, at least!

By

Andrea