Talk:(208996) 2003 AZ84

Post from 2007

The discovery of a satellite for 2003 AZ 84 has been published in IAUC 8812.RandomCritic 02:05, 25 February 2007 (UTC)

mass

Why the 2-sig figure for the mass in the info box if the mass is unknown? Is that calc'd from the orbit of the satellite, and the text hasn't been updated? — kwami (talk) 21:12, 4 July 2011 (UTC)

Uruguayo

Dwarf Planet & Plutoid Headquarters = Yes? -- Kheider (talk) 17:03, 17 January 2012 (UTC)

Name?

Known for more than ten years. Have any names been proposed/considered yet? Steinbach (talk) 13:17, 27 September 2013 (UTC)

I doubt Mike Brown will name it before he confirms the satellite does NOT exist. Maybe he should name it Nibiru since the satellite is now invisible. -- Kheider (talk) 13:34, 27 September 2013 (UTC)

Physical properties, diameter

A stellar occultation by that asteroid has been observed on November 15, 2014, which revealed that the asteroid in fact is a very elongated body with a dimension of 833 km x 576 km, in contradiction to the assumption that the body is a spheroid. I'm not sure if this should be added to the article before the result has found it's way into a peer-reviewed publication. Source: http://sendaiuchukan.jp/data/occult/1411-2003AZ84-red.gif

Not necessarily. Its rotation period is rather short, at 6.75±0.04 hr, which means it should be at least moderately elongated. To compare, Haumea, at 3.9155±0.0001 h, has a longest axis roughly twice that of its shortest axis, and it is more rocky than icy. And 2003 AZ₈₄ likely contains more ice. --JorisvS (talk) 14:06, 18 May 2015 (UTC)

True, but the question is not about hydrostatic equilibrium, as in the case of Haumea, but lightcurve amplitude, which is stated to be very low, resulting in the statement that the form of the object is likely not far from a sphere. Haumea, in contrast, shows very large amplitude. (The statement that 2003 AZ84's amplitude is low might be questionable at all, I'll have a look at the source...)

OK, I've had a look at the source, and it states that the asteroid is likely "a Sphere or MacLaurin ellipsoid with small albedo spots". So the term "spheroid" should be replaced by "ellipsoid" (that possibility has been omited in the Wikipedia-article). Do you agree? Renerpho (talk) 22:54, 18 May 2015 (UTC)

Yes, "ellipsoid" is better. As for the small lightcurve amplitude, that can be due to a nearly pole-on orientation of our viewing angle. --JorisvS (talk) 09:15, 19 May 2015 (UTC)

That was what I thought, too.

Should the new estimation for the dimension (833 by 576 km, in good agreement with but more exact than the previous estimates) and the assumption about the orientation be added to the Wikipedia-article? Renerpho (talk) 15:07, 19 May 2015 (UTC)

Oh, you already did that. Alright! Renerpho (talk) 15:09, 19 May 2015 (UTC)

Yes, except that the assumption would be OR, AFAIK. Unless, you could find a source that says that, of course. --JorisvS (talk) 15:34, 19 May 2015 (UTC)

I've discovered another problem... In another section the wiki-article states that the asteroid's lightcurve amplitude is large (abt. 0.15 mag). Isn't that a contradiction to the other statement? Renerpho (talk) 15:13, 19 May 2015 (UTC)

I think that in the lead, it tries to says that the lightcurve's deviations from what would be expected for an ellipsoid are small, but a perfect ellipsoid already has a sine as its lightcurve, which can lead to a significant light-curve amplitude, even in the absence of albedo spots or deviations from the ellipsoid. But I agree it could be worded more clearly. I'll take a look at it later. --JorisvS (talk) 15:34, 19 May 2015 (UTC)

2003 AZ84's physical properties

The study on 2003 AZ84's ellipsoidal shape is quite interesting yet it isn't mentioned as much in the article. I've added a bit of information on it. — Preceding unsigned comment added by 107.210.28.247 (talk) 00:50, 6 February 2019 (UTC)

The sources contradict each other

(Disclaimer. I realise that the following may in part be original research. I believe it is still relevant to how the sources are presented/used in the article.)
I believe that the sources used in this article contradict each other. That itself isn't a problem (reaching scientific consensus often includes opposing views), but here the situation is different, because those conflicting sources heavily rely on each other, by cherry-picking results from the other papers without realising the apparent contradictions.
This Wikipedia article cites the paper (Dias-Oliveira, 2017) as its source for the derived density of 0.87±0.01 g/cm³. That paper finds that the shape of 2003 AZ84 is highly elongated, and derives a density based on an assumed shape (an assumption that is equivalent to hydrostatic equilibrium - a strong assumption, as mentioned in the article), but also based on the rotation period.
In the article lead, this Wikipedia article also cites (Tangredi, 2008), which lists 2003 AZ84 as a "Case II - Sphere or MacLaurin ellipsoid with small albedo spots". If taken at face value, (Tangredi, 2008) means that the period determination by (Sheppard, 2003) is only consistent with the double-peak solution of 13.4 hours, not the single-peaked 6.7 h. (Compare page 2 of the Sheppard paper.) That's also the value that the Lightcurve Database prefers.[1]
There are two problems with this:
1. (Dias-Oliveira, 2017) assumes the period from the single-peaked solution. They cite (Thirouin, 2010) as their main source, which, citing (Sheppard, 2003), states that the possible double-peaked solution is "apparently no more likely" than a single peak. However, that conclusion is no longer valid in light of the findings from (Dias-Oliveira, 2017) itself, namely its highly elongated shape, as explained in (Sheppard, 2003). Consequently, the density derived in (Dias-Oliveira, 2017) is based on a value for the rotation period that is inconsistent with the findings of that very paper.
2. If the density derivation was correct, and the lightcurve was single-peaked, then (Sheppard, 2003) concludes that it must be caused by albedo spots, in contradiction with (Tangredi, 2008). That paper's classification of 2003 AZ84 was doubtful to begin with (note the "?"), so a contradiction is not surprising. This doesn't resolve problem #1 though, since the density and assumed shape from (Dias-Oliveira, 2017) imply that 2003 AZ84 is a "Case III – Jacobi ellipsoid with reasonable density". In any case, (Tangredi, 2008) is outdated and probably shouldn't be used as the sole support for a claim in the article lead. Renerpho (talk) 08:10, 7 July 2019 (UTC)

I added question marks before all values that assume HE, since the resulting density of <1 suggests it's not in HE. Removing the "volumetric" values as OR, since the underlying assumptions conflict and you can't derive one from the other. — kwami (talk) 04:12, 10 October 2021 (UTC)