Talk:Chelyabinsk meteor

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Impactor orbital elements[edit]

The article lists several attempts to estimate the orbital elements of the object before impact. However, as I tried to check the data, there seems to be a problem with the epochs of the elements shown, especially those by "Zuluaga, Ferrin, Greens", and "de la Fuente Marcos". The first source states to give the elements 3 days before impact (so, unperturbed by encounter). The second states to give an estimation based on elements at the epoch of the actual impact. Not only that those different epochs should be mentioned in the article, as they make a BIG difference in the orbit... The source "de la Fuente Marcos" seems to mix up all those epochs, simply assuming they all give epochs at time of impact (see http://arxiv.org/pdf/1405.7202v2.pdf page 8). However, the source that they choose to be most appropriate (Nakano, see http://www.icq.eps.harvard.edu/CHELYABINSK.HTML) explicitely gives elements at the last perihelion before impact, on Dec 31, 2012. And it doesn't end here... The source with that elements is not a scientific article, but a website that states that somebody has made calculations - but I was unable to find them, looks like they have not been published anywhere... Trying to calculate orbital elements for the epoch of impact, using Nakano's orbit, gives a PERTURBED orbit with a=4.0 AU, e=0.82 and i=10.9. Just to show what a difference that makes... As the orbit given by "de la Fuente Marcos" seems to be inappropriate, I doubt that the given closest matches for parent bodies are in any way well-founded. Can anybody please check if my notices are reasonable? Thanks. Renerpho (talk) 00:15, 27 June 2015 (UTC)

Edit: I've written an email to Mr. de la Fuente Marcos, so it's possible that he can dispel my concerns.Renerpho (talk) 00:49, 27 June 2015 (UTC)

Presumably the orbital elements are before being affected by earths gravity ? How much was direction and speed affected by earths gravity ? - Rod57 (talk) 10:29, 29 June 2015 (UTC)

Indeed, it's much more complicated. I've had an email discussion about the subject with Carlos de la Fuente Marcos. The main results are as follows.

1. His (Mr. de la Fuente Marcos) article does not account for earth's gravity. It's a simple geometric approach, and the elements he gives are of epoch of impact IF EARTH WOULD NOT HAVE AFFECTED the impactor. 2. Most of the other articles neither state which epoch they refer to (in general, not the same as above, that is epoch of impact), nor do they make clear if they take Earth's gravity into account. 3. The subject is much more uncertain than many of the articles state. In fact, most of them are contradictious even if one takes the different epochs and models into account. It's simply IMPOSSIBLE to calculate the exact elements with only daytime observations of atmospheric entry. 4. The error estimates are mostly not reflecting true uncertainty, as they do not account for systematic errors of the model each approach uses for determination. 5. There is much work to be done. I think points 1+2 are the most annoying. It's simply IMPOSSIBLE to compare the sources.Renerpho (talk) 13:06, 5 July 2015 (UTC)

Here is Mr. de la Fuente Marcos' statement.

Thank you very much for your interest in our work. Our approach in that paper is purely geometric. We look for an osculating ellipse that passes through the impact point at the time of impact. Therefore, the epoch is the time of impact, you may say +/-a few minutes. There is no big difference using the ephemerides of the Earth around the time of impact. However, in this particular case, the impact time is known with very high precision (less than one second). The values in Table 1 are coming form the various sources cited, all of them primary. Indeed there is no standard epoch. Each author used his/her own and in many cases they do not even tell which one is in their works. However, the elements of this particular object probably did not change very much (down to the second or third decimal figure) during the last few decades or so prior to impact. This is why we did not include the epoch information, because it is not too relevant. If the orbit did not change too much before impact, all the orbits (if properly computed) should give very similar results no matter the method used (even geometric). What tells you that something could be wrong is the velocity. The impact velocity computed by Miller et al. (2013) using satellites is 17.7 km/s, the one given by NASA is 18.6 km/s. The error in Miller et al. is 0.5 km/s, no value for the error is quoted by NASA. NASA data are coming from "U.S. Government sensors". We asked for the specific details as well as the errors and they said that all the information that can be made public is already in http://neo.jpl.nasa.gov/fireball/, the rest is classified. The values of the impact velocity quoted in most of the papers cited in Table 1 are around 14-15 km/s so the associated solutions are probably quite wrong. Ours is not given in the paper, but it is around 18 km/s so within the observational values. Nakano indeed did his own computations, perhaps based on some data from http://www.icq.eps.harvard.edu/CBET3423.html, where an impact velocity of 17.5 km/s is given. So his work (published in that link) is a primary source, no doubt about that. We did our geometric Monte Carlo without any pre-conceived ideas and we ended up computing a solution that is very close to that of Nakano so you may say that ours is an independent confirmation. The errors quoted in the case of Nakano are assumed (by us) using his significative figures, not computed using a statistical framework. We asked him explicitly and he said that his approach does not produce any errors. The Chelyabinsk event is still a controversial topic. The actual pre-impact orbital solution is far from settled. During the last year or so a few more orbital determinations have been published, all of them based on video data. All of them are inconsistent, between themselves and with the previously published determinations. It happened in daytime (like Tunguska) and that is always a major challenge. Also the solutions published in Nature and Science have been regarded by many as written in stone, but that may well not be the case. The asteroid cited as source in Nature appears not to be linked to the event at all, http://adsabs.harvard.edu/abs/2015Icar..252..129R.

The orbital elements in our first two papers are the result of a geometric Monte Carlo approach. Therefore, the perturbation resulting from the Earth-Moon system has not been taken into account. I cannot tell about the other authors. In most cases, that particular piece of information is not included in their published work. I believe that Nakano's included some level of perturbations. Regarding the changes induced in the orbital elements of an object that approaches the Earth, the fractional changes depend strongly on the geocentric velocity. A very low velocity implies that the object remains in the neighbourhood of the Earth for a long time during the encounter (or prior to impact). In that case, the orbital solution can change significantly within hours and for many hours. However, this is not the case of the Chelyabinsk impactor. At 17.7 km/s the impactor travels the Hill sphere, radius, in less that 30 hours (outside the Hill sphere the orbit is fully controlled by the Sun, inside is progresively more controlled by the Earth-Moon system). However, including the perturbation of the Earth-Moon does not change the pre-impact scenario very much. It is the post-encounter phase what matters in that respect. If you do an actual N-body simulation of a close encounter with the Earth, then you realise that most of the changes in the orbital elements of the incoming object take place as the object recedes from the Earth. The magnitude of these changes is (for practical purposes) inversely proportional to the encounter velocity. The higher the speed (e.g. a hyperbolic encounter), the smaller the changes. When a new study is submitted to a peer-reviewed journal, it is the responsibility of both editor and reviewers to make sure that no loose ends remain. The Chelyabinsk event has very precise impact parameters and that makes the calculations of the pre-impat orbit particularly challenging. Besides there were no astrometric observations, only the videos that are affected by huge parallax errors because the object was less than 100 km from the ground. And all of them were recorded in daylight! It is indeed a difficult task. That explains why the orbit is still controversial. However, our statisitical analysis of the other orbits included in the paper that you read clearly shows (in our opinion) that the other orbits are quite bad and I am not saying that our orbit (sorry, more properly Nakano's) is the real orbit, not at all. However, it is probably closer than the others to the real one. It is essential to perform some serious quality control when you compute an orbital solution. Does it reach the intented point at the intended time (within reason)? If the answer is no, the orbit is invalid, no doubt about that. — Preceding unsigned comment added by Renerpho (talkcontribs) 13:09, 5 July 2015 (UTC)

What angle of impact[edit]

Article says "low" and "shallow" but what angle was it ? - Rod57 (talk) 10:27, 29 June 2015 (UTC)

[1] says 17° above horizontal. [2] says "20° above the horizontal", [3] says "relatively shallow: about 16 degrees". - Rod57 (talk) 10:49, 29 June 2015 (UTC)

Wording accuracy[edit]

The wording "explosion created panic among local residents" isn't accurate. It was fright rather than panic, so I propose "Its explosion caused fright among some local residents" as more accurate. 109.252.37.152 (talk) 08:34, 2 November 2017 (UTC)

Restoring. The wording is correct as is, "caused fright" appears to be a bad translation from another language. Tarl N. (discuss) 01:34, 3 November 2017 (UTC)

External links modified[edit]

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Both links seem useful now. Dhtwiki (talk) 21:38, 10 March 2016 (UTC)

Article rename[edit]

I don't see any discussion on the move, and the mechanics of the move appear to have been done incorrectly (losing all the edit history and detaching the talk page). Is there an explanation I missed? Tarl N. (discuss) 02:12, 12 January 2017 (UTC)

For what it's worth, I think the rename is extremely poor; other events have happened at Chelyabinsk. The meteor, while being the most spectacular recent event, is far from being the only event to ever happen there. The name is thus neither self-explanatory nor unambiguous. I expect this change to be un-done, please comment here if there is disagreement on this point. Tarl N. (discuss) 02:56, 12 January 2017 (UTC)
And, after looking around some more, I came to the conclusion that this move was reversible and have done so. Please discuss here before re-attempting. Tarl N. (discuss) 03:02, 12 January 2017 (UTC)

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