Wednesday, March 16, 2011

From Super Moons to Comet Elenin – we will NOT get killer earthquakes from the sky

I was wondering why Comet 2010 X1 Elenin was attracting all the attention from the apocalypse and Nibiru crowd rather than Comet 2009 P1 Garrad. It turns out it’s Leonid Elenin’s fault.

According to a video* going around the web at the moment, Leonid Elenin isn’t a real person (Leonid, a long time comet observer who contributes to the comet-obs discussion group and has his own blog, may be surprised at his non–person status, but bear with me for a moment). Leonids' name is a secret code, ELE for Extinction Level Event and NIN for some tatty old goddess. I mean, you just can’t make a decent code from Garrad or McNaught.

The same video claims that it is comet Elenin, rather than “supermoons” that caused the Chilean and Japanese earthquakes.

Now, I see this as another “teachable moment” as in the case of the so-called “supermoons”. There are two issues here; first the statistical issues and then the ideas of scale.

First off, let’s try thinking statistically. In the video much is made of the claim that within 5 days of the alleged closest approach of Elenin and the Earth there was a large earthquake. Now, in any given year there are 1319 quakes between magnitudes 5-5.9, 134 earthquakes of magnitude 6-6.9 (this includes the earthquake that demolished Christchurch) and 15 earthquakes of magnitude 7-7.9. So, choose any random date and within 5 days of that you will almost certainly, on average have a quake of magnitude 6-6.9 in that date range and a roughly 20% chance of having a larger magnitude quake in that time slice. Thus a simple “earthquake somewhere near a comet close approach” is not by itself convincing. You need some sort of physical plausibility.

As we saw in the “supermoon” article, gravitational tidal effects could plausibly trigger earthquakes. The Moon is large and close, but even with the Moon the effect is quite small, it only occurs for certain types of shallow earthquake, and even then less than one percent of these types of earthquake are triggered by lunar tides. Now, The Moon is 7x1022 Kg in mass and 384401Km away. At the March closest approach mentioned in the video, comet Elenin was 273137000 Km away. We don’t know the mass of Elenin, but it is likely to be much smaller than comet Halley, which has a mass of 2.2×1014 Kg. We can use the mass of Halley as a proxy of Elenin for the calculations below.

You can already see that the tidal force due to Elenin is much, much less than that due to the Moon, and we know that the tidal force falls off as the cube of the distance. Now we know the formula for tidal force and we can calculate the tidal force of Elenin relative to the Moon (using Halley's mass for Elenin, an overestimate). It’s a staggering 1034 times less than that of the Moon. So the plausibility of Elenin causing an earthquake is similarly low.

Finally, the video claims that the “alignments” of Elenin and Earth and Sun were on February 27 2010 and March 11-15 2011. The “alignments” were apparently determined by eye from the JPL orbit widget (which explicitly says not to use the orbit widget for this purpose). Fortunately, there are programs that can analytically determine when the closest approach of the comet too Eath is (when the comet, Earth and Sun are aligned). I use SkyMap with the latest orbital elements. It turns out that the comet was aligned with Earth on 27 March 2010 (nowhere near the Chile Earthquake) and will only next be aligned in May 5 2011 (before closest approach on 16 October 2011, again, nowhere near the Japanese Earthquake). No alignment, no earthquake to explain.

The take home message is to keep a sense of proportion (proportion, get it) and don’t try to estimate astronomical alignments by eye on tiny JAVA animations (oh, and check to see that the guy you are claiming is imaginary really does exist).

*I’m not going to link to the video, if you want to destroy your brain cells, go to this comment and copy and paste the URL. On your own head be it.


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