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On August 12th, 1883, Mexican astronomer José Bonilla was preparing to study the Sun at the recently opened Zacatecas Observatory. However, the Sun’s surface was marred by numerous objects quickly travelling across its disk. Over the course of the day and the next, Bonilla exposed several wet plates to take images of the 447 objects he would observe. They weren’t released publicly until January 1st, 1886 when they were published in the magazine L’Astronomie. Since then, UFOlogists have crowed these photographs as the first photographic evidence of UFOs. The chief editor of L’Astronomie passed the observations off as migrating animals, but a new study proposes the observation was due to the breakup of a comet that nearly hit us.
The only piece of evidence the authors, led by Hector Manterola at the Universidad Nacional Autónoma de México, use to suggest that this was a comet in the process of breaking up, was the descriptions of the objects as being “fuzzy” in nature and leaving dark trails behind them. Assuming this were the case, the authors consider how close the object would have been. Since astronomers at observatories in Mexico City, or Puebla had not reported the objects, this would imply that they did not cross the disc of the Sun from these locations due to parallax. As such, the maximum distance the object could have been is roughly 80,000 km, roughly 1/5th the distance to the moon.
But the team suggests the fragments may have passed even closer. By the time comets reach the inner solar system, they have a significant velocity of some tens of kilometers per second. In such a case, to transverse the disc of the Sun in the time reported by Bonilla (a third to a full second), the object would have been, at most, at a distance of ~8,000km.
At such distances, the overall size of the fragments would be in rough agreement of sizes of other fragmented comets such as 73P/Schwassmann-Wachmann 3, which gave off several fragments in 2006. Based on the number of fragments, estimated sizes, and density of an average comet, the authors estimate that the mass may be anywhere between 2 x 1012 and 8 x 1015 kg. While this is a very large range (three orders of magnitude), it roughly brackets the range of known comets, again making it plausible. The upper range of this mass estimate is on par with Mars’ moon Deimos, which is generally held to be similar in mass to the progenitor of the impact that killed the dinosaurs.
One oddity is that one would likely expect such a close breakup to result in a meteor storm. The timing of these events is just before the annual Perseid meteor shower, but reports for that year, such as this one, do not depict it as being exceptional, or having a different radiant than should be expected. Instead, it notes that 157 of the 186 meteors observed on the 11th were definitively Perseids, and that the “year’s display cannot be reckoned as a fine one by any means.” Meanwhile, the Leonid meteor shower (peaking in November), was exceptional that year, generating an estimated 1,000 meteors an hour, but again, no records seem to indicate an unusual origin.
In total, I find the characterization of Bonilla’s observation as a comet plausible, but generally unconvincing. However, if it were a fragmented comet, we’re very lucky it wasn’t any closer.
At the last paragraph, in the first line: “compet”?
A compet is an instrument that is usually overplayed in concert, by trumpets.
How compets would plausibly obscure the Sun I don’t know.
“Compet” Acronym for competitive and others forms of the word so it could be correct in the context if a little awkward and far fetched.
It would have been better if I didn’t make a mistake myself of course but I blame it on the fact it is early here and I haven’t finished my first coffee yet.
Other(S) forms……doh!
While its “cute” to point out a spelling error, the last sentence is the one that really matters. If it were a comet, and it had not missed, even the fragments, we would not be having this conversation.
It is a nice tested hypothesis, but I have to agree that it is rather unparsimonious.
Much simpler is to note that the wet collodion process is very amenable to defects in the gel, its dissolution as liquid, the plates and their preparation process, rinse water or fixing gas heat and varnish. And the manual individual preparation minutes before the exposure should make those a recurrent feature. Note the constant mention of defects in the many steps described.
Such defects could fit the “mist” characteristic, as well as “dark against the solar disc, but bright outside”. As a prediction that could pass a test, the diagonal appearance shown above is exactly what gel defects would leave during the regular diagonal excess removal pour.
Bonilla could have noticed a series of defects after exposure and invented a “just so” story to fit, a story much more fitting than that he botched two days of likely expensive work. Unfortunately, that is also a recurrent feature among people. =D
Re the “wet collodion process”: It sounds like plausible counter-hypothesis. If so, there should be ample examples of this kind of defect in other plates from the same observatory.
That is unfortunately the “just so” part of the hypothesis. It could be rare, which is (according to my hypothesis) why Bonilla felt he had to explain it. Or it could be common, in which case there could be other explanations.
Still, the better test than the one I suggested is along the lines you make, probably looking at other observatories as well. The process was common for decades, and it seems (to this layman) to have a resolution that maybe wasn’t matched for yet another long time.
So…for it to be “wet collodion process” then José Bonilla was lying about making the observations? Maybe a non-eventful time in his career so when these things showed up on all those plates after the fact he just decided to make up a UFO story?
Maybe, but I didn’t suggest consciously lying.
its either a sunspot or a comet twice the size of earth?
According to Bonilla, the objects were moving across the Sun in ~1 second. This is not characteristic of a Sunspot.
The silhouette of a typical comet nucleus in front of the bright solar disk would have been much too small to be seen even through a telescope let alone be noticeable in old photographic plates. So it cannot be a comet either. The original explanation of migratory birds is still the best.
Apparently the objects were seen visually as well but over a period of two days. One bit of the analysis that seems a bit odd though I am not expert is the use of the velocity of comets to determine the height via the transit time. I always though the raw speed of the comets was higher than meteorites. The meteorites of course come from the dust that was left behind and thus travelling slower.