© UnknownSchwassmann-Wachmann 3 comet which broke apart as it re-entered the inner Solar System in 2006
A re-analysis of historical observations suggest Earth narrowly avoided an extinction event just over a hundred years agoOn 12th and 13th August 1883, an astronomer at a small observatory in Zacatecas in Mexico made an extraordinary observation. José Bonilla counted some 450 objects, each surrounded by a kind of mist, passing across the face of the Sun.
Bonilla published his account of this event in a French journal called
L'Astronomie in 1886. Unable to account for the phenomenon, the editor of the journal suggested, rather incredulously, that it must have been caused by birds, insects or dust passing front of the Bonilla's telescope. (Since then, others have adopted Bonilla's observations as the first evidence of UFOs.)
Today, Hector Manterola at the National Autonomous University of Mexico in Mexico City, and a couple of pals, give a different interpretation. They think that Bonilla must have been seeing fragments of a comet that had recently broken up. This explains the 'misty' appearance of the pieces and why they were so close together.
But there's much more that Manterola and co have deduced. They point out that nobody else on the planet seems to have seen this comet passing in front of the Sun, even though the nearest observatories in those days were just a few hundred kilometres away.
That can be explained using parallax. If the fragments were close to Earth, parallax would have ensured that they would not have been in line with the Sun even for observers nearby. And since Mexico is at the same latitude as the Sahara, northern India and south-east Asia, it's not hard to imagine that nobody else was looking.
Manterola and pals have used this to place limits on how close the fragments must have been: between 600 km and 8000 km of Earth. That's just a hair's breadth.
What's more, Manterola and co estimate that these objects must have ranged in size from 50 to 800 metres across and that the parent comet must originally have tipped the scales at a billion tonnes or more, that's huge, approaching the size of Halley's comet.
That's an eye opening re-examination of the data. Astronomers have seen a number of other comets fragment. The image above shows the Schwassmann-Wachmann 3 comet which broke apart as it re-entered the inner Solar System in 2006. There's no reason why such fragments couldn't pass close by Earth.
One puzzle is why nobody else saw this comet. It must have been particularly dull to have escaped observation before and after its close approach. However, Manterola and co suggest that it may have been a comet called Pons-Brooks seen that same year by American astronomers.
Manterola and co end their paper by spelling out just how close Earth may have come to catastrophe that day. They point out that Bonilla observed these objects for about three and a half hours over two days. This implies an average of 131 objects per hour and a total of 3275 objects in the time between observations.
Each fragment was at least as big as the one thought to have hit Tunguska. Manterola and co end with this: "So if they had collided with Earth we would have had 3275 Tunguska events in two days,
probably an extinction event."
A sobering thought.
Ref:
Interpretation Of The Observations Made In 1883 In Zacatecas (Mexico): A Fragmented Comet That Nearly Hits The Earth
They had me going for a while there. That is, until I read the full paper. And realized how much they managed to estimate, assume from one old account..
They include a picture of the fragments of comet 73P/Schwassmann-Wachmann 3. But there are no pictures of the objects Bonilla saw. And it’s not clear how Bonilla calculated his times.
They did do some interesting calculations though. Their paper would make a great exercise for a science, or math class.
But my real problem with the paper is the idea that a great comet, 8 times the mass of Halley’s comet could make it into the inner solar system, pass through perihelion, break up into a cluster of dangerously large fragments, cross the Earth’s orbit, and then head on out of the inner solar sytem again. Yet only one astronomer saw the thing?
And in spite its size, the estimated number of large fragments, and the closeness of its approach, there wasn’t even one confirmed, or even reported, meteor shower, or impact, that coincides with it’s arrival.
Howzatt?
They estimate the size of the comet they think Bonilla saw to be something like a billion tons. For comparison, if we work from the postulate that the Taurid Progenitor was the Younger Dryas comet, then Bill Napier’s estimate is that something like 1.1 billion tons of cometary debris collided with the Earth 12,900 YA, causing in the so called Younger Dyras cooling, the demise of the Clovis culture, and the megafaunal extinctions.