Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883
A reanalysis of historical observations suggest Earth narrowly avoided an extinction event just over a hundred years ago.
10/17/2011
On 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 kilometers 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 tons or more, that's huge, approaching the size of Halley's comet.
That's an eye opening reexamination 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 reentered 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.
October 18, 2011 at 12:02 pm
Meteors, comets and why we’re lucky to be alive
New analysis of data collected over 100 years ago suggests that the human race may have narrowly escaped extinction.
Image courtesy couleewinds ( flickr.com/12057715@N00 )
Scientists at the National Autonomous University of Mexico have shed new light on data collected by Mexican astronomer José Bonilla in 1883. Hector Manterola and his team at UNAM suggest that the event Bonilla witnessed over 100 years ago was evidence of a highly fragmented comet missing the Earth by mere hundreds of kilometres, the impact of which would probably have caused “an extinction event”.
Over the course of two days in August of 1883, Bonilla observed and recorded 447 objects passing in front of the sun from an observatory in Zacatecas, Mexico. Bonilla’s findings were published in the French journal, L’Astronomie, in 1886. With no explanation as to why other larger observatories never witnessed the phenomenon the editor of L’Astronomie speculated that it must have been caused by birds, insects or dust passing in front of Bonilla’s telescope. Subsequent interpretations of the event have suggested yet another explanation – that Bonilla’s observations may have been evidence of UFO’s.
The team at UNAM now hypothesize that what Bonilla observed were actually fragments of an astounding, billion-ton comet and the reason this went unnoticed by other observatories is that the comet fragments passed so close to the Earth as to only be visible to a miniscule swath of the planet.
Manterola and his team point out that Bonilla observed these fragments for about three and a half hours over two days thus implying an average of 131 per hour and a total of 3,275 fragments during the time between his observations. They estimate that each fragment was at least as large as one thought to have touched down in Tunguska, Siberia in 1908 – an impact calculated to be 1,000 times more powerful than Hiroshima. It doesn’t take an astronomer to envision what 3,275 impacts over the span of two days might do to the Earth and its ecosystems.
Some have been quick to criticize the team’s interpretation of the historical observations, one astronomer, Phil Plait, stating that “When a comet breaks up, it spreads out. Even when intact, the material surrounding a comet can be tens or even hundreds of thousands of kilometers across!”
We’ll most likely never know for certain what it was that Bonilla witnessed, but if it was a comet, I hope for our sake that it’s not careening around for a second pass.