Did a doomsday comet almost end life on earth?

Scientists have suggested that a mysterious photograph depicted a comet that may have come within 300 miles of striking Earth.
Written by Tuan Nguyen, Contributor

In 1883, a mysterious photograph surfaced depicting what appeared to be unidentified flying objects crossing the heavens above. Considering that photographic technology was really rough around the edges back in those days, you can see how easily the objects can be made out to be almost anything from a flock of birds to, as some scientists have recently suggested, massive chunks from a comet that came within a hair's breath of ending all life as we know it.

Now that I have your attention, let's backtrack a bit. That year in mid-August Astronomer Jose Bonilla of the Zacatecas Observatory in Mexico peered through a telescope and saw what he described as a swarm of objects, misty in appearance, passing in front of the sun. Like any good scientist would have done, Bonilla dutifully published the details of his observations in a French journal called L'Astronomie in 1886. Far from being alarmed, the journal's editor dismissed it as nothing more than perhaps migrating geese or, somewhat more insultingly, a speck of dust on the telescope lens. It seemed the most logical explanation at the time since no one else had reported seeing the same event.

But what's particularly unsettling about the report was that Bonilla claimed to have watched the unidentified objects move across the sky over the course of two days, which suggests there may be something more dramatic happening here. Now a trio of Mexican astronomers (Hector Javier Durand Manterola, Maria de la Paz Ramos Lara, y Guadalupe Cordero) have released a paper claiming that the objects in question were actually fragments from a colossal comet named Pons-Brooks, which may have narrowly missed striking the earth by a mere 300 miles. We're talking a massive ball of ice and dust weighing more than a billion tons breaking apart into 3275 scattered bits, with each measuring 50 to 800 meters across. They estimate that one chunk of the comet pelting the earth would have been equivalent to the explosive impact felt at Tunguska in 1908.  A sequence of 3275 Tunguska events over the course of two days basically would have amounted to nothing short of mass extinction or, as if you prefer a fancier term, Armageddon.

So how did the researchers deduce that the object in question was a killer comet instead of, you know, a mob of angry birds? In their paper titled "Interpretation of the observations made in 1883 in Zacatecas (Mexico): A fragmented Comet that nearly hits the Earth," the authors surmised that comets are "the only bodies in the Solar System which are surrounded by a bright mistiness." They attempt to bolster their argument by reasoning that when a comet swings that close to the earth, a strong visual effect occurs where an object easily visible from one standpoint can be out of the line of sight at another.

"It’s like a bird flying by just outside your window; someone looking out a different window wouldn’t have seen it, but a bird a few hundred meters away would be visible to both," wrote Phil Plait on Discover's Bad Astronomy blog, where he assessed the findings.

However, if the blog's name is any indication, the tone of his article was highly skeptical of the researchers' account of what may have happened that day. For instance, he found it questionable that there wasn't a subsequent meteor shower, which normally occurs following disintegration. And while its plausible that parallax may have come into play, the effect is a temporary one, meaning the comet should have appeared visible elsewhere before and after Bonilla's observations were made. Add to that a series of questionable mathematical calculations that have the hurling bundle of debris as stretching a few thousand kilometers across when in fact just the material surrounding an intact comet "can be tens or even hundreds of thousands of kilometers across" and the theory starts to, well, crumble.

Plait writes:

If there were hundreds of objects this size, there would’ve been millions as small a few centimeters across. Objects that size make brilliant fireballs as they burn up in our atmosphere, and would’ve been visible during the day, even with the Sun shining. Again, no reports of any meteor storms, despite a comet being a few thousand kilometers away and a million kilometers long.

Also, the Earth is moving, and covers a lot of ground (OK, space) in a day. Having the Earth move at least 2.5 million km during that time, and never getting closer or farther than 500 – 65,000 km is too much to ask.

And for those very same reasons, Donald K. Yeomans, Manager of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, finds the paper to be nothing more than a runaway case of unsubstantiated speculation.

"It's virtually impossible that a comet would come this close, suddenly appear to only one person and then disappear, and not have meteor showers associated with it," he told SmartPlanet. " It's ridiculous I think. I'm surprised that this story had legs."

He also added that astronomers have very reliable coordinates for the orbits of Brooks-Swift and Pons–Brooks, the two known comets spotted that year. The closest, he says, that the fragments from either comet could have approached the Earth in 1883 was several million miles.

But the overarching problem Yeomans and Plait have hinted at is how a theory, no matter how tenuous or ill-conceived, can easily be spread through news media reports without any semblance of rigorous skepticism. In this case, the analysis was fished from arXiv, an online archive of pre-prints, scientific papers that have yet to be published in a peer-review journal. Although that shouldn't prevent journalists from bringing them to light, such a tiny detail would have at least given us all a more accurate picture of what happened on that fateful night.

(via Discover, arXiv)


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This post was originally published on Smartplanet.com

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