It's not another doomsday story, but the possibility of life on Earth getting wiped out by a comet collision just gained another scientific support in a study published last Tuesday in the Royal Astronomical Society's journal. A joint team of astronomers from the University of Buckingham and Armagh Observatory found historical and scientific evidence that gigantic comets may have caused dinosaur extinction millions of years ago.
The team, consisting of Professors Bill Napier and Duncan Steel of the University of Buckingham and Professor Mark Bailey and Dr. David Asher from the Armagh Observatory, believed that the farther reaching Centaurs pose a much greater threat to life on Earth than the nearer celestial rocks in the Asteroid belt.
No, we're not talking about the half-man and half-horse Centaur from Mythology, but those huge delinquent masses of ice that have unstable orbits and get flung towards the Earth by the outer planets' gravitational pull. It seems Earth has been affected by these giant comets thousands of years prior, in a lengthy game of interplanetary survival dodgeball.
"The disintegration of such giant comets would produce intermittent but prolonged periods of bombardment lasting up to 100,000 years. ... Over the past 10,000 years, Earth has been experiencing the intermittent arrival of dust, meteoroids and comet fragments from the disintegration of comet 2P/Encke, trapped within the orbit of Jupiter," the team wrote (PDF).
It seems we have 100,000 years more of intermittent comet fragments courtesy of 2P/Encke to expect, in that case.
The Basic Facts
To say that Centaurs are big is an understatement. Centaurs are massive and are usually about 50 to 100 kilometers (30 to 60 miles) across and that's just the "regular" sized ones. These Centaurs originate from beyond Neptune and have unstable elliptical orbits. Since the outer planets, Jupiter, Saturn, Uranus, and Neptune have strong gravitational fields, when Centaurs get close enough, they get flung towards the inner part of the Milky Way, hurtling towards Earth. This usually happens every 40,000 to 100,000 years.
The bright side is that we're not looking at an end-of-days scenario like in "Armageddon" so there's no need to panic. If you remember your Astronomy lessons, the closer these heavenly bodies get to the sun and the Earth's atmosphere, the faster they melt. That, however, does not mean that the Earth is spared because we still get showered with dust and debris. Some comets, which are larger than others can cause impact craters like the ones in Texas and Arizona.
The Effects
So how would these massive celestial bodies cause mass extinction? To be sure, a direct impact is still in the running as a possible cause for extinction if heat from the sun and the Earth's atmosphere do little to melt away a Centaur's massive size.
A more likely cause, however, would be the collapse of the food chain. Food chain collapse may be caused by a Centaur dust blocking the atmosphere which may damage the ozone layer and also block the sunlight needed to sustain life. If we follow the chain, we know that without sunlight, plants would die and the animals would follow if their food source is eliminated.
"The effects of running through the debris trail of a large comet are liable to be complex, and to involve both the deposition of fine dust into the mesosphere and, potentially, the arrival of hundreds or thousands of megaton-level bolides over the space of a few hours. ... Dusting of this intensity is expected to reduce the level of sunlight to that of moonlight, and result in a global cooling sufficient to destroy commercial agriculture," the study said.
If you think that the climate change happening at present is too fast, think of what will happen if Centaurs are involved. It will be an immediate cooling in the climate and drought would follow since the soil would become too cold to sustain plant life. Society and even civilization could collapse and it's not just a hypothesis. The team found two major societal collapses with historical and geographical proof in 10,800 BCE and 2,300 BCE, which aligned with their calculations of when a Centaur reached the Earth's orbit and affected the planet's climate.
Not only that, the study found that there was a presence of high temperature melt-glass at the border of known impact areas which were exposed to temperatures higher than 2,100 degrees Centigrade. As to why such a thing exists, the team suggested that the exposure to high temperatures were caused by fireballs that flanked the main debris and created the impact crater.
The possibility of humanity's extinction may arise from fire and ice so "Game of Thrones" author, George R.R. Martin, may have been on to something since the latest lunar rocks found by the Apollo Program in craters were dated to about 30,000 years ago.
The Conclusion
Napier and colleagues didn't publish their study to create fear and confusion. Rather, they wanted to show that these celestial rocks in the Asteroid belt aren't the only things threatening life on Earth, but those from far beyond are also dangerous. Their goal is to draw the scientific community's attention to the realistic impacts – in all sense of the word – that Centaurs have on the planet, and invite others to study the celestial bodies in a theoretical and observational point of view.
