The researchers have produced a mathematical model demonstrating that our Sun ‘bounces’ up and down through the plane of the Milky Way Galaxy. According to the model, as we pass through the densest parts of the galaxy’s plane, gravitational forces tear comets from their paths, and send them plunging into the depths of our solar system. Inevitably, some of them collide with Earth.
The idea presented in the collision model is not new in the scientific community. In 1998, researchers concluded that at least two mass extinctions of life forms on Earth had taken place at a time when the Sun was passing through the spiral arms of the galaxy. The Cardiff team, composed of Dr. Janaki Wickramasinghe and Professor Bill Napier, has uncovered further evidence to support this theory. According to their calculations, the Sun goes through the plane of the galaxy every 35-40 million years. The researchers evaluated the age of craters on the face of the Earth, and discovered that every 36 million years or so, the collision frequency of comets with the Earth increases by an order of magnitude.
There is no doubt that a collision with comets can threaten life as we know it. According to astronomers, our previous encounter with one of the spiral arms of the galaxy (Sagittarius-Carina), 65 million years ago, resulted in the extinction of almost all the dinosaurs, along with 57% of all kinds of terran vegetation.
On the bright side, the scientists claim it is possible that the collision periods enable microbial forms of life to leave the Earth, carried on the dust sprays and stony shards that break off the Earth at the moment of impact. Those miniscule ‘shuttles’ may eventually leave the solar system entirely, spreading the ‘seeds of life’ throughout the nebulae and the gas and dust clouds that are scattered throughout the galaxy. In fact, according to the Panspermia Theory, the early forms of life reached Earth in this manner, carried safely in the core of a passing comet. However, no solid evidence has been supplied for this theory, and many scientists treat it with suspicion.
Whether or not the Panspermia Theory is correct, the Cardiff scientists believe that more money and efforts should be invested in searching for near-Earth objects (NEO), and into developing possible strategies for dealing with such a high velocity encounter.
“There are two areas where I think we are deficient,” says Professor Bill Napier, one of the paper’s authors and an Honorary Professor at Cardiff University. “First, the inner solar system is almost unexplored in the sub-kilometer range, which is where I think a lot of cometary fragments exist. Second, we should be looking for extremely dark bodies – dormant comets – which may not be getting picked up in current search programs. They should be bright in the satellite infrared.”
The researchers deduce from both the impact crater records and the Sun’s position near the Galactic plane that we are currently in a potential bombardment period. Luckily for human kind, the collisions’ period has a half-life of about two million years, meaning that the collisions are spread over a long time. This also means that the risk for the next mass extinction might be nearer we suspect, and we must prepare ourselves for that option. Should we be caught unprepared, the result may be the end of the human race.
TFOT has recently reported on a theory about the near-extinction of the human race 70,000 years ago, and also covered a new method for the estimation of meteorite impacts, including the meteorite that was the trigger for the mass extinction of the dinosaurs. TFOT also covered the recent Peruvian meteorite and some new potential findings regarding the Tunguska meteorite.
The paper is to be published in the Monthly Notices of the Royal Astronomical Society.
For further reading, visit The Cardiff Center for Astrobiology.
Top image – Credit: NASA.