We posted yesterday about NASA's Dawn mission, which will launch from Cape Canaveral July 7th, on a mission to study the "dwarf planets" Ceres and Vesta in the Asteroid Belt between Jupiter and Saturn.
Asteroids are believed to be the building blocks of planets - primordial relics left over from the formation of the Solar System 4.6 billion years ago.
We thought it would be a perfect follow up to examine what the scientific world thinks would happen to the human species and life on Earth in general if an asteroid the size of the one that created the famous K/T Event of 65 million years ago at the end of the Mesozoic Era that resulted in the extinction of the dinosaurs impacted our planet.
The general concensus is that any comet or asteroid greater than 20 kilometers in diameter that strikes the Earth will result in the complete annihilation of complex life - animals and higher plants. (The asteroid Vesta, for example, one of the destinations of the Dawn Mission, is the size of Arizona).
How many times in our galaxy alone has life finally evolved to the equivalent of our planets and animals on some far distant planet, only to be utterly destroyed by an impact? Galactic history suggests it might be a common occurance.
The first this to understand about the KT event is that is was absolutley enormous: an asteroid (or comet) six to 10 miles in diameter streaked through the Earth's athmosphere at 25,000 miles an hour and struck the Yucatan region of Mexico with the force of 100 megatons -the equivalent of one Hiroshima bomb for every person alive on Earth today. Not a pretty scenario!
Recent calculations show that our planet would go into another "Snowball Earth" event like the one that occurred 600 million years ago, when it is believed the oceans froze over (althought some scientists dispute this hypothesis -see link below).
While microbial bacteria might readily survive such calamitous impacts, our new understanding from the record of the Earth's mass extinctions clearly shows that plants and animals are very susceptible to extinction in the wake of an impact.
Impact rates depend on how many comets and asteroids exist in a particular planetary system. In general there is one major impact every million years -a mere blink of the eye in geological time. It also depends on how often those objects are perturbed from safe orbits that parallel the Earth's orbit to new, Earth-crossing orbits that might, sooner or later, result in a catastrophic K/T or Permian-type mass extinction.
What keeps the Earth "safe" at least the past 65 million years is the massive gravitational field of Jupiter, our cosmic guardian, with its stable circular orbit far from the sun, which assures a low number of impacts resulting in mass extinctions by sweeping up and scatters away most of the dangerous Earth-orbit-crossing comets and asteroids.
In 1995, astronomer George Wetherill calculated that without Jupiter, the impact rate on Earth by comets and asteroids would be 10,000 times higher. Under such bombardment it is hard to conceive of how complex life would survive.
Related Galaxy Posts
The End of the World -A Video (the most terrifying short film ever!)
Past as Prelude -Asteroids & the Origin of LIfe (Includes "Impact Map of the World")