CHESHIRE
STAR WATCH
(Someday)by Jim Maynard
Star date: 04:2:97
Perhaps Chicken Little was almost right: the sky itself may not be falling, but it is a virtual certainty that someday, an asteroid or comet large enough to do some serious damage is going to once again land on the Earth.
We know that these unwelcome visitors from the solar system have landed on the Earth in the past- sometimes with great destruction.
The most famous meteor strike of all time was the Chicxulub explosion 65 million years ago. Though some scientists debate whether this was the sole reason for the extinction of the dinosaur, the fact that the Earth was hit by a large asteroid at the time of the demise of the dinosaur now seems certain.
However, Dr. Robert Baker, one of the
most highly respected paleontologists in the world, strangely disbelieves
an asteroid was responsible for the end of the dinosaurs reign and points
out that dinosaurs were steadily declining in numbers for ten million years
before their demise. Those who hold to the asteroid theory (often astronomers)
believe the dinosaurs were done in by a one/two punch delivered by an extraterrestrial
body. The Earth, it is believed, suffered a hit from an asteroid l0km (6
mi.) across. First, it is believed, this caused most of the forests in the
world to burn in a world wide fire, thus releasing a tremendous amount of
smoke high into the atmosphere. Evidence for this global inferno has been
found all around the globe. It is believed that most of the world's land
animals perished in the fire. Next, smoke and debris caused a sudden ice
age, putting a stranglehold on photosynthesis. Without light from the Sun,
plankton could not survive. This caused starvation in the marine food pyramid
from the bottom up. This is what, it is believed, killed off most of the
life in Earth's oceans.
What is the evidence for a "great extinctor" as they are known landing 65 million years ago? In 1978, Walter and Lius Alverez of the University of California at Berkeley wished to measure the rate of sediment collection at the bottom of oceans. They reasoned that a common space borne material known as Iridium would rain down from space and collect on the ocean floor at a steady pace. What they found instead was an abundance of Iridium at what is known as the
Cretaceous/Tertiary or K/T boundary, sediment laid down 65 million years ago. It has been found world wide in concentrations ranging from dozens to hundreds of times the normal amounts otherwise expected. In 1991, a crater was found which is consistent with such an impact. It lies under Mexico's Yucatan Peninsula, and is believed to have exploded with a force of 100 million megatons (that's 5 billion Hiroshima bombs, or 8000 times all the world's nuclear warheads at the height of the cold war going off at one time in one area).
In June, 1908, a large stony asteroid or comet exploded with a force of 15 megatons 8km (5 mi.) above Tunguska. Siberia. No one was injured (after all, it happened in Siberia!), but trees were felled in a radiant circle leading out in all directions from just beneath the explosion.
The site was so remote, no one visited there for 17 years.
Every planet in our solar system has been subject to repeated bombardment. The craters of the Moon, and Mercury, Mars, and many of the satellites of the outer solar system testify to millions of years of accidental impacts. Only the erosion caused by Earth's atmosphere and water prevent us from viewing many of the scars created on our home world in the 4.5 billion years since the formation of the solar system.
In
1994, the inhabitants of Earth got to watch a large impact of a comet at
a safe distance when comet Shoemaker/Levy 9 collided with Jupiter. As the
pieces of the comet entered the atmosphere of Jupiter, they produced huge
fireballs of hot gas which rose high into the Jovian atmosphere. The hot
gas and dust from Jupiter's atmosphere rose above the planet and re-entered,
releasing energy readily detectable from Earth. Had it been the Earth, the
forests worldwide would have once again been set on fire.
It is only in the last 20 years that scientists have seriously considered the idea that an asteroid or a comet colliding with the Earth could affect the delicate biological balance. It is now believed asteroids and comets colliding with the Earth have made a significant contribution to evolution during the history of life on the Earth.
An asteroid only 50 meters (160 feet) across hitting the Earth would explode with a force of 10 megatons; about the same as one of the world's most powerful nuclear weapons, easily wiping out an entire city. An asteroid twice as large, 100 meters (320 feet) across would explode with the force of 100 megatons, destroying a continent. An unwelcome extraterrestrial visitor with a diameter of 1 km (5/8 of a mile) would wreak havoc over a hemisphere with an explosion of 100,000 megatons (nearly ten times all the world's total nuclear arsenal combined). An asteroid with a diameter of 10km (6 miles; smaller than comet Hale/Bopp) similar to the one which landed at the K/T boundary, would cause another global catastrophe. A 10km asteroid is not large at all and quite common flying around the solar system. An asteroid that size striking the Earth could easily kill at least a billion people, de-stabilizing civilization. Comets, being made mostly of ice, would explode several kilometers in the air doing little damage to the ground. Asteroids are much more dangerous.
The
search is underway for such Earth threatening objects from sites in Australia,
California, and Arizona. The total number of people worldwide looking for
such comets and asteroids which may endanger our planet is less then the
number of people who work one shift at a fast food restaurant.
In 1972 the Earth barely missed a 10 megaton impact when an asteroid 50 meters (180 feet) across skimmed through our atmosphere.
Good skies and clear viewing.
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