Recently rumors have been swirling that the Earth
is in immediate danger of being hit by a large comet or asteroid
These rumors have prompted a flurry of questions about the likelihood of
such impacts. So, to address those concerns, we have created this
page in an attempt to answer some of the common questions, put to rest
some of the rumors, and increase general awareness of the true dangers
of impacts from outer space. This page is by no means a comprehensive review,
but merely a starting point for people interested or concerned about this
subject. We have included some links and references at the end for
those who wish to learn more.
Meteors hit the Earth constantly. Most
of these are small pieces of dust that burn up upon entering Earth's atmosphere.
On any clear night, you can see about 8 meteors per hour from any given
spot on the Earth. Sometimes during the year, the Earth crosses meteor
streams, and the rate of meteors can go up to over 100 meteors per hour.
These meteor showers are not the least bit dangerous.
Sometimes, the meteors are larger than normal and can survive the trip through Earth's atmosphere. If a meteor strikes the Earth, it is called a meteorite. Meteorites have many different sizes, ranging from pebbles up to several feet across. These large meteorites are very rare, but smaller meteorites have been found all over the Earth. Every few years, a news report surfaces that somebody's house or car was hit by a meteorite, but these are fairly rare occurrences. There are currently no known cases of a person being killed by a meteorite.
So, meteorites hit the Earth daily, and should be of no big concern to the average person. However, there are many larger bodies in the solar system, notably asteroids and comets, that would cause a large amount of damage if they were to hit the Earth. As of the present, there are no known comets or asteroids that will impact the Earth in the foreseeable future.
There have been reports recently made by reputable scientists that various asteroids may hit the Earth in the next century. However, follow-up work by many different astronomers has shown that none of these asteroid will impact the Earth in the foreseeable future. The original predictions were made before enough information was available to accurately predict the asteroid's orbit far into the future. This illustrates one of the dangers of the search for asteroids that cross the Earth's orbit, that of jumping to conclusions. Astronomers want to give the people of Earth as much advanced warning as possible about any asteroid impacts, but it is dangerous to jump the gun and make an announcement before all the facts are known.
One other rumor that has been swirling about recently is that the Earth will pass through the tail of a comet and hit a large rock hidden in the tail. This rumor is also false. There are no comets currently in view that the Earth will pass anywhere close to. There are several comets visible to people who own binoculars or telescopes, but these are all far away from the Earth. The Earth did pass through the tail of Halley's comet in 1910, but nothing happened to the Earth then, despite a large panic among the population. Most scientists now think that comets are a loose collection of dust and ice, like a "dirty snowball." While the ices melt and the dust flies off of the comet to form a tail, the chances that there are very large (several hundred yards wide or so) meteorites hidden in these tails are very, very small.
So, let us repeat once more: there are no known
asteroids or comets that will impact the Earth at any point in the foreseeable
future. This "foreseeable future" means several hundred years. Beyond
that, computers just cannot predict orbits of asteroids with very high
precision.
On June 30, 1908, an explosion rocked the Siberian forests near Tunguska. Trees were flattened over 2100 square kilometers (approximately a nine mile radius). Reports of a fireball streaking across the sky prior to the explosion were also recorded. The nature of this event has been debated for a long time, but the vast majority of reputable scientists now agree that the Tunguska event was caused by the explosion of a stony asteroid or a comet in the air above the blast zone. The explosion had about the same energy as a 40-megaton nuclear bomb. Scientists continue to study both the explosion and its aftermath in order to understand what happens when an asteroid impacts the Earth.
Over time, large asteroids will hit the Earth,
but it may be millions of years before the next one occurs. Therefore,
we as humans need to be concerned about the possibility of an impact, but
we do not need to worry or panic about this. Most likely, we have
thousands of years to think about impacts and develop a plan of attack
should an asteroid or comet threaten the Earth.
Astronomers also need to develop plans for dealing with an asteroid that will hit the Earth. Current ideas range from putting rocket motors onto an asteroid to using nuclear weapons to knock the asteroid off course. Ideas proposed in the movies - using nuclear weapons to plow an asteroid apart - are also an option, although nobody really knows what would happen if we tried to blow an asteroid apart. The best means for choosing a course of action is to study asteroids. What are they made of? How are they built - are asteroids flying mounds of gravel, or are they solid rock? Surprisingly, astronomers and planetary scientists don't know these answers yet. Upcoming missions to asteroids, such as NASA's NEAR (Near -Earth Asteroid Rendezvous) mission are a step toward understanding asteroids. Once we know what an asteroid truly is, we can begin to develop a plan of attack.
Astronomers also need to better inform the public about asteroids and comets. It is important that people understand that asteroids and comets can be dangerous, but that the danger is small and, most importantly, predictable. Large asteroids don't appear out of nowhere to hit the Earth. They orbit the sun in well-defined orbits, just like the Earth and other planets do. If we can see an asteroid, we can calculate where it is going for hundreds of years into the future. So, as long as we make serious efforts to look for asteroids, surprise impacts by large asteroids will not occur.
Comets are a slightly different matter.
Comets spend most of their time far from the sun, and plunge into the inner
solar system for a few months before returning to the outer reaches of
the solar system. For this reason, it is usually hard to spot most
comets very many years into the future. Comets such as Hale-Bopp
drop in unexpectedly. But, again, we are in luck. The solar
system is an absolutely huge place, and the Earth is a very tiny target.
We should have a few year's notice of impending comet danger, which is
plenty of time to protect the Earth from the comet. We only need
to know how we will deal with a rogue comet. Again, some of science's best
minds are working on plans to protect the Earth.
A good book on the impact which many scientists believe killed the
dinosaurs is T. Rex and the Crater of Doom. by Walter Alvarez, a
geologist at UC Berkeley. While the title is a bit over-dramatic,
the book is a detailed description of the scientific evidence for a large
asteroid impact at the end of the Cretaceous period. The book also
describes the effects of such an impact upon the Earth.
Do you still have questions? Go back to our main page and ask!
