One hundred years ago today, a cataclysmic event occurred, the only one of its kind that we know of in modern times. On June 30th, 1908, in the remote Tunguska region of Siberia, an object descended from space and impacted planet Earth at a speed of thousands of miles per hour, causing tremendous devastation in an area covering nearly a thousand square miles. Hundreds of thousands of gigantic pine trees were flattened and incinerated in the event, houses were blown apart by the shock wave, human eyewitnesses were thrown through the air and injured, and the region still bears the scars of this event. Seismographs thousands of miles away registered the impact, and people as far away as London could read newspapers that night by the light generated by the event. Particulate matter rode the jet streams around the world for months. Tunguska was, and still is, a largely unsettled and uncivilized area and it was several years until scientists made their way to the impact site, and when they finally did they were overwhelmed by the evidence that still remained for the amount of power the event released.
There have been many attempts to explain what happened. To this day, many people espouse the notion that an interstellar spacecraft of unearthly origin suffered some overwhelming technical problems and exploded high in the atmosphere. Most astronomers initially suspected that a large meteorite had impacted the Earth, but the absence of a large single crater, like the Barringer Crater in Arizona, made that theory untenable for some time. Since the late Sixties, the most common explanation was that a comet, those wanderers of the Solar System likened to vast dirty snowballs, was the culprit. A comet would evaporate a lot of its mass in the brief second required to traverse our hundred-mile deep atmosphere, and would not be expected to leave a large crater. However, in the last few years our understanding of asteroids and meteors has changed and we now realize that many asteroids are not solid masses of rock but are rather more like accreted dirt-clods which can be broken into much smaller particles by wind resistance from entering atmosphere at thousands of miles per hour, and at this point in time that is taken to be the most likely candidate for the object that caused this historic event, which would explain the lack of a singular impact crater and the presence of enormous amounts of small meteoritic particulate matter in the area.
The Tunguska impactor devastated nearly a thousand square miles of Siberian forest and is estimated to have released the energy of thousands of Hiroshima-type nuclear bombs. If it had been delayed by just a couple of hours, it would have likely hit somewhere in Europe and caused death and destruction of a region the size of an entire European country and disrupted the course of history.
Events like this are expected to have a frequency from every couple of hundred years to every couple of thousand years. The Solar System is a violent place and always has been. The Earth has been hit millions of times in its over four billion years of existence, and will continue to be hit regularly in the future. The question is not if we will be struck by another large object, but when. The next one could be large enough to cause extinctions of higher species, including us. There is a historical record of this, it is the way of the universe, and silly films like "Armageddon" aside, we have absolutely no way to prevent it. It's quite likely that we will not have any warning, as there are only a tiny handful of people who watch for near-Earth objects that are potential impactors. When it happens, it is far more likely to be a catastrophic surprise rather than something we can plan for and try to change.
Our species is threatened by extinction from space every second of every day of every year. All members of the human species are eggs in one gigantic basket, a basket that can be obliterated by one mountain-sized rock. The only hope our species has for continuing to exist in a violent universe is to find other baskets for we human eggs. While traveling to other stars grows less likely every day, we do have other places in the Solar System where humankind can make a stand and survive. We have the Moon, the planet Mars, the Jovian satellites Ganymede, Callisto, and even Europa, we have the Saturnian satellites Titan and Enceladus, and we have the possibility of constructing large orbital stations with self-contained biospheres in which humans can live and thrive.
If you do not support human space exploration, you are condemning the human race to inevitable extinction. The miniscule NASA budget of about sixteen billion dollars per year represents roughly one month of George W. Bush's Most Excellent Adventure in Iraq.
Please support manned space exploration, it is the most effective approach to our continuing existence. Humanity must colonize the Solar System, or we will eventually face an astronomical event that causes the extinction of our species. It may be the only chance your offspring have.