Space is an unwelcome place for humans, with unimaginable pressures, freezing temperatures and deadly radiation entailing instant death for unprepared astronauts. But the human race is not totally immune from extraterrestrial perils, even back on planet Earth. For once in a while Earth is hit by asteroids large enough to wipe out most of life from the face of the planet.
How often do asteroids hit Earth?
US space agency NASA is charged with the vitally-important task of monitoring any potentially lethal asteroids barrelling towards Earth.
It may surprise some that Earth is in fact bombarded with hundreds of tons of space debris every day.
About once a year, one car-sized asteroid will slam into the Earth’s atmosphere.
Asteroids of this size will transform into an awe-inspiring fireball which thankfully burns up before it can impact Earth.
Space rocks smaller than about 80ft (25m) will therefore cause little or no damage.
A meteorite the size of house will explode in Earth’s atmosphere with a force greater than the nuclear weapon dropped on Hiroshima in World War Two.
Such an asteroid could flatten most buildings within 1.5 miles of ground zero, spelling death for many thousands.
Once every other millennia, a meteoroid the size of a football field will collide with our planet, understandable causing catastrophic damage to the area.
Such a space rock could easily obliterate New York, also causing a magnitude 8 earthquake that might be felt than 1,000 miles away.
And once every few million years, an asteroid large enough to threaten the existence of life Earth arrives.
NASA believes asteroids larger than one mile (two kms) will have worldwide effects.
Apart from the main impact, the quantities of dust tossed would block the sun and lead to rapid changes in climates across Earth.
At 5.4kms in diameter, the largest known potentially hazardous asteroid is Toutatis.
NASA calculated if Toutatis were to hit Earth, the resulting crater would stretch more than 100 miles wide.
In fact, this is similar in size to the space rock that is believed to have killed the dinosaurs.
Deep impact craters on Earth, the moon and other planets in our soar system are evidence of these apocalyptic occurrences.
Space rocks that comprise the main asteroid belt between Mars and Jupiter have been measured at 600 miles (1000 kms) across.
How is an Asteroid Orbit Calculated?
Space agency NASA computes an asteroid’s orbit by finding the elliptical path about the sun that best fits the available observations of the object.
So the asteroid’s computed path about our star is adjusted until the predictions of where the asteroid should have appeared in the sky at several observed times match the positions where the object was actually observed to be at those same times.
As more and more observations are used to further improve an object’s orbit, NASA becomes increasingly confident where the object will be in the future.