Thanks to movies like Armageddon, Deep Impact and Asteroid, as well as a number of scientific factors, like asteroids actually hitting the ground and leaving huge, smoldering craters, it would be fair to say that humans are considerably scared of asteroids. At least, they’re as scared as one can be of wildly unpredictable extraterrestrial objects. The story of how a huge asteroid 65 million years ago caused the entire dinosaur race to be wiped off the face of the planet doesn’t help alleviate that fear either.
However, a lot of folks – including myself – want to know if the fear of asteroids is truly justified. Will asteroids ever threaten the continuation of life on Earth?
We all know what asteroids are, right? They are rocky bodies that can be as small as a stone or as large as a mini-planet (like Ceres). These rocky bodies revolve around the Sun in an orbit that lies between the orbits of Mars and Jupiter. They are so great in number that they’ve formed an entire belt of asteroids known as the asteroid belt.
Every once in a while, an asteroid or two is pulled away from the belt and falls into the gravitational tug of a neighboring planet, causing it to race towards other celestial bodies. The history of our solar system is riddled with violent impacts on celestial bodies. To see that truth for yourself, all you need to do is peek at the moon through a telescope; the hundreds of lunar craters created in the wake of fierce impacts offer proof of the battering it has sustained. In fact, there was an epoch in the solar system’s history known as the ‘heavy bombardment era’.
Yucatan crater (Chicxulub crater)
The K-T impact that occurred approximately 65 million years ago in the Yucatan Peninsula involved an asteroid – quite a big one, in fact!
It was said to be 10 kilometers across (6 miles); big enough to cause huge firestorms and extinguish most life on Earth.
The Tunguska event
In 1908, an air blast along the Tunguska river in Siberia flattened 2150 square kilometers (1330 square miles) of forest area. The cause of the blast is believed to be an asteroid. Had the same blast occurred over a populated area, the consequences would have been disastrous.
The most recent example is when a near-Earth asteroid entered our planet’s atmosphere over the southern Urals of Russia on 15 February, 2013 and subsequently exploded near the town of Chelyabinsk.
That asteroid measured around 20 meters across and it raced towards Earth at a staggering 19 kilometers/second. It’s explosion unleashed an energy burst equivalent to 500 kilotons of TNT (equivalent to 20-30 Hiroshima atomic explosions), injuring around 1500 people.
Frequency of asteroid strikes
It turns out that there are still plenty of near-Earth objects (NEOs) around the planet that hurtle towards us all the time. To determine how frequently our planet is struck by asteroids, scientists use data from mass extinction events (like the dinosaur extinction), records of explosions in Earth’s upper atmosphere and most importantly, the orbits of NEOs. Artificial satellites record the amount of heat generated in the upper atmosphere by explosions; if such data over the past thirty years is to be believed, meteoroids erupting in Earth’s atmosphere produce an explosive impact of 5 kilotons every year!
The damage that a meteorite strike can potentially cause is proportional to its size. A 300-foot asteroid with the probability of striking once every thousand years can unleash an explosion equivalent to 20 megatons of TNT, whereas a 3000-foot (0.6 mile) asteroid can cause an explosion of 20,000 megatons! Essentially, the smaller the asteroid is, the lesser its destructive power.
A silver lining
The good thing is that the number of smaller asteroids and other NEOs is greater than the large ones; this is good in a way because such small objects often burn up in the atmosphere and sometimes don’t survive the heat to hit the ground at all.
LINEAR: An initiative to predict future impacts
Given that these impacts pose such hazardous consequences for life on Earth, space agencies all over the world try to obtain the latest information regarding the orbits, positions and speed of NEOs. LINEAR or Lincoln Near-Earth Asteroid Research is one such project jointly run by NASA, the US Air Force and MIT’s Lincoln Laboratory to detect and track NEOs. As of 2011, it had detected 2423 near-Earth asteroids and 279 comets.
What if, by some chance, an asteroid threat looms over the planet? If the asteroid in question is detected in time, a spacecraft carrying a charge (explosive material) could possibly be sent to detonate in the proximity of the oncoming asteroid to alter its trajectory and miss Earth entirely. If not, well… good luck everyone!