The last big impact experienced by Earth occurred 65-million-year ago in Chicxulub, the Yucatan peninsula (southeastern Mexico) and doomed the world of the dinosaurs. If a similar asteroid would shock again with our planet, our very existence would be menaced.
Smaller asteroids frequently hit Earth. For instance, the Tunguska explosion from 1908 devastated an area bigger than that of Greater London. The effects could vary from major modifications on the Earth's crust to huge quakes, tsunamis and reactivated volcanoes. In fact, this may happen soon. Apophis will miss the Blue Planet in 2029 just by 100,000 miles (160,000 km), but it could hit us when it swings by in 2036. The main reason for concern because of the asteroid is for April 13, 2029, when it will approach enough the Earth to be deflected in its orbit. If said deflection makes it pass through a particular space point (keyhole), a 600 m (2,000 ft) space patch, it will impact the Earth on its next passage, in 2036, with a chance of 1 in 5,500.
Dumitru Prunariu, a Romanian astronaut who is a member of the international team that will propose an intervention plan in the case of an impact with an asteroid to the UN Security Council, explained some of these possible effects. The commission reunited last week in Costa Rica.
"We do not have the capacity to prevent such an event, but we can forecast an eventual impact, by many years before it actually occurs. NASA says the Apophis won't reach the level of the geostationary satellites. Such an impact could head the asteroid towards the Earth. Worst case scenario, Apophis enters the Earth above Siberia, crosses the Pacific, and the maximum possibility of impact would be in the Pacific-Central America area, close to the impact site of the asteroid that finished off the dinosaurs. Apophis has a diameter of about 320 m (1,066 ft). In case of impact in the Pacific, it would cause a huge tsunami that would wipe out California but, if it falls on the continent, the damages would be even higher," Prunariu told the Romanian newspaper "Gardianul".
"An asteroid with a diameter of 0.5-1 km (0.3-0.6 mi) could finish life on Earth. At this size, the impact would break the terrestrial crust until the magma zone. A hole of hundreds meters would release gases at temperatures of thousands degrees Celsius, evaporating the oceans, and a large cloud of hot gases would surround the Earth, killing vegetation and any life form, just like in the case of an atomic war. Such an impact could also tear apart a piece of our planet, in the same way that the Moon appeared," explained Prunariu.
As expected, humankind is not ready for such an event.
"There is a working group making calculations in order to forecast the impact. We are analyzing all the sky objects approaching the Earth. Intervention scenarios are being made, involving personalities from various fields, including juridical, social or psychological. A document will be analyzed by the General Meeting of the UN and it will include responsibilities and possible measures to be taken by mankind. The measures must be taken years before the asteroid reaches the neighborhoods of Earth. Prevention measures include the development of displacement technologies to the asteroid and deviation of its orbit. The best solution would be spaceships endowed with engines working on non-conventional energies. At the moment, plasma engines, 10 times more powerful than conventional ones, are in development. One solution would be that of the ship entering in contact with the asteroid and pushing it, thus changing its trajectory or exerting a gravitational influence on it. In order to achieve this, the ship should have a weight of a least several tens of tonnes," added Prunariu.
What about bombarding, the solution chosen by Bruce Willis in one of the most popular films of his career?
"If this does not work, the last resort is the risky option of sending a nuclear load, whose explosion would change the orbit of the asteroid or break it in smaller pieces, that cannot inflict major damages. As of now, ships or technologies for both variants do not exist. The nuclear load requires a rocket able to transport it on large distances, and there is not even a project of such a ship."
The nuclear explosion would be followed by flying debris that must remain at high altitudes in order to not affect life on Earth.
A solution proposed by a team at the University of Glasgow in 2007 is that of the flying mirrors. No less than 5,000 mirrors would be necessary to focus a sunlight fascicle on to the asteroid, melting the rock and shifting its orbital route away from Earth. The orbiting mirrors would concentrate the sunlight on a side of the asteroid, rising its temperature to about 2,100 °C. This would push the asteroid off its course. Calculations showed that the orbit of an asteroid 150 m (500 ft) wide would be sufficiently changed by a group of 100 mirrors in a matter of days. For an asteroid the size of that suspected to have ended the dinosaur life 65 million years ago, a fleet made of 5,000 mirrors would furnish a beam that would then complete its job in three or more years. With only 10 spacecrafts flying in formation, each with a 20m mirror, humans could deflect a Tunguska asteroid into a safe orbit in about six months.
An eventual collision with Apophis would release over 100,000 times the energy expelled in the nuclear blast over Hiroshima. Everything on thousands of square kilometers would be wiped out, but the most severe effect will be induced by the dust lifted into the atmosphere. If Apophis collided with Earth, how would the impact affect our civilization?
"The number of human victims could be low because the affected areas would be evacuated in time, but the material damage would be enormous. Those countries would have to move large populations rapidly and without social convulsions, to ensure for them shelter and food reserves. There would also be the issue of maintaining order in the weeks following the impact, when all communications would be interrupted and law enforcement forces overwhelmed by the magnitude of the intervention," Prunariu explained.
In 2007, Aerospace company Astrium came up with a proposal for a mission, named Apex, scheduled for 2013, that will investigate Apophis. The mission is funded by the Planetary Society, an international scientific (and not only) group founded by Carl Sagan, that has offered a $50,000 prize for a mission meant to track Apophis. Right now, scientists agree that the Apophis issue must be tackled before 2025.