If you ask anyone if they know what Apophis 99942 is then the answer will likely be a blank one. Ask the same question again in 2029 and then in 2036 then people will most definitely be more aware. Apophis 99942 is a near-Earth asteroid and for a brief while was considered the most likely object to collide with Earth. In 2029 it will make a record-breaking near miss of our planet and in 2036 it will return with a 1 in 45,000 chance of hitting Earth.
Apophis is estimated to be 415m long and incredibly heavy, in 2029 it will pass within the range of geosynchronous satellites. Objects of this size are only thought to pass this close every 1,300 years. It will be visible to the naked eye as it makes its approach and will appear as a starlike object moving across the night sky. When the asteroid was first discovered initial estimates put the impact probability at 1 in 37, moving it up to four out of ten on the Torino scale, the highest anything has ever been.
However with more work on computing the orbit of Apophis astronomers were able to rule out an impact in 2029 and state that an impact in 2036 looked unlikely. The asteroid was discovered and named by Roy Tucker and David Tholen. Apophis was the Greek name for the Egyptian god Apep the Uncreator. Apep lived in the underworld and tries to swallow Ra as he passes. Despite a seemingly appropriate name it is rumoured that Tholen and Tucker named the asteroid after the character of the same name from their favourite TV show, Stargate SG-1, a being who sought to destroy the Earth.
Although in 2010 the likelihood of Apophis hitting the Earth has been proven to be very small it did for a while start to make scientists wonder what the effects would be should the asteroid actually strike our planet. An object of the size of Apophis would generate an explosion with the equivalent energy of 880 megatons of TNT. By comparison the eruption of Krakatoa was 200 megatons and the Tunguska event released 3-10 megatons of TNT equivalent energy. The impact would be severe and affect a huge area, but thought to be light enough that the Earth would avoid some of the more serious events, such as an impact winter.
Although Apophis is considered a low risk, its initial status of 4/10 on the Torino scale prompted talk of how we would deal with any future Earthbound asteroids. Many possible ideas have been looked at including deflection and nuking. Deflecting asteroids is seen as favourable to blowing them up as all that may do is create a stream of smaller asteroids that still hit the Earth. To deflect an orbit of an asteroid a small craft would drill into the surface of the rock and then eject material to slowly move the asteroid off-course.
For the moment we’re safe from asteroid impact, but NASA cannot possibly track every single body out there. Thankfully our atmosphere takes care of much of the smaller bodies and provides fantastic protection from asteroid impact. However, there is one body over 1km in diameter with a probability of hitting Earth. Asteroid 29075 1950 DA is rated 2/10 on the Torino scale and will make its pass in the year 2880.
Fortunately for us its still a long way off and gives us ample time to work out an effective defense mechanism. An object the size of 1950 DA would have serious consequences for human civilisation and be very harmful for the climate and biosphere. Luckily for us we have nearly 900 years to work on a solution.