Apophis and 2036 - what will be the outcome?

Recently, I was asked for some information about Apophis, the asteroid formerly known as 2004MN4, which has a slight chance of impacting the earth in 2036.

So, in response to that request I put together the following information which I figured would be worth sharing here with whoever it is who may read these ramblings.

Asteroid 2004 MN4 was first discovered on 19 June 2004, by Roy Tucker, David Tholen and Fabrizio Bernardi of the NASA-funded University of Hawaii Asteroid Survey (UHAS), from Kitt Peak, Arizona, and observed over two nights. It was then lost. On December 18, 2004, the object was then rediscovered by Gordon Garradd of the Siding Spring Survey in Australia.

Further observations from around the world over the next several days allowed the Minor Planet Center to confirm the connection to the June discovery, at which point the possibility of impact in 2029 was realized by the automatic SENTRY system of NASA's Near-Earth Object Program Office.

The asteroid stirred up a flurry of concern in the media around December 2004, when the risk of collision was raised temporarily to as high as 1 out of 40 for the year 2029.

Essentially, this asteroid is a smaller rock, with an estimated diameter of 1,300 feet or 400 metres, and probably won’t cause a global disaster, but will certainly “rock the planet”. Localized damage could be significant in the region struck or nearby if it hit in the ocean and a major tsunami resulted.

More precise plotting has ruled out a collision in 2029. However, Apophis will still make an extremely close pass — missing Earth by mere tens of thousands of miles. At that distance, Earth's gravitational pull could perturb Apophis' orbit enough to put it on a track to hit during another pass in 2036. The current, but still uncertain, best estimate of the flyby distance in 2029 is about twice the distance of the moon, or about 780,000 km (480,000 miles). On average, an asteroid of this size would be expected to pass within 2 lunar distances of Earth every 5 years or so.

Experts say that a 2036 impact could happen if, during the 2029 close encounter, the asteroid passes through an outer-space "keyhole" that measures about 2,000 feet or 600 metres across.

In statistical terms, the risk of an impact is now set at 1 in 5,560, based on the uncertainties surrounding Apophis' orbit.

A quarter of a mile wide and large enough to cause considerable damage, asteroid 2004 MN4 was the first asteroid in history to be ranked 4 on the Torino Scale, a measuring tool like the Richter Scale that measures the threat of space rocks.

Most of this object's orbit lies within the Earth's orbit, and it approaches the sun almost as close as the orbit of Venus. Apophis’s orbital period about the sun is 323 days, placing it within the Aten class of NEAs, which have an orbital period less than one year. It has a low inclination with respect to the Earth's orbit and the asteroid crosses near the Earth's orbit twice on each of its passages about the sun.

In an article on msnbc.com, NASA has outlined what it could do, and in what time frame, in Apophis is on a course to slam into Earth in the year 2036.

The timetable was released in 2005, by the B612 Foundation, a group that is pressing NASA and other government agencies to do more to head off threats from near-Earth objects.

The plan runs like this: In 2013, if there's still a chance of a collision in 2036, NASA would start drawing up plans to put a probe on the space rock or in orbit around it in 2019. Measurements sent back from the probe would characterize Apophis' course to an accuracy of mere yards (metres) by the year 2020.

If those readings still could not rule out a strike in 2036, NASA would try to deflect the asteroid into a non-threatening course in the 2024-2028 time frame by firing an impactor at it — using the deep impact comet-blasting probe of 2005 as a model. Experts would start planning for the "Son of Deep Impact" mission even before they knew whether or not it was needed.