A gravitational keyhole, also known as resonance keyhole, is a small section in a planet’s gravitational region where gravity would alter the orbit of a passing asteroid, causing that asteroid to change its path on a future orbital approach. The keyhole refers to the exact distance, from the planet, an asteroid needs to pass in order to collide with the planet on a future fly-by. If the asteroid follows a path that doesn’t match the keyhole, the asteroid will most likely not collide with that planet in the future. Scientists calculate that if Apophis goes through the section of space known as the gravitational keyhole, it will collide with the Earth on a future orbital pass.
As an asteroid passes near a planet, it is pulled and deflected from its original trajectory by the planet’s gravitational pull. The amount its trajectory is deflected depends on the distance the asteroid approaches the planet. The closer the asteroid passes to the planet, the larger its trajectory is deflected. The distance that Apophis has to pass from Earth in order to be deviated enough for a future collision is 18,893 miles (keyhole). If the asteroid passes above or below the keyhole distance, it will not enter the planet’s orbit, so as to impact it.
Upon its discovery in 2004, Apophis was estimated at a 2.7% (1 in 37) chance of impacting the Earth in 2009; however, additional observations have ruled out an impact in 2029. Scientists estimate that if Apophis passes at a distance of exactly 18,893 miles from Earth, it will enter a gravitational keyhole. This small region in space, which is approximately ½ mile wide, would alter Apophis’orbit to about seven sixths that of earth’s. This will place Apophis into a path that will cause it to impact Earth seven years later, on April 13, 2936.
Apophis’gravitational keyhole is about 660 meters (2,170 ft.) across. Estimations demonstrated that if Apophis’speed could be altered by just 0.00016 km/h, its orbit could be deflected by up to a mile, which is sufficient to miss the keyhole. Calculations made in 2006 resulted in a margin of error of approximately 3,200 km (2,000 miles). Scientists believe that the margin of error will be reduce as time passes; however, scientists may have to gather more data in order to reduce the margin of error to about one 1.6 km (1 mile) before an exact estimate of a possible future impact between Apophis and the Earth can be made.
In recent years, there has been public awareness of the catastrophic consequences of near Earth objects (NEO) with Earth. 5431 NEOs have been discovered, as of March 2008. Nine hundred and twenty eight have been classified as potentially hazardous. A case study for gathering scientific data for a possible mitigation mission has been designed. The study gets into meticulous design for a meeting mission for a two-stage spacecraft with Apophis. The analysis of this study focuses on asteroid Apophis, which is predicted to pass near the gravitational keyhole around April 13, 2029.