Apophis (99942)

Apophis was discovered on June 19, 2004. Image credit: UH/IA

Orbit of Apophis around the Sun

Previously known as 2004 MN4, a member of the Aten group of near-Earth asteroids which had been estimated by NASA as having a 1 in 5500 chance of striking the Earth in 2036 (see update below). That estimate, however, depends on whether the asteroid passes through a 600-meter-wide region, known as a gravitational keyhole, during its close swing past Earth in 2029. If Apophis sneaks through the keyhole, its orbit could be perturbed, possibly putting it on a collision course with our planet seven years later. Until radar observations of the asteroid are taken in 2013, however, it will remain unclear where Apophis is headed. Currently, Apophis has a ranking of 1 on the Torino scale, down from an earlier value of 4 (the highest ever assigned). In October 2009, based on updated computational techniques and newly available data, NASA scientists announced a sharply reduced estimate of the chances of collision – about one in 250,000.

Apophis was discovered in 2004 and is thought to measure between 320–400 meters in diameter. An asteroid of this size could destroy a large city. It was given its permanent name in 2005. "Apophis" is the Greek name of the Ancient Egyptian god Apep (the Destroyer).

The B612 Foundation, a non-profit group studying ways to deflect Earth-bound asteroids, has urged NASA to consider mounting a mission to nudge the asteroid off course to avoid a potential catastrophe. In response, NASA has decided to carry out radar measurements in 2013 to determine if Apophis really is a threat; if it is, the plan is to send a spacecraft to the asteroid, for arrival in about 2019, to learn more about it. The spacecraft could drop a radio transponder onto the surface or leave it close to the asteroid. This would help scientists refine their prediction of the asteroid's orbit, and learn whether its future path would include a fatal rendezvous with Earth. If those radio coordinates were to indicate that Apophis poses a threat to Earth in 2036, NASA could launch a second spacecraft to deflect the asteroid between 2024 and 2028. The deflection would occur before the asteroid could pass through the gravitational keyhole in 2029, thus safely turning it from a potentially deadly course.

diameter	320-400 m
mass (est.)	50 million tons
eccentricity	0.191
semi-major axis	0.922 AU
perihelion	0.746 AU
aphelion	1.099 AU
orbital period	323.59 days
inclination	3.33°

• potentially hazardous asteroids

Related categories

• NOTABLE ASTEROIDS, CENTAURS, AND KUIPER BELT OBJECTS
• MEGACATASTROPHES

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Apophis (99942)

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