Expert BlogExpert Panel Q&A

Is there any new information on the Asteroid ”Apophis”? Could the trajectory of this 11 million ton chunk of iron & rock be miscalculated?



(submitted via the Asteroid Day Facebook page)

Is there any new information on the Asteroid ”Apophis”? Could the trajectory of this 11 million ton chunk of iron & rock be miscalculated?



Dear Adrian:

Asteroid 99942 Apophis, a 325 meter sized near-Earth asteroid, will safely pass within 32,000 kilometers of Earth’s surface on April 13, 2029.  That’s well within the ring of geosynchronous Earth communications satellites that will be announcing the asteroid’s arrival.  Fortunately, this asteroid has been extensively observed with optical and radar observations over a 10-year period from 2004 March 15 through Feb. 26, 2014 so that its orbit is very well determined and there is no chance of an Earth impact in 2029.  According to JPL’s SENTRY system (http://neo.jpl.nasa.gov/risk/), which keeps track of all known Earth collision possibilities, the most likely (or perhaps least unlikely) Earth impact for Apophis occurs on April 12, 2068 when the possibility of an Earth encounter is only 1 chance in about 250,000 and this is the highest impact possibility until at least 2105.
As more and more future observations are received for Apophis, its orbit will continue to improve, its orbital uncertainties will continue to shrink, and these improvement’s in the asteroid’s orbital path will almost certainly allow JPL’s Near-Earth Object Program Office team to completely rule out a collision in 2068.

(BTW, Don’s comment above re the continual improvement in our knowledge of the orbit of Apophis as we get additional tracking data applies to all the asteroids that are currently being tracked.  Early warning is a continual process, not something that stops after an asteroid is discovered and an initial orbit is determined.  Our knowledge is continually refined and our predictions of the future become more and more accurate through the thousands of asteroid observations made every night by both professional and amateur observers around the world. Rusty)

Don Yeomans


Thank You. I forgot to ask the question of why this Asteroid was named Apophis? 99942 and many more Asteroid discoveries are usually given the name of the person who discovered it! Apophis however is the God of destruction sent to destroy the Earth! Mythical yes but interestingly named. A 325 meter in diameter lump of rock and iron travelling at over 100.000 mph would certainly hit the description of doom. Thanks again, Your response is much appreciated.



Thanks… an interesting question.

Don Yeomans says “Asteroid discoverers have naming rights – subject to the approval of the IAU Committee on Small Body Nomenclature (CSBN).  Asteroids are not normally named after the discoverers.  They are most often named after a loved one of the discoverer, a colleague or an important individual.”

In this instance Apophis (then labeled 2004 MN4) was discovered by Dave Tholen from the Institute for Astronomy at the University of Hawaii (think of Dave as an “astronomer’s astronomer”!)  And Dave was well aware of the fact that 2004 MN4 would make a very close pass by Earth on 13 April 2029!  (see JPL’s news item)

BTW, asteroids, when first discovered, are assigned a designation which is the year of discovery followed by a letter/number combination based on when during the year it was discovered.  Once the asteroid is tracked for a significant time and its orbit very well established, it is given an official number and name.  Hence 2004 MN4 became 99942 Apophis.

Rusty Schweickart, Asteroid Day Expert

Tags : asteroid dayasteroid day expert paneldon yeomansrusty schweickart
Rusty Schweickart

The author Rusty Schweickart

Russell L. (Rusty) Schweickart is a retired business and government executive and from 2002-2015 served as Chairman of the Board and Chairman Emeritus of B612 Foundation. The organization, a non-profit private foundation, champions the development and testing of spaceflight concepts to protect the Earth from future asteroid impacts.