Encyclopedia of Astrobiology

Living Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James Cleaves, Daniele Pinti, José Cernicharo Quintanilla, Michel Viso

Apophis Asteroid

  • Gerhard Hahn
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_5207-1



(99942) Apophis is an Aten-type asteroid, which will make a very close approach to our planet on April 13, 2029, passing within less than 40,000 km, close to the ring of geostationary satellites. Its size is about 375 m and its rotation period 30.6 h. This close approach will change the orbit substantially, from Aten type to Apollo.


Apophis was discovered on June 19, 2004 by R. A. Tucker, D. J. Tholen, and F. Bernardi at Kitt Peak. It was temporarily lost and rediscovered in December 2004. Shortly thereafter, the close approach in 2029 was realized; even a collision at that time was possible. This has been ruled out based on extensive observations, including radar; the orbital evolution after 2029 is still uncertain allowing an impact probability of 5.7 × 10−6 (see impact monitoring sites at JPL and the University of Pisa).

See Also


Bioorganic Chemistry Rotation Period Monitoring Site Close Approach Geostationary Satellite 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

References and Further Readings

  1. Farnochia D, Chesley SR, Chodas PW, Micheli M, Tholen DJ, Milani A, Elliott GT, Bernardi F (2014) Yarkovsky-driven impact risk analysis for asteroid (99942) Apophis. Icarus 224:192–200CrossRefADSGoogle Scholar
  2. JPL NEO Program Site Risk Page. http://neo.jpl.nasa.gov/risk/. Last accessed 5 May 2014
  3. NEODyS Risk Page. http://newton.dm.unipi.it/neodys/index.php?pc=4.0. Last accessed 5 May 2014
  4. Sansaturio ME, Arratia O (2008) Apophis, the story behind the scenes. Earth Moon Planet 102:425–434ADSGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Asteroids and CometsDLR, Institute of Planetary ResearchBerlinGermany