Earth, Moon, and Planets

, Volume 102, Issue 1–4, pp 425–434 | Cite as

Apophis: the Story Behind the Scenes



On December 20, 2004 the Minor Planet Center issued the Minor Planet Electronic Circular (MPEC) 2004-Y25 announcing the discovery of a new Near Earth Asteroid (NEA) with designation 2004 MN4. Only two days later, when the Christmas holidays were about to begin, it was already apparent that this asteroid, currently known as Apophis, would be notorious: our close-approach monitoring system, CLOMON2, was already showing a Virtual Impactor (VI) in 2029 reaching the level 2 in the Torino Scale, the first asteroid to reach that level since our monitoring system had been operational. However, this was just the beginning of what it was to come in the subsequent days. In this paper we will give an overview of the NEODyS-CLOMON2 system and provide the details on how Apophis’ collision scenario evolved, the way NEODyS’ team handled it and the crazy 2004’ Christmas holidays we had due to this unexpected guest.


Apophis Near Earth Asteroids Impact risk Impact probability Virtual asteroids Virtual impactors NEODyS 



This work has been partially supported by: (a) the Spanish Ministerio de Ciencia y Tecnología and the European funds FEDER through the grant AYA2007-64592 and (b) the Junta de Castilla y León through the grant VA060A07. The authors would like to acknowledge the other people who were most involved in the work on Apophis during the days from Dec 20 to 27, 2004: A. Milani, G.B. Valssecchi and G. Tommei, in Italy; S.R. Chesley, D. Tholen and F. Bernardi in U.S.A.; G. Garrad and R. McNaught in Australia, as well as all the amateur observers, who greatly contributed to gather observations of Apophis and the MPC staff, who issued so many MPECs during that week. Without their contributions, the work described in this paper would not have been possible. Finally, we thank the referees (Clark Chapman and Andrea Milani) for their constructive comments.


  1. R.P. Binzel, The torino impact hazard scale. Planet. Space Sci. 48, 297 (2000)CrossRefADSGoogle Scholar
  2. M. Carpino et al., Error statistics of asteroid optical astrometric observations. Icarus 166, 248 (2003)CrossRefADSGoogle Scholar
  3. S.R. Chesley, Potential impact detection for near-earth asteroids: the case of 99942 Apophis (2004 MN4). In: Asteroids, Cometes, Meteors—Proceedings IAU Symposium No. 229, ed. by D. Lazzaro, S. Ferraz-Mello, J. A. Fernández (Cambridge University Press, Cambridge New York Port Melbourne Madrid Cape Town 2006) pp. 215–228Google Scholar
  4. S.R. Chesley, A. Milani, NEODyS: an online information system for near-Earth objects. AAS/Division for Planetary Sciences Meeting Abstracts, vol. 31 (1999), pp. 28–34Google Scholar
  5. S.R. Chesley et al., Quantifying the risk posed by potential earth impacts. Icarus 159, 423 (2002)CrossRefADSGoogle Scholar
  6. A.C. Gilmore et al., 2004 MN4. Minor Planet Electr. Circ. Y25, 12 (2004)Google Scholar
  7. A.E. Gleason et al., 2004 MN4. Minor Planet Electr. Circ. Y70, 70 (2004)Google Scholar
  8. A. Milani et al., Nonlinear impact monitoring: line of variation searches for impactors. Icarus 173, 362 (2005a)CrossRefADSGoogle Scholar
  9. A. Milani et al., Multiple solutions for asteroid orbits: Computational procedure and applications, A&A 431, 729 (2005b)CrossRefADSGoogle Scholar

Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  1. 1.E.T.S. de Ingenieros IndustrialesUniversity of ValladolidPaseo del CauceSpain

Personalised recommendations