( , previously known by its provisional designation
) is a near-Earth asteroid
caused a brief period of concern in December 2004 because initial
observations indicated a small probability (up to 2.7%) that it
would strike the Earth
in 2029. Additional
observations provided improved predictions that eliminated the
possibility of an impact on Earth
in 2029. However, a possibility
remains that during the 2029 close encounter with Earth, Apophis
would pass through a gravitational
, a precise region in space no more than about
600 meters across, that would set up a future impact on
April 13, 2036. This possibility kept the asteroid at
Level 1 on the Torino impact hazard
until August 2006. It broke the record for the highest
level on the Torino Scale, being, for only a short time, a
level 4, before it was lowered.
Additional observations of the trajectory of Apophis revealed the
keyhole would likely be missed and on August 5, 2006 Apophis was
lowered to a Level 0 on the Torino Scale. As of
October 7, 2009, the impact probability for April 13,
2036, is calculated as 1 in 250,000. An additional impact date in
2037 was also identified; the impact probability for that encounter
was calculated as 1 in 12.3 million.
agree that Apophis
warrants closer scrutiny and, to that end, in February 2008 the
in prize money to companies and students
submitted designs for space probes
would put a tracking device on or near the asteroid.
the observed brightness, Apophis' length was estimated at ; a more
refined estimate based on spectroscopic observations at NASA's Infrared
Telescope Facility in Hawaii by Binzel, Rivkin, Bus, and Tokunaga
(2005) is .
In October 2005 it was predicted that the asteroid will pass just
below the altitude of geosynchronous satellites
are at . Such a close approach by an asteroid of this size is
expected to occur only every 1,300 years or so. Apophis’s
brightness will peak at magnitude
3.3, with a maximum
angular speed of 42° per hour. The maximum apparent angular diameter
will be ~2 arcseconds
, so that it will be barely resolved
by telescopes not equipped with
When first discovered, the object received the provisional
designation (sometimes written 2004 MN4), and news and
scientific articles about it referred to it by that name. When its
orbit was sufficiently well calculated it received the permanent
number 99942 (on June 24, 2005). Receiving a permanent number
made it eligible for naming, and it received the name "Apophis" on
July 19, 2005. Apophis
is the Greek
name of the Ancient Egyptian
enemy of Ra
, the Uncreator, a serpent
that dwells in the eternal darkness of the Duat
(earth's middle) and tries to swallow Ra during His nightly
passage. Apep is held at bay by Set
the Ancient Egyptian god of Chaos.
Although the Greek name for the Egyptian
may be appropriate, Tholen
Tucker — two of the co-discoverers of the asteroid — are reportedly
fans of the TV series Stargate
. The show's most persistent villain is an alien
for the Egyptian
The white bar indicates uncertainty in
the range of positions
Minor Planet Center confirmed the June discovery of Apophis, an
April 13, 2029 close approach was flagged by NASA's automatic
Sentry system and
NEODyS, a similar automatic program run by
the University of Pisa and the
On that date, it will become as bright as
magnitude 3.3 (visible to the naked
from rural as well as darker suburban areas, visible with
from most locations). This
close approach will be visible from Europe
, and western Asia
As a result of its close passage, it will move from the Aten to the
After Sentry and NEODyS announced the possible impact, additional
observations decreased the uncertainty in Apophis' trajectory. As
they did, the probability of an impact event temporarily climbed,
peaking at 2.7% (1 in 37). Combined with its size, this caused
Apophis to be assessed at level 4 on the Torino Scale
and 1.10 on the Palermo scale
scientists use to represent the danger of an asteroid hitting
Earth. These are the highest values for which any object has been
rated on either scale.
On Friday, April 13, 2029, Apophis will pass Earth within the
orbits of geosynchronous communication satellites
. It will
return for another close Earth approach in 2036.
observations from March 15, 2004
were identified on December 27, and an improved orbit was
refined the orbit. The 2029 pass will actually be much closer than
the first predictions, but the uncertainty is such that an impact
is ruled out. Similarly, the pass on April 13, 2036 carries
little risk of an impact.
The close approach in 2029 will substantially alter the object's
orbit, making predictions uncertain without more data. "If we get
radar ranging in 2013 [the next good opportunity], we should be
able to predict the location of out to at least 2070." said Jon
Giorgini of JPL. Apophis will pass within 0.09666 AU
(14.4 million km) of the
Earth in 2013 allowing astronomers to refine the trajectory for
future close passes.
In July 2005, former Apollo
, as chairman of
the B612 Foundation
, formally asked
NASA to investigate the possibility that the asteroid's post-2029
orbit could be in orbital
with Earth, which would increase the probability of
future impacts. Schweickart asked for an investigation of the
necessity of placing a transponder on the asteroid for more
accurate tracking of how its orbit is affected by the Yarkovsky effect
History of impact estimates
Illustration of a common trend where
progressively reduced uncertainty regions result in an asteroid
impact probability increasing followed by a sharp decrease.
- The original NASA report on December 23, 2004, mentioned impact
chances of "around 1 in 300", which was widely reported in the
media. The actual NASA estimates at the time were 1 in 233; they
resulted in the Torino scale rating of 2, the first time any
asteroid had received a rating above 1.
- Later that day, based on a total of 64 observations, the
estimates were changed to 1 in 62 (1.6%), resulting in an update to
the initial report and an upgrade to a Torino scale rating of
- On December 25, the chances were first reported as 1 in 42
(2.4%) and later that day (based on 101 observations) as 1 in 45
(2.2%). At the same time, the asteroid's estimated diameter was
lowered from 440 m to 390 m and its mass from 1.2×1011
kg to 8.3×1010 kg.
- On December 26 (based on a total of 169 observations), the
impact probability was still estimated as 1 in 45 (2.2%), the
estimates for diameter and mass were lowered to 380 m and
7.5×1010 kg, respectively.
- On December 27 (based on a total of 176 observations), the
impact probability was raised to 1 in 37 (2.7%); diameter was
increased to 390 m, and mass to 7.9×1010 kg.
- On December 27 in the afternoon, a precovery increased the span
of observations to 287 days and allowed more accurate calculations
to re-rate the asteroid's 2029 approach as level zero on the Torino
scale (no threat). The cumulative impact probability was estimated
to be around 0.004%, a lower risk than asteroid , which once again
became the greatest risk object. A 2053 approach to Earth still
poses a minor risk of impact, and Apophis was still rated at level
one on the Torino scale for this orbit.
- On December 28 at 12:23 GMT and (based on a total of 139
observations), produced a value of one on the Torino scale for
2044-04-13.29 and 2053-04-13.51.
- By 01:10 GMT on December 29 the only pass rated 1 on the Torino
scale was for 2053-04-13.51 based on 139 observations spanning
287.71 days (2004-Mar-15.1104 to 2004-Dec-27.8243).
- By 19:18 GMT on December 29 this was still the case based upon
147 observations spanning 288.92 days (2004-Mar-15.1104 to
2004-Dec-29.02821), though the close encounters have changed and
been reduced to 4 in total.
- By 13:46 GMT on December 30 no passes were rated above 0, based
upon 157 observations spanning 289.33 days
(2004-Mar-15.1104 to 2004-Dec-29.44434). The most dangerous pass
was rated at 1 in 7,143,000.
- By 22:34 GMT on December 30, 157 observations spanning 289.33
days (2004-Mar-15.1104 to 2004-Dec-29.44434). One pass at 1 (Torino
scale) 3 other passes.
- By 03:57 GMT on January 2, 2005, 182 observations spanning
290.97 days (2004-Mar-15.1104 to 2004-Dec-31.07992) One pass at 1
(Torino scale) 19 other passes.
- By 14:49 GMT on January 3, 2005 observations spanning 292.72
days (2004-Mar-15.1104 to 2005-Jan-01.82787) One pass at 1 (Torino
scale) 15 other passes.
- Extremely precise radar
observations at Arecibo Observatory on January 27, 28, and 30 refine the orbit
further and show that the April, 2029 close approach will occur at
only 5.6 Earth radii, approximately one-half the distance
- A radar observation on August 7, 2005, refines the orbit
further and eliminates the possibility of an impact in 2035. Only
the pass in 2036 remains at Torino Scale 1.
- A new radar observation at Arecibo Observatory on May 6, 2006
slightly lowered the Palermo scale rating, but the pass in 2036
remained at Torino Scale 1 despite the impact probability
dropping by a factor of four.
- Additional observations through 2006 resulted in Apophis being
lowered to Torino Scale 0 on August 6, 2006. Around this
time, the impact probability was lowered to 1 in 45,000.
- As of
October 7, 2009, refinements to the precovery images of Apophis by the University of
Hawaii's Institute for
Astronomy, the 90-inch Bok
Telescope, and the Arecibo Observatory have generated a refined path that reduces the odds
of a April 13, 2036 impact to about 1 in 250,000.
Possible impact effects
NASA initially estimated the energy that Apophis would have
released if it struck Earth as the equivalent of
. A later, more refined NASA estimate was
880 megatons. The impacts which created the Barringer
Crater or the Tunguska event are estimated to be in the 3–10 megaton range
The 1883 eruption of Krakatoa was the
equivalent of roughly 200 megatons.
Path of risk where 99942 Apophis may
impact Earth in 2036.
The exact effects of any impact would vary based on the asteroid's
composition, and the location and angle of impact. Any impact would
be extremely detrimental to an area of thousands of square
kilometres, but would be unlikely to have long-lasting global
effects, such as the initiation of an impact winter
The B612 Foundation
of Apophis' path if a 2036 Earth impact were to occur as part of an
effort to develop viable deflection strategies
is a narrow corridor a few miles wide, called the path of risk, and
it includes most of southern Russia, across the
north Pacific (relatively
close to the coastlines of California and Mexico), then right
between Nicaragua and Costa
Rica, crossing northern Colombia and Venezuela, ending in the Atlantic, just before reaching Africa.
Using the computer simulation tool
NEOSim, it was estimated that the hypothetical impact of Apophis in
countries such as Colombia and Venezuela, which are in the path of
risk, would have had more than 10 million casualties. An impact
several thousand miles off the West Coast of the US would produce a
- Nico Marquardt, a 13-year-old from Germany, was reported to
have produced a collision estimate of 1 in 450 (100 times
NASA's calculation) in April 2008, by factoring in the possibility
of Apophis running into one or more of the geosynchronous
satellites orbiting Earth during its flyby on April 13, 2029.
estimate was allegedly then confirmed by ESA and NASA but
in an official statement, NASA denied having contact with
Marquardt. The release went on to explain that the angle of
Apophis' approach to the Earth's equator means the asteroid will
not travel through the belt of existing equatorial geosynchronous satellites and the
extremely small size of satellites relative to the size of their
orbits means that there is currently no risk of collision; and the
effect on Apophis' trajectory of any such impact would be
Potential space missions
Planetary Society competition
The Planetary Society, a California-based space advocacy group, organized a $50,000
competition to design an unmanned space probe that would 'shadow'
Apophis for almost a year, taking measurements that would
"determine whether it will impact Earth, thus helping governments
decide whether to mount a deflection mission to alter its
The society received 37 entries from
20 countries on 6 continents.
The commercial competition was won by a design called 'Foresight
' created by SpaceWorks Engineering
proposes a simple orbiter with only two instruments and a radio
beacon at a cost of ~140 million USD, launched aboard a
between 2012 and 2014,
to arrive at Apophis five to ten months later. It would then
rendezvous with, observe, and track the asteroid.Foresight would
orbit the asteroid to gather data with a multi-spectral imager for
one month. It would then leave orbit and fly in formation with
Apophis around the Sun at a range of two kilometers
(1.2 miles). The spacecraft would use laser ranging to the
asteroid and radio tracking from Earth for ten months to accurately
determine the asteroid's orbit and how it might change.
Pharos, the winning student entry, would be an orbiter with four
science instruments (a multi-spectral imager, near-infrared
spectrometer, laser rangefinder, and magnetometer) that would
rendezvous with and track Apophis. Earth-based tracking of the
spacecraft would then allow precise tracking of the asteroid. The
Pharos spacecraft would also carry four instrumented probes that it
would launch individually over the course of two weeks.
Accelerometers and temperature sensors on the probes would measure
the seismic effects of successive probe impacts, a creative way to
explore the interior structure and dynamics of the asteroid.
place, for $10,000, went to a European team led by Deimos Space S.L. of Madrid, Spain, in
cooperation with EADS Astrium,
Friedrichshafen, Germany; University of Stuttgart, Germany; and Università di Pisa, Italy.
Juan L. Cano was Principal Investigator.
Another European team took home $5,000 for third place.
team lead was EADS Astrium Ltd,
United Kingdom, in conjunction with EADS Astrium SAS, France; IASF-Roma, INAF, Rome, Italy; Open
Institut für Umweltforschung, Germany; Royal
Observatory of Belgium; and Telespazio,
The Principal Investigator was Paolo D'Arrigo.
tied for second place in the Student Category: Monash University, Clayton Campus,
Australia, with Dilani Kahawala as Principal Investigator; and
of Michigan, with Jeremy Hollander as Principal
Each second place team won $2,000.
from Hong Kong Polytechnic
University and Hong Kong University of Science and
Technology, under the leadership of Peter Weiss, received an
honorable mention and $1,000 for the most innovative student
Orion Asteroid Mission
NASA's Project Constellation
is researching a manned Orion
, with 99942 Apophis being one of the potential
destinations of the mission. The mission would use the Orion spacecraft
to land astronauts on the
surface of the asteroid. Such a mission would provide valuable
testing for a later manned Orion Mars Mission.
Proposed deflection strategies
Scenarios for Dealing with Apophis, a paper presented by Donald B.
at the 2007 Planetary Defense Conference held in Washington,
DC, outlines a number of proposals for deflecting
Apophis including gravitational
impact, and nuclear bomb
Don Quijote mission
is one of two asteroids under consideration by the European
Space Agency as the target of its Don Quijote mission to study the
effects of impacting an asteroid.
Apophis in Pop Culture
- In 2005 the Goth Metal band Type O
Negative released their album "Dead Again", Featuring a song
entitled the "Profit of Doom", in which a reference to Apophis is
- In 2009 the Rock band Enter
Shikari released their album "Common Dreads", featuring a song
entitled "Zzzonked", in which a reference to Apophis is made.
- (naming the asteroid and how Earth's gravity may change its
trajectory in 2029)
- The astronomical magnitude scale.
Center for Astrophysics
- MPEC 2004-Y70 : 2004 MN4 Minor Planet Electronic
Circular, issued 2004-12-27
- Friday the 13th, 2029 (Science@NASA
- Range of Possible Impact Points on April 13, 2036
in Scenarios for Dealing with Apophis, by Donald B.
- Scenarios for Dealing with Apophis, author Donald
B. Gennery, presented at the Planetary Defense Conference.
Washington, DC. March 5-8, 2007
- AFP: German schoolboy, 13, corrects NASA's asteroid
- Ich hab den Weltuntergang ausgerechnet! –
Berlin - Bild.de
These sources are updated as new orbital data becomes available:
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