Home | Discovery and Naming | Physical Characteristics | Future Approaches
On the evening of June 19, 2004, three astronomers working at the Kitt Peak National Observatory in Arizona made a discovery that would soon capture global attention and forever change our understanding of near-Earth asteroid threats. Roy A. Tucker, David J. Tholen, and Fabrizio Bernardi identified what would become one of the most closely monitored objects in the solar system: asteroid 99942 Apophis, initially designated 2004 MN4.
The discovery was particularly remarkable for several technical reasons that highlighted the skill and dedication of the observing team. The asteroid was detected at a very low solar elongation of just 56 degrees, meaning it was positioned relatively close to the Sun in the sky from Earth's perspective. Observing at such low elongations is challenging because the sky is brighter and the observing window is limited to twilight hours before sunrise or after sunset. Additionally, the asteroid was discovered at a considerable distance of 1.1 astronomical units, or about 165 million kilometers from Earth, requiring careful attention to faint objects moving against the background of stars.
In the months following the initial discovery, astronomers worked diligently to track the newly identified object and refine their understanding of its orbit. This effort took on special urgency when precovery observations from March 15, 2004, were identified on December 27, 2004. These earlier images, captured before the official discovery but identified retrospectively, extended the observational arc and allowed for significantly improved orbital calculations. The identification of precovery images is a critical tool in asteroid astronomy, as each additional observation, particularly those separated by long time intervals, helps constrain the orbital parameters and reduce uncertainty in future position predictions.
Like all newly discovered asteroids, Apophis initially received a provisional designation based on the timing of its discovery. The designation 2004 MN4 follows the systematic naming convention established by the International Astronomical Union for minor planets. The number 2004 indicates the year of discovery, while the letters MN and the subscript number 4 encode the specific half-month period and sequence within that period when the object was first observed. This provisional designation served as the asteroid's official name in scientific papers and news reports during the initial months after discovery.
For an asteroid to receive a permanent number and become eligible for a proper name, its orbit must be sufficiently well determined that astronomers can reliably predict its position far into the future and relocate it during subsequent observing opportunities. This typically requires observations spanning multiple oppositions or several years. In the case of 2004 MN4, the combination of the original discovery observations, the identified precovery images from March 2004, radar astrometry conducted in January 2005, and continued optical tracking through early 2005 provided sufficient data to secure the orbit.
On June 24, 2005, the asteroid received its permanent number: 99942. This number placed it in the catalog of over 99,000 asteroids whose orbits had been sufficiently well determined to warrant permanent designation by that date. The five-digit number became the asteroid's permanent identifier, appearing in all subsequent scientific literature and databases. With this permanent number assigned, the discoverers earned the right to propose a name for their find, subject to approval by the International Astronomical Union's Committee on Small Body Nomenclature.
On July 19, 2005, less than a month after receiving its permanent number, the asteroid was officially named Apophis. The selection of this name reflected both scholarly knowledge of ancient mythology and, perhaps, contemporary popular culture. Apophis is the Greek rendering of Apep, one of the most significant malevolent deities in ancient Egyptian mythology. This choice proved particularly fitting given the asteroid's initial assessment as a potential impact threat and its role in raising public awareness about planetary defense.
In ancient Egyptian cosmology, Apep (or Apophis in Greek transliteration) occupied a uniquely terrifying position. He was depicted as an enormous serpent dwelling in the eternal darkness of the Duat, the Egyptian underworld. According to myth, Apep embodied chaos, dissolution, and darkness, standing in direct opposition to the forces of order, creation, and light represented by the sun god Ra. Each night, as Ra journeyed through the underworld in his solar barque, Apep would attempt to swallow the sun god and prevent the dawn from arriving. The god Set, associated with storms and the desert, was tasked with defending Ra against Apep's attacks, engaging in an eternal struggle that ensured the sun would rise each morning.
The symbolism inherent in this mythological reference was not lost on observers. Just as Apep threatened to end the cycle of day and night by destroying Ra, the asteroid Apophis represented a potential threat to Earth and the continuation of human civilization. The dramatic nature of the mythology aligned well with the unprecedented level of concern that the asteroid generated during late 2004 and early 2005, when impact probabilities for the 2029 approach temporarily reached as high as 2.7 percent.
The name also served a practical astronomical purpose related to the classification conventions for near-Earth asteroids. At the time of discovery and initial naming, Apophis was classified as an Aten-type asteroid, meaning its orbit has a semi-major axis less than one astronomical unit, smaller than Earth's orbit. The convention for naming Aten asteroids calls for using names from Egyptian mythology. However, orbital calculations showed that the close Earth encounter scheduled for April 13, 2029, would gravitationally perturb Apophis's orbit, transforming it from an Aten-type asteroid into an Apollo-type asteroid with a semi-major axis greater than one astronomical unit. Apollo asteroids are traditionally named after Greek deities.
By choosing Apophis, the Greek name for an Egyptian deity, the discoverers elegantly bridged both naming conventions. The name honored the Aten classification at the time of naming while acknowledging the future transformation to Apollo classification. This thoughtful choice demonstrated both creativity and deep understanding of asteroid taxonomy and orbital dynamics.
The selection of the name Apophis sparked considerable speculation and discussion about potential influences from popular culture. Two of the asteroid's three discoverers, David Tholen and Roy Tucker, were reportedly fans of the science fiction television series Stargate SG-1, which aired from 1997 to 2007. In this series, one of the principal antagonists was an alien character named Apophis, portrayed as a powerful and malevolent being who posed an existential threat to Earth throughout the first several seasons of the show.
The character Apophis in Stargate SG-1 was conceived as one of the Goa'uld, a race of parasitic aliens who had lived on Earth during ancient times and posed as gods to early human civilizations. According to the show's mythology, this alien Apophis had adopted the persona of the Egyptian deity Apep, establishing himself as a god-figure and building a power base that extended across multiple worlds. The character's storylines frequently involved plots to destroy or conquer Earth, making him one of the series' most persistent and dangerous villains.
Given the timing of the asteroid's discovery in 2004, during the later seasons of Stargate SG-1's run, and the reported fandom of the discoverers, many observers assumed that the asteroid was named after the television character. News reports and internet discussions frequently made this connection, suggesting that the name represented a playful reference to science fiction by astronomers who appreciated the show's treatment of space exploration and alien threats.
However, David Tholen has directly addressed these reports and clarified the naming decision. In official statements, he denied that the asteroid was named after the television character, instead confirming that the name derives from the authentic mythological source. Tholen acknowledged that both he and Tucker were familiar with the Stargate SG-1 character and that they appreciated the connection, describing it as "icing on the cake" that the name they had selected for legitimate mythological reasons also happened to appear in a television show they enjoyed. Nevertheless, he emphasized that the primary motivation was the classical mythological reference to the Egyptian deity, not the science fiction character.
This clarification highlights an important aspect of astronomical naming practices. While astronomers are certainly human and may enjoy incorporating subtle references or playful elements into their naming choices, the formal process of naming celestial objects through the International Astronomical Union requires meaningful, appropriate names that will stand the test of time. The Committee on Small Body Nomenclature evaluates proposed names to ensure they meet established criteria, including avoiding names that are primarily commercial, political, or frivolous in nature. By grounding the name Apophis in genuine ancient mythology, the discoverers ensured their choice would be taken seriously and approved by the committee.
An interesting linguistic detail emerged regarding how the asteroid's name should be pronounced. In classical Greek and traditional academic contexts, the name Apophis is typically accented on the first syllable, pronounced approximately as "AP-oh-fis." This pronunciation follows standard rules for classical Greek names where the penultimate syllable is short. Scholars of ancient languages and classical mythology would generally use this traditional pronunciation.
However, the asteroid Apophis has become more commonly pronounced with the accent on the second syllable, as "ah-POH-fis" or "ah-PAH-fis." This pronunciation pattern appears to have been influenced by the Stargate SG-1 television series, where the character's name was consistently pronounced with second-syllable stress. David Tholen himself, when discussing the asteroid in public presentations and interviews, uses the second-syllable pronunciation, effectively endorsing this as the accepted form for the astronomical object.
This divergence between traditional classical pronunciation and contemporary astronomical usage illustrates how scientific nomenclature can evolve through common usage, even when the origins lie in ancient languages. The astronomical community has generally accepted the second-syllable stress as standard when referring to the asteroid, creating a distinction between how one might pronounce the mythological figure versus the celestial object bearing his name.
In the early history of asteroid astronomy, during the 19th century, newly discovered asteroids were assigned special symbols, similar to the planetary symbols used for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The first asteroid, Ceres, received a symbol resembling a sickle. Pallas, Juno, Vesta, and several dozen subsequent asteroids each received unique symbols that appeared in astronomical tables and publications. However, as the number of known asteroids rapidly expanded into the hundreds and then thousands, this practice became impractical and was abandoned. Modern asteroids are identified solely by their numbers and names, without special symbols.
Despite this general abandonment of asteroid symbols, Denis Moskowitz, a software engineer and designer who had previously created most of the dwarf planet symbols used in Unicode, proposed a symbol for Apophis in 2008. Moskowitz had an interest in astronomical symbols and had worked on creating standardized symbols for Pluto, Eris, Makemake, Haumea, and other dwarf planets. His proposal for an Apophis symbol drew inspiration from ancient Egyptian artistic depictions of the deity Apep.
The proposed symbol features a serpentine form consistent with Apep's representation as a giant snake, combined with a star element. The inclusion of a star is similar to many 19th-century asteroid symbols, which frequently incorporated stars, crosses, or circles to indicate their nature as celestial bodies rather than mythological concepts. Moskowitz documented his symbol design in the book "One Hundred Year Star-Diary: 2008-2107," published in April 2008 by Platform Projects and Morning Star Publications.
While the Apophis symbol has achieved some recognition in certain astronomical and typographical circles, it has not been adopted for general astronomical use. Professional astronomers continue to refer to the object as "99942 Apophis" or simply "Apophis" in technical papers and databases, without employing any special symbol. The symbol remains primarily a curiosity and a link to the historical practices of early asteroid astronomy, representing an interesting intersection of ancient mythology, modern astronomical discovery, and graphical design.
The three astronomers who discovered Apophis each brought important expertise to the observational program that led to the detection. Roy A. Tucker had extensive experience in asteroid discovery and was known for his careful systematic searches for near-Earth objects. David J. Tholen, a professor at the University of Hawaii, specialized in the study of asteroids and comets, with particular interest in their physical properties and compositions. Fabrizio Bernardi contributed expertise in astrometry and orbit determination, essential skills for confirming discoveries and calculating accurate orbital elements.
Their collaborative work at Kitt Peak represented part of a broader effort by the astronomical community to identify and catalog potentially hazardous asteroids. The discovery of Apophis, while initially causing concern due to its potential impact threat, ultimately validated the importance of these systematic search programs. The ability to identify such objects decades before any potential close approach provides crucial time for detailed study, orbit refinement, and, if necessary, the development and implementation of mitigation strategies.
The discovery and naming of Apophis marked a watershed moment in public awareness of asteroid impact hazards. While astronomers had been tracking near-Earth asteroids for decades and the broader scientific community understood the risks posed by potential impacts, Apophis brought these concerns into mainstream public consciousness in an unprecedented way. The progression from initial discovery to the brief period of heightened impact probability to eventual elimination of near-term threats provided a real-world case study in how the asteroid detection and tracking system functions.
The name Apophis itself has become synonymous with the concept of asteroid threats, appearing in discussions of planetary defense, space policy, and scientific outreach. The evocative mythological reference helped make the asteroid memorable to the general public, while the scientific significance of its close approach in 2029 ensured continued professional interest. The discoverers' choice of name, whether influenced by ancient mythology, modern science fiction, or both, created a lasting connection between humanity's ancient fears of cosmic forces and our modern scientific efforts to understand and potentially mitigate real celestial threats.
As we approach the historic 2029 close encounter, when Apophis will pass within 31,600 kilometers of Earth's surface, the discovery made on that June evening in 2004 continues to shape scientific research, public engagement with astronomy, and our collective understanding of Earth's place in a dynamic and sometimes hazardous solar system. The name Apophis, carrying echoes of ancient mythology and contemporary culture, serves as a fitting designation for an object that bridges past fears and future opportunities for scientific discovery.