3200 Phaethon (previously sometimes spelled Phaeton),

provisional designation Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calcu ...

, is an

active Active may refer to: Music * ''Active'' (album), a 1992 album by Casiopea * Active Records, a record label Ships * ''Active'' (ship), several commercial ships by that name * HMS ''Active'', the name of various ships of the British Royal ...

Apollo asteroid The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth-crossing asteroids that have an orbital semi-major axis greater than that of the Earth ...

with an orbit that brings it closer to the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

than any other named asteroid (though there are numerous unnamed asteroids with smaller perihelia, such as ). For this reason, it was named after the

Greek myth A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities of ...

of Phaëthon, son of the sun god

Helios In ancient Greek religion and Greek mythology, mythology, Helios (; grc, , , Sun; Homeric Greek: ) is the deity, god and personification of the Sun (Solar deity). His name is also Latinized as Helius, and he is often given the epithets Hyper ...

. It is in

diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...

and is the

parent body In meteoritics, a parent body is the celestial body from which originates a meteorite or a class of meteorites. Identification The easiest way to correlate a meteorite with a parent body is when the parent body still exists. This is the case fo ...

of the

Geminids The Geminids are a prolific meteor shower caused by the object 3200 Phaethon, which is thought to be a Palladian asteroid with a " rock comet" orbit. This would make the Geminids, together with the Quadrantids, the only major meteor showers ...

meteor shower A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extre ...

of mid-December. With an

observation arc In observational astronomy, the observation arc (or arc length) of a Solar System body is the time period between its earliest and latest observations, used for tracing the body's path. It is usually given in days or years. The term is mostly use ...

of 35+ years, it has a very well determined orbit. The 2017 Earth approach distance of about 10 million km was known with an accuracy of ±700 m.

Discovery

Phaethon was the first asteroid to be discovered using images from a spacecraft. Simon F. Green and John K. Davies discovered it in images from October 11, 1983, while searching

Infrared Astronomical Satellite The Infrared Astronomical Satellite (Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten mont ...

(IRAS) data for moving objects. It was formally announced on October 14 in IAUC 3878 along with optical confirmation by Charles T. Kowal, who reported it to be asteroidal in appearance. Its provisional designation was , and it later received the numerical designation and name in 1985.

Orbital characteristics

Phaethon is categorized as an

, as its orbital

semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...

is greater than that of the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

's at . It is also suspected to be a member of the

Pallas family The Pallas family (''adj. Palladian''; ) is a small asteroid family of B-type asteroids at very high inclinations in the intermediate asteroid belt. The namesake of the family is 2 Pallas, an extremely large asteroid with a mean diameter of about 5 ...

of asteroids. Its most remarkable distinction is that it approaches the Sun closer than any other named asteroid: its

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...

is only — less than half of

Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

's perihelial distance. It is a Mercury-, Venus-, Earth-, and

Mars-crosser A Mars-crossing asteroid (MCA, also Mars-crosser, MC) is an asteroid whose orbit crosses that of Mars. Some Mars-crossers numbered below 100000 are listed here. They include the two numbered Mars trojans 5261 Eureka and . Many databases, for i ...

as a result of its high orbital eccentricity. The surface temperature at perihelion could reach around . Phaethon is a possible candidate for detecting general relativistic and/or solar oblateness effects in its orbital motion due to the frequent close approaches to the Sun. The Apollo asteroids (155140) 2005 UD and (225416) 1999 YC share similar orbits with Phaethon, suggesting a possible common breakup origin.

Potentially hazardous asteroid

Phaethon is categorized as a

potentially hazardous asteroid A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and is large enough to cause significant regional damage in the event of impact. They are ...

(PHA), but that does not mean there is a near-term threat of an impact. It is a potentially hazardous asteroid merely as a result of its size (

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...

) and Earth

minimum orbit intersection distance Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. It is defined as the distance between the closest points of the osculating orbits of ...

). The Earth minimum orbit intersection distance (E-MOID) is , which is defined by the shortest distance between the orbit of Phaethon and the orbit of Earth. With a 30+ year observation arc, the orbit of Phaethon is very well understood with very small uncertainties. Close approaches of Phaethon are well constrained for the next 400 years.

Physical characteristics

Phaethon is an asteroid with fairly unusual characteristics in that its orbit more closely resembles that of a

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...

than an asteroid; it has been referred to as a "rock comet". In studies performed by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

STEREO Stereophonic sound, or more commonly stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configuration ...

spacecraft in 2009 and 2012, rapid brightening and dust tail have been observed. It is possible that the Sun's heat is causing fractures similar to

mudcrack Mudcracks (also known as mud cracks, desiccation cracks or cracked mud) are sedimentary structures formed as muddy sediment dries and contracts.Jackson, J.A., 1997, ''Glossary of Geology'' (4th ed.), American Geological Institute, Alexandria, VA, ...

s in a

dry lake A dry lake bed, also known as a playa, is a basin or depression that formerly contained a standing surface water body, which disappears when evaporation processes exceeds recharge. If the floor of a dry lake is covered by deposits of alkaline c ...

bed. This occurs because Phaethon's orbit takes it closer to the Sun than any other named asteroid (0.14 AU at

) causing extreme heating and enough

solar radiation pressure Radiation pressure is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of any wavelength that is a ...

to push any separated pieces off the asteroid's surface. Since its discovery, several other objects were found exhibiting mixed cometary and asteroidal features, such as 133P/Elst–Pizarro, leading to a new class of objects dubbed "

active asteroid Active asteroids are small Solar System bodies that have asteroid-like orbits but show comet-like visual characteristics. That is, they show comae, tails, or other visual evidence of mass-loss (like a comet), but their orbit remains within Jup ...

s". In 2018, observations revealed that Phaethon was blue in color. This is extremely rare, as most asteroids tend to be grey or red. In 2020,

polarimetric Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves. Typically polarimetry is done on electromagnetic waves that have traveled through or ...

study revealed Phaethon has a surface with steep slopes covered by a mix of

regolith Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestria ...

with larger pebbles. Phaethon's composition fits the notion of its cometary origin; it is classified as a

F-type asteroid F-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group. Characteristics F-type asteroids have spectra generally similar to those of the B-type asteroids, but lack the "water" absorption feature ar ...

because it is composed of dark material or a B-type asteroid because of its blue color. In 2022 it was shown How the bluest asteroid in the solar system got its color
Tereza Pultarova, Space.com. June 16th, 2022 how Phaethon's blue color and its rock-comet-like emission activity can be explained by the effects of the intense solar heating at perihelion causing sublimation of any darkish-red refractory organic, nano-phase iron (nFe0), and pyroxene materials on its surface.

Meteor shower

Shortly after its discovery,

Fred Whipple Fred Lawrence Whipple (November 5, 1906 – August 30, 2004) was an American astronomer, who worked at the Harvard College Observatory for more than 70 years. Amongst his achievements were asteroid and comet discoveries, the " dirty snowball" h ...

observed that the "orbital elements of 1983 TB shown on IAUC 3879 are virtually coincident with the mean orbital elements of 19 Geminid meteors photographed with the super-Schmidt meteor cameras". In other words, Phaethon is the long-sought parent body of the

of mid-December.

Planned flyby

DESTINY⁺ (Demonstration and Experiment of Space Technology for INterplanetary voYage Phaethon fLyby dUSt science) is a planned mission to fly by 3200 Phaethon, as well as various minor bodies originating from it. The spacecraft is being developed by the Japanese space agency

JAXA The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into orb ...

, and will demonstrate advanced technologies for future deep space exploration. DESTINY⁺ is planned to be launched no earlier than 2024.

Close approaches

Phaethon approached to of Earth on December 10, 2007, and was detected by

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

Arecibo Arecibo (; ) is a city and municipality on the northern coast of Puerto Rico, on the shores of the Atlantic Ocean, located north of Utuado and Ciales; east of Hatillo; and west of Barceloneta and Florida. It is about west of San Juan, the ...

. When Phaethon came to perihelion in July 2009, it was found to be brighter than expected. During its approach, the

-A spacecraft detected an unexpected brightening, roughly by a factor of two.

2010 approach

2017 approach

On December 16, 2017, at 23:00 UT, Phaethon passed from Earth (27 lunar distances). The Earth approach distance was known with a 3-sigma precision of ±700 m. This was the best opportunity to date for radar observations by Goldstone and

, with a resolution of . The asteroid was bright enough to see in small telescopes, peaking at magnitude 10.8 between December 13–15 while dimming slightly to magnitude 11 on December 16 at closest approach. Arecibo made observations of Phaethon from December 15–19. It will not make an Earth approach closer than the 2017 passage until December 14, 2093, when it will pass from Earth.

Notes

References

IAU The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...

Minor Planet Center * * * {{DEFAULTSORT:Phaethon 003200 003200 003200 Named minor planets 003200 003200 003200 Mercury-crossing asteroids Venus-crosser asteroids Earth-crosser asteroids 003200 003200 003200 003200 003200 003200 19831011