65489 Ceto
Encyclopedia
65489 Ceto provisionally known as 2003 FX128, is a binary
trans-Neptunian object
(TNO) discovered on March 22, 2003 by C. A. Trujillo and M. Brown
at Palomar
. It is named after the sea goddess Ceto
from Greek mythology. The object was identified as a binary
on April 11, 2006 by K. Noll, H. Levison, W. Grundy and D. Stephens using the Hubble Space Telescope; the companion object is named Phorcys (ˈ, formally (65849) Ceto I Phorcys), after the Greek sea god
. The Ceto system is considered the second known binary centaur, using an extended definition of a centaur as an object on an non-resonant (unstable) orbit with the perihelion inside the orbit of Neptune. It came to perihelion
in 1989.
and the Hubble Telescope allow the diameter of Ceto itself to be estimated at 174 km and the diameter of Phorcys at 132 km, assuming equal albedo
for both components.
The binary nature of Ceto enables direct calculation of the system mass, allowing estimation of the masses of the components and providing additional constraints on their composition. The estimated density
of Ceto is 1.37 g/cm3, significantly less than that of the large TNOs (Haumea: 3.0 g/cm3, Eris
: 2.26, Pluto
: 2.03, Charon
: 1.65) but significantly more than that of smaller TNOs (e.g. 0.7 g/cm3 for ). Phorcys has a mass of about 1.67×1018 kg. Unless the bodies are porous
, the density is consistent with rock–ice composition, with rock content around 50%.
It has been suggested that tidal forces, together with other potential heat sources (e.g. collisions or 26Al
decay
) might have raised the temperature sufficiently to crystallise amorphous
ice and reduce the void space inside the object.
The same tidal forces could be responsible for the quasi-circular orbits of the components of Ceto.
Binary asteroid
A binary asteroid is a system of two asteroids orbiting their common center of mass, in analogy with binary stars. 243 Ida was the first binary asteroid to be identified when the Galileo spacecraft did a flyby in 1993...
trans-Neptunian object
Trans-Neptunian object
A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater distance on average than Neptune.The first trans-Neptunian object to be discovered was Pluto in 1930...
(TNO) discovered on March 22, 2003 by C. A. Trujillo and M. Brown
Michael E. Brown
Michael E. Brown has been a professor of planetary astronomy at the California Institute of Technology since 2003....
at Palomar
Palomar Observatory
Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...
. It is named after the sea goddess Ceto
Ceto
In ancient Greek, the word ketos - Latinized as cetus - denotes a large fish, a whale, a shark, or a sea monster. The sea monsters slain by Perseus and Heracles were each referred to as a cetus by ancient sources. The term cetacean originates from cetus. In Greek art, cetea were depicted as...
from Greek mythology. The object was identified as a binary
Binary asteroid
A binary asteroid is a system of two asteroids orbiting their common center of mass, in analogy with binary stars. 243 Ida was the first binary asteroid to be identified when the Galileo spacecraft did a flyby in 1993...
on April 11, 2006 by K. Noll, H. Levison, W. Grundy and D. Stephens using the Hubble Space Telescope; the companion object is named Phorcys (ˈ, formally (65849) Ceto I Phorcys), after the Greek sea god
Phorcys
In Greek mythology, Phorcys , a primordial sea god, generally cited as the son of Pontus and Gaia. According to the Orphic hymns, Phorcys, Cronus and Rhea were the eldest offspring of Oceanus and Tethys. Classical scholar Karl Kerenyi conflated Phorcys with the similar sea gods Nereus and Proteus...
. The Ceto system is considered the second known binary centaur, using an extended definition of a centaur as an object on an non-resonant (unstable) orbit with the perihelion inside the orbit of Neptune. It came to perihelion
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
in 1989.
Physical characteristics
65489 Ceto is an example of a close binary TNO system in which the components are of similar size. Combined observations with the infrared Spitzer Space TelescopeSpitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
and the Hubble Telescope allow the diameter of Ceto itself to be estimated at 174 km and the diameter of Phorcys at 132 km, assuming equal albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
for both components.
The binary nature of Ceto enables direct calculation of the system mass, allowing estimation of the masses of the components and providing additional constraints on their composition. The estimated density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of Ceto is 1.37 g/cm3, significantly less than that of the large TNOs (Haumea: 3.0 g/cm3, Eris
Eris (dwarf planet)
Eris, formal designation 136199 Eris, is the most massive known dwarf planet in the Solar System and the ninth most massive body known to orbit the Sun directly...
: 2.26, Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
: 2.03, Charon
Charon (moon)
Charon is the largest satellite of the dwarf planet Pluto. It was discovered in 1978 at the United States Naval Observatory Flagstaff Station. Following the 2005 discovery of two other natural satellites of Pluto , Charon may also be referred to as Pluto I...
: 1.65) but significantly more than that of smaller TNOs (e.g. 0.7 g/cm3 for ). Phorcys has a mass of about 1.67×1018 kg. Unless the bodies are porous
Porosity
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
, the density is consistent with rock–ice composition, with rock content around 50%.
It has been suggested that tidal forces, together with other potential heat sources (e.g. collisions or 26Al
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
) might have raised the temperature sufficiently to crystallise amorphous
Amorphous solid
In condensed matter physics, an amorphous or non-crystalline solid is a solid that lacks the long-range order characteristic of a crystal....
ice and reduce the void space inside the object.
The same tidal forces could be responsible for the quasi-circular orbits of the components of Ceto.
External links
- Orbital simulation from JPL (Java) Horizons Ephemeris
- Binary asteroids at johnstonsarchive