65489 Ceto

Physical characteristics

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 Telescope and the Hubble Space Telescope allow the diameter of Ceto itself to be estimated at and the diameter of Phorcys at , 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 , significantly less than that of the large TNOs (Haumea: , Eris: 2.26, Pluto: 2.03, Charon: 1.65) but significantly more than that of smaller TNOs (e.g. for ). Phorcys has a mass of about . 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.

Satellite

. primary/secondary ratio

Ceto's satellite 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 object was named Phorcys after the Greek sea god, formally (65489) Ceto I. Using an extended definition of a centaur as an object on a non-resonant (unstable) orbit with its perihelion inside the orbit of Neptune, |name-list-style=amp the Ceto system can be considered the second known binary centaur.

Phorcys's diameter has been estimated to be and .

References

References

1. Santos-Sanz, P., Lellouch, E., Fornasier, S., Kiss, C., Pal, A., Müller, T. G., Vilenius, E., Stansberry, J., Mommert, M., Delsanti, A., Mueller, M., Peixinho, N., Henry, F., Ortiz, J. L., Thirouin, A., Protopapa, S., Duffard, R., Szalai, N., Lim, T., Ejeta, C., Hartogh, P., Harris, A. W., & Rengel, M. (2012). [https://arxiv.org/abs/1202.1481 “TNOs are Cool”: A Survey of the Transneptunian Region IV - Size/albedo characterization of 15 scattered disk and detached objects observed with ''Herschel'' Space Observatory-PACS]
2. Origin of the Homeric Poems, in ''The Quarterly Review'', vol. LXXXVII, Jan. 1831, p. 164
3. Henry Tytler (1828) ''Punics of Caius Silius Italicus'', vol. 1, p. 48 [with the stress on the first syllable, consistent with the short 'y' in Greek and Latin]
4. The form ''Phorcian'' is also found, but derives from the assimilated Latin ''Phorcus / Phorci'' rather than ''Phorcys / Phorcyos''.[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0059%3Aentry%3DPhorcus]
5. [http://johnstonsarchive.net/astro/astmoons/am-65489.html Johnston's Archive]