Hati (moon) — Saturn XLIII, a small retrograde irregular satellite

Physical characteristics

Because Hati is very small and faint, detailed physical information is limited. Observations indicate that it is likely an irregularly shaped, rocky or icy body with a dark surface typical of many outer satellites. Its small size implies low surface gravity and no atmosphere. Like other members of its class, Hati is probably a fragment of a larger body or a captured object from the outer Solar System.

Orbit and group

Hati orbits Saturn at an average distance of about 20,303,000 kilometres and completes one orbit in approximately 1080.1 days. Its orbit is markedly inclined and eccentric: the inclination is around 163° to the ecliptic (about 165° relative to Saturn's equator), and the eccentricity is near 0.291. These parameters place Hati within the Norse group, a collection of retrograde irregular satellites that share broadly similar orbits and are thought to be related by a common origin or capture process.

Discovery and name

The discovery of Hati was announced on 4 May 2005 by a team of astronomers after analysis of images taken between December 2004 and March 2005. The announcement credited observers including Scott S. Sheppard and David C. Jewitt, along with collaborators. Precise orbital elements were derived from follow-up observations that established its long, inclined retrograde path around Saturn. In April 2007 the moon received the name Hati, drawn from Norse mythology: Hati is a giant wolf, son of the monstrous Fenrir and twin brother of Sköll, a naming choice consistent with the mythological theme used for this group of Saturnian moons; see Norse myth sources for background.

Scientific context and significance

Small irregular moons such as Hati are important to planetary scientists because they provide clues about the history of the Saturn system and the wider outer Solar System. Their eccentric, inclined and often clustered orbits suggest histories involving gravitational capture, collisions and fragmentation. Studying the population, sizes and orbital configurations of these satellites helps constrain models of how giant planets acquired their retinues of small bodies and how collisional families form and evolve.

Notable facts and distinctions

• Designation: Saturn XLIII (S/2004 S 14) reflects the provisional naming convention for newly discovered satellites.
• Retrograde motion and high inclination mark Hati as an irregular satellite, contrasting with the closer, larger regular moons that have low-inclination, prograde orbits.
• Its orbital eccentricity is relatively large for satellites, a trait that contributes to the dynamical diversity of the Norse group; see orbit data references inclination notes and eccentricity details.

Because of its small size and faintness, Hati is observable only with substantial telescopes and careful image analysis. It remains one of many minor, but scientifically useful, members of Saturn's extended satellite system.