Saturn's Moon Helene

Helene
Saturn XII - 1980S6

Helene was discovered by P. Laques and J. Lecacheus in 1980 through ground based observations. Helene is called a Dione Trojan satellite because it shares the same orbit as Dione at about 60 degrees ahead of its larger companion. Its diameter is about 36 x 32 x 30 kilometers (22 x 20 x 19 miles).

Helene Statistics
Discovered by	P. Laques & J. Lecacheus
Date of discovery	1980
Mass (kg)	?
Radius (km)	18x16x15
Radius (Earth = 1)	2.8222e-03
Mean density (gm/cm^3)	?
Mean distance from Saturn (km)	377,400
Rotational period (days)	?
Orbital period (days)	2.7369
Mean orbital velocity (km/sec)	10.03
Orbital eccentricity	0.005
Orbital inclination (degrees)	0.2
Visual geometric albedo	0.7
Magnitude (Vo)	18.5

Views of Helene

Helene of Troy
The Cassini spacecraft reveals details on the surface of small, irregularly shaped Helene in this close-up view, obtained during the spacecraft's closest encounter with this moon during its four-year primary mission.

Helene (32 kilometers, or 20 miles across) is a Trojan moon, sharing Dione's orbit but staying 60 degrees or 400,000 kilometers (250,000 miles) ahead of the much larger moon.

The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on July 20, 2007. The view was acquired at a distance of approximately 39,000 kilometers (24,000 miles) from Helene and at a Sun-Helene-spacecraft, or phase, angle of 61 degrees. Image scale is 231 meters (758 feet) per pixel. (Courtesy NASA/JPL/Space Science Institute)

Helene
Cassini came close to Saturn's small moon Helene on Feb. 25, 2006, acquiring this high-resolution view. This object seems to be buried in its own crater debris, like another Saturnian moon, Telesto.

Helene (32 kilometers, or 20 miles across) orbits 60 degrees ahead of Dione in the larger moon's orbit, making it a "trojan" moon of Dione. Trojan moons are named for the Trojan group of asteroids that orbit 60 degrees ahead of and behind Jupiter as it circles the sun.

This image was taken in visible light with the Cassini spacecraft narrow-angle camera at a distance of approximately 68,000 kilometers (42,000 miles) from Helene and at a sun-Helene-spacecraft, or phase, angle of 99 degrees. Image scale is 406 meters (1,334 feet) per pixel. (Courtesy NASA/JPL/Space Science Institute)

Helene's Close-up
This set of images exposes details on small and crumpled-looking Helene. Large portions of this Trojan moon of Dione appear to have been blasted away by impacts.

Cassini passed within 50,000 kilometers (31,000 miles) of Helene (32 kilometers, or 20 miles across) on Aug. 17, 2006, when these images were acquired. The views were obtained over the course of an hour, and are presented here in reverse order (i.e., the leftmost image was taken latest).

The images were taken in visible light with the Cassini spacecraft narrow-angle camera. As presented here, the views were acquired at distances ranging from 62,000 to 51,000 kilometers (39,000 to 32,000 miles) from Helene and at a Sun-Helene-spacecraft, or phase, angle of 111 to 120 degrees. Image scale is 375 to 300 meters (1,230 to 984 feet) per pixel, from left to right. (Courtesy NASA/JPL/Space Science Institute)

Helene
This image of Helene was acquired by the Voyager 2 spacecraft on August 25, 1981. (Copyright Calvin J. Hamilton)

Saturn Dione Rhea