And the Award for Leading Trojan Moon Goes To…

Raw image of Telesto from Cassini's narrow-angle camera on Jan. 14, 2016. (NASA/JPL-Caltech/SSI)
Raw image of Telesto from Cassini’s narrow-angle camera on Jan. 14, 2016. (NASA/JPL-Caltech/SSI)

Drumroll please… the little moon Telesto! (You like it, you really like it!) This image, captured by Cassini on Jan. 14, 2016, shows Saturn’s moon Telesto – a “leading trojan” of the much larger satellite Tethys.

A trojan moon is one that orbits a parent body within the same path as a more massive satellite, positioned at the Lagrangian points L4 and L5… usually at 60º ahead and behind within the orbit relative to the overall center (which, in the case of Tethys, is Saturn.)

The irregularly-shaped, 15-mile (24-km) -wide Telesto rides around Saturn ahead of Tethys, making it the moon’s “leading” trojan. Its slightly larger sister Calypso follows behind Tethys as the trailing trojan. All three orbit the ringed planet at a distance of over 183,000 miles (294,000 km).

The oddly smooth appearance of Telesto’s surface is likely due to a coating of fine icy dust, which fills in smaller cracks and craters and gives it a soft, velvety look. This material may very well have its source in the jets of Enceladus.

Trojans are found throughout the Solar System, the largest group of which orbits the Sun ahead and behind Jupiter. But while there may be up to a million trojan minor planets over 1 km within Jupiter’s orbit the only known trojan moons are around Saturn, located within the orbits of Tethys (Telesto and Calypso) and Dione (Helene and the tiny, wandering Polydeuces).

(Apologies to Helene for the award snub. There’s always next year!)

Source: NASA/JPL


  1. I love astronomy.Astronomy is a mystery as we can not be sure about a certain thing.For example-If we say Milky Way is the largest galaxy for instance then it might be possible that there is a galaxy that is unknown to us and is larger than Milky way.(JUST AN EXAMPLE)

    Liked by 1 person

    1. Jason Major says:

      Luckily galaxies are pretty big and thus relatively easy to find… and our Milky Way is far from the largest! Check out this article I put up on Universe Today about galaxy sizes:
      But yes, we are always learning about the Universe and will continue to do so for a long time, hopefully. That’s what makes science so cool.


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