Hello, Helene!

by Jason Major on June 20, 2011

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Color composite of Helene from June 18, 2011 flyby. NASA / JPL / SSI / J. Major

On June 18, 2011, the Cassini spacecraft performed a flyby of Saturn’s moon Helene. Passing at a distance of 6,968 km (4,330 miles) it was Cassini’s second-closest flyby of the icy little moon.

The image above is a color composite made from raw images taken with Cassini’s red, green and blue visible light filters. There’s a bit of a blur because the moon shifted position in the frames slightly between images, but I think it captures some of the subtle color variations of lighting and surface composition very nicely!

3D anaglyph of Helene assembled by Patrick Rutherford.

At right is a 3D anaglyph view of Helene made by Patrick Rutherford from Cassini’s original raw images … if you have a pair of red/blue glasses, check it out!

Cassini passed from Helene’s night side to its sunlit side. This flyby will enable scientists to create a map of Helene so they can better understand the moon’s history and gully-like features seen on previous flybys.

(When Cassini acquired the images, it was oriented such that Helene’s north pole was facing downwards. I rotated the image above to reflect north as up.)

Helene orbits Saturn at the considerable distance of 234,505 miles (377,400 km). Irregularly-shaped, it measures 22 x 19 x 18.6 miles (36 x 32 x 30 km).

Helene is a “Trojan” moon of the much larger Dione – so called because it orbits Saturn within the path of Dione, 60º ahead of it. (Its little sister Trojan, 3-mile-wide Polydeuces, trails Dione at the rear 60º mark.) The Homeric term comes from the behavioral resemblance to the Trojan asteroids which orbit the Sun within Jupiter’s path…again, 60º in front and behind. These orbital positions are known as Lagrangian points (L4 and L5, respectively.)

Read more on the Cassini mission site here.

An irregular crescent: Cassini's flyby of Helene on June 18, 2011.

Images: NASA / JPL / Space Science Institute.

About 

A graphic designer in Rhode Island, Jason writes about space exploration on his blog Lights In The Dark, Discovery News, and, of course, here on Universe Today. Ad astra!

Michal Kowalski June 20, 2011 at 4:31 PM

Any ideas what is the origin of this surface features?

Anonymous June 20, 2011 at 7:44 PM

Via Twitter, Carolyn Porco said of the Helene pics; “Nothing is `wind-blown’. Just downslope motion of debris created in crater-producing impacts”

J. Major June 20, 2011 at 8:31 PM

That’s what she told me too.

Anonymous June 21, 2011 at 7:37 PM

Yes, that makes sense.

Jon Hanford June 20, 2011 at 5:09 PM

There seems to be a paucity of fresh “young” craters, and several examples of filled craters, in this image. Is this an indication of some long-term resurfacing mechanism that works over short time scales? Or has this small moon been recently impacted (say in the last ~1000 yrs) and subsequently (episodically) resurfaced?

This tiny moon was only recently discovered (1980) by Pic du Midi astronomers imaging Saturn during the ring-plane crossing occurring around that time: http://en.wikipedia.org/wiki/Helene_%28moon%29

(There are several earlier images of Helene at different angles at the wiki page, too)

WaxyMary June 20, 2011 at 5:13 PM

I too am curious to the gully features origins.

Mary

EarthlingX June 20, 2011 at 8:17 PM

Fly-by video on YouTube :
http://www.youtube.com/watch?v=HiHSM-_fes4

J. Major June 20, 2011 at 8:30 PM

Excellent!

Anna June 21, 2011 at 10:31 AM

How is north defined?

Anna June 21, 2011 at 10:31 AM

How is north defined?

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