Register for an account


Enter your name and email address below.

Your email address is used to log in and will not be shared or sold. Read our privacy policy.


Website access code

Enter your access code into the form field below.

If you are a Zinio, Nook, Kindle, Apple, or Google Play subscriber, you can enter your website access code to gain subscriber access. Your website access code is located in the upper right corner of the Table of Contents page of your digital edition.

The Sciences

Helene of Saturnian Troy

Bad AstronomyBy Phil PlaitMarch 11, 2010 6:24 PM


Sign up for our email newsletter for the latest science news

The Cassini spacecraft recently passed very near the tiny moon Helene and returned amazing pictures of it.


Helene is a dinky iceball, only about 36x32x30 km (22x19x18 miles) in size (this picture has an incredible resolution of about 113 meters (123 yards) per pixel). It circles Saturn in the same orbit as the much larger Dione, and is in fact in the larger moon's leading Trojan point: a peculiar artifact of gravity when an object orbits another. It's a gravitational stable point, like a valley between two mountains. Clearly battered, Helene has an oddly smooth appearance, which may be due to the feeble gravity of the moon collecting dust also trapped in the Trojan point. At The Planetary Society Blog, Emily has more info on Helene and speculates about its appearance. She also has a good description of how the Trojan points work. Credit: NASA/JPL/Space Science Institute

3 Free Articles Left

Want it all? Get unlimited access when you subscribe.


Already a subscriber? Register or Log In

Want unlimited access?

Subscribe today and save 50%


Already a subscriber? Register or Log In