The 2009 Saturn Ring Plane Crossings

The Sun and Earth pass through Saturn's ring plane on August 10th and September 4th, 2009. However, unlike the Saturn ring plane crossing of 1995, the 2009 events will occur when Saturn, viewed from Earth, is close to the sun. As consequence, none of the major ground based or Earth orbiting telescopes will be able to observe the actual ring plane crossing events.

However, Earth based observations made within a few months on either side of the ring plane crossings can take advantage of the near edge-on viewing geometry to measure the timing of satellite eclipses and mutual events. This data can be used to improve the accuracy satellite orbits and our knowledge of the overall geometry of the Saturn sytem.

• In March 2009, HST captured an image of satellites transiting Saturn. Similar opportunities will arise after the ring plane crossings. More information on this and other HST observations can be obtained from HST news web site.

Cassini is positioned to obtain unique observations of the effects of the changing lighting geometry. As early as May of 2009, Cassini began returning spectacular images of shadows cast by Saturnian satellites onto the rings of Saturn such as:

• In May, the shadow of Janus shown in the image at the top of this page.
• In July, Cassini captured images of Daphnis orbiting within the Keeler Gap near the outer edge of the A ring. We've previously seen images of the waves that it generates in the material at the edges of the gap. However, this set of images show that in addition to Daphnis, the Daphnis waves cast shadows onto the rings. Hence the ring material in the wakes must be perturbed vertically as well as horizontally.
• In August, the shadow it cast on the B ring led to the discovery of a tiny moonlet orbiting in the B ring.
• Many other images show shadows cast by satellites and ring material onto the rings, providing new information on the vertical displacement of ring material at various locations. Many of these images may be viewed in our May and subsequent Cassini press release web pages.

Data Sets

• The PDS Rings Node intends to archive as much of the HST and highest quality ground based SRPX data as is made available. Observers interested in archiving data should contact Mark Showalter or Mitch Gordon.
• We will post additional links as data become available.

Tools

• The Rings Node On-Line Tools are available for visualizing the changing geometry and assisting with observation planning.

Links Outside the Rings Node

Additional sites for Cassini images include

• The Cassini imaging team's web site,
• NASA Planetary Photojournal.

HST press release images are available through

• Hubble Gallery.