Moody Saturn

Saturn as seen from the Cassini spacecraft

Saturn as seen from the Cassini spacecraft during the planet's equinox in July 2009. The rings are edge-on to the Sun.

The shadows of Saturn’s rings are cast onto the planet and appear as a thin band at the equator in this image taken as the planet approached its August 2009 equinox.

Approximately every 15 years, Saturn’s experiences equinox. Just like on Earth, the equinox occurs when the Sun is directly over the equator. And because Saturn’s rings orbit around its equator, the Saturnian equinox also means that the rings are exactly edge on to the Sun.

This angle makes the rings appear significantly darken than normal, and causes anything sticking up out of the plane of the rings to look anomalously bright and to cast shadows across the rings.

These sorts of scenes are possible only during the few months before and after Saturn’s equinox, at which times Cassini’s cameras have spotted not only the predictable shadows of some of Saturn’s moons, but also the shadows of newly revealed vertical structures in the rings themselves.

The planet’s southern hemisphere can be seen through the transparent D ring in the lower right of the image. The rings have been brightened by a factor of 9.5 relative to the planet to enhance visibility.

The view overall looks toward the northern, unilluminated side of the rings from about 30 degrees above the ringplane.

See a larger version of the image here.

Images taken using red, green and blue spectral filters were combined to create this natural colour view. The images were obtained with the Cassini spacecraft wide-angle camera on July 18, 2009 at a distance of approximately 2.1 million kilometres from Saturn. Image scale is 122 kilometres (76 miles) per pixel.

Saturn facts:

  • Saturn is a gas giant planet, composed mainly of hydrogen and helium.
  • There are trace amounts of ammonia, phosphine, methane and other gases.
  • We see only the tops of Saturn’s clouds and outer atmospheric layers.
  • Underneath the clouds is thought to be a thick layer of liquid hydrogen, under which is a layer of metallic hydrogen.
  • Deep inside is thought to be a core about 12,000km wide, made of rock plus water and other gases solidified under extreme pressure.
  • The core temperature is probably 10,000 to 15,000 degrees Celsius.
  • Saturn has clouds, winds, rain, snow, storms and lightning.
  • Saturn’s overall density is less than that of water…so if you could find a lake large and deep enough, Saturn would float in it!

Adapted from information issued by NASA / JPL / Space Science Institute.

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