As NASA celebrates 10 years of Cassini at Saturn, here's a Top-Ten list of the spacecraft's amazing discoveries and incredible images
Tuesday, July 1, 2014, 1:12 PM - Ten years ago today, on July 1, 2004, NASA's Cassini arrived at Saturn, dropping into the ringed gas giant's gravity well and beginning the first of its four-year missions to investigate the planet, its extensive ring system and its multitude of mysterious moons.
When the Cassini-Huygens mission arrived at its destination back in 2004, the scientists and engineers involved in the mission were understandably quite happy, as the video below shows:
After all, while the team had a few milestones on the spacecraft's trip - flybys of Venus, Earth and Jupiter, and testing out Einstein's Theory of Relativity - the day they had all been awaiting for nearly 7 years had finally arrived. It was well-worth the wait, too, as Cassini has returned some incredible discoveries and spectacular images over the past 10 years. Here's a personal "Top Ten" from Cassini's first 10 years:
1. Titan's surface is revealed, giving us a glimpse of what Earth was like in the distant past.
Dropping its Huygens probe into the hazy methane atmosphere of Titan, and then following that up with radar images over the past nine-and-a-half years, NASA and the European Space Agency captured the first images of the moon's surface (left) and produced extensive maps of the features on the surface, such as the various hydrocarbon lakes (right). These views revealed that Titan is very much like Earth way, before life developed on our planet, nearly 4 billion years ago.
2. Cassini catches icy moon Enceladus blasting out water vapour plumes, hinting at subsurface ocean
This image, taken by Cassini on Nov. 27, 2005, shows plumes of water vapour streaming off the south polar region of Enceladus, one of Saturn's innermost moons. Nearly two years later, researchers completed a study on these plumes, using enhanced images like in the colour overlay to identify the individual fountains. More recently, flybys of Cassini detected a region under these plumes where the pull of gravity is lower than the surrounding area, suggesting that there is an extensive ocean of liquid water under the icy surface.
3. Tall vertical structures reach high above the edges of Saturn's rings
In late July of 2009, just weeks before Saturn reached its equinox - when the planet's northern and southern hemispheres would receive equal light from the Sun - Cassini snapped this image of the outer edge the B ring and the Cassini division. With the light from the Sun hitting the rings nearly edge-on, towering spires, some reaching to 2.5 kilometres above the 'surface' of the rings, cast long shadows across the ice.
4. Saturn's northern polar hurricane imaged in stunning detail
This image shows off a false-colour view of 'the hexagon' - a persistent feature that surrounds Saturn's north pole (click here for a larger, animated version). Although astronomers have known about the hexagon for years now, thanks to other spacecraft missions and the Hubble Space Telescope, what lay at the heart of the feature remained a mystery until just recently, when the north pole emerged from winter into the Sun's light. Revealed to us for the first time was an immense swirling hurricane, directly over the pole. For a sense of scale, you could fit two Earths side-by-side across the entire hexagon, and the central hurricane (shown in the deepest pinks and purples) has an eye roughly 50 times larger than the eye of your typical Earth hurricane. A beautiful, natural colour still image of the hexagon, which has been named Spring at the North Pole, can be seen on NASA's website (click here).
5. Saturn's rings may still be making moons!
The above picture may not be the best one to show off Saturn's rings, but it reveals something amazing. The 'disturbance' at the very edge of the ring (bottom centre) is quite possible a new moon in the works. The object causing the disturbance, which members of the Cassini team nicknamed 'Peggy' is too small to see in this image. It's estimated at around 1 kilometre in diameter, whereas the pixels in the image are 7 kilometres on a side. It's possible Peggy may simply be smashed to bits and thus rejoin the ring, however if it survives it will likely continue to accumulate more mass and migrate beyond the ring to become Saturn's newest moon.
NEXT PAGE: ALL THAT SCIENCE IS COOL, BUT HOW ABOUT SOME AWESOME PICTURES?
6. Saturn storm catches its own tail
In December 2010, a powerful storm spun up in Saturn's northern hemisphere and over the next several months, it tracked all the way around the planet. The whirls and vortices left behind in the wake of the storm were so strong that they were still there when the primary storm made its full circuit of the hemisphere. This image, snapped in early February 2011, shows the storm actually catching its own tail! False colour images from the same time (click here) reveal the intricate patterns of clouds inside the storm.
7. The striking details of Enceladus' icy surface
Scientists may be keenly interested in what lies beneath icy surface of Saturn's moon, Enceladus, but the surface itself is an incredible mosaic of cracks, fissures, impact craters and subtle shading that can captivate for hours. The above image doesn't even do it justice. Click here to see the full 50-million-pixel version, so you can zoom in and pan around to see all the amazing detail Cassini captured.
8. The subtle beauty of Saturn's rings in radio waves
If you were able to see in radio waves, specifically three different wavelengths (0.94, 3.6, and 13 centimeters: the Ka-, X-, and S-bands, respectively), this is what Saturn's rings would look like to you. NASA beamed these three wavelengths at Cassini while the rings were between Earth and the spacecraft. The particles that make up the rings scattered the radio waves, and Cassini gathered the results to produce a view that showed the team the distribution of particle sizes throughout the entire ring system. The full version can be seen on NASA's website (click here), but the above image uses a special colour scheme to really show off the subtle differences throughout the rings.
9. Almost the best image of Saturn, ever
Taken in 2009, this image of Saturn was captured by Cassini just as the planet was in spring equinox - the point where the Sun was illuminating both hemispheres equally, and the sunlight was catching the rings edge-on. Without being directly illuminated, the ring system turned to dusky shades, showing off their structure beautifully.
10. Probably the best view of Saturn ever taken, and we're in it too!
In July of 2013, Cassini dipped behind Saturn, letting the planet eclipse it and scoring an absolutely spectacular view of the rings with sunlight streaming through them. This is yet another picture where the small image here is nice, but it simply doesn't do the original justice. Click here to see it in its full splendor. Another very cool part of this is that we're in the picture too! Can't see us? Click here for some assistance in picking us out (along with Mars and Venus too). Another version is fully annotated, pointing out all the other features and objects that can be seen in the picture. Click here to check it out. Cassini will be hard-pressed to outdo this one, but I look forward to the attempts.
Although Cassini is currently on its third four-year mission, it will only be given one more renewal in 2016. This final mission, newly named Cassini's 'Grand Finale', will put the spacecraft into a highly-elliptical orbit that will fly it over the planet's poles, far out to swing past the F ring and icy Enceladus, and then diving between the inner edge of Saturn's rings and the planet itself. These 22 orbits will return even more science for the spacecraft's team here on Earth (and undoubtedly more incredible images for us to pore over).