Category Archives: cassini

astronomy news, cassini, cassini mission, evolution of galaxies, galaxies, globular clusters, omega centauri

Cassini Catches a Cluster

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Omega Centauri as Ring Backdrop

Well, this is kind of cool. The Cassini Mission out at Saturn happened to be studying the planet’s F ring and during the course of the observations caught view of the globular cluster Omega Centauri as it passed through the camera’s field of view.

The movie above is actually 13 images taken three minutes apart and then surgically joined together by the Cassini team to make the animation.  It clearly shows the cluster moving through the background.

Omega Centauri is really a spectacular naked-eye sight. It’s visible from throughout the southern hemisphere and lucky folks in more southerly parts of the northern hemisphere closer to the equator have a good vantage point for it, too. It has several millions stars packed into an area less than 90 light-years across.

The cluster lies about 15,800 light-years away from us, and is the largest of the globular clusters that are associated with the Milky Way Galaxy.  Omega Centauri may have played an interesting role in the evolution of our galaxy. Some astronomers suspect that it could have been part of a dwarf galaxy that was consumed by the Milky Way billions of years ago.  If this is true, then the cluster is what’s left of that galaxy’s core.  It’s an intriguing idea and one that astronomers are still researching.

On an unrelated note, if you’re a fan of the Carnival of Space, check out this week’s Carnival, written by Emily Lakdawalla.  Great stuff in there, including one of my own entries.

cassini, moons, planetary science

Ah Enceladus

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I Remember You Well

The first time I “met” the Saturnian moon Enceladus was during the Voyager 2 flyby in August, 1981. I was a wet-behind-the-ears science writer/editorial assistant at The Denver Post, and somehow I got the managing editor to send me out to JPL to cover the mission. I had an idea there was a “local angle” and that I’d pursue it. Turns out there was–a guy named Jim Warwick at the University of Colorado had a planetary radio astronomy team hooked up to the Voyager mission, and so I hooked on to him as a sort of science guide. It was fateful.

The first closeups of Enceladus came a day or so into the flyby, and when they appeared on the TV screen in the Von Karman auditorium at JPL, we were all entranced by the details. This was quite a moon! Cratered, cracked, covered with strange grooved areas. I was hooked on planetary science for life!

Last week, the Cassini Mission at Saturn flew REALLY close to Enceladus, looking to study the polar regions. It flew through some icy water plumes jetting out from fractured, geyser-like openings in the south polar region, and took some time to look around the north pole area, which has also been modified by geysers and cratering in the past.

This image shows this icy moon’s north polar region, and a LOT of evidence for internal activity (driven by heat). The surface is cratered, sure, but those craters have disrupted regions that were resurfaced sometime in the distant past. And, some flow-like formations seem to have gone right through some craters. What would be resurfacing Enceladus? One explanation is tectonism, surface activity driven by heating from within.

Since Enceladus is largely ice with a rocky core, heating from below the surface could easily melt the interior ices. Eventually that melt is forced out through cracks in the surface–where it acts as a kind of repaving material. Incoming impactors AND pressure from below continue to disrupt the surface, and you get these terrains where craters are interrupted by flow features and smooth plains are torn up by craters. It’s quite an interplay of planetary activity and surface modification out there. The next step is to figure out the timeline for these activities. Obviously Enceladus is undergoing resurfacing pretty often, given that there are geysers shooting out material around its south pole. But, the big question now is, “How long ago was the north polar region active?” Stay tuned!