A spotlight on Saturn’s rings

Saturn is without a doubt my favorite object to look at in the night time sky. The first time I viewed it through my first telescope I was instantly mesmerized by the rings. It’s really a celestial treasure right in our own backyard. If you’ve never looked at Saturn through a telescope, do it. I promise, you won’t regret it. Now you might be wondering, what will Saturn look like through a telescope? Well you won’t see this:

This natural color image of Saturn was created from a series of images that were taken by the Cassini spacecraft during its encounter with the planet in October 2004. Credit: NASA

…but you probably will be able to see something like this:

Here’s a glimpse of Saturn taken through the UNH Observatory‘s C14 by UNH Observatory volunteer and SkyGuy John S. Gianforte on February 21, 2007.

So you see why it’s something that sticks with you. So yes, you should definitely look at Saturn through a telescope. Now let’s learn a little bit more about the 2nd largest planet in our solar system!

Of the five planets visible to the naked eye from Earth, Saturn is the furthest and slowest moving across the sky. That’s actually how Saturn got its name; the ancient Greeks named the planet after Chronos (Saturn to the Romans), the father of Zeus (Jupiter) and the God of time (a reason why chronos is a root of time-related words, like chronology). Galileo was the first to resolve and discover the rings of Saturn when he looked at it through his telescope in 1610. It’s incorrect status as the only ringed planet in the solar system survived until well into the latter half of the 20th century. In 1977, Saturn was joined in the ringed planet club by Uranus, after scientists observed a star passing behind the planet, a phenomenon called an occultation. Most unexpectedly, the star’s light blinked on and off nine times before disappearing behind the disc of the planet; this proved that although the rings were too dim to be seen from Earth, the material was present. Only a few years later, Voyager 1 discovered the rings of Jupiter and it wasn’t until the mid-1980’s that another stellar occultation proved the existence of Neptune’s ring system. So it’s true, all of the gaseous outer planets, or “gas giants”, have rings, but Saturn’s are by far the most visually impressive and the only ones visible from Earth. So that leads us to a very interesting and mysterious question…why? What makes Saturn’s rings special?

As telescopes on Earth have become more and more advanced and we continue our extensive exploration of the solar system, we have pieced together a much more comprehensive understanding of Saturn’s rings than Galileo had 400 years ago. Although the rings look solid and sheet-like from Earth, we now know that the rings of Saturn are actually comprised of billions of particles of rock, ice, and dust ranging in size from microscopic to meters-wide. The brighter, more dense regions of the rings have more material to reflect light while the dark regions or “gaps” are much more scarcely populated. The debris that makes up the planet’s rings are in a very well-defined plane, only a few tens of meters thick, but extending almost 130,000 km (80,778 mi) above the planet’s surface. The gallery below shows the evolution of our understanding and imaging of Saturn’s rings.

But many questions still remain about why Saturn’s rings are so much brighter than the other gassy planets. The answer scientists think, lies with the sixth-largest of Saturns 60+ moons: a small, icy world called Enceladus(shown below).

Saturn’s 6th largest moon, Enceladus, as imaged by NASA’s Cassini spacecraft. The blue fissures in the surface seen in the southern hemisphere are known as tiger stripes. Credit: NASA

Enceladus is roughly 500 km in diameter (14% of the Moon) and 1.1 × 10²º kg in mass (0.2% of the Moon), but what it lacks in stature it makes up for in output. Literally. Discovered by William Herschel in 1879 (only 2 years before his discovery of the planet Uranus), Enceladus first came into the spotlight for scientists in early 1980. As John Spencer recalls in a recent article in Physics Today, that was

“…when scientists using Earth-based telescopes acquired new images of a faint outer ring of Saturn—the E ring—which had been discovered in the 1960’s. Those images revealed that the E ring’s brightness peaked at the orbit of Enceladus. They also showed that unlike Saturn’s other rings, the E ring scattered sunlight more efficiently at shorter wavelengths, which indicated that the ring was dominated by particles not much larger than the wavelength of light. Sputtering by charged particles in Saturn’s magnetosphere would erode away such micron-sized particles on time scales of decades to hundreds of years, so something had to be replenishing the ring on comparable time scales. The peak in ring density at Enceladus pointed to that moon as the likely source.”

Since then interest in the small ice-world increased exponentially and as a result Enceladus became a primary target of investigation for the joint NASA/ESA mission of the Cassini spacecraft. After only slightly whetting their appetite with two flybys of the small moon in early 2005, researchers decided to make a third flyby at a much closer range, 170 km (105 mi) instead of the planned 1000 km (621 mi). The dramatic results from this third Enceladus flyby in July 2005 were released in a special March 2006 issue of the journal Science. It was this flyby that got the high-resolution images seen above and first discovered the “four prominent parallel fractures, dubbed tiger stripes, surrounded by an intensely tectonically disrupted landscape” that the image depicts. In an even more interesting find, Cassini caught evidence of multiple plume jets erupting from the four tiger stripe fractures seen near Enceladus’s south pole.

Multiple plume jets erupting from the four tiger-stripe fractures near Enceladus’s south pole are visible in this Cassini image. The jets appear not only on the edge of Enceladus’s disk but also where they rise up into sunlight from sources on the night side of the moon. Credit: NASA/JPL/SSI; Mosaic: Emily Lakdawalla

These plumes (shown above), currently ejecting mass at an astounding 200 kg/s, have two observable components: micron-sized ice grains and gas (99% water vapor). It is speculated that the water vapor and ice crystals that are being deposited into Saturn’s ring system by Enceladus are what have kept the planet’s rings so bright and reflective for so long.

In spite of all of this other extremely intriguing science, the most interesting thing for scientists is Enceladus’ potential for life. As one of the few places in the solar system where we know water exists, Enceladus has become a key target in the search for extraterrestrial life. Scientists speculate that liquid water might occur in several places on the tiny moon: as a global ocean between the silicate core and the ice crust, as a more local south polar sea beneath the ice shell), or as localized bodies of water in the ice shell itself.

Here is Saturn’s tiny icy moon Enceladus, imaged by NASA’s Cassini spacecraft. Just above the smaller moon we can see the planet’s rings and Saturn’s largest moon, Titan, looming in the background. Credit: NASA/JPL-Caltech/Space Science Institute

So there you have it, Enceladus is our celestial ring-bearer, if you will. Hope you learned something! Until next time, friends!

– Cheers,
Ian Cohen
Manager, UNH Observatory

References:

Modified version of original blog post from The Sky’s the Limit.

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A Brief History of NEFAF

Welcome to the official blog of the New England Fall Astronomy Festival or NEFAF! In the future this blog will be the place to find updates and insider info about NEFAF as well as fun and insightful educational astronomy tidbits. But I figured since this is the first post, I’d give you a little background on NEFAF.

NEFAF started as an idea between two huge astronomy-lovers- John Gianforte and Tom Cocchiaro- who dreamed of an event where they could spread their love and excitement about space to children and families all over New England. Luckily, John, an accomplished local astronomer,  is extremely involved with the UNH Physics Department, where he teaches astronomy courses in the summer, and has been involved as a volunteer with the UNH Observatory since it was founded in the mid-1980s. So in the winter of 2011 John approached the powers that be within the UNH Physics Department about hosting such an event. Meanwhile, Tom, an active member of the New Hampshire Astronomical Society (NHAS), approached that organization about participating in the event as well. Both the UNH Physics Department and NHAS were extremely excited about the idea and wanted to get involved, but both agreed that what the was still missing was a suitable location to host the event. It was immediately decided that the UNH Observatory was the ideal locale and a the dates were selected: Friday, October 14 and Saturday, October 15, 2012. And then the ball really got rolling!

Next, the organizers, a rag-tag group consisting of UNH employees, students, Observatory volunteers, NHAS members, and friends began to raise funds and work with UNH departments to coordinated logistics for the event. Joining the UNH Physics Department, contributions came in from the UNH Office of the President, the UNH Office of the Provost, the UNH Alumni Association, the UNH Parents Association, the New Hampshire Space Grant Consortium, and the New Hampshire High Technology Council. On top of all the monetary support, Tom was able to solicit the donation of over $2000 in telescopes and equipment from Oceanside Photo and Telescope and Orion Telescopes and Binoculars. In addition to that, we received raffle donations of UNH windbreakers from the UNH Alumni Association, a signed Jonathan Papelbon baseball from the Boston Red Sox, and a certificate for free dog training from the NH SPCA! UNH food staple RRRamon’s Food and Coffee Cart also got involved, offering to be our food sponsor!

But the event still didn’t have a name! After several meetings and dozens of emails throwing words and acronyms around, the organizers finally settled on “New England Fall Astronomy Festival”. We liked making the geographic region large, to encompass all of New England and we wanted to highlight the autumnal feel of the festival. I think the Astronomy part is pretty obvious and “festival”, well that just plain sounds fun! So we had our name. Next we met with UNH’s Editorial & Creative services team who helped us develop a poster for the event.

The poster for the first-ever New England Fall Astronomy Festival, created for us by UNH Editorial & Creative Services

While we were working on the logistics and fundraising, we also had to try to put together a program of activities, talks, and demonstrations for the festival. We were lucky enough to secure NASA astronaut and UNH alumnus Lee Morin to give our keynote talk and invited well-known solar photographer Alan Friedman to speak as well. Joining them were former UNH Observatory Manager Matt Giguere, former NASA researcher Dr. Suzanne Young, Brother Albert Heinrich, Profs. Jim Ryan and Mark McConnell of the UNH Physics Department, and several NHAS members. We also amassed a group of volunteers, led by John’s wife Doris and daughter Becky, to coordinate hands-on astronomy activities for children and their parents. We also got a whole lot of other participants to join in the fun. Before we knew it we had science organizations from all over the state manning tables next to NHAS. ARLISS Team New Hampshire, the Earth, Sea & Space Center, the International Occultation Timing Association (IOTA), the McAuliffe-Shepard Discovery Center, the Oyster River High School FIRST Robotics Team, and Project SMART were all represented.

Before we knew it, October was on us and there were just a few short days left before the big event. Ignoring a few small logistical hiccups everything was going swimmingly until the Friday of the event, then the skies opened up. It rained almost all day Friday, soaking the fields around the Observatory where the event was scheduled to be held. But we didn’t let that deter us! Despite a relatively small turnout Friday night, we remained optimistic for Saturday, the main day of the festival. The organizers and volunteers arrived early Saturday morning to prepare and to assess the rain situation. The ground was still very wet, but otherwise it turned out to be a crisp, clear New England fall day! Much to our excitement, over 500 people from around the Seacoast and beyond showed up to enjoy the event. Guests filled the day with solar observing, talks, and kids activities. Many a happy child could be found with planets painted on their cheeks and a hand-made mini-model of the Hubble Space Telescope clutched in a hand as they peered through one of a dozen-plus scopes set up around the UNH Observatory dome. After his talk, Lee Morin signed well over 200 autographs and took countless pictures with grateful children and their parents. As the day wore on, some children faltered, but the overall excitement and enthusiasm surrounding the day sure did not. As the sun dropped and night fell, nearly 300 people came out to join UNH Observatory staff and NHAS members for several hours of stargazing.

All in all the event was a huge success and the organizers immediately decided to try to make the New England Fall Astronomy Festival an annual event! So here we are, preparing for the second-annual NEFAF, scheduled (in conjunction with International Observe the Moon Night) for Friday, September 21 and Saturday, September 22, 2012. We hope to see you there! Please be sure to follow this blog and “Like” our Facebook page for the most up-to-date information about the event. And of course visit our website as well!

– Cheers,
Ian Cohen
Manager, UNH Observatory