Visiting the Icy Outpost of Enceladus

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Carolina Martinez

Carolina Martinez, JPL News Team

As we head into the close brush with the geysers of Enceladus, scientists, engineers and the public can come along on the ride as we count down to this amazing flyby, Cassini’s closest flyby yet of any of Saturn’s moons. On this blog we’ll post regular updates directly from the science and spacecraft teams.

Enceladus jumped to the top of scientists’ short list of places to look for life when the mission discovered giant geysers ejecting water-ice crystals and gas into space.  Few people know that Michele Dougherty of Imperial College London and principal investigator on the Magnetometer instrument was the one who pushed to have Cassini’s flyby altitude of 1,300 kilometers lowered to just 175 kilometers during the third Enceladus flyby on July 14, 2005.
 
This was after two flybys of Enceladus in February and March 2005.  Magnetometer data from those flybys showed strange things going on in the magnetic field lines.  Michele and others thought if they could just come close enough, they might be able to figure out what was happening.  She and others convinced the project to change the flyby altitude and lower it substantially. Not an easy task as these things are planned months in advance, but with a little luck and a lot of work everything fell into place and the team went closer.  Lo and behold, the little moon, the brightest in the solar system, was active, and geysers of water and vapor were erupting from mysterious hot spots at the moon’s south pole. 
 
You can see the original news release on the Magnetometer discovering an atmosphere around Enceladus at: https://www.nasa.gov/mission_pages/cassini/media/cassini-031605.html
 
For a timeline of Enceladus discoveries, and a  mission description with flyby details put together by Amanda Hendrix, Cassini scientist on the Ultraviolet Imaging Spectrograph (UVIS), see our media page:  
https://www.nasa.gov/mission_pages/cassini/media/enceladus-20080312.html 

While you’re there, check out the preview video, Taking the Plunge. 
Oh and a real nice Enceladus interactive that lets you leapfrog from place to place all over the little moon is now online: http://saturn.jpl.nasa.gov/multimedia/flash/Enceladus/enceladus.html
 
Stay tuned for exciting events ahead. 
 

Enceladus Play-by-Play Movie

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Amanda Hendrix,  Cassini Scientist on the Ultraviolet Imaging Spectrograph (bio)

This is a neat movie (click here to download or click here to watch it) put together by Brent Buffington, on the Cassini Navigation team. I love these kinds of movies, because you can really get a good idea of what the spacecraft is doing during a flyby. Everything goes pretty fast, so you may want to watch this a few times to really absorb what’s going on!

In the big left-hand window (you can see a still from the first frame of the movie below), you can see Cassini and a projection of the active (or “prime”) instrument’s field-of-view (FOV) (see key below). The right-hand windows show a view of what the boresights are seeing. Sometimes they’re staring, sometimes they’re scanning. Generally, since the optical remote sensing (ORS) instruments are pretty much bore-sighted (as shown in the upper right window), that means that when one of them is “prime,” the others are “riding along” and also getting data, resulting in a wonderful multi-wavelength suite of measurements.
view of Cassini video
So we start off with a long, distant stare, with the Visual and Infrared Mapping Spectrometer (VIMS) prime. Even though Enceladus is still far away and small, staring for such a long time gives all the optical remote sensing instruments a nice chance to build up signal and get a good spectrum, useful especially for investigating surface composition.

After VIMS, ISS (i.e., the camera) takes over for a stare at Enceladus (notice that Enceladus is still smaller than a Narrow Angle Camera–NAC, here). Also notice that the phase angle is pretty high, meaning that the body is only partially illuminated and will appear as a crescent (not unlike our own Moon last night!).

After the cameras, radar does a scan of Enceladus. To do this, we have to turn the spacecraft 90 degrees, since the radar is mounted on the spacecraft at a different orientation from the cameras.

After radar, the Composite Infrared Spectrometer (CIRS) is prime and does a scan and a stare to get temperature information, of the north polar region.

Then Ultraviolet Imaging Spectrograph (UVIS) does a slow scan of Enceladus to do surface composition (and potentially gas) measurements.

The Composite Infrared Spectrometer then does another scan (notice that we are getting pretty close to Enceladus and it’s looking bigger!).

For the final remote sensing observation before closest approach, the camera system does a three-panel mosaic of the cratered northern hemisphere. This will be our best look yet at this terrain.

After the cameras, the spacecraft does a big turn to put the in situ instruments’ sensors into the proper orientation for the closest approach (facing into the direction of motion, so they can “scoop up” particles around Enceladus). Remember that the closest approach (about 50 kilometers, or 31 miles) occurs near 20 degrees south latitude – not in the plume. About a minute after the closest-approach, we’ll be over the south pole and in the plume (at about 641 kilometers, or 398 miles). So we’re diving in the plume a little more than we’ve done before! The in situ instruments will get great measurements of particle size and composition, and gas composition, both in the plume and close to the surface of Enceladus.

Now, it isn’t obvious from this movie, but Enceladus goes into eclipse (i.e., it passes into the shadow behind Saturn), very close to the time that Cassini is making its closest approach, and remains in eclipse for a couple of hours. This is a prime opportunity for the Composite Infrared Spectrometer to do temperature mapping of the hot, active south pole region (which is now in view, after Cassini has swung through its closest approach), with no contribution or heating from solar illumination. The other remote sensing instruments will ride along, but without light from the sun, it isn’t clear exactly what they’ll measure – so that will be a surprise! While Enceladus is in eclipse is also a nice time to do radar measurements (radar doesn’t need the sun to illuminate the surface), which we do next, followed by another Composite Infrared Spectrometer scan, post-eclipse.

We complete the flyby with an Ultraviolet Imaging Spectrograph-prime stare at Enceladus (note that by this time, Enceladus is distant and small again), followed by a turn to Earth to downlink the data!

Key to instrument Field of Views:

Optical Remote Sensing, or ORS, instruments:
UVIS (Ultraviolet Imaging Spectrograph) – long narrow magenta field of view
VIMS (Visible-Infrared Mapping Spectrometer) – big red square
ISS (Imaging Subsystem, i.e., the camera) – white square (small=Narrow Angle Camera; large=Wide Angle Camera)
CIRS (Composite Infrared Spectrometer) – red circular field of view and two small red parallel narrow fields of views

HGA – high gain antenna, used for communication with Earth

Radar – green circle (centered on the high gain antenna)

Cheers,
Amanda, still in Houston

Trying to Be Patient

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John SpencerJohn Spencer, Cassini Scientist on the Composite Infrared Spectrometer (bio)

Yeah!  We made it!  I wasn’t too worried about the plume passage, as I wrote yesterday, but it was still wonderful to hear last night that Cassini had contacted Earth and was sending home its precious cargo of Enceladus data.  Not only did we survive, which was never much in doubt, but the spacecraft was healthy and the data were looking good.  This morning, the beautiful images of Enceladus posted on the Cassini raw image Web site provided further confirmation that things had gone well.  And there was more welcome news from the folks at Goddard Spaceflight Center in Maryland, where our Composite Infrared Spectrometer (CIRS) instrument was built and is operated.  The CIRS data have been collected from the Deep Space Network, compiled at JPL, transferred to Goddard, and everything looks as expected.  The data are now going through the time-consuming calibration process, converting the raw bits into spectra that will reveal some of the secrets of the active south polar region.  We should be able to transfer the calibrated data to Boulder and start work on it in an hour or two–I can’t wait!

RSS Feeds and More

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Carolina MartinezCarolina Martinez, JPL News Team

Thank you to all for the wonderful comments of encouragement on this new blog.  We hope we can live up to your expectations and it’s wonderful to read all the well-wishes.  For those who’d like to get updates via the RSS feed, click here to get updates directly to your computer.  You’ll find the RSS icon in the light gray panel near the top – near where it says Enceladus-flyby-Mar2008. The RSS feed is for all NASA blogs, not just this one.  Thanks for all the inputs as well, we’ll try to incorporate this feedback on future blogs.  When you submit a comment, please keep comments on the subject of this blog and please do not include links to other sites.

A preview of what’s to come . . . later today Todd will join us to tell us what the spacecraft and navigation teams are up to and we hope to post some Optical Navigation images today.  John and/or Amanda are writing up more details on plume hazards.  Meanwhile, Amanda’s at the Lunar and Planetary Society Conference and will be reporting briefly from there.  Speaking of the LPSC, there are lots of Cassini results being presented there; to get summaries on those abstracts check out this feature.

Dipping Our Toes

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John SpencerJohn Spencer, Cassini Scientist on the Composite Infrared Spectrometer (bio)

Today’s Enceladus flyby is a bit more adventurous than most satellite flybys by Cassini. 
We are dipping into the jet of water vapor and ice spewing from Enceladus’ south pole, because by doing so we can take full advantage of the amazing opportunity to study
fresh samples from inside this strange world.  The mass spectrometer, dust, and plasma
instruments will be running flat-out, gathering priceless information on the composition
of the gases and the ice particles for the sixty seconds or so that Cassini will be in
the dense part of the plume.

graphic showing Enceladus flybyPlume particles are wonderful things to study, but it’s possible to have too much of a
good thing – at the speed that Cassini is going, particles as small as a millimeter in
size could cause serious damage to the spacecraft if we ran into one.  So the decision to
enter the plume was not taken lightly.  The project convened an “Enceladus plume working group”, led by fellow-blogger Amanda Hendrix, which held a series of meetings to determine whether there was any hazard to the spacecraft from flying as close as we plan to go.  Though we fly 50 kilometers (30 miles) above Enceladus’ surface, this happens near the equator and away from the plumes–the closest approach to the source of the plumes is more like 200 kilometers (120 miles)–see the graphic on the left by David Seal (E3 is the official name of today’s Enceladus flyby).

We know from the Cassini images, and from observations from the dust detector during the July 2005 flyby, that there are many ice particles a few microns (a few 1000ths of a
millimeter) in diameter in the parts of the plume we’ll be traversing, and these provide
juicy samples without posing any hazard.  But was there any way that much bigger
particles could be lofted into Cassini’s path?  We reviewed the observational evidence,
and theories about how the plumes might work (for instance, figuring out how much gas it would take to accelerate an ice grain of a dangerous size to a speed high enough to reach the spacecraft) and we decided that the danger was very small.  Still, it will be good to hear from the spacecraft when it turns its antenna back to Earth and sends home word that the flyby was safely negotiated.  That will be at 7:05 p.m. Pacific time this evening, not that I’m counting…

Future flyby plans could probe even deeper into the plume, coming as close as 100 kilometers (62 miles) from the source on November 2, 2009 (though this depends on official approval of the proposed extended mission).  But we’ll review the results from this flyby before committing to anything that close.  If Cassini reports “come on in, the water’s fine!”, as we expect, we’ll dip our toes in a little further next time.

 

Post-Flyby Data Less Than Two Hours Away

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Todd BarberTodd Barber, Cassini Lead Propulsion Engineer (bio)

Hello again from the realm of Cassini engineering!  Even though many of the engineering events of this flyby are now behind us, I wanted to take a minute to say how much the flight teams (science AND engineering) have enjoyed all your wonderful blog comments.  We are chomping at the bit for the first data playback in less than three hours, just like you.  A lot of hard work and planning went into this daringly close flyby of Enceladus.  We hope all our efforts will be rewarded very soon.
 
As an engineer, I’m looking forward to seeing telemetry that would show we’ve come through the Enceladus flyby safely and successfully.  However, as a scientist-wannabe myself, I think I’m more anxiously awaiting the first images and science results from this historic encounter. 
 
Fortunately, my engineering “plate” has been full today, helping the hours and minutes pass more quickly.  Even in the midst of this encounter, we have been preparing to open the main-engine cover and execute a roughly 17-second rocket firing on Thursday afternoon PDT.  This maneuver will change Cassini’s zippy speed by only 2.76 meters per second, or 6.17 miles per hour, but yet it is critical to set up our next encounter, a 1,000-kilometer (621-mile) Titan flyby on March 25, 2008.  Even as we pause briefly to revel in what we hope is the success of our Enceladus rendezvous, the spacecraft always looks forward to the next encounter and a continued flood of science data.  Go, Cassini, go!

Raw (Unprocessed) Images In

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Carolina MartinezCarolina Martinez, JPL News Team

To see all of the raw images go to this Web site and click on the “latest images” icon or select Enceladus as the target: http://saturn.jpl.nasa.gov/multimedia/images/raw/index.cfm

Below is a selection of different views.

Our blog team is still poring over their data but I’m sure they will check in soon. Todd will have a spacecraft checkout report and Amanda and John will fill us in on their reaction to seeing their data come in.  We will also have a post from Linda on all the questions they hope to answer from their treasure trove of goodies.

Enceladus
Enceladus
Enceladus

Enceladus Data Back on Planet Earth!

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Todd BarberTodd Barber, Cassini Lead Propulsion Engineer

Howdy, folks.  We’ve just heard from the Cassini mission control area and
can report that the data downlink has started!  The signal was received via
the Goldstone, California, Deep Space Network station at roughly 7:01 pm
PDT.  Our engineers are assessing the first post-flyby data as we speak,
but everything looks great at first blush.

The downlink data playback will run through the evening, and we hope to
have raw images hit the Cassini Web site before dawn, about 5 a.m. Pacific,
Thursday, March 13.  Check here for images:
 http://saturn.jpl.nasa.gov/multimedia/images/raw/index.cfm

Just click on the “latest images” icon…or you might select Enceladus from
the drop-down menu.

Yay!  Does this job rock or what?  Now let the flood of science commence!

Todd  

Enceladus – Then and Now

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Linda SpilkerLinda Spilker, Cassini Deputy Project Scientist

As the hours tick down and Cassini gathers data during our closest flyby yet of Enceladus I am thinking about the two Voyager flybys of the Saturn system that took place over 25 years ago.  How in the world did we miss the Enceladus plumes back then???

In a nostalgic mood, I am looking over some of my old Voyager timelines today.  (Yes, I actually kept all of my old timelines from each Voyager flyby)!  I see that we took pictures of Enceladus during the first Voyager flyby in 1980, discovering a tiny, sparsely cratered world at the heart of the E ring. I remember wondering how such a tiny moon could create such a huge, tenuous ring.  That mystery was one of the puzzles left for Cassini to solve.  Remember that Cassini is in orbit around Saturn so we do multiple flybys, but the Voyagers only flew by Saturn, and each only had one encounter with Enceladus in their itinerary.

Enceladus< This view of Enceladus was taken by Voyager 2 in 1981.

My timelines show that we planned to take more pictures of Enceladus during the Voyager flyby in 1981.  Alas, the Voyager 2 scan platform containing the cameras and spectrometers stuck just as we flew close to Saturn, and the observation of our outbound pictures and spectra of Enceladus (and everything else!) were never made.  I remember feeling sad about how much unique data we wouldn’t get on that fateful day and the days that followed.  What discoveries remained for some other lucky scientists to make, I wondered?  Little did I know that I would be one of those lucky scientists! Good thing Cassini is there to keep an eye on Enceladus!

Flyby Complete – Scroll for 'Enceladus Data Back on Earth'

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Carolina Martinez Carolina Martinez, JPL News Team

Here is a video clip of the Cassini mission control area with Grant Eller, mission control engineer at the helm, confirming with the Deep Space Station in Goldstone, California that data has begun transmitting from Cassini to Earth. Play clip 

Here is a clip of fellow blogger Todd Barber: Play clip

Follow this link to download high-resolution, broadcast-quality clips: https://www.nasa.gov/mission_pages/cassini/media/enceladus-clips-20080312.html

Be sure to look for Todd Barber’s post: “Enceladus Data Back on Earth!” Also, as some of you have probably noticed, some of the blog entries are out of order.  We apologize for this bug.  We are working on a solution, though, and appreciate the feedback. 
 
A lot of you have been posting really excellent questions, and the Cassini team has been really great about responding to them individually or responding to them through a blog entry…….but we haven’t had a chance yet to post all the answers to the blog.  I am working on pulling the questions and answers together and we plan to post that in the coming days, as time permits. 
 
That is it for today.  Check back tomorrow morning with new postings from our scientists and engineers.  Images are expected to hit the raw image site at around 5 a.m. PDT at: http://saturn.jpl.nasa.gov/multimedia/images/raw/index.cfm

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