Saturn's moon Enceladus

In the News

Saturn’s icy moon Enceladus has been making news lately, and it could make even bigger news soon! In September, scientists confirmed that there was a global ocean underneath Enceladus’ thick icy shell. That was just the latest in a long history of exciting finds dating back to the beginning of NASA’s Cassini-Huygens Mission to Saturn in 2004 that have helped scientists to better understand this fascinating world!

Even while Cassini was still on its way to Saturn, its Cosmic Dust Analyzer detected microscopic grains of silica (tiny grains of sand). On Earth, grains of silica similar in size to those detected near Saturn form when hydrothermal activity -- the processes involving heated water beneath Earth’s surface or ocean -- causes salty water to chemically interact with rocky material to form silica. But where were these grains coming from in the space around Saturn?

In 2005, scientists were surprised to find out that Enceladus’ south pole is both warmer than expected and warmer than the surrounding areas, suggesting there is a heat source inside Enceladus. Not only that, but they also discovered long parallel cracks in the ice on Enceladus’ south pole. The young age of these cracks, nicknamed Tiger Stripes, meant that Saturn’s icy moon is a geologically active place.

Color image of the cracks, or Tiger Stripes, on the South Pole of Saturn's moon Enceladus
This enhanced color view of Saturn's moon Enceladus shows the south polar terrain, where jets of material spray out form long cracks called Tiger Stripes. Image credit: NASA/JPL-Caltech/Space Science Institute | Full image and caption

Heat map of Saturn's moon Enceladus
This image shows the infrared (heat) radiation at the south pole of Saturn's moon Enceladus, including the dramatic warm spot centered on the pole near the moon's Tiger Stripes feature. The data were taken during the spacecraft's third flyby of Enceladus on July 14, 2005. Image credit: NASA/JPL-Caltech/Space Science Institute | Full image and caption

Another piece of this puzzle was put in place with the discovery of jets of material spraying out of the Tiger Stripes. Studies have shown these jets are composed of mostly of water vapor, tiny ice particles and small amounts of other material (for example, microscopic silica grains). Together, over 100 jets make up a feature called a plume. Investigating further, scientists have hypothesized that these silica grains are the result of hydrothermal activity on the ocean floor below Enceladus’ icy crust.

Movie of the Plume on Saturn's moon Enceladus
Jets of icy particles burst from Saturn’s moon Enceladus in this brief movie sequence of four images taken on Nov. 27, 2005. Credit: NASA/JPL-Caltech/Space Science Institute | Full image and caption

On October 28, Cassini will fly right through the plume jetting out of Enceladus’ south pole at an altitude of only 49 kilometers (30 miles) – closer than any previous passes directly through the plume! This is an exciting moment in the mission -- one that allows science teams to use a combination of tools on board the spacecraft to strengthen previous findings and potentially make new discoveries.

Why It's Important

Cassini will use its Cosmic Dust Analyzer to study the solid plume particles and an instrument called the Ion and Neutral Mass Spectrometer to “sniff” the gas vapor in order to determine the composition of the jets. Specifically, the latter instrument is looking for H2, or molecular hydrogen. Finding H2 in the plume will strengthen the evidence that hydrothermal activity is occurring on Enceladus’ ocean floor. And the amount of H2 in the plume, will tell scientists just how much activity is happening.

In addition to indicating that hydrothermal activity is taking place, figuring out the amount of hydrothermal activity will give scientists a good indication of how much internal energy there is deep inside Enceladus.

That Cassini is making a pass through the plume at such a low, 49-kilometer-high altitude is also important. Organic compounds -- substances formed when carbon bonds with hydrogen, nitrogen, oxygen, phosphorus or sulfur -- tend to be heavy and would fall out of the plume before reaching the heights of Cassini’s previous, higher altitude flybys and be undetected. Organic compounds are the building blocks of life on Earth. Without them, life as we know it wouldn’t exist. If they are present in Enceladus’ oceans, they could be detected when Cassini passes through the plume on this encounter.

Perhaps more important, though, are the implications of finding hydrothermal activity somewhere other than Earth. It was once believed that all forms of life needed sunlight as a source of energy, but in 1977, the first hydrothermal vent -- essentially an underwater geyser of hot, mineral-rich water -- was discovered and it was teeming with life. The organisms were using the heat and minerals as a source of energy! Some scientists have hypothesized that hydrothermal vents could be where life on our planet first took hold and could represent environments in the solar system with the necessary ingredients to support life.

Teach It

Here are a handful of lessons and resources you can use to teach key concepts related to the October 28 Enceladus flyby and help your students feel connected to this exciting moment in science at Saturn.



  • NGSS 5-ESS2-1 - Develop a model using an example to describe ways the geosphere, biosphere, hydrosphere, and/or atmosphere interact.


Because scientists can’t dig beneath the ice and see what’s below, they rely on creating models that show what is happening beneath the surface. A model helps us imagine what can’t be seen and explains the things that we can see and measure. A model could be a drawing, a diagram or a computer simulation. For this model, students will draw a cut away model of Enceladus and iterate, or improve, their model as you provide more description, just as scientists improved their models as they learned more about Enceladus.

  1. Tell students there is a moon around Saturn. They should draw a moon (likely a circle, half-circle, or arc, depending on how big you want the drawing to be).

  2. Explain to students that the moon is covered in a shell of ice (students will need to modify their model by drawing a layer of ice). Thus far, everything students are modeling is observable by looking at the moon.

  3. Share with students that temperature measurements of the south pole revealed spots that are warmer than the rest of the moon’s surface. Ask students to brainstorm possible sources of heat at the south pole and explain what might happen to ice near a heat source. Based on this new information, and what they think might be causing the heat, allow them to modify their drawing. (Depending on what students brainstorm, their drawing might now include volcanoes, hot spots, magma, hydrothermal vents and a pool of liquid water beneath the ice).

  4. The next piece of information the students will need to incorporate into their drawing is that there are large cracks in the ice over the warmer south-pole region.

  5. Explain that students have now received images that show jets expelling material from the cracks. They will need to incorporate this new data and add it to their drawing.

  6. Tell students that by studying the gravity of the moon, scientists now believe there is an ocean covering the whole surface of the moon beneath the ice. Ask students to share how they would represent that in the model. Allow them to modify their drawing.

  7. Show students the following image depicting a model of Enceladus:

    Saturn's moon Enceladus global ocean model

    This model shows what scientists believe the interior of Enceladus may look like. Have students compare it to what they drew and note similarities and differences.

Particle Travel Rate


  • CCSS.MATH 6.RP.A.3.B - - Solve unit rate problems including those involving unit pricing and constant speed. For example, if it took 7 hours to mow 4 lawns, then at that rate, how many lawns could be mowed in 35 hours? At what rate were lawns being mowed?


Based on the size of the silica grains (6 to 9 nanometers), scientists think they spend anywhere from several months to a few years (a longer time than that means the grains would be larger) traveling from hydrothermal vents to space, a distance of 40 to 50 km.

  1. What rate (in km/day) are the particles traveling if it takes them 6 months to travel 50 km (assume 182 days)?

    50 km ÷ 182 days = 0.27 km/day

  2. What rate are they traveling if it takes two years to travel 40 km?

    40 km ÷ 730 days = 0.05 km/day

  3. Do you think the particles in each example traveled at the same speed the entire time they moved?

  4. Why might the particle rate vary?

  5. At what point in their journey might particles have been traveling at the highest rate?

Plume Data


  • CCSS.MATH 6.RP.A.3.B - Solve unit rate problems including those involving unit pricing and constant speed. For example, if it took 7 hours to mow 4 lawns, then at that rate, how many lawns could be mowed in 35 hours? At what rate were lawns being mowed?
  • CCSS.MATH 8.G.B.7 - Apply the Pythagorean Theorem to determine unknown side lengths in right triangles in real-world and mathematical problems in two and three dimensions.


Cassini will be flying past Enceladus at a staggering 8.5 km per second (19,014 mph). At an altitude of 49 km, the plume is estimated to be approximately 130 km across.

  • How long will Cassini have to capture particles and record data while within the plume?

    130 km ÷ 8.5 km/sec ≈ 15 seconds

  • If Cassini is 49 km above the surface of Enceladus at the center of the plume, what is its altitude as it enters and exits the plume (the radius of Enceladus is 252.1 km)?

    252.1 km + 49 km = 301.1 km
    (301.1 km)2 + (65 km)2 ≈ 95,000 km2
    √(95,000 km2) ≈ 308 km
    ≈ 308 km – 252.1 km ≈ 56 km

  • This information can help scientists determine where in the plume heavy particles may fall out if they are not detected on the edge of the plume but are detected closer to the middle of the plume. It is also important because the Cosmic Dust Analyzer uses a high-rate detector that can count impacting particles at over 10,000 parts per second to tell us how much material is being sprayed out.

Volume of Enceladus’ Ocean


  • CCSS.MATH 8.G.C.9 - Know the formulas for the volumes of cones, cylinders, and spheres and use them to solve real-world and mathematical problems.
  • CCSS.MATH HSG.GMD.A.3 - Use volume formulas for cylinders, pyramids, cones, and spheres to solve problems.


Gravity field measurements of Enceladus and the wobble in its orbital motion show a 10 km deep ocean beneath a layer of ice estimated to be between 30 km and 40 km thick. If the mean radius of Enceladus is 252.1 km, what is the minimum and maximum volume of water contained within its ocean?

Volume of a sphere = 43πr3

Minimum volume with a 40 km thick crust
43 π212.1 km3 - 43π202.1 km3 ≈ 40,000,000 km3 – 35,000,000 km3 ≈ 5,000,000 km3

Maximum volume with a 30 km thick crust
43 π222.1 km343 π212.1 km3 ≈ 46,000,000 km3 – 40,000,000 km3 ≈ 6,000,000 km3

This is important because if scientists know how much water is in the ocean and how much vapor is escaping through the plume, they can make estimates about how long the plume has existed -- or could continue to exist.

Download the Full Problem Set

Explore More!

TAGS: Enceladus, moon, Saturn, Cassini, flyby, spacecraft, plume, jets, geysers, science, math

  • Lyle Tavernier

Pi in the Sky Infographic

UPDATE - March 17, 2014: The pi challenge answer key is now available for download.

In honor of everyone's favorite mathematical holiday, Pi Day, which celebrates the mathematical constant 3.14 on March 14, NASA/JPL Edu has crafted a set of stellar middle- and high-school math problems to show students that pi is more than just a fancy number.

Pi is all over our skies! It helps power our spacecraft, keeps our Mars rovers' wheels spinning, lets us peer beneath the clouds on Jupiter and gives us new perspectives on Earth. Take part in the fun and see if your classroom can solve some of the same problems that real NASA scientists and engineers do.

Each pi-filled word problem gets a graphic treatment in this printable infographic (available in both poster-size and 8.5-by-11 handouts) that helps students visualize the steps they need to get to a solution. A companion answer key is also available below and walks students through each step of the solutions. It can be printed on the back of the problem-set infographic for an educational classroom poster.

"Pi in the Sky" Downloads:

TAGS: Pi Day, Infographics, Curiosity, Mars, SMAP, Earth, Juno, Jupiter, Cassini, Saturn, K-12

  • Kim Orr

Andrew Crawford and Todd Barber in mission control at JPL

There are certain people in life that exude such enthusiasm and passion, that you are helpless to escape their tractor beam of positivity. This summer, during my second internship at NASA's Jet Propulsion Laboratory in Pasadena, Calif., I was fortunate enough to meet and befriend just that kind of person. Todd Barber has such passion and talent for exploring and doing what humans do best: pushing the boundaries of what humankind is capable of. As the lead propulsion engineer for the Cassini spacecraft, he was at the controls for the tricky insertion of the spacecraft into Saturn's orbit and recently was at the helm for the cruise stage of the Mars Science Laboratory's Curiosity rover during its "seven minutes of terror" descent through the Martian atmosphere. As if that's not interesting enough, during his free time, he goes on math-based adventures, inspires students through NASA outreach activities and plays in at least two jazz bands. I caught up with Todd just days before he helped successfully land NASA's Curiosity rover on Mars to learn a bit about his path to success and how he inspires others.

How did you get to be the lead propulsion engineer for Cassini, one of my personal favorite missions?

"I started here 22 years ago. Often when they bring you in, they put you on mission operations, flying something, because you get to interface with all the other sub-system engineers and what they do, including thermal, power, communications, propulsion, essentially a boot camp. I started at JPL on the Galileo mission, doing mission ops. I loved mission ops so much, and I had a penchant for ops work. I think I'm a planetary science geek. The Voyager missions are what grabbed me. My way to contribute to planetary science is by being a propulsion engineer. I didn't know what missions I'd work on after Galileo, and luckily a Cassini engineer moved on. Six months before launch, they sought me out, and I've been on Cassini ever since. I get to work on other missions part-time, including the Mars Exploration Rovers, Deep Impact and a Mars airplane study."

"The Cassini job opened up, and my mentor, Dick Cowley, was the lead propulsion engineer at the time, but near retirement. He worked on Apollo -- the F1 engine -- so this guy was the propulsion guru. I picked his brain every day until he retired, and then one day, he said, 'I think it's time we make you the lead propulsion engineer.' This was a couple years before Saturn orbit insertion, and I had the privilege of presenting to the review boards, getting barbecued at the flight reviews. But all went smoothly and we had a marvelous orbit insertion, and now the Cassini spacecraft is still sending amazing images and data home every day. I like to say that if everything goes well, I'll be 51 years old after these missions and wonder what I'll do when I grow up, because I've been having so much fun on these outer planet missions!"

What exactly does a lead propulsion engineer for Cassini do?

"I am responsible for the health and safety of the propulsion system. We are like 'space plumbers.' All the engines, regulators, tanks, valves, we are responsible for all these systems. The Cassini propulsion system is the most complex propulsion system ever flown by JPL. It's a plumber's nightmare! My job also includes figuring out the gas mileage of the spacecraft -- bean counting the propellant, if you will -- and that is getting very important now as our monopropellant gas tank on the spacecraft is half full. (I'm an optimist.)"

What happens to Cassini when it runs out of its propellant?

"At the end of the mission, we will cross inside Saturn's rings, getting views and pictures we've never seen before, and then go out in a blaze of glory. On September 15, 2017, Cassini will be crushed and vaporized by Saturn's atmosphere."

Why not save the spacecraft?

"Actually, it's for astrobiological reasons. We would never want to accidently crash the spacecraft into Enceladus or Titan, two of Saturn's moons, and possibly contaminate them. Even though it's hard to imagine 'hearty spores' could have hitched a ride on the spacecraft from Earth that are just waiting for liquid water, we would never want that to happen before we can answer the most fundamental question, 'Did indigenous life start on its own?' It's called 'forward planetary protection.' The opposite is true as well, which is called 'backward planetary protection,' where if you bring things back to Earth from other planets, you would never want to bring back something that could wipe out humanity. We want to be as careful as we can."

Do you have to dodge asteroid belts, space junk, etc.?

"Yes. We have to worry about Saturn's ring plane, made up of dust and small particles. The rings are very thin, like a phonograph record, but huge across. There's a ton of dust and particles that make up the rings, and sometimes we have to turn the spacecraft around with the antenna facing forward, which acts as a giant dust shield. The dust can damage the engines, so we built a dust cover similar to a baby stroller sun shield that folds down. We've had to use it 70 times on the mission, and the engine is still working great! Our engine has a wonderful heritage, as it was the same reaction control thruster that carried Neil Armstrong and Buzz Aldrin on Apollo!"

Where do you think we should explore next?

"Well, I love the outer planets, I would love to work a Neptune orbiter and would love to go to Saturn's moons Titan and Enceladus, or Jupiter's moon Europa. There are very complex propulsion trajectories to get there, but the payoff could be huge!"

Were you an intern before you worked here at JPL?

"No, I was not. I actually interviewed here three times and got turned down twice. The third time was a charm. After getting turned down the first time after getting my undergrad in aerospace engineering, I went back and got my masters in aerospace engineering at MIT, and then I got my dream job. I remember the summer of my 8th grade year, I saw a National Geographic with the Voyager spacecraft flying by Jupiter and Saturn and was hooked. I said, 'I have to work there at JPL!'"

I know that you are very involved with NASA's educational outreach and are constantly inspiring and trying to get kids involved with NASA and JPL. What do you feel is the most vital thing we need to tell young people today to get them inspired?

"Well, I think the most vital thing is showing them that math and science are cool. Math and science are not generally thought of as cool, but when you see math and science in action at NASA, it's the coolest -- especially during our missions such as the Mars Science Laboratory. For the U.S. to stay competitive, I think we really need to focus on new innovation, for that's what made this country great!"

"I've had strange hobbies that have helped me apply math and science. One of my hobbies is 'confluence hunting,' basically geeks with GPS devices trying to find and visit integer (whole counting numbers) latitude and longitude intersections [across the globe]. There are 850 confluence points in the continental United States, and I visited 17 of the last 50. They gave me the nickname 'The Closer' on the website."

Do you think innovation is a learned trait, or something people are just naturally good at?

"I'm here because of great teachers. I'm the first to sing the praises of teachers who got me fired me up about math and science. I went to public schools and got really lucky that my teachers were world class and fired up on math and science, and I'm still in touch with them. They follow all my missions and tell the kids that I was once a former student of theirs and to shoot for the stars."

"I had two dreams as a kid, to work for NASA, and to compose music. I'm so happy that they both came true, and I feel like I have an explorer's spirit, and need to share that with others."

Speaking of music, I hear that you are in a Jazz band called "The Big Band Theory," and that you have a minor from MIT in music? Well, I play the classical violin, and I was wondering if we could jam sometime?

"Haha, absolutely! I'm in two bands, The Big Band Theory and The Jazz Propulsion Band, and I'm always playing music. Let's make that happen!"

TAGS: Todd Barber, Propulsion, Engineering, Cassini, Math

  • Andrew Crawford