Cassini’s Legacy: Enigmatic Enceladus Will Inspire Us for Generations to Come

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NASA’s Cassini mission captured this view of icy moon Enceladus on March 29, 2017. The crescent is lit by the sun, but the near-side green hue is reflected sunlight bouncing off Saturn’s atmosphere — a.k.a. “Saturn glow” (NASA/JPL-Caltech/Space Science Institute)

The day before Cassini plunged into Saturn’s atmosphere, dramatically ending 13 years of Saturn exploration (and nearly two decades in space), I was sitting on a bench outside the Von Karman Visitor Center on the NASA Jet Propulsion Laboratory campus in La Cañada Flintridge with Linda Spilker, who served as the mission’s project scientist since before Cassini was launched.

What was supposed to be a quick 5-minute chat before lunch, turned into a wonderful 20-minute discussion about Cassini’s discoveries. But it was also about what the spacecraft meant to Spilker and how other space missions have shaped her life.

“I feel very fortunate to be involved with Cassini since the very beginning … and just to be there, to be one of the first to see SOI [Saturn Orbital Insertion] with those first incredible ring pictures,” she told me. “I love being an explorer. I worked on the Voyager mission during the flybys of Jupiter, Saturn, Uranus and Neptune; that sort of whet my appetite and made me want more, to become an explorer to go to the Saturn system.”

Spilker especially loved studying Saturn’s rings, not only from a scientific perspective, but also because they are so beautiful, she continued. “It’s been a heartwarming experience,” she said.

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Before Cassini crashed into Saturn’s atmosphere, it took a series of observations that created this mosaic of Saturn and its rings. Cassini plunged into the Saturnian atmosphere on Sept. 15 (NASA/JPL-Caltech/Space Science Institute/Mindaugas Macijauskas)

But Cassini’s “legacy discovery,” said Spilker, was the revelation that the tiny icy moon of Enceladus is active, venting water vapor into space from powerful geysers emerging from the moon’s “tiger stripes” — four long fissures in the moon’s south pole. After multiple observations of these geysers and direct sampling of the water particles during flybys, Cassini deduced that the icy space marble hides a warm, salty ocean.

“What Cassini will be remembered for — its legacy discovery — will be the geysers coming from Enceladus with the ocean with the potential for life. It’s a paradigm shift.” — Linda J. Spilker, Cassini project scientist, NASA Jet Propulsion Laboratory (JPL), Sept. 14, 2017.

Alongside Jupiter’s moon Europa, Enceladus has become a prime destination for future explorations of life beyond Earth. Its subsurface ocean contains all the ingredients for life as we know it and Cassini was the mission that inadvertently discovered its biological potential. So now we know about this potential, Spilker is keen to see a dedicated life-hunting mission that could go to Enceladus, perhaps even landing on the surface to return samples to Earth.

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Artist impression of Cassini flying through Enceladus’ water plumes venting from the moon’s south pole (NASA/JPL-Caltech)

As Enceladus is much smaller and less massive than Europa, its gravity is lower, meaning that landing on the surface is an easier task. Also, the radiation surrounding Saturn is much less aggressive than Jupiter’s radiation belts, meaning less radiation shielding is needed for spacecraft going to Saturn’s moons.

But if we ever send a surface mission to Enceladus (or any of the icy moons in the outer solar system), the planetary protection requirements will be extreme.

“If any life were found on these moons, it would be microbial,” said Larry Soderblom, an interdisciplinary scientist on the Cassini mission. “Some [terrestrial] bacteria are very resilient and can survive in hot acid-reducing environments. They can be tenacious. We have to make sure we don’t leave any of these kinds of Earthly bacteria on these promising moons.”

Soderblom has a unique perspective on solar system exploration. His career spans a huge number of NASA missions since the 1960’s, including Mariner 6, 7, 9, Viking, Voyager, Galileo, Magellan, Mars Pathfinder, the Mars Exploration Rovers, Deep Space 1, to name a few. While chatting to me under the shade of a tree on the JPL campus, he pointed out that the outer solar system was seen as a very different place over half a century ago.

“When I started to explore the solar system as a young guy just out of graduate school, our minds-eye view of the outer solar system was pretty bleak,” he remembered. “We expected lifeless, dead, battered moons with no geologic activity.”

After being involved with many outer solar system missions, this view has radically changed. Not only have we discovered entire oceans on Enceladus and Europa, there’s active volcanoes on Jupiter’s tortured moon Io, an atmosphere on Titan sporting its own methane cycle and surface lakes of methane and ethane. Other moons show hints of extensive subsurface oceans too, including distant Triton, a moon of Neptune. When NASA’s New Horizons flew past Pluto in 2015, the robotic spacecraft didn’t see a barren, dull rock as all the artistic impressions that came before seemed to suggest. The dwarf planet is a surprisingly dynamic place with a rich geologic history.

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With a diameter of only 313 miles, tiny Enceladus is a surprising powerhouse of internal activity. Subsurface oceans are heated through tidal interactions with Saturn (and, possibly, radioactivity in its rocky core), forcing water through its south pole fissures (NASA/JPL-Caltech)

Sending our robotic emissaries to these distant and unforgiving places has revolutionized our understanding of the solar system and our place in it. Rather than the gas and ice giant moons being dull, barren and static, our exploration has revealed a rich bounty of geologic variety. Not only that, we’re almost spoilt for choices for our next giant leap of scientific discovery.

Missions like Cassini are essential for science. Before that spacecraft entered Saturn orbit 13 years ago, we had a very limited understanding of what the Saturnian system was all about. Now we can confidently say that there’s a tiny moon there with incredible biological potential — Enceladus truly is Cassini’s legacy discovery that will keep our imaginations alive until we land on the ice to explore its alien ocean.

For more on my trip to JPL, read my two HowStuffWorks articles:

Why Cassini Crashed: Protecting Icy Moon Enceladus at All Costs

What Epic Space Missions Like Cassini Teach Us About Ourselves

KCRW ‘To The Point’ Interview: Cassini’s Grand Finale

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Artist’s impression of Cassini passing through the gap between Saturn and the planet’s rings (NASA/JPL-Caltech)

After all the excitement of last night’s Cassini mission checking in and transmitting data to NASA’s Deep Space Network, I joined Warren Olney on his NPR-syndicated show “To The Point” this morning to chat about the mission and why the “Grand Finale” is an awesome, yet bittersweet, part of Saturn exploration. Listen to the 10 minute segment here. It was great as always to chat with Warren, thanks for having me on the show!

Cassini Survives First Saturn Ring Dive and Returns Historic Photos

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NASA/JPL-Caltech

UPDATE (1:30 a.m. PT): A firehose of Cassini data has opened up and raw images of the spacecraft’s approach to the ring plane are coming in at a rapid pace. You can see the raw images appear online at the same time Cassini’s science team sees them here. At time of writing (and without any scientific analysis) the images have been of Saturn’s polar vortex and various views of the planet’s upper atmosphere. It’s going to take some time for more detailed views to become available, but, wow, it’s exhilarating to see Cassini images arrive at such a rate. Here are a few:

Original: As NASA planned, just before midnight on Wednesday (April 26), the veteran Cassini spacecraft made radio contact with the Goldstone 70-meter antenna in California, part of the Deep Space Network (DSN), which communicates with missions in space. Within minutes, Goldstone was receiving data, meaning the spacecraft had not only survived its first ring dive of the “Grand Finale” phase of its mission, but that it was also transmitting science data from a region of space that we’ve never explored before.

“We did it! Cassini is in contact with Earth and sending back data after a successful dive through the gap between Saturn and its rings,” tweeted the official NASA Cassini account just after the DSN confirmed it was receiving telemetry.

“The gap between Saturn and its rings is no longer unexplored space – and we’re going back 21 times,” they added.

Around 22 hours prior to Cassini’s signal, the spacecraft made its daring transit through the gap between Saturn’s upper atmosphere and innermost ring after using the gravity of Titan on Friday (April 21) to send it on a ballistic trajectory through the ring plane. But during that time the spacecraft went silent, instead devoting resources to carrying out science observations during the dive.

Of course there was much anticipation for Cassini to “phone home” tonight and it did just that right on schedule and now we can look forward to another 21 dives through Saturn’s rings before Cassini burns up in the gas giant’s upper atmosphere on Sept. 15, ending its epic 13 year mission at the solar system’s ringed planet.

“No spacecraft has ever been this close to Saturn before. We could only rely on predictions, based on our experience with Saturn’s other rings, of what we thought this gap between the rings and Saturn would be like,” said Earl Maize, Cassini Project Manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., in a statement. “I am delighted to report that Cassini shot through the gap just as we planned and has come out the other side in excellent shape.”

So now we wait until images of this never-before-explored region of Saturn are released.

Read more about Cassini’s historic ring dive in my Space.com interview with Cassini deputy project scientist Scott Edgington.

Cassini Sees Earth and Moon Through Saturn’s Rings

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NASA/JPL-Caltech/Space Science Institute

NASA’s Cassini mission sure has a knack for putting stuff into perspective — and this most recent view from Saturn orbit is no different. That dot in the center of the image isn’t a dud pixel in Cassini’s camera CCD. That’s us. All of us. Everyone.

To quote Carl Sagan:

“Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives…”

Sagan wrote that passage in his book “Pale Blue Dot: A Vision of the Human Future in Space” when reflecting on the famous “Pale Blue Dot” image that was beamed back to Earth by NASA’s Voyager 1 spacecraft in 1990. That’s when the mission returned a profound view of our planet from a distance of 3.7 billion miles (or 40.5AU) as it was traveling through the solar system’s hinterlands, on its way to interstellar space. Since then, there’s been many versions of pale blue dots snapped by the armada of robotic missions around the solar system and Cassini has looked back at us on several occasions from its orbital perch.

Now, just before Cassini begins the final leg of its Saturnian odyssey, it has again spied Earth through a gap between the gas giant’s A ring (top) and F ring (bottom). In a cropped and enhanced version, our moon is even visible! The image is composed of many observations captured on April 12, stitched together as a mosaic when Saturn was 870 million miles (roughly 9.4AU) from Earth.

On April 20 (Friday), Cassini will make its final flyby of Titan, Saturn’s largest moon, using its gravity to fling itself through Saturn’s ring plane (on April 26) between the innermost ring and the planet’s cloudy upper atmosphere, revealing a view that we’ve never before seen. For 22 orbits, Cassini will dive into this uncharted region, possibly revealing new things about Saturn’s evolution, what material its rings contain and incredibly intimate views of its atmosphere.

This daring maneuver will signal the beginning of the end for this historic mission, however. On Sept. 15, Cassini will be intentionally steered into Saturn’s atmosphere to burn up as a human-made meteor. It is low in fuel, so NASA wants to avoid the spacecraft from crashing into and contaminating one of Saturn’s potentially life-giving moons — Titan or Enceladus.

So, appreciate every image that is captured by Cassini over the coming weeks. The pictures will be like nothing we’ve seen before of the ringed gas giant, creating a very bittersweet phase of the spacecraft’s profound mission to Saturn.

Cassini Says “Ciao!” to Pan, Saturn’s Ravioli Moon

Never before has a space probe come so close to the pint-sized moon embedded in Saturn’s rings — and when NASA’s Cassini buzzed Pan, the spacecraft revealed what a strange moon it really is.

NASA/JPL-Caltech/Space Science Institute

This is Pan, a 22 mile-wide moon that scoots through Saturn’s rings, orbiting the gas giant once every 13.8 hours. And it’s weird.

Resembling a giant ravioli or some kind of “flying saucer” from a classic alien invasion sci-fi comic, Pan is known as a “shepherd moon” occupying the so-called Encke Gap inside Saturn’s A Ring. This gap is largely free of particles and it has become Pan’s job to hoover up any stray material — the moon’s slight gravity pulls particles onto its surface and scatters others back out into the ring system. This gravitational disturbance creates waves that ripple through the ring material, propagating for hundreds of miles.

On March 7, NASA’s Cassini mission came within 15,268 miles of Pan, revealing incredible detail in the moon’s strange surface. It’s thought that its characteristic equatorial ridge (a trait it shares with another Saturn moon Atlas) is caused by the gradual accumulation of ring material throughout the moon’s formation and with these new observations, scientists will be able to better understand how Pan came to be.

NASA/JPL-Caltech/Space Science Institute

As Cassini rapidly approaches the end of its mission, eventually orbiting through Saturn’s ring plane as a part of its “Grand Finale,” we can expect more of these striking views from orbit before the veteran probe is steered into Saturn’s atmosphere in September, bringing its historic mission to an end.

Tethys Plays Hide and Seek with Cassini

Which planet does Tethys orbit again?

I do admit, I’m terrible with names, but I never forget a face. In this case, the face I didn’t forget was a little moon orbiting Saturn (it’s the one that looks like the Death Star from Star Wars). However, after seeing this photo, I doubt I’ll ever forget Tethys’ name again.

In a photo snapped by the awesome Cassini Equinox mission back in November, the little moon with characteristic impact crater carved into its crust can be seen to be drifting behind Titan. Tethys only disappears for 18 minutes behind Titan’s thick atmosphere, but it was enough to ignite my interest in the icy world.

It’s strange how a simple photograph and perfect timing can ignite the imagination, as I doubt “just another moon shot” would have the same effect. No, this is a moon drifting in front of another moon as seen by a veteran spaceship orbiting the second largest planet in the solar system millions of miles away. Sometimes words are insufficient to describe the enormity of what we are doing in space.

So, sod the words and look at this, you won’t be disappointed:

And 18 minutes later:

Lovely.

Source and full-res images: NASA, Discovery News

Cassini Discovers a New Moonlet in Saturn’s Rings

The ~400 meter moonlet casts a 25 mile shadow across Saturn's B-ring (NASA)
The ~400 meter moonlet casts a 25 mile shadow across Saturn's B-ring (NASA)

As Saturn approaches its August 11th equinox (during which the Sun will be directly above the gas giant’s equator at noon for 27 months), the Cassini Equinox Mission can do some moonlet spotting. During this time, sunlight will cast long shadows of any object protruding from the 10 metre-thick rings.

In this case, hidden inside Saturn’s B-ring, a moonlet with a diameter of approximately 400 metres becomes obvious when sunlight hits the rings edge-on. The result is a very obvious 25 mile-long shadow. This discovery wouldn’t have been possible during any other time, as Cassini can only see the small rock because of its shadow. If the Sun was above or below the rings, no shadow would be cast, and therefore no moonlet would be visible.

Saturn experiences an equinox twice every Saturnian year (once every 15 terrestrial years), and NASA planned the Cassini mission to coincide with this interesting period to economise on the position of the Sun, spotting small objects like this little satellite…

Source: Wired, thanks to Helen Middleton (@herroyalmaj).

Cassini Detects Salt: Enceladus Probably Has a Liquid Ocean

The small icy Saturn moon might have liquid sub-surface oceans after all (NASA)

In October 2008, Cassini flew very close to the surface of Saturn’s icy moon Enceladus. From a distance of only 50 km from the moon, the spacecraft was able to collect samples of a plume of ice. In an earlier “skeet shot”, Cassini captured detailed images of the cracked surface, revealing the source of geysers blasting the water into space. At the time, scientist were able to detect that it was in fact water ice, but little else would be known until the molecular weight of chemicals in the plume could be measured and analysed.

At the European Geophysical Union meeting in Vienna this week, new results from the October Enceladus flyby were presented. Frank Postberg and colleagues from the Max Planck Institute for Nuclear Physics have discovered traces of sodium salts and sodium bicarbonate in the plume for the first time.

It would appear that these chemicals originated in the rocky core of the moon and were leached from the core via liquid water. The water was then transported to the surface where it was ejected, under pressure, into space. Although scientists are aware that the chemical composition in the plume may have originated from an ancient, now frozen, sub-surface ocean, the freezing process would have isolated the salt far from the surface, preventing it from being released.

It is easier to imagine that the salts are present in a liquid ocean below the surface,” said Julie Castillo of NASA’s Jet Propulsion Laboratory in Pasadena, California. “That’s why this detection, if confirmed, is very important.”

This is the best evidence yet that Enceladus does have a liquid ocean, bound to cause a stir amongst planetary scientists and re-ignite excitement for the search for life living in a salty sub-surface ocean.

Source: New Scientist

A Mystery Aurora above Saturn’s Mysterious North Pole Hexagon

The aurora above Saturn's North Pole hexagon (NASA)

Not only does Saturn have a mysterious hexagonal shape etched into the bands of cloud above its north pole, it also has a unique magnetic structure. This is suggested by recent results recorded by the NASA Cassini probe that passed over the pole to see a huge active auroral region, much larger and more dynamic than expected. Interestingly, the NASA press release has not linked the strange aurora with the long-lived hexagonal shape in the gas giant’s atmosphere. Could the hexagon be formed by a unique magnetic structure above Saturn? Or could both phenomena be connected in some other way?
Continue reading “A Mystery Aurora above Saturn’s Mysterious North Pole Hexagon”

Saturn’s Hexagonal North Pole: What is Causing It?

Infrared observations of the south pole of Saturn as taken by the Cassini mission in 2007 and 2008 (NASA)
Infrared observations of the south pole of Saturn as taken by the Cassini mission in 2007 and 2008 (NASA)

The mystery of Saturn’s hexagonal shape embedded in its violent north polar cyclone just became more intriguing.

NASA’s Cassini probe has been orbiting the ringed gas giant for four years and has just returned some of the most detailed images of the planet’s stormy atmosphere to date. The south pole has been mapped and the north polar region has been imaged in near-infrared wavelengths. The north pole is currently facing away from the Sun, so by observing the atmosphere in these wavelengths, Cassini scientists can see Saturn’s cloud formations silhouette against the background glow of the gas giant’s internal heat. This provides the perfect opportunity to see the hexagon in unprecedented detail.

So what is generating this mysterious six-sided shape?
Continue reading “Saturn’s Hexagonal North Pole: What is Causing It?”