Cassini Finds ‘Nothing’ in Saturn’s Ring Gap


It’s official, there’s a whole lot of nothing in Saturn’s innermost ring gap.

This blunt — and slightly mysterious — conclusion was reached when scientists studied Cassini data after the spacecraft’s first dive through the gas giant’s ring plane. At first blush, this might not sound so surprising; the 1,200-mile-wide gap between Saturn’s upper atmosphere and the innermost edge of its rings does appear like an empty place. But as the NASA spacecraft barreled through the gap on April 26, mission scientists expected Cassini to hit a few stray particles on its way through.

Instead, it hit nothing. Or, at least, far fewer particles than they predicted.

“The region between the rings and Saturn is ‘the big empty,’ apparently,” said Earl Maize, Cassini’s project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected.”

Using Cassini’s Radio and Plasma Wave Science (RPWS), the scientists expected to detect multiple “cracks and pops” as the spacecraft shot through the gap. Instead, it picked up mainly signals from energetic charged particles buzzing in the planet’s magnetic field. When converted into an audio file, these signals make a whistling noise and this background whistle was expected to be drowned out by the ruckus of dust particles bouncing off the spacecraft’s body. But, as the following audio recording proves, very few pops and cracks of colliding debris were detected — it sounds more like an off-signal radio tuner:

Compare that with the commotion Cassini heard as it passed through the ring plane outside of Saturn’s rings on Dec. 18, 2016:

Now that is what it sounds like to get smacked by a blizzard of tiny particles at high speed.

“It was a bit disorienting — we weren’t hearing what we expected to hear,” said William Kurth, RPWS team lead at the University of Iowa, Iowa City. “I’ve listened to our data from the first dive several times and I can probably count on my hands the number of dust particle impacts I hear.”

From this first ring gap dive, NASA says Cassini likely only hit a handful of minute, 1 micron particles — particles no larger than those found in smoke. And that’s a bit weird.

As weird as it may be, the fact that the region of Cassini’s first ring dive is emptier than expected now allows mission scientists to carry out optimized science operations with the spacecraft’s instruments. On the first pass, Cassini’s dish-shaped high-gain antenna was used as a shield to protect the spacecraft as it made the dive. On its next ring dive, which is scheduled for Tuesday at 12:38 p.m. PT (3:38 p.m. ET), this precaution is evidently not needed and the spacecraft will be oriented to better view the rings as it flies through.

So there we have it, the first mysterious result of Cassini’s awesome Grand Finale! 21 ring dives to go…


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

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 Sees Earth and Moon Through Saturn’s Rings

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.

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:


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

Astroengine Interview with Dr Richard Greenberg: “Unmasking Europa”

A future mission to the Jovian moon Europa could incorporate a life-searching robotic submersible under the icy crust (NASA)
A future mission to the Jovian moon Europa could incorporate a life-searching robotic submersible under the icy crust (NASA)

On Wednesday (Feb. 18th), NASA and ESA decided to “prioritize” a mission to Jupiter. Set to be launched in 2020 (for a 2026 arrival in the Jovian system), NASA will work on a spacecraft called the Jupiter-Europa mission and ESA will work on the Jupiter-Ganymede mission. Both probes will be launched at the same time to carry out this unprecedented planetary mission. However, this doesn’t mean a mission to Saturn will be off the cards; NASA hinted that a return trip to the ringed gas giant will also be planned in tandem (following in the footsteps of the Cassini Equinox Mission). But Jupiter comes first.

In an enlightening interview earlier today, Dr Richard Greenberg, an eminent Europa scientist, discussed this recent NASA/ESA announcement with Astroengine Live and his excitement that there will be a return mission to the Jovian system. He is an expert in celestial mechanics and worked on several NASA projects at the University of Arizona’s Lunar and Planetary Laboratory. Dr Greenberg has also published a book called “Unmasking Europa” (of which I am very excited to receive a copy soon), detailing the science under the icy crust of the moon, where there is a tantalizing possibility life may thrive in tidally-heated sub-surface oceans.

But that’s not the best part. Dr Greenberg provides an exciting narrative about what form this Europa (European?) life may take… It’s not just microbial extraterrestrials that could survive in these environments

Be sure to listen in to my radio show, Astroengine Live on Wednesday, February 25th to hear the full recording of my conversation with Dr. Richard Greenberg.

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?”

Using Cassini to Test Radioactive Decay Rate Variation

Artist impression of Cassini orbiting Saturn (NASA)
Artist impression of Cassini orbiting Saturn (NASA)

In a previous Astroengine article, I explored the possibility that the variation in radioactive decay rates may be synchronised with Earth’s orbital variations in distance from the Sun. Naturally, this would be a huge discovery, possibly questioning the fundamental law that nuclear decay rates are constant, no matter where the material is in the Universe. One of the conclusions in the original decay rate research suggested that we should attach a sample of a radioisotope onto an interplanetary mission far beyond the orbit of Earth. By doing this, the relationship between decay rates and distance from the Sun should become obvious, and terrestrial decay rate variations can be tested.

But wait a minute, let’s have a think about this. Haven’t we already sent radioactive material on board interplanetary missions? What about all that plutonium we use to power interplanetary probes like Voyager, Pioneer, Galileo or Cassini? Plutonium is pretty radioactive… isn’t it?
Continue reading “Using Cassini to Test Radioactive Decay Rate Variation”