Bumper Car Moonlets Crash and Crumble in Saturn’s F Ring

Nothing stands still. Everything evolves. So why shouldn’t Saturn’s kookie, clumpy F ring put on a new face from time to time? 

A recent NASA-funded study compared the F ring’s appearance in six years of observations by the Cassini mission to its appearance during the Saturn flybys of NASA’s Voyager mission, 30 years earlier.

Example of a kink in part of Saturn's F ring. While the ring is held together by the shephard moons Prometheus and Pandora, which orbit just inside and  outside the ring, embedded moonlets are believed responsible for the kinks and clumps. Credit: NASA
A kink in part of Saturn’s F ring. While the ring is held together by the shepherd moons Prometheus and Pandora, which orbit just inside and outside the ring, embedded moonlets are believed responsible for the kinks and clumps. The rings is several hundred kilometers wide. Credit: NASA

While the F ring has always displayed clumps of icy matter, the study team found that the number of bright clumps has nose-dived since the Voyager space probes saw them routinely during their brief flybys 30 years ago. Cassini spied only two of the features during a six-year period.

Scientists have long suspected that moonlets up to 3 miles (5 km) wide hiding in the F ring are responsible for its uneven texture. Kinks and knots appear and disappear within months compared to the years of observation needed changes in many of the other rings.

Saturn's F ring is extremely narrow compared to the historic A, B and C rings. It measure just a few hundred kilometers across. Credit: NASA/Cassini
Saturn’s F ring is extremely narrow compared to the historic A, B and C rings. It measures just a few hundred kilometers across. Credit: NASA/Cassini

“Saturn’s F ring looks fundamentally different from the time of Voyager to the Cassini era,” said Robert French of the SETI Institute in Mountain View, California, who led the study along with SETI Principal Investigator Mark Showalter. “It makes for an irresistible mystery for us to investigate.”

A 2007 artist impression of the aggregates of icy particles that form the 'solid' portions of Saturn's rings. These elongated clumps are continually forming and dispersing. The largest particles are a few metres across.They clump together to form elongated, curved aggregates, continually forming and dispersing. Credit: NASA/JPL/Univ. of Colorado
A 2007 artist impression of small boulder-like chunks of ice that comprise Saturn’s rings. The largest are about 10-12 feet across.They clump together to form elongated, curved aggregates, continually forming and dispersing. Credit: NASA/JPL/Univ. of Colorado

Because the moonlets lie close to the ring and cross through it every orbit, the research team hypothesizes that the clumps are created when they crash into and pulverize smaller ring particles during each pass. They suspect that the decline in the number of exceptionally bright kinks and the clumps echoes a decline in the number of moonlets available to do the job.

So what happened between Voyager and Cassini? Blame it on Prometheus. The F ring circles Saturn at a delicate point called the Roche Limit. Any moons orbiting closer than the limit would be torn apart by Saturn’s gravitational force.

A possible culprit! Prometheus measures 74 miles (119 km) across and orbits the inner edge of Saturn's F ring. Credit: NASA
The culprit? Prometheus measures 74 miles (119 km) across and orbits the inner edge of Saturn’s F ring. Credit: NASA

“Material at this distance from Saturn can’t decide whether it wants to remain as a ring or coalesce to form a moon,” said French.  “Prometheus orbits just inside the F ring, and adds to the pandemonium by stirring up the ring particles, sometimes leading to the creation of moonlets, and sometimes leading to their destruction.”

Every 17 years the orbit of Prometheus aligns with the orbit of the F ring in a way that enhances its gravitational influence. The researchers think the alignment spurs the creation of lots of extra moonlets which then go crashing into the ring, creating bright clumps of material as they smash themselves to bits against other ring material.

Sounds like a terrifying version of carnival bumper cars. In this scenario, the number of moonlets would gradually drop off until another favorable Prometheus alignment.

The Voyagers encounters with Saturn occurred a few years after the 1975 alignment between Prometheus and the F ring, and Cassini was present for the 2009 alignment. Assuming Prometheus has been “working” to build new moons since 2009, we should see the F ring light up once again with bright clumps in the next couple years.

Cassini will be watching.

Stunning Amateur Timelapse of Jupiter ‘Re-enacts’ Voyager Flyby

Back in the 1970’s when NASA launched the two Voyager spacecraft to Jupiter, Saturn, Uranus, and Neptune, I remember being mesmerized by a movie created from Voyager 1 images of the movement of the clouds in Jupiter’s atmosphere. Voyager 1 began taking pictures of Jupiter as it approached the planet in January 1979 and completed its Jupiter encounter in early April. During that time it took almost 19,000 pictures and many other scientific measurements to create the short movie, which you can see below, showing the intricate movement of the bright band of clouds for the first time.

Now, 35 years later a group of seven Swedish amateur astronomers achieved their goal of replicating the Voyager 1 footage, not with another flyby but with images taken with their own ground-based telescopes.

“We started this joint project back in December of 2013 to redo the NASA Voyager 1 flyby of Jupiter,” amatuer astronomer Göran Strand told Universe Today. “During 90 days we captured 560 still images of Jupiter and turned them into 90 complete maps that covered the whole of Jupiter’s surface.”

Their newly released film, above details the work they did and the hurdles they overcame (including incredibly bad weather in Sweden this winter) to make their dream a reality. They called their project “Voyager 3.”

Animated gif of the 'Voyager 3' team re-enactment of the Voyager 1 flyby. Credit: Voyager 3 team, via Kristoffer Åberg.
Animated gif of the ‘Voyager 3’ team re-enactment of the Voyager 1 flyby. Credit: Voyager 3 team, via Kristoffer Åberg.
It is really an astonishing project and those of you who do image processing will appreciate the info in the video about the tools they used and how they did their processing to create this video.

The seven Swedish astronomers who participated in the Voyager 3 project are (from left to right in the photo below) Daniel Sundström, Torbjörn Holmqvist, Peter Rosén (the project initiator), Göran Strand, Johan Warell and his daughter Noomi, Martin Högberg and Roger Utas.

The Swedish team of amateur astronomers who compiled the 'Voyager 3' project. Image courtesy Peter Rosén.
The Swedish team of amateur astronomers who compiled the ‘Voyager 3’ project. Image courtesy Peter Rosén.

Congrats to the team of Voyager 3!

You can read more about the Voyagers visits to Jupiter here from NASA.

Voyager3Movie from Peter Rosén on Vimeo.

Video: Carolyn Porco Discusses Her Life at Saturn

Space historian Andrew Chaikin sat down with planetary scientist Carolyn Porco, and she discusses how her career has ended up focusing on the Saturn system. I love how Porco relates how even she has been “blown away” by some of the imagery sent back by the missions — just like the rest of us! — saying she’s had to call members of her team several times to verify she wasn’t looking at computer simulations vs. real images.

Enjoy this candid interview of one of the leading planetary scientists of our day.


Hoping Aliens are Hipsters Who Enjoy Vinyl

The Colbert Report
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JPL’s venerable Ed Stone, the Project Scientist for the Voyager spacecraft for over 40 years, made an appearance on the Colbert Report last night, bantering easily with the no-holds-barred host and discussing the significance of the Voyager mission, from the two launches in 1977 to Voyager 1’s recent celebrated arrival in interstellar space.

Colbert also was tasked by NASA to present Stone with NASA’s Distinguished Public Service Medal for a lifetime of scientific achievement. See below:

The Colbert Report
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The Eerie Music of Interstellar Space

While it’s true that there’s no air to carry sound in space, starship explosions would be strangely silent and no one can hear you scream, this latest Science @ NASA video reminds us that “space can make music, if you know how to listen.”

And the “how” in this case is with the Plasma Wave Science Experiment aboard the Voyager 1 spacecraft, which is now playing the sounds of interstellar space — with a little help from University of Iowa physics professor and experiment principal investigator Don Gurnett. Watch the video above for a front-row seat (and read more about Voyager’s historic crossing of the heliosphere here.)

Astro Poetry: The First Starship

Our favorite astro-poet, Stuart Atkinson, has written a wonderful ode to Voyager 1 in commemoration of the spacecraft reaching interstellar space. Stu has a knack for turning science into poetry!

The First Starship

I needed no nacelles to push me onwards;
No dilithium crystals crackled in my heart.
Yet I have left Sol so far behind me she is
Just a star now, a golden spark in a salt grain sea,
And I can feel her gentle breath on my cheek
No more.

In my ears now the whalesong of the universe
Drowns out the sounds of distant, troubled Earth.
Oh, the blissful peace!
Out here all I can hear
Is the fabled music of the spheres.
Each trembling tone rolling under me,
Every mellow note washing over me
Was sung somewhere Out There.
Melodies ripped from ravenous black holes’ throats,
Screamed from the broken hearts of dying stars
Swirl around me, multi-wavelength whispers
In the dark and endless night.

My head is full of memories…
Skimming Titan’s marmalade-haze atmosphere;
My first sight of Jove’s great bloodshot eye,
Staring back at me, into me, as I flew by;
Earth as Pale Blue Dot, a Sagan sequin
Dancing in a sunbeam…

Ahead now – the solar system’s Barrier Reef.
Terra will whip around Sol 300 times before
I reach the Oort’s icy inner harbour wall
And tens of thousands of times more before
I finally leave port, sailing on in serene silence
For forty millennia more before I venture anywhere
Near another star…

And in ten million years, when Earth’s proud citadels
And cities have crumbled and whatever evolves
In their dust to take Mankind’s place
Stares out into space with curious, alien eyes,
I will still be flying through the stars.
Your legacy. Proof that once you dared to dream
Noble, Camelot dreams
And reached out, through me, to explore eternity.

(c) Stuart Atkinson Sept 13th 2013

Written to commemorate and celebrate the Sept 12, 2013 announcement that Voyager 1 had entered interstellar space.

Read more of Stu’s poetry at this Astropoetry website and his other musings at Cumbrian Sky.

Messages To Voyager: Welcome to Interstellar Space

On the Voyager spacecraft are the famous Voyager Golden Records, which send messages from planet Earth to … whatever or whoever may find it in the future. In celebration of Voyager 1 making it into interstellar space (read all the details here) a few friends put together a video to congratulate the spacecraft and the team. Neil deGrasse Tyson, Wil Wheaton, Carl Sagan’s son and others shared their messages to the Voyager 1 spacecraft.

Feel free to leave your message to Voyager in the (new and improved) comment section.

It’s Official: Voyager 1 Is Now In Interstellar Space

This artist's concept shows the Voyager 1 spacecraft entering the space between stars. Interstellar space is dominated by plasma, ionized gas (illustrated here as brownish haze), that was thrown off by giant stars millions of years ago.Credit: NASA.

In a cosmically historic announcement, NASA says the most distant human made object — the Voyager 1 spacecraft — is in interstellar space, the space between the stars. It actually made the transition about a year ago.

“We made it!” said a smiling Dr. Ed Stone, Voyager’s Project Scientist for over 40 years, speaking at a briefing today. “And we did it while we still had enough power to send back data from this new region of space.”

While there is a bit of an argument on the semantics of whether Voyager 1 is still inside or outside of our Solar System (it is not farther out than the Oort Cloud — it will take 300 more years reach the Oort cloud and the spacecraft is closer to our Sun than any other star) the plasma environment Voyager 1 now travels through has definitely changed from what comes from our Sun to the plasma that is present in the space between stars.

There’s also been a recent debate on if Voyager was really in or out of the Solar System – a debate between the latest various science papers and their authors. (More on that later…)

But Stone now says the evidence in clear: Voyager 1 has made the transition.

“This conclusion is possible from the space craft’s plasma wave instrument,” Stone said. “The 36-year old probe is now sailing through uncharted waters of a new cosmic sea and it has brought us along for the journey.”

Voyager 1’s 36-year, 13 billion mile journey began in 1977.

Scientists thought that when the spacecraft had crossed over into interstellar space, the magnetic field direction would change. However, it turned out that didn’t happen, and scientists determined they needed to look at the properties of the plasma instead.

The Sun’s heliosphere is filled with ionized plasma from the Sun. Outside that bubble, the plasma comes from the explosions of other stars millions of years ago. The main tell-tail difference is the interstellar plasma is denser.

Unfortunately, the real instrument that was designed to make the measurements on the plasma quit working in the 1980’s, so scientists needed a different way to measure the spacecraft’s plasma environment to make a definitive determination of its location.

Instead they used the plasma wave instrument, located on the 10-meter long antennas on Voyager 1 and an unexpected “gift” from the Sun, a massive Coronal Mass Ejection.

The antennas have radio receivers at the ends – “like the rabbit ears on old television sets,” said Don Gurnett, who led the plasma wave science team at the University of Iowa. The CME erupted from the Sun in March 2012, and eventually arrived at Voyager 1’s location 13 months later, in April 2013. Because of the CME, the plasma around the spacecraft began to vibrate like a violin string.

The pitch of the oscillations helped scientists determine the density of the plasma. Stone said the particular oscillations meant the spacecraft was bathed in plasma more than 40 times denser than what they had encountered in the outer layer of the heliosphere.

“Now that we have new, key data, we believe this is mankind’s historic leap into interstellar space,” said Stone, “The Voyager team needed time to analyze those observations and make sense of them. But we can now answer the question we’ve all been asking — ‘Are we there yet?’ Yes, we are.”

Artist's impression of Voyager 1's position on the sky when observed by the Very Long Baseline Array (VLBA) on February 21, 2013, at which point -- according to NASA's Jet Propulsion Laboratory -- Voyager was already outside of our Solar System. The actual image from the data (enlarged section) is 0.5 arcseconds across. The radio signal as shown is a mere 1 milliarcsecond across. Credit: Alexandra Angelich, NRAO/AUI/NSF.
Artist’s impression of Voyager 1’s position on the sky when observed by the Very Long Baseline Array (VLBA) on February 21, 2013, at which point — according to NASA’s Jet Propulsion Laboratory — Voyager was already outside of our Solar System. The actual image from the data (enlarged section) is 0.5 arcseconds across. The radio signal as shown is a mere 1 milliarcsecond across.
Credit: Alexandra Angelich, NRAO/AUI/NSF.

The plasma wave science team reviewed its data and found an earlier, fainter set of oscillations in October and November 2012 from other CMEs. Through extrapolation of measured plasma densities from both events, the team determined Voyager 1 first entered interstellar space in August 2012.

“We literally jumped out of our seats when we saw these oscillations in our data — they showed us the spacecraft was in an entirely new region, comparable to what was expected in interstellar space, and totally different than in the solar bubble,” Gurnett said. “Clearly we had passed through the heliopause, which is the long-hypothesized boundary between the solar plasma and the interstellar plasma.”

The new plasma data suggested a timeframe consistent with abrupt, durable changes in the density of energetic particles that were first detected on Aug. 25, 2012.

At that time, Stone said, “We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space,” adding that the data are changing in ways that the team didn’t expect, “but Voyager has always surprised us with new discoveries.”

Now, after further review, the Voyager team generally accepts the August 2012 date as the date of interstellar arrival. The charged particle and plasma changes were what would have been expected during a crossing of the heliopause. This reinforces that definitive science results don’t always come fast.

“The team’s hard work to build durable spacecraft and carefully manage the Voyager spacecraft’s limited resources paid off in another first for NASA and humanity,” said Suzanne Dodd, Voyager project manager, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We expect the fields and particles science instruments on Voyager will continue to send back data through at least 2020. We can’t wait to see what the Voyager instruments show us next about deep space.”

There has been some back and forth about whether Voyager 1 was in or out of the Solar System. As we said, it was first questioned in August of 2012, with more speculation in December 2012, then in March of 2013 a paper by William Webber and F.B. McDonald claimed Voyager 1 had exited the Solar System the previous December, but Stone insisted the data wasn’t positive yet. Then about a month ago a paper came out by Marc Swisdak from the University of Maryland saying Voyager 1 was out of the solar system, but at that point Ed Stone and the Voyager team put out a statement saying they were still making that determination.

Today, Gurnett revealed that the timing of all scientists being in “official” agreement was off due to the timing of the review process for scientific papers. “Our paper was submitted a month before theirs, they just got through the review cycle before ours,” he said. “But theirs was basically a theory paper.”

Voyager 1 and its twin, Voyager 2, were launched 16 days apart in 1977. A fortuitous planetary alignment that only happens every 176 years enabled the two spacecraft to join together to reach all the outer planets in a 12 year time period. Both spacecraft flew by Jupiter and Saturn. Voyager 2 also flew by Uranus and Neptune. Voyager 2, launched before Voyager 1, is the longest continuously operated spacecraft. It is about 9.5 billion miles (15 billion kilometers) away from our Sun.

Voyager mission controllers still talk to or receive data from Voyager 1 and Voyager 2 every day, though the emitted signals are currently very dim, at about 23 watts — the power of a refrigerator light bulb. By the time the signals get to Earth, they are a fraction of a billion-billionth of a watt. Data from Voyager 1’s instruments are transmitted to Earth typically at 160 bits per second, and captured by 34- and 70-meter NASA Deep Space Network stations. Traveling at the speed of light, a signal from Voyager 1 takes about 17 hours to travel to Earth. After the data are transmitted to JPL and processed by the science teams, Voyager data are made publicly available.

“Voyager has boldly gone where no probe has gone before, marking one of the most significant technological achievements in the annals of the history of science, and adding a new chapter in human scientific dreams and endeavors,” said John Grunsfeld, NASA’s associate administrator for science in Washington. “Perhaps some future deep space explorers will catch up with Voyager, our first interstellar envoy, and reflect on how this intrepid spacecraft helped enable their journey.”

Scientists do not know when Voyager 1 will reach the undisturbed part of interstellar space where there is no influence from our Sun. They also are not certain when Voyager 2 is expected to cross into interstellar space, but they believe it is not very far behind.

“In a sense this is only really the beginning. We’re now going into a completely alien environment and what Voyager is going to discover truly unknown,” said Gary Zank, from the Department of Space Sciences at the University of Alabama, Huntsville, speaking at today’s press conference.

While Voyager 1 will keep going, we will not always be able to communicate with it, as we do now. In 2025 all instruments will be turned off, and the science team will be able to operate the spacecraft for about 10 years after that to just get engineering data. Voyager 1 is aiming toward the constellation Ophiuchus. In the year 40,272 AD, Voyager 1 will come within 1.7 light years of an obscure star in the constellation Ursa Minor (the Little Bear or Little Dipper) called AC+79 3888. It will swing around the star and orbit about the center of the Milky Way, likely for millions of years.

Read more: NASA, JPL