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Listening in on Enceladus

When I was a boy, I used to scan shortwave frequencies with an old Lafayette receiver in search of distant stations. When I learned that Jupiter was a radio source, my passion for radio DXing took a new turn, merging with my interest in astronomy. When I tried to log the planet’s violent outbursts, I learned with a little digging in the library that Jupiter could be detected from about 15 MHz up to 40 MHz, with the best window somewhere between 18 MHz and 28 MHz.

Called ‘decametric noise storms,’ the Jovian bursts sometimes sounded like ocean waves hitting a shore, but there were also short bursts that could be confused with local lightning, and to this day I’m not really sure whether I really heard Jupiter or not. When you’re listening for something that sounds like the ocean in the shortwave bands, it’s all too easy to think you’re hearing it in the background noise, and a little imagination makes you think you’ve found your target.

These days we can listen to just about anything on the Internet, so I’ll point you to the Io B storm of November 27, 2001, on a page that offers charts, links and an anecdotal account of a reception. Jupiter seems to have acquired a fan base among amateur radio astronomers.

But enough of Jupiter. This morning we need to talk about Saturn and the plasma waves Cassini detected moving from the planet to its rings and the moon Enceladus. These produce the distinctive sound you can hear in the YouTube video below. (If you get Centauri Dreams through email, the video isn’t going to show, but go to this link to see it). Here the recording time was compressed from 16 minutes to 28.5 seconds.

Image: New research from the up-close Grand Finale orbits of NASA’s Cassini mission shows a surprisingly powerful interaction of plasma waves moving from Saturn to its moon Enceladus. Researchers converted the recording of plasma waves into a “whooshing” audio file that we can hear — in the same way a radio translates electromagnetic waves into music. Much like air or water, plasma (the fourth state of matter) generates waves to carry energy. The recording was captured by the Radio Plasma Wave Science (RPWS) instrument Sept. 2, 2017, two weeks before Cassini was deliberately plunged into the atmosphere of Saturn. Credit: NASA/JPL-Caltech/University of Iowa.

The plasma wave interactions are the subject of a recent paper from lead author Ali Sulaiman (University of Iowa), who is a member of the Radio Plasma Wave Science team, RPWS being the instrument on Cassini that recorded these waves traveling on magnetic field lines.

“Enceladus is this little generator going around Saturn, and we know it is a continuous source of energy,” says Sulaiman. “Now we find that Saturn responds by launching signals in the form of plasma waves, through the circuit of magnetic field lines connecting it to Enceladus hundreds of thousands of miles away.”

Image: NASA’s Cassini spacecraft’s Grand Finale orbits found a powerful interaction of plasma waves moving from Saturn to its rings and its moon Enceladus. Credit: NASA/JPL-Caltech.

Enveloped by Saturn’s magnetic field, Enceladus is a geologically active place, emitting the famous geysers we’ve so often examined in Cassini imagery. The plumes of water vapor from what appears to be an inner ocean become ionized, accounting for the strong interaction between Enceladus and the planet; similar interactions occur between Saturn and its rings.

We get this information thanks to Cassini’s high-inclination Grand Finale orbits, which brought the spacecraft both to its closest approach to the cloud tops and to the inner edge of the D ring. The recording itself was captured on September 2, 2017, just two weeks before Cassini’s final plunge. Measurements of the top of the ionosphere as well as the environment around the rings showed the plasma wave interactions and underline the dynamic nature of the Saturn system.

The paper is Sulaiman et al., “Enceladus auroral hiss emissions during Cassini’s Grand Finale,” published online by Geophysical Research Letters 7 June 2018 (abstract).


{ 10 comments… add one }
  • Matterbeam July 10, 2018, 10:19

    Are there any estimates of the mass flow rate and velocity of this plasma flow?

    In other words, the watts of power it contains.

    • Paul Gilster July 10, 2018, 12:24

      Am trying to obtain some numbers on this right now. Will get back with more when I find them.

      • Paul Gilster July 10, 2018, 19:24

        Matterbeam, I just had this response from Dr. Sulaiman:

        “Unfortunately the instrument responsible for measuring particles in the appropriate energy range was not operating at the time. However, we know the power in the electric field was over 10^(-10) V^2 m^-2 Hz-2 and the associated meridional current per radian was ~1 MA rad^-1. This magnitude was comparable to the auroral field lines.”

  • galacsi July 10, 2018, 16:51

    “Now we find that Saturn responds by launching signals in the form of plasma waves, through the circuit of magnetic field lines connecting it to Enceladus hundreds of thousands of miles away.”

    How enceladus could have a magnetic field ? Or is there some electrostatic interraction between Enceladus and the Saturn magnetosphere ? Maybe we have there a cause for Enceladus energy ?

    • ericSECT July 11, 2018, 6:17

      I have also been thinking for a while, induction heating of Enceladus and it’s interior, as it’s magnetic field cuts through Saturn’s magnetic field.

      Perhaps a combination of tidal and EMF induction heating is the source? Or perhaps this system of moons, including Enceladus, are not as old as our solar system and there is still residual heat of formation (but why not a other moons?).

    • Alex Tolley July 11, 2018, 10:20

      Wouldn’t a saltwater subsurface ocean act as the conductor to induce a magnetic field?

  • Andrew Palfreyman July 10, 2018, 23:30

    I can’t tell whether all this is a net plus or minus for potential life in the Enceladus ocean.

  • Gerald Cecil July 11, 2018, 8:44

    “Morbius, something is approaching from the south west. It is now quite close.” Robby in Forbidden Planet

  • ljk July 11, 2018, 8:50

    Senior scientist argues that we should bypass Europa for Enceladus

    “We just don’t know that much about Europa with certainty.”

    Eric Berger – 7/5/2018, 8:51 AM

    In its quest to find extant life in the Solar System, NASA has focused its gaze on the Jovian moon Europa, home to what is likely the largest ocean known to humans. Over the next decade, the space agency is slated to launch not one, but two multi-billion dollar missions to the ice-encrusted world in hopes of finding signs of life.

    Europa certainly has its champions in the scientific community, which conducts surveys every decade to establish top priorities. The exploration of this moon ranks atop the list of most desirable missions alongside returning some rocky material from Mars for study on Earth. But there is another world even deeper out in the Solar System that some scientists think may provide an even juicer target, Saturn’s moon Enceladus. This is a tiny world, measuring barely 500km across, with a surface gravity just one percent of that on Earth. But Enceladus also has a subsurface ocean.

    “I have a bias, and I don’t deny that,” says Carolyn Porco, one of the foremost explorers of the Solar System and someone who played a key imaging role on the Voyagers, Cassini, and other iconic NASA spacecraft. “But it’s not so much an emotional attachment with objects that we study, it’s a point of view based on the evidence. We simply know more about Enceladus.”

    Full article here:


    We can, should, and must explore BOTH worlds. It should not be about budgets or bias. Both moons are fascinating places in their own right and both have a strong possibility for containing native life forms. This should not even be a debate.

    NASA is no longer the only player in this game. Let us not forget this when we make such decisions. Plus, Europa is 400 million miles closer to Earth.

  • ljk July 11, 2018, 8:52

    Bacterial survival in salty antifreeze raises hope for life on Mars and icy moons

    By Joelle Renstrom – Jul 4, 2018

    New research by a trans-Atlantic team of scientists suggests that bacteria could survive in briny chemicals that exist on Mars, Enceladus, Europa, Pluto and possibly elsewhere.

    The discovery of plumes and subsurface oceans on Jupiter’s moon Europa, organic materials on Mars, and the likelihood of hydrothermal vents in the oceans of Saturn’s moon Enceladus, inches humanity closer to discovering life elsewhere. Such life would have to withstand extreme environments, and previous studies indicate that various types of bacteria can.

    Liquid oceans on some bodies far from the Sun have lower freezing points because of chemicals and salts that amount to antifreeze, so microbial life would have to survive both the temperatures and the elements. To hone in on parameters for microbial survivability, researchers from the Technical University of Berlin, Tufts University, Imperial College London, and Washington State University conducted tests with Planococcus halocryophilus, a bacteria found in the Arctic permafrost.

    They subjected the bacteria to sodium, magnesium and calcium chloride cocktails, as well as solutions of perchlorate, which is a chemical compound that may help Mars sustain liquid water during the summer. Lead author Jacob Heinz, of the Technical University of Berlin’s Center of Astronomy and Astrophysics, says that the researchers expanded beyond the conventional sodium chloride solution because “there’s much more than that on Mars.”

    Full article here:


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