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What Io Can Teach Us

Io doesn’t come into play very much on Centauri Dreams, probably because of the high astrobiological interest in the other Galilean satellites of Jupiter — Europa, Callisto and Ganymede — each of which may have an internal ocean and one, Europa, a surface that occasionally releases material from below. Io seems like a volcanic hell, as indeed it is, but we saw yesterday that its intense geological activity produces interactions with Jupiter’s powerful magnetosphere, leading to radio emissions that might be a marker for exomoon detection.

The exoplanet hunt has diverse tools to work with, from the transits that result from chance planetary alignments to radial velocity methods that measure the motion of a host star in response to objects around it. Neither is as effective at planets in the outer parts of a solar system as we’d like, so we turn to direct imaging for large outer objects and sometimes luck out with gravitational microlensing, finding a planetary signature in the occultation of a distant star. All these methods work together in fleshing out our knowledge of exoplanets, and it will be helpful indeed if electromagnetic detection is a second way beyond transits of looking for an exomoon.

That first exomoon detection will be a major event. But in studying Io’s interactions with Jupiter, the paper from Zdzislaw Musielak’s team at the University of Texas at Arlington (see yesterday’s post) leaves open the question of just how common such moons are, and of course we don’t know the answer, other than to say that we do have the example of Titan as a large moon with a thick, stable atmosphere. Clearly Io rewards study in and of itself, and its recent intense activity reminds us what can happen to an object this close to a gas giant’s enormous gravity well. With Musielak’s work in mind, then, lets have a run at recent Io findings.

What we learn from Imke de Pater (UC-Berkeley) and colleagues is that a year ago, Io went through a two-week period of massive volcanic eruptions sending material hundreds of kilometers above the surface, a pattern that may be more common than we once thought. Io is small enough (about 3700 kilometers across) that hot lava rises high above the surface, and in the case of the most recent events, pelted hundreds of square kilometers with molten slag.

Never a quiet place, Io is usually home to a large outburst every few years, but the scale here was surprising. Says de Pater colleague Ashley Davis (JPL/Caltech):

“These new events are in a relatively rare class of eruptions on Io because of their size and astonishingly high thermal emission. The amount of energy being emitted by these eruptions implies lava fountains gushing out of fissures at a very large volume per second, forming lava flows that quickly spread over the surface of Io.”


Image: Images of Io obtained at different infrared wavelengths (in microns, μm, or millionths of a meter) with the W. M. Keck Observatory’s 10-meter Keck II telescope on Aug. 15, 2013 (a-c) and the Gemini North telescope on Aug. 29, 2013 (d). The bar on the right of each image indicates the intensity of the infrared emission. Note that emissions from the large volcanic outbursts on Aug. 15 at Rarog and Heno Paterae have substantially faded by Aug. 29. A second bright spot is visible to the north of the Rarog and Heno eruptions in c and to the west of the outburst in d. This hot spot was identified as Loki Patera, a lava lake that appeared to be particularly active at the same time. Image by Imke de Pater and Katherine de Kleer, UC Berkeley.

De Pater discovered the first two outbursts on August 15, 2013, with the brightest at a caldera called Rarog Patera. The other occurred at the Heno Patera caldera (a caldera is not so much a crater but the collapse of surface after a volcanic eruption, leaving a large, bowl-shaped depression with surrounding scarps). The Rarog Patera event produced, according to observations conducted at the Keck II instrument in Hawaii, a 9-meter thick lava flow, one that covered 80 square kilometers. The Heno Patera flow covered almost 200 square kilometers.

But the main event was on August 29, revealed in observations led by Berkeley grad student Katherine de Kleer at the Gemini North telescope on Mauna Kea and the nearby Infrared Telescope Facility (IRTF). The actual thermal source of the eruption had an area of 50 square kilometers in an event apparently dominated by lava fountains. Usefully, the de Pater team tracked the third outburst for almost two weeks, providing data that will help us understand how such volcanic activity influences Io’s atmosphere. That, in turn, will give us insights into how eruptions support the torus of ionized gas that circles Jupiter in the region of Io’s orbit.


Image: The Aug. 29, 2013, outburst on Io was among the largest ever observed on the most volcanically active body in the solar system. Infrared image taken by Gemini North telescope, courtesy of Katherine de Kleer, UC Berkeley.

Here again we have helpful synergies between different tools, in this case the Japanese HISAKI (SPRINT-A) spacecraft, whose own observations of the Io plasma torus supplement what de Kleer observed in Hawaii. The correlation of the data sets may provide new insights into the process and, if Musielak’s methods at exomoon detection pay off through future radio observations, may help us interpret those results. The gravitational tugs of Jupiter, Europa and Ganymede feed Io’s volcanic activity, surely a scenario that is repeated around gas giants elsewhere. If so, the Io ‘laboratory’ will turn out to have surprising exomoon implications.

Three papers came out of this work, the first being de Pater et al., “Two new, rare, high-effusion outburst eruptions at Rarog and Heno Paterae on Io,” published online in Icarus 26 July 2014 (abstract). We also have de Kleer et al., “Near-infrared monitoring of Io and detection of a violent outburst on 29 August 2013,” published online in Icarus 24 June, 2014 (abstract) and de Pater, “Global near-IR maps from Gemini-N and Keck in 2010, with a special focus on Janus Patera and Kanehekili Fluctus,” published online in Icarus 10 July 2014 (abstract). This UC-Berkeley news release is also helpful.


Comments on this entry are closed.

  • ljk August 14, 2014, 13:38

    Could life exist on Io? Some speculation here:


    …and here…


    …and here:


    Did you know that Io’s volcanoes are not where they are supposed to be?


    A very informative and illustrative slide presentation all about that hot little satellite:


    Although there was a famous paper in Science that came out just days before Voyager 1 revealed Io’s true nature in March of 1979, the idea of active volcanoes on that moon were shocking to most, even though huge and relatively young volcanoes had been discovered on Mars just eight years earlier by Mariner 9.

    I recall in the 1978 book on the Voyager Interstellar Record titled Murmurs of Earth there was a chapter speculating on what the Voyager probes might find at the Jovian system. Written by Carl Sagan, he declared there may be seas of salt on Io that were blown off the moon into space by Jupiter’s influence and the solar wind. Although he and others knew about the Io torus, Sagan did not speculate further on how or why particles were emanating from the moon.

    Here is a paper on the history of observations of Io. Even back in the day the Galilean moons were not featureless to big telescopes:


    If only Pioneer 10 and 11 had been equipped with better imaging systems, and I am not just talking about the technology of the time.


    These days it would be unthinkable not to have good electronic eyes on a space probe; even Juno has a camera despite the fact that its mission was not about imaging Jupiter. NASA PR knows better now.

  • Joëlle B August 14, 2014, 23:33

    It’s been 404 years since the discovery of Io. Funny that when Galileo first observed the satellites, the power of his telescope was so poor that he couldn’t initially distinguish it from Europa and that they are all called Galilean moons, yet the source of their individual names comes from Marius. I guess both parties won in the end.

  • ljk August 15, 2014, 10:36

    We may want to credit the discovery of at least one of the so-called Galilean moons – probably Ganymede – to a Chinese astronomer/astrologer named Gan De:


    And supposedly in the European Middle Ages there were reports of people seeing little “fireflies” around Jupiter, as technically the four big moons can be seen with unaided vision except for the giant planet’s glare. However the one time I read this I could not find any sources – any help here?

  • ljk August 15, 2014, 10:50

    By the way, Joelle B., Galileo may not have been working with the most powerful of telescopes, but he could tell the four Jovian moons apart, as his records show here in Siderius Nuncius:



    So I am not quite certain where you got your comment about Io and Europa being indistinguishable. When I was a kid my father gave me a telescope that was about the same size as Galileo’s and I could see all four moons clearly. I could even do it with 7×35 binoculars with only a little effort.

    Galileo also saw distant Neptune in 1612-13 with his telescopes, although he did not recognize it as a planet:


  • Joëlle B. August 15, 2014, 20:51

    ljk said on August 15, 2014 at 10:50

    “So I am not quite certain where you got your comment about Io and Europa being indistinguishable.”


    Go down to the Jovian System section, it’s in the “Discoverer” subsection of Jupiter II (Europa).

  • Joëlle B. August 15, 2014, 21:02
  • ljk August 17, 2014, 17:26

    I stand corrected. Nice sites, by the way.

  • ljk August 18, 2014, 10:06

    On one of the pages to the site linked above which details Galileo’s discovery observations of the main Jovian moons in 1610, I came across this interesting tidbit which I think someone could turn into an interesting project. I quote it after the link:


    This observation on the 12th is the only time Galileo sketches a moon that isn’t there. Both Europa and Io are moving from east to west (toward the right in the figure). They pass in front of Jupiter before sunset and remain to the west of it all night. There are no other Jovian moons within reach of Galileo’s telescope (the first non-Galilean moon, Amalthea, was discovered in 1892 by E.E. Barnard using the Lick Observatory’s 36-inch refractor), and no stars brighter than magnitude 9.5 are within 10 arcminutes of Jupiter (a circle almost as big as the width of this diagram).

    Galileo may be seeing an asteroid. Unfortunately, JPL’s search for small bodies doesn’t support dates prior to 1800, in part because of the difficulty of calculating accurate orbits for these objects further into the past.

    So we don’t yet know what Galileo sees here, and he writes that at the fourth hour the little star that was close to Jupiter to the east no longer appears.