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Enceladus Hotspots, and Memories of Orion

Although we’ve been preoccupied largely with theoretical matters this week, I don’t want it to close without reference to the new Cassini imagery of Enceladus. This shot was made at a phase angle of 145 degrees when Cassini was about 14,000 kilometers from Enceladus, during the flyby of November 21. The remarkable jets spraying from the fractured surface in the south polar region are clearly visible.

Image: Dramatic plumes, both large and small, spray water ice out from many locations along the famed “tiger stripes” near the south pole of Saturn’s moon Enceladus. The tiger stripes are fissures that spray icy particles, water vapor and organic compounds. More than 30 individual jets of different sizes can be seen in this image and more than 20 of them had not been identified before. At least one jet spouting prominently in previous images now appears less powerful. Credit: NASA/JPL/SSI.

I keep thinking about Project Orion, back in the crazy days before the Test Ban Treaty of 1963 closed down the nuclear option. The prospect of taking a huge vessel with a crew of 100 all the way to Saturn as early as 1968 was much in the air at Los Alamos, and Enceladus was to have been the ultimate destination, chosen because observations of the distant moon seemed to show plenty of ice on the surface. So gleefully did the Orion team ponder its propulsive capabilities that project leader Ted Taylor wanted to install a two-ton barber’s chair on the ship, a poke in the eye to chemical rocketry and all its limitations. The atomic spaceship was going to be big.

As to Enceladus, Dyson recalled:

“We knew very little about the satellites in those days. Enceladus looked particularly good. It was known to have a density of .618, so it clearly had to be made of ice plus hydrocarbons, really light things, which were what you need both for biology and for propellant, so you could imagine growing your vegetables there…”

The quote is from George Dyson’s Project Orion: The True Story of the Atomic Spaceship (New York: Henry Holt, 2002), and it always makes me wonder what Dyson and crew would have thought of Enceladus, with its extraordinary sprays of fine material showing geological activity and the possibility of liquid water, when they actually arrived. The new Cassini imagery shows us more jets than ever before, more than thirty individual geysers in one mosaic, with changes to previously seen jets that are telling:

“This last flyby confirms what we suspected,” said Carolyn Porco, imaging team lead based at the Space Science Institute in Boulder, Colo. “The vigor of individual jets can vary with time, and many jets, large and small, erupt all along the tiger stripes.”

The section of Baghdad Sulcus shown below combines heat data with visible-light images for a 40-kilometer stretch of this, the longest of the so-called ‘tiger stripes.’ Peak temperatures along Baghdad Sulcus reach 180 kelvin, perhaps as high as 200 kelvin, which the Cassini team believes is the result of heating by upwelling water vapor. This is an intense effect — the heat is confined to a narrow region about a kilometer wide along the fracture, and its strength varies along the length of the fissure.

Image: A mosaic combining high-resolution data from the imaging science subsystem and composite infrared spectrometer aboard NASA’s Cassini spacecraft. Pockets of heat appear along one of the mysterious fractures in the south polar region of Saturn’s moon Enceladus. The fracture, named Baghdad Sulcus, is one of the so-called “tiger stripe” features that erupt with jets of water vapor and ice particles. It runs diagonally across the image. This mosaic, obtained on Nov. 21, 2009, shows a 40-kilometer (25-mile) segment of Baghdad Sulcus and illustrates the correlation between the geologically youthful surface fractures and anomalously warm temperatures recorded in the south polar region. It shows the highest-resolution data yet of the heat leaking from the moon’s interior along the tiger stripes.

This JPL news release goes into more detail:

While the heat appears to emanate mostly from the main Baghdad tiger stripe, some of the fractures branching off or parallel to it also appear warmer and active to varying degrees, though this needs to be confirmed by further analysis. The total amount of infrared energy and the relative amounts given off at different wavelengths show that the highest temperatures along Baghdad Sulcus are limited to a region no more than tens of meters (yards) across. Most of the heat measured by the infrared spectrometer probably arises from the warm flanks of the active fractures, rather than their central fissures. The narrow central fissure is probably even warmer than the 180 Kelvin (minus 140 degrees Fahrenheit) detected – possibly warm enough for liquid water in the fractures to be the source of the observed jets.

Carolyn Porco refers to Enceladus’ “organic-rich, liquid sub-surface environment” as “the most accessible extraterrestrial watery zone known in the Solar System.” The temperature differential between places like Baghdad Sulcus and the 50 kelvin reading of the surrounding surface is fascinating, and tells us that melting underground ice in these regions may not be all that difficult. Too bad we missed out on Orion’s 1968 journey, but the eight Cassini flybys thus far are telling us much about this unexpectedly interesting moon, surely the target of a future mission of its own.


Comments on this entry are closed.

  • Gregory Benford February 26, 2010, 14:00

    Orion memories remind us that nuclear propulsion is still the only efficient way to explore the solar system. For further expeditions, our work from that same era, that gave us a Nerva craft tested for 100 hours, remains the guide. We need only take up the challenge.

  • Chris Jenkins February 26, 2010, 14:10

    Ah, Project Orion. I first learned about it watching Cosmos (first run!) when I was a kid, and I have to agree with Dr. Sagan that it’s a great pity it never went forward.

    Being older and more aware as I am now, though, I do think I’d be rather concerned about the “exhaust” it would produce. Even if it wasn’t launched anywhere near the Earth, wouldn’t the debris and hard radiation potentially cause severe problems down the line? I realize that the solar wind could probably blow a lot or even all of it away, but who knows what all the ramifications would really be?

    How about a ship of similar design, but with a cluster of huge VASIMR-type engines strapped to it instead? ;^)

  • Eniac February 27, 2010, 0:29

    If that Orion trip had taken place, who knows, we might be booking fishing trips to Enceladus today. Exotrout, anyone?

  • Adam February 27, 2010, 2:43

    Hi All

    Agree with Greg 100%. Solar or chemical are fine for robots taking their time – tho try to tell that to anyone waiting for their experiment results – but manned flights and sample-returns need nukes, for propulsion and power.

    Chris Jenkins, the “Orion” style pulse units were small nukes with very focussed fission-debris plasma that moved faster than the solar escape velocity – it would all blow-away into deep-space. But outside the magnetosphere. Not so healthy when set off in near-Earth orbit (except at the poles) as some of the debris comes showering down following the magnetic field-lines. But Greg’s the plasma expert around here, so he might be able to tell us more.

    VASIMR isn’t such a fantastic performer as you seem to imagine without a low-mass power source. Chang-Diaz’s high-powered VASIMR uses a gas-core reactor feeding plasma through an MHD generator in a closed cycle. Low-mass, but a bit past state-of-the-art.

  • Elukka February 27, 2010, 2:59

    The exhaust wouldn’t mean anything in space. A nuke in space is just x-rays and gamma rays, in very minute amounts compared to what would make any difference for anything.
    I think it wouldn’t necessarily be a bad idea to launch a few big Orions off the surface to get space stuff really going. Even if you took no precautions and launched off some sandy island, creating lots of radioactive dust, the fallout would likely be a lot less than that of any one cold war nuclear test.
    Obviously you would never do that and would take every precaution you could to minimize fallout.

    I wish someone would make a new design study of nuclear pulse propulsion, but with the test ban treaty I don’t think even that is going to happen. It would be nice to see what the characteristics of a modern Orion would be, and whether we could minimize fallout to tolerable levels.

  • drpayton February 27, 2010, 3:04

    I think I saw a fish in one of those geisers lol… No seriously these photographs are beautiful and priceless! It would not surprise me at all to find extraterrestrial life in places like these. I truly believe that life is much more hearty than it might seem. Even a small ecology of microscopic life would be amazing to find and could really boost us into a more robust phase of exploration in our system. Finding life on a moon of saturn is exactly what our space program needs!

  • Michael Spencer February 27, 2010, 8:39

    When contemplating the far future I’m reminded of Henry Ford’s supposed-observation that had he given people what they wanted, we’d all have faster horses.

    Because the rate of change in technology nowadays is so great, we’ve catapulted ourselves, in a single lifetime, into an historically special perch. Vision from this perch, alas, extends only backwards, but still: to take into view, at the same time, the notion of NERVA and Orion and VASIMR!


  • ericick SECT February 27, 2010, 10:56

    We really should send a fly-by mission to Enceladus; picture a spacecraft similar to that used on the “Stardust” mission. This mission could capture some of these geyser exhaust particles in aerogel and bring them back home for a look-see under the microscope…

  • drpayton February 28, 2010, 3:47

    Sect… That is the obvious step… We are on a second mission to the same comet with the same craft that went the first time… What solar winds do to a comet is important because the knowledge could teach us something about shielding but to fly through the highest geysers known to man (so far) and to bring back samples to test for microbial life…. that might get some public interest. I suggest polar cell as the name of the first single cell life form found…lol…jk

  • Adam February 28, 2010, 9:02

    New nuclear pulse designs exist, but they’re strictly space-vehicles not launchers. Fred Winterberg’s pure deuterium pulse rocket is a launcher, but isn’t as detailed in design. Non-fission triggered fusion-pulse bombs might exist, but they’d be strictly classified as a major proliferation risk. Winterberg’s pulse units are too small for weapons and use implosion pumped argon x-Ray lasers for fusion triggering.

  • Terraformer (a.k.a Tobias Holbrook) February 28, 2010, 12:29

    Can’t you trigger them with explosives? A core chemical explosive, with TD (Tritium-Deuterium) wrapped around that, followed by perhaps Lithium Deuteride, and followed by some more chemical explosive. The chemical explosive goes off at the same time, compressing the TD enough to intiiate fusion, the neutrons produced splitting the Lithium Deuteride into Tritium and Deuterium.

  • Eniac February 28, 2010, 17:30

    Chemical explosives are not energetic enough to create the right conditions for fusion. Neutrons travel too far to effectively breed tritium from lithium in a small volume. And you do not want to waste the core by putting chemical explosives there, it is the point of highest compression where you want to put the neutron trigger instead.

  • Gregory Benford February 28, 2010, 18:49

    Adam’s right, the debris problem is minute. The solar wind brushes outward any low energy stuff, and the magnetosphere defends the biosphere against any low energy plasma.
    The test ban treaty is a piece of paper with a one year exit clause. If we make the case for deep space exploration properly, no reason to not modify it.
    NASA’s safety obsession with radiation on a Mars expedition can be lessened with faster missions, though it’s very expensive in fuel. A big reactor onboard (which can be the base power supply) can provide a decent magnetic shielding too.

  • Adam February 28, 2010, 20:45

    The killer for a 1950s style “Orion” is the precedent – basically a massive nuclear warhead magazine is put into orbit. Doesn’t matter that they’re all 1 kT pulse units, since they’d be deadly as ASAT weapons and MIRVs aren’t all that much bigger in yield. As a launch system the fall-out is bad news, but it’s cumulatively not as bad as the open-air weapons tests in the 1950s… but only if we launch one or two “Orion” vehicles. If we want serious space-access via “nuke pulse” then the fallout issue has to be solved. Fission-bombs and fission-triggered units just won’t do. Even Winterberg’s D-D fusion produces tritium, which isn’t terribly healthy, though it’s relatively mild as a radiological health-hazard. The ultimate space-launcher capable fusion drive would be the fusion-powered scramjet that Dr. Bussard designed based on a working proton-boron fusion/fission reactor. But such reactors don’t yet exist and may well take a lot longer to develop than D-T & D-D versions of Bussard’s Polywell fusor.

    For the meantime I think a successful implementation of SpaceX’s Falcon program is a good start for cheaper space-access. Next step would be an air-breathing hybrid like SKYLON.

  • Marsbug March 1, 2010, 11:06

    Amazing images! Could a stardust type aerogel collector mission to Enceladus be done? I assume that if we can put a probe onto Titan we can fly one through the enceladus plumes.

  • ljk March 2, 2010, 19:56

    I wrote this elsewhere in CD and will rephrase it here:

    If the United States does not pursue an Orion ship concept, I can think of
    one other major spacefaring nation that has nuclear technology, a big
    space infrastructure, some very remote deserts in which to test this
    concept, and the imperial will to pursue it.

    We may end up with a different kind of nuclear “war” in the future, not one
    where the nukes are used as weapons, but instead to see who colonizes the
    Sol system and explore beyond the Oort Cloud first. Or if things keep going
    the way I see it right now, this new space race may be very one-sided.

  • ljk October 8, 2010, 5:40

    FEATURE: Saturn’s Icy Moon May Keep Oceans Liquid with Wobble

    Saturn’s icy moon Enceladus should not be one of the most promising places in our solar system to look for extraterrestrial life. Instead, it should have frozen solid billions of years ago. Located in the frigid outer solar system, it’s too far from the sun to have oceans of liquid water — a necessary ingredient for known forms of life — on its surface.



    CONTACT: Bill Steigerwald, William.a.steigerwald@nasa.gov; Tel. 301-286-5017

  • ljk January 20, 2011, 20:21

    Orion on an asteroid

    A mid 1960s Convair artwork depicting a deep-space manned mission through the asteroid belt (to Jupiter or beyond) using Orion spacecraft. To provide protection during the obviously dangerous passage through the belt, the Orion craft are landed (docked?) on an asteroid of their own.

    Of course, for this to make any sort of sense, the asteroid itself would have to be on a pretty eccentric orbit, with a perisol somewhere near the orbit of Earth, and an aposol somewhere beyond the asteroid belt or the orbit of Jupiter. The existence of such an asteroid on a “cycler” orbit would prove occasionally useful, serving as a spacegoing hotel for part of the journey.