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At Jupiter’s Core

I first encountered the surface of Jupiter decades ago, in a study hall in John Burroughs School in St. Louis, Missouri. It was a warm spring day and I was theoretically trying to bone up for a math test two periods hence. But deciding to squeeze in a little reading before I hit the algebra, I read the paragraphs that follow and spent little of the next two hours thinking about anything else:

The wind came whipping out of eastern darkness, driving a lash of ammonia dust before it. In minutes, Edward Anglesey was blinded.

He clawed all four feet into the broken shards which were soil, hunched down and groped for his little smelter. The wind was an idiot bassoon in his skull. Something whipped across his back, drawing blood, a tree yanked up by the roots and spat a hundred miles. Lightning cracked, immensely far overhead where clouds boiled with night.

As if to reply, thunder toned in the ice mountains and a red gout of flame jumped and a hillside came booming down, spilling itself across the valley. The earth shivered.

Thus the opening of Poul Anderson’s “Call Me Joe,” published in Astounding Science Fiction in April of 1957, though I was reading it in a later anthology. “…a tree yanked up by the roots and spat a hundred miles…” — hard to keep your mind on studying after reading that! The cover illustration at left gives you an idea of the images this story creates as it follows the exploration of the Jovian surface by remote telepresence technologies. I couldn’t help recalling these images as I looked through new work on Jupiter’s core. Computer simulations studying what happens to hydrogen/helium mixtures at the extreme pressures and temperatures of Jupiter’s interior imply a rocky core of 14 to 18 Earth masses, a twentieth of the planet’s total mass.

I had more or less gotten used to the idea that there was no core in Jupiter at all, although some recent theories had suggested a smaller core of about seven Earth masses. Anderson’s bizarre life-forms, some native and some created by humans, move through a low-temperature world that eventually absorbs the story’s protagonist (you have to read this story if you haven’t already), but the reality of Jupiter may be far stranger, and certainly more complex than we fully understand. And it certainly seems to preclude wandering about on any kind of surface.

It now appears that the pressure and temperatures involved within the planet change hydrogen from a molecular to a metallic state, producing a material with high electrical conductivity that gives rise to the intense magnetic field. The core, in this latest view, would be made of metals, rocks and ices of methane, ammonia and water, with an Earth-like ball of iron and nickel at the very center. Burkhard Militzer (University of California, Berkeley) sums up the work this way:

“Our simulations show there is a big rocky object in the center surrounded by an ice layer and hardly any ice elsewhere in the planet. This is a very different result for the interior structure of Jupiter than other recent models, which predict a relatively small or hardly any core and a mixture of ices throughout the atmosphere… Basically, Jupiter’s interior resembles that of Saturn, with a Neptune or Uranus at the center.”

And that big rocky core gives an affirmative nod to the core accretion model of planetary formation, formed as it would have been by the collision of planetesimals from the primordial solar nebula. All of which is exciting stuff, but how much better to realize that the Juno mission to Jupiter, scheduled for a 2011 launch, should be able to return hard data to confirm or modify the new model. Juno will enter a highly elliptical polar orbit around the planet, studying the core question along with the planet’s magnetic field. Says Caltech’s Dave Stevenson:

“Juno’s extraordinarily accurate determination of the gravity and magnetic fields of Jupiter will enable us to understand what is going on deep down in the planet. These and other measurements will inform us about how Jupiter’s constituents are distributed, how Jupiter formed and how it evolved, which is a central part of our growing understanding of the nature of our solar system.”

Image: The Juno spacecraft in front of Jupiter. Juno is one of the largest planetary spacecraft to ever be launched. Credit: NASA.

Jupiter’s structure, then, can be critical in helping us understand how giant planets form, providing a way to look back at the early history of the Solar System. We’ll also learn about the relative abundance of water and oxygen, and gather data about the planet’s gravitational field and polar magnetosphere. Juno will use an Earth flyby for a gravity assist two years after launch, with arrival in Jupiter space in 2016. And rather than drawing on Radioisotope Thermal Generation (RTG) power, Juno will tap three solar panels to supply the needed juice despite its distance from the Sun. Efficient panels indeed.

The paper on Jupiter’s core is Militzer et al., “A Massive Core in Jupiter Predicted from First-Principles Simulations,” Astrophysical Journal Letters 688 (November 20, 2008), pp. L45–L48 (abstract, also available here).

Comments on this entry are closed.

  • ljk December 1, 2008, 14:52

    So does this new model preclude Jupiter’s core being made of diamond?

    Arthur C. Clarke would be very disappointed if so. However, most
    diamond merchants might be happy, as having a world with a diamond
    the size of Earth could do nasty things to their market, once we’re
    able to reach the Jovian center – and we will when the Artilects start
    disassembling the planets to make the Solarian Dyson Swarm. I bet
    all that diamond could come in handy as construction material.

    Regarding the Juno probe: Just wait until the folks who protested
    Cassini in 1997 regarding its RTGs find out that NASA can send a
    space probe all the way to Jupiter using only solar power, because
    that was NASA’s big argument back then. that nuclear power was
    needed to fuel a spacecraft beyond the Planetoid Belt.

    Personally I have no issues with nuclear fuel for spacecraft and for
    powering our society on Earth. In regards to deep space vessels
    with RTGs and similar power sources, one might think the anti-nuke
    forces would be glad to see the material permanently removed from
    our planet to a vast place where the radiation is many, many times
    worse than anything we can generate with our puny technologies.

    And wait until they find out about the Orion nuclear bomb-powered
    spaceship concept – though Carl Sagan once said that Orion was a
    pretty good use for such devices and got them off the planet in the

    Regarding Jovian life forms, check out Ben Bova’s 2001 SF novel
    titled Jupiter, about the possible creatures that could live in the
    liquid portion of the giant planet. And Carl Sagan along with E. E.
    Salpeter wrote a paper in 1976 about possible Jovians that live in
    the more temperature layers of the planet’s atmosphere. This
    was depicted in one of the early episodes of Cosmos in a very
    memorable painting:


  • Adam December 2, 2008, 3:16

    Hi Paul & Larry

    I think I answered Larry about diamond in a post to the HabitableZone that we both frequent – basically the pressure and temperature mean if there’s diamond it’s going to be liquid. But methane and ammonia both would be tiny compared to the complement of water down in Jupiter’s core, so it’s unlikely you’ll get diamond in any great quantities. Not enough carbon.

    Poul Anderson’s story is set on the metallic hydrogen layer, assumed to be solid in his story. Of course now we know Jupiter is much too hot for it to be solid – instead it becomes liquid metallic hydrogen/helium, since the latest evidence is that the two alloy quite well. What form the water/ammonia/methane layer takes is anyone’s guess as all the pressure and temperature data falls short – though the article Paul references takes a good stab at the problem. The “ices” could well be solid, but only because of the pressure. Otherwise they’d explode into plasma. And such solids might be more fluid than what we normally imagine as “solid”, so it could be described as a sea, though I very much doubt anything could live in such a pyroabyssal environment, contra Bova’s novels.

  • ljk December 3, 2008, 0:07

    And here are these guys, from the Time-Life Science Series book,
    Planets, first published in 1966 and edited by Carl Sagan:


  • ljk October 12, 2009, 0:27

    Forming Jupiter, Saturn, Uranus and Neptune in Few Million Years by Core Accretion

    Authors: Omar G. Benvenuto, Andrea Fortier, Adrian Brunini

    (Submitted on 2 Oct 2009)

    Abstract: Giant planet formation process is still not completely understood. The current most accepted paradigm, the core instability model, explains several observed properties of the solar system’s giant planets but, to date, has faced difficulties to account for a formation time shorter than the observational estimates of protoplanetary disks’ lifetimes, especially for the cases of Uranus and Neptune.

    In the context of this model, and considering a recently proposed primordial solar system orbital structure, we performed numerical calculations of giant planet formation.

    Our results show that if accreted planetesimals follow a size distribution in which most of the mass lies in 30-100 meter sized bodies, Jupiter, Saturn, Uranus and Neptune may have formed according to the nucleated instability scenario.

    The formation of each planet occurs within the time constraints and they end up with core masses in good agreement with present estimations.

    Comments: 11 pages, 3 figures, in press (Icarus)

    Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

    DOI: 10.1016/j.icarus.2009.07.003

    Cite as: arXiv:0910.0468v1 [astro-ph.EP]

    Submission history

    From: Andrea Fortier [view email]

    [v1] Fri, 2 Oct 2009 20:01:39 GMT (28kb)


  • ljk December 13, 2009, 0:21

    Did James Cameron Steal the Plot for ‘Avatar’?

    10.26.09 By: Peter Hall

    While geeks the world over are eagerly awaiting Avatar, the return of James Cameron to the original sci-fi territory he’s proven a master over with The Abyss and Terminator/Terminator 2, fans of obscure science fiction novellas from 1957 are being struck with deja vu.

    A reader tipped off genre champions io9 to the story Call Me Joe by Poul Anderson, a story that sounds remarkably like Cameron’s supposedly original script that revolves around humans that use the bodies of an alien species via a mental connection as physical avatars, and proceed to use said avatars to exploit the resources of the alien’s home world.

    From the io9 post, “Like Avatar, Call Me Joe centers on a paraplegic – Ed Anglesey – who telepathically connects with an artificially created life form in order to explore a harsh planet (in this case, Jupiter). Anglesey, like Avatar’s Jake Sully, revels in the freedom and strength of his artificial created body, battles predators on the surface of Jupiter, and gradually goes native as he spends more time connected to his artificial body.”

    Now that certainly sounds awfully similar to Avatar, and if that simple description is not evidence enough to inspire doubt, Avatar’s integrity is done no favors by the cover art for Call Me Joe. As seen at the top of this post, the life forms on the surface of Jupiter in Anderson’s story are large, blue-tinged hybrids between humanoids and cats; which are not unlike the Na’vi, the humanoid-cat race that roams Cameron’s Pandora.

    Full article here: