Messenger Results: Mercury is a Giant Ball of Iron

By Veronique Greenwood | March 24, 2012 8:28 am


Mercury is an odd little planet, tiny but incredibly dense, relatively close by but hard to study via telescope. The MESSENGER probe‘s latest findings, 57 papers presented two days ago at conference, bring new weirdness to our understanding of the planet closest to the Sun.

Take, for instance, the new revelations about Mercury’s core. We always knew that Mercury had a proportionally larger core than Earth does; geologists thought that it might make up a whopping 42% of the planet’s volume, in comparison to Earth’s 17%. The newest estimate, though, blows that out of the water: We now think the number is 85%. To boot, there appears to be an extremely dense layer more than a hundred miles thick encasing the core, perhaps a shell of iron sulfide. That makes the mantle and crust—to use the memorable analogy of a planetary scientist interviewed by Wired—like a mere orange peel on a giant orange of metal.

Another memorable finding: the largest crater on Mercury, Caloris Basin, isn’t actually much of a basin. It seems that the crater’s center gradually rose at some point in the not-too-distant past until it was higher than its edges. This has geologists revising their impressions that Mercury stopped being geologically active 4.5 billion years ago to something more like 2 billion years ago.

[via Wired]

Image courtesy of Case Western Reserve University

  • Aidan

    It only makes sense if you think about it. Gaseous elements stay far from the sun, due to their light weight, and the denser elements are pulled by the suns gravity and far accelerated rate. That’s probably why the rock planets are all so close to the sun while the gas giants are so tremendously far off.

  • jemand

    Fascinating. It’s interesting to me that the iron core of Mercury is apparently roughly comparable in size to the iron core of Earth, just perhaps could the lighter elements have been disproportionately blown off? It reminds me of how the rocky core of Jupiter is, if I’m remembering correctly, not that much off the size of earth, most of the bulk of that planet is made of various states of Helium, which really isn’t stable at the average temps of a planet as far from the sun as Earth is.


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