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The Non Sequitor Thread


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Summertime, and the University hires out their space to workshops of all flavors. Down the hall from me this week is a middle-school program about volcanism. Had a brief conversation with the woman running it about volcanism elsewhere in the Solar System, sent her a few things. Copy-pasting from that email

 

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I am giving links to NASA Planetary Photojournal. The root url is http://photojournal.jpl.nasa.gov/ You can "drill down" from that root page clicking on the planet system you want, then selecting which particular target object you want (or mission from which images came, or instrument used, etc.). This can be frustrating if you don't really know what you're looking for, since there are hundreds if not thousands of images of just about everything. If you have hours to kill, it can be fun to browse randomly, but it's not an efficient way to find things of specific interest when you aren't fully acquainted with the targets. So I give specific links to particular images showing volcanic features on some of the other Solar System worlds.

 

First the real deal, Io. Io is the closest-in of the four large moons of Jupiter. ("Large moons" are more than 1000 km in diameter; Jupiter has four, Saturn has one, Neptune has one.) Io is the most volcanically active world in the Solar System: its entire surface is volcanic landforms.

 

http://photojournal.jpl.nasa.gov/catalog/?IDNumber=PIA02294 is a mosaic of most of one side of Io, from the Voyager mission back in the early 1980s.

 

http://photojournal.jpl.nasa.gov/catalog/?IDNumber=PIA09360 is also of Io, taken from the New Horizons mission (the one that passed through the Pluto system earlier this month), looking back at the moon. At top, seen in forward-scattered light, is a big volcanic plume. When these plumes were first seen in the Pioneer missions of the mid-1970s they provided the first definitive proof that Io had active volcanism. They were entirely unexpected at the time.

 

Second, cryovolcanism.

 

The clearest case, the currently-active moon is Enceladus, one of the medium-sized moons of Saturn. ("Medium-size" moons are 400 to 800 km in diameter; Saturn and Uranus both have several and Neptune has a couple.) Other moons are strongly suspected of having recent, if perhaps episodic, cryovolcanism but clear specific ongoing events have not (I think) been captured as we watch for other moons. The case is clearest for Enceladus because it is the most active moon of Saturn, and the Cassini spacecraft in the Saturn system has been operating for close to a decade now so we have long-term more or less continuous monitoring there, something we've never had at all for Uranus and Neptune and we have had only with sharp limits in the Jupiter system.

 

http://photojournal.jpl.nasa.gov/catalog/PIA00347 shows one of the early images of Enceladus from the Voyager 2 spacecraft in the early 1980s. At that time ice volcanoes were suspected but not proven, hence the very tentative statement in that figure caption about it.

 

http://photojournal.jpl.nasa.gov/catalog/PIA06249 is a false-color image of the moon, with the "tiger stripes" in the south being the interesting very young terrain.

 

http://photojournal.jpl.nasa.gov/catalog/PIA07794 The stripes are warm, as well: the surface at the stripes is distinctly warmer (brighter in infrared images) than the rest of the moon's surface, as shown in this amalgam of visual image and thermal infrared mapping.

 

http://photojournal.jpl.nasa.gov/catalog/PIA06247 is the highest-resolution look at the area of the "tiger stripes". Note that there are **no** impact craters there. This means the surface is very young, and there's intense geologic activity in that part of the moon.

 

http://photojournal.jpl.nasa.gov/catalog/PIA07758 is the smoking gun. Again looking back sunward past Enceladus, you see in forward-scattered light the fountains of ice particles being ejected from the volcanic fissures on Enceladus. When you correlate the location of the spacecraft, and the moon, and the viewing angles involved, the base of those fountains is the "tiger stripes", with no ambiguity.

 

http://photojournal.jpl.nasa.gov/catalog/PIA08321 At least some of the particles ejected from Enceladus end up making Saturn's E ring, a faint and thin ring around the planet outward from the big bright rings that you can see from Earth.

 

Third, Mars.

 

The biggest single volcano in the Solar System is Olympus Mons on Mars. The whole Tharsis Ridge and the three volcanoes on it (Arsia Mons, Pavonis Mons, and Ascraeus Mons) is also largely volcanic. Paradoxically, people are much more excited about sedimentary rocks on Mars, things that indicate the planet had much more water on its surface in the past than it does now.

 

http://photojournal.jpl.nasa.gov/catalog/?IDNumber=pia02982 is a grand image of Olympus Mons from the old Viking orbiter (1976!). Note the scale: the base of the volcano is 600 km across, larger than Washington State.

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As the cackling, leering, gap-toothed old woman raked in the pot over her queens-over-threes that had beat my king-high diamond flush, I stood up and walked around the table, drew the revolver, and shot her carefully in the back of the hip to make sure she wouldn't go anywhere. Then I walked out to my pack mule out front, retrieved my pickaxe, and brought it back inside. She flailed there among the money and the cards, including the three queens of clubs lying face up by her head, and spat curses at me. She was too gross a card cheat to be allowed to live, but too despicable to waste ammunition on, so I dug a hole in the badly worn carpet and creaky, warped floorboards through her rib cage with the pickaxe. That chore done, I tipped my hat and went back outside and led my mule back up into the hills towards my claim up in the Bitterroots. I was getting tired of having to do that.

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More than half a billion years ago the last of them slipped into oblivion so deeply that we don't know if they were kin to us at all. And yet ... in the gritty enigmatic traces they left behind, there are clues of how they lived, how they bred.

 

See, O Death? Yes, there are things we can never recover from your grip. But not even you can guess what those might be, and where the gaps in your dark mantle are, as the light of reason pierces the darkness in ways that yesterday were impossible. Neither can we.

 

But we will never stop trying....

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