Lifestyles Of The Hydrogen-rich And Erratically Famous

A huge glacial erratic versus a small human on the Superior Hiking Trail this week. Photo: Bob King

Wait a minute. What is this thing? Asteroid, alien spacecraft, rock of doom? No, it’s only a 20-foot-high glacial erratic astride the Superior Hiking Trail 5 miles east of Finland, Minn. The guidebook indicated its location but I wasn’t prepared for the sight of this behemoth. Erratics are boulders plucked by glaciers and deposited miles from their source. This one , composed of the mineral anorthosite, appeared to have been dropped in the middle of nowhere, hence it’s otherworldly appearance.

A very tight closeup of lichens (center) and crystal structure (right) on a small patch of the erratic. Photo: Bob King

When seen up close up, the bland, gray exterior of the rock proved to be composed of coarse crystals. Tiny patches of tough lichens hid parts of the weathered surface.

The boulder probably parted company with the glacier 10,000 years ago. Anything around that long in one place becomes a time machine into the past. Through its dark crystal panes, we glimpse a long-gone world of mile-thick ice and numbing cold. Given enough time, life’s tiny fungal tentacles, working in tandem with nature’s freeze-thaw cycle, will reduce this titan to shards and finally soil.

The Dawn spacecraft used its gamma ray and neutron detectors to discover hydrogen hot spots on the asteroid Vesta this past year. Red indicates the greatest amount of hydrogen; gray the lowest. Credit: NASA/JPL-Caltech

Another big rock – this one in the asteroid belt – shares an even more ancient past than my erratic. Rather than rocks dropped by ice, Dawn was hit with hunks of water-rich asteroids from the asteroid belt called carbonaceous chondrites. The probe found Vesta’s equatorial zone laced with hydrogen from water chemically bound to the rocks as -OH, also called hydroxyl. Free water’s formula is OHH, described more simply as H2O.

“The source of the hydrogen within Vesta’s surface appears to be hydrated minerals delivered by carbon-rich space rocks that collided with Vesta at speeds slow enough to preserve their volatile content,” said Thomas Prettyman, the lead scientist for Dawn’s gamma ray and neutron detector (GRaND) at the Planetary Science Institute in Tucson, Ariz.

Hundreds of small pits inside Vesta’s crater Marcia may have formed when late bombardment heated earlier materials deposited by water-rich asteroids. Heated by impact, water bound in rocks escaped to create the pits. Credit: NASA/JPL-Caltech/University of Arizona/MPS/DLR/IDA/JHUAPL

If any ice itself were to survive, you’d think Vesta’s polar regions would be the best places for preservation just as on the moon. The moon’s rugged terrain and an axis tipped just 1.5 degrees to the plane of Earth’s orbit create permanently shadowed havens for ice in craters at its north and south poles. Unlike the moon, Vesta’s axis has a considerable 29-degree tilt. As it rotates and orbits the sun, both north and south polar regions are repeatedly exposed to sunlight just as they are on Earth. If ice once languished there, it’s long gone.

The Sutter’s Mill carbonaceous chondrite, which fell on April 22, 2012 in California, is dark colored like most of its class. Photo: Bob King

In fact, most of the hydrogen was found in darker-colored rocks encircling the equator. Since carbonaceous chondrites are themselves dark and water-rich compared to other meteorites, they’re a good match for what Dawn found on Vesta.

More evidence for ancient water comes from strange clusters of pits measuring about 100-800 feet across discovered in the 40-mile diameter crater Marcia. They resemble similar features on Mars that likely formed when water within the rocks vaporized explosively during an impact leaving behind pothole-shaped depressions.

Similar pits on Mars from water boiling from the surface by the heat of impact. Credit: NASA/JPL-Caltech

It’s thought that a second round of high-speed impacts accomplished the same on Vesta. Marcia’s center is pocked with pits and has very low levels of hydrogen, consistent with water boiling off into space when the crater was formed.

Water. It’s always at the center of the story when it comes to space exploration. Earth’s water is believed to have arrived the same way as Vesta’s through comet and “wet” asteroid bombardment. Much later, water would build the glacier that plucked the boulder that now reposes alongside a woodland trail. You never know what adventures may lie ahead when you go with the flow.

22 Responses

  1. lynn

    Hi Bob
    Not left a comment in a while, but I still read your blog every night.
    Just wondering what your thoughts were on the bright lights that were seen over the UK on Friday night, some are saying it was a meteor and others are saying it was a piece of space junk, or a bit of a space rock but nobody has a definitive answer, but some of the pictures I have seen were awesome and great that someone captured them at that moment. It would seem that a meteor shower just doesn’t seem to fit the picture and just wondered what you think.
    Thanks Bob 🙂

    1. astrobob

      Hi Lynn,
      Nice to hear from you again. The bright lights over the UK were from the fall of a meteorite that broke into many fragments, some of which may have landed on the Isle of Man. It was probably not man-made space junk since the meteor traveled from east to west. Almost all satellites travel the other direction from west to east.

  2. lynn

    Thanks Bob, just a big deal being made over here in the UK probably becauase we don’t seem to see them very often like this unlike the U.S.
    Thanks again and it was nice to hear from you too, but you really need to get some sleep lol.

  3. Wait a minute here buddy……… I heard the earth was formed only 6000 years ago. How can a rock be that old? ??!
    How anyone can believe that fairy tale is beyond me, rocks don’t lie. Thanks for all your awesome photos and information, if you can open even one more mind………………..

    1. astrobob

      Hi Maggie,
      Even with the little we know, it makes the universe a far grander place than anyone could have imagined.

  4. M Munn

    reminds me of Issac Azimov’s “Marooned off Vesta” 1938
    Inaccurate (due to the era) but amusing
    he described it as a CO2 ice-ball

  5. Richard Keen

    Bob, a few months ago the little asteroid 2012 KT42 flew by earth, and you posted….
    “25 minutes with asteroid 2012 KT42
    “Posted on May 29, 2012 by astrobob
    “… 2012 KT42, a space rock estimated at 10-30 feet across, blew by Earth earlier today at a distance of only 8,700 miles”
    I always fantasize what it would be like to stand on such a little world. Then I saw your picture of the glacial erratic – and there it is!
    One giant leap for Bob!

  6. Richard Keen

    Bob, interesting how a “huge” glacial rock can be the same size as a “minuscule” asteroid. All depends on the perspective!
    I remember back in ’80 when an “earth grazer” named Alinda came by. In a telescope the mile-wide asteroid was a 12th magnitude dot, even though it was the same size as the newly formed crater on Mt. St. Helens, which was quite enormous to anyone within earshot.

  7. MBZ

    Escaped convict in prison garb nabs 2012KT42!
    Last seen scurrying down mountain carrying stolen asteroid on his back.
    Please report any unusually lumpy lawns to your nearest authorities.

  8. Steven Senenfelder

    Hi Bob,
    It’s funny how those glacial erratics sometimes look just like cosmic debris. That anorthosite is real common up there, that’s the same rock Split Rock lighthouse is sitting on. The rock in your photo looks a lot like a meteorite. Did you try to stick a magnet on it, or look for any melted surfaces?

    1. astrobob

      Hi Steven,
      I didn’t have a magnet with me but there’s no doubt that rock was not a meteorite. I have samples of the same rock from the large anorthosite inclusions along Hwy. 61 in Silver Bay, and they are not attracted to a magnet. Anorthosite is an igneous rock from deep below the crust with a wonderful coarse crystals very obvious to the eye. The stuff in Silver Bay is very pretty up close – have you seen it?

      1. Richard Keen

        Anorthosite – that’s what the bright surface areas of the moon are made of (the lunar highlands). I bet Bob has a NWA 482 lunar meteorite that looks just like that erratic rock, only a little smaller.
        Which, of course, raises the question – is there a dark side of the moon? If so, it’s the near side, with all the basalt “seas”.
        There is an anorthosite point on the moon – Cape Heraclides – that juts into the Mare Imbrium, and looks a bit like Split Rock point. Without the trees and lighthouse.

          1. Richard Keen

            Bob, thanks for the link to your older article about anorthosite and Split Rock – good story!
            Question: the picture of the lighthouse shows it sitting on the light anorthosite, but the left portion of the white cliff is much darker. Is that the basalt, or Duluth gabbro? Sure is a nice sharp contact line.

          2. astrobob

            Thanks Richard. I’m not exactly sure about the darker rock since I haven’t been down in person in a while to see it but my guess would be rhyolite. There’s a large cliff nearby called Palisade Head that’s composed largely of rhyolite. Color is similar too.

      2. steven senenfelder

        Hi Bob,
        Yes, real anorthosite should not be attracted to a magnet. And no, I have not looked at the rocks around Silver Bay, or Split Rock up close, although I’ve stood on them many times. I’ve been planning a trip up the North Shore with my magnet and magnifying glass, maybe I’ll try sticking it to your glacial erratic. Do you want to go with?

        1. astrobob

          Just so you know, I brought back a piece that had flaked off the rock and tested it – no attraction. You’ll definitely get attraction from Duluth gabbro. A friend of mine had a rock that stuck to a magnet that he dug up in his backyard. We had it ID’d by geologist Jim Miller as classic Duluth gabbro.

  9. steven senenfelder

    Thanks for checking it. I’m still going up there, I know there’s some of that classic Duluth gabbro near Slit Rock, because Slit Rock has a negative magnetic anomaly, just like Esko.

Comments are closed.