Majestic mountains of the Moon

By Phil Plait | June 30, 2011 6:30 am

The Lunar Reconnaissance Orbiter takes amazing pictures of the Moon; I’ve posted dozens over the past couple of years. One of my favorite things is when the spacecraft snaps features I know: craters, mountains, winding valleys that I’ve seen myself behind the eyepiece. When I was younger I spent countless hours scouring the lunar surface with my telescope, and it’s still a fun target when I haul my ‘scope out to the end of the driveway.

And among the best of the best is the crater Tycho. You probably know it already; when the Moon is full the crater is bright, and the rays extending from it — plumes of material ejected radially during the impact that formed the crater — are extremely obvious. At 86 km (50 miles) across, it’s a decent-sized hole in the surface, with a beautifully-defined system of central mountain peaks 15 km (8 miles) across. So when LRO sets its sights on Tycho’s peaks, well… you get a gorgeous panorama like this:

You must click that to enlunenate it and see it in incredible detail. It’s truly spectacular!

That peak rises about 2 km (1.2 miles) about the crater floor. Look how steep it is! I was mentally comparing it to the local foothills of the Rockies near where I live in Boulder, and realized it’s not a bad analogy as far as size and shape go. In one way, hiking to the top of Tycho’s peak would be easier, since the gravity is only 1/6th of Earth’s… but while the air is thin here in Boulder, it’s literally nonexistent on the Moon. So I’m thinking hiking Tycho would be somewhat more taxing.

But what a sight when you reached the top! Sitting smack dab on that largest peak is a boulder I’d very much like to see up close:

The view on the left is a closeup from the image above (here’s a higher-res version), and the one on the right is from May 2010. The big difference is lighting and viewing angle; the left shot is lit obliquely and seen from the side, while on the right it’s seen with a higher angle of sunlight and the view is nearly straight down.

That rock is huge, 120 meters across. An American football field would fit right on top of it, goalpost to goalpost. The smooth terrain around it is what’s called impact melt, rock that was melted when the impactor hit over one hundred million years ago. That’s why it looks smooth; it was probably molten material that flew off the surface and then rained back down.

But how did that rock get there? I have a hard time picturing something that big getting ripped off the surface by the impact and landing softly enough to stay intact. It looks out of place there, unlike the craggy peaks around it. I had thought perhaps it was fractured off one of those peaks and rolled to the local depression between them. I’m not so sure, and a web search didn’t turn anything up on it. The top of the boulder appears to have some of the melt on it, too, so perhaps it really was blown out intact from the impact, fell back down after the peak formed, and then suffered through the rain of molten rock after.

I bet lunar geologists have lots of ideas about it… and I also bet we won’t know for sure until one of them (or more likely, a colleague who is as yet in grade school right now) stands there with a pick and a bag, ready to take some samples back to the lab. Will her equipment be at Clavius base, I wonder?

Image credit: NASA/GSFC/Arizona State University

Related posts:

I think the Moon watched Bad Universe
A flower bloom on the Moon
What, no monolith?
Watermelon planet (great pic of Mercury showing rays like Tycho’s

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (35)

Links to this Post

  1. Vesta’s odd bottom | CRBiDS.COM | September 17, 2011
  2. Vesta’s odd bottom | Bad Astronomy | September 18, 2011
  1. Your Name's not Bruce?
  2. PhilW

    Tycho Base maybe?

  3. Paul

    I have an idea about the boulder – feel free to tell me how and why it’s wrong … 😉

    It’s my understanding that the central peaks in left in major craters aren’t an accretion feature – stuff piling up after the impact – but more a rebound feature of material crushed beneath the center of the crater. As it rebounds, the area of greatest pressure in the center of the crater tends to rise above the newly-formed crater plain and form the peaks.

    Now, is it possible, though admittedly really unlikely, that the boulder was deposited at whatever decent velocity should be expected after bouncing around the impact site, then happened to land right on top of the rebounding peak in time to be hoisted up? Then the entire assemblage could be coated with the molten material?

    A couple reasons I think this idea is unlikely, myself – the odds of the solid rock landing on the (presumably) still pretty molten crater plain as the central peak is rebounding have to be pretty much impossible, and I don’t see any sign of a “shadow” of molten material around the rock that I would expect if it was shielding the mountaintop.

    Pretty neat – wish I could go look.

  4. rob

    ha, i know! it’s from glacial activity…or not.

    it’s still pretty cool.

    reminds me of a rock in northern Minnesota off the gunflint trail. it’s about 40 feet tall. a forest fire cleared out the area about 6 years ago, so it really stands out:

  5. QuietDesperation

    Not sure majestic is the word I’d use. To me that also implies snow capped peaks, maybe a plume of mist from the high winds up there, against a deep azure sky or glowy clouds at sunset.

    Related image:

  6. Nigel Depledge

    What an outstanding shot!

  7. A lot of amateur astronomers look down on us moongazers. The moon is considered somewhat passé. But I dunno. After 30+ years of exploring its surface, with cheap 60mm refractors and not-so cheap Schmidt-Cassegrain reflectors, I still find endless wonder in the lunar landscape.

    I love shots like this, for the very same reason as the good BA. A familiar feature revealed in utterly unfamiliar detail. Spectacular!

    BTW, this month’s issue of Sky and Telescope has a nice article on observing cool lunar features.

  8. Digital Atheist


    Kuhnigget, don’t feel bad. My first telescope was a 60mm refractor, and my present (which I’ve had for years) is a 114mm reflector. I love looking in to space, but the things that always keep me glued to the eyepiece are the Moon and the planets (in particular Jupiter and Saturn, but any planet can do). Look at it this way, we need to explore our own neighborhood and figure out how things work before we can understand others. Let amateurs who wanna do the nebulae thing do it… I’ll take one of my planets or the moon any old clear night.

  9. VinceRN

    Sadly it’s more likely that notional geologist is in grad school in China right now, and the base she keeps her stuff at is more likely to be called Ouyang Ziyuan moon base or something like that. Perhaps one day that little girl in grade school today can work for her.

    I suppose as long as the science gets done it doesn’t matter who does it, but I wish we were still trying to be part of it here in America.

  10. What doesn’t show up is interesting – no sign of the roll/tumble tracks common for smaller boulders, so it didn’t roll to that position any time after all the surrounding regolith was emplaced.

  11. valdemort15

    -DISCLAIMER- I’m a geology graduate student and have limited experience with planetary geology (I do isotope geochemistry on large-volume ignimbrites and caldera systems). Because of that, I’ll just list a few observations from the photos that may or may not parallel with this boulder.

    1. The mountains look like enormous shatter cones based entirely on their morphology, which may mean their constituent rocks were not moved substantially from their pre-impact position, which is what Paul (#3) brought up.

    2. My field area is in the San Juan Mountains in south-central Colorado, which experienced substantial large-volume caldera collapses and eruptions for a period of approximately 10 million years. While certainly not on the same instantaneous energy level as an impact, the boulder Phil’s curious about reminds me of the “megabreccia” blocks seen in a few places in the San Juan Volcanic Field.

    Breccia refers to a rock formed from another rock that was broken up and/or shattered in some way. Looks like conglomerate rocks, but the chunks of rock tend to be angular, whereas conglomerates tend to have rounded pebbles (or other grain sizes) in them. So when I say megabreccia, I’m talking about very large boulders (house-sized on average) sitting in a place where you’d otherwise never expect to find a boulder (short of its being moved by glaciers). They were probably surrounded by other material at some time or another, but the region I’m familiar with underwent substantial erosion and the large, more resistant blocks are pretty much what’s left.

    Hm. A quick Google search gave me this: – looks like similar megabreccias are associated with impact structures on Mars. Maybe I’m not that far off the mark. My next question to someone more qualified: How much erosion would’ve taken place in the crater, given this is the Moon? Hard to say if this giant boulder was ever covered with additional material (leaning toward doubtful) at one point or if it sort of ended up on top of everything from the get-go.

  12. JP

    Hmm…how long would central peak mountains take to solidify after an impact on the Moon, and what is the lowest altitude to which a boulder could be thrown such that it lands on them after they do? Maybe it wouldn’t shatter after all, in lunar gravity.

  13. Skip Huffman

    That big bolder doesn’t really look that out of place to me. Look along the ridgeline below and to the right of it. There are a number of rather similar, though somewhat smaller boulders nearby. It looks to me like something formed a bunch of boulders at that point, and this one slipped off the ridge where it rolled down. It also looks like it dislodge some material that has come to rest around its uphill side, just like what would happen if any large earth rock were to fall through a scree slope.

    In fact if you look around the image a bit, you can see some other boulders in similar places. Look at the smaller mountain halfway out of the frame to the left and down. I see one boulder that looks to be at almost as large as our big boy, plus about a half dozen smaller. There is also three more lined up on a ridge just below straight left of Big Boy. And one more that seems to have slipped about 10% of the way down that slope.

    Now I want to do an experiment where I mix sand and gravel on a table then force it into a similar ridge in some way to see what happens.

    Darn you Phil! I am supposed to be working.

  14. Well, obviously it’s a fake. I mean, just look at the shadows. They’re going in opposite directions just as if there was a second light source. :)

  15. jrpowell

    It’s obviously a Moon-beast egg. Best to leave it alone.

  16. Anchor

    I think the boulder and the many other smaller ones scattered all over the central peak were initially brecciated from rock-regolith layers at depth during the impact and acquired greater tensile strength. The chunks were then elevated with the rising central peak immediately following the impact and deposited atop it, gently enough to keep them intact. Many may have been lofted off the surface of the central mound when it stopped rising, but it’s quite evident they cannot have fallen from a height sufficient to break them up when they fell back down. Interestingly, one can see a nice apron of rubble-like ‘ejecta’ around the base of the boulder, exactly as one would expect if it had plopped back down from a relatively short drop.

    “I have a hard time picturing something that big getting ripped off the surface by the impact and landing softly enough to stay intact.”

    It’s no wonder: the dramatic “ripped off the surface” isn’t a good characterization to make in the first place. It isn’t at all hard to picture the basic mechanism at work, and we ought to know better from our mundane experience of watching raindrops splashing to the surface: impact central peak rebound develops for the same reason that raindrops splashing down often produce a rebounding central droplet.

    “It looks out of place there, unlike the craggy peaks around it.”

    I don’t agree. It doesn’t at all look out of place. The craginess of the peak’s top is easily accounted for as a consequence of subsidence and sliding caused by the local slope angle of repose. Sharp-edged ridges are a very common consequence of this process. It is also evident in many places in the image that much of the central peak is composed of conglomerated or brecciated chunks. The ‘cragginess’ of the peak and the presence of numerous large boulders are mutually consistent.

    valdemort15 @#11 is exactly right: many central peaks look like enormous shatter-cones in form. I also predict that this will be found to be the case with the large impact feature on Vesta as well. The famed diamond-shaped asteroid Steins visted by the Rosatta spacecraft has already been likened to an enormous shatter cone – like a free-floating ‘central peak’ without its crater.

  17. Douglas Troy

    One of the Deceptacons put it there just to mess with your head Phil.

    They’re mean like that.


  18. Skip Huffman

    Actually snow might be a better analog than sand. Particularly “sugar snow”. I know that I have seen very similar looking patterns on snowy slopes.

  19. Scott D.

    Clearly its camo for an alien telescope put there to study humanity in preperation for the day they invade. Duh.

  20. Anchor

    Here’s a fun comparison to make: the Near-Earth Object, asteroid MD-2011 which sailed by Earth last Monday is – at an estimated 10-meters or so across – smaller than that ‘small’ but prominent boulder one sees immediately above the behemoth in that May 2010 image.

  21. Allen Thomson

    Another thing that strikes me as odd is the apparent lack of smaller craters. Either the cratering rate has been very small since Tycho was formed, or some process is operating in the vicinity of the peaks that erases craters.

  22. Anchor

    @Allen#21…You’re right – there is a paucity of small craters, but Tycho is a relatively young impact crater (only about 100 million years old) and the nominal impact rate hasn’t had much of a chance to pockmark it as much as older regions have been. Vast ancient highland areas are ‘saturated’ with craters, meaning that new impacts erase as many craters as they add. But one can still determine which craters were formed later than others in a locale, and some regions which had been wiped clean begin to accumulate impacts over time so that a record is literally written into the surface.

    The primary way planetary geologists determine the age of terrain and features is by counting craters according to their size. It can get complicated by secondary impacts, which can’t always be distinguished from primary impacts (especially when they are themselves old and eroded from the constant rain of impactors) but the basic principle is generally sound for determining relative ages.

  23. Pete Jackson

    You can see some craters in the hummocky flat terrain, although they are hard to see in the hummocky chaos. But there are none on the mountain slopes. They must get erased by landslides.

    Fantastic pictures, Phil

  24. Grand Lunar

    I love me some lunar mountains.

    Perhaps one should write a song, entitled “Luna the Beautiful”.

    For ashen mountains, jet black sky……

  25. Messier Tidy Upper

    Magnificent image. :-)

    Reminds me of the classic spaceart of Chesley Bonestell who painted jagged lunar peaks long before we landed there :

    See :

    For more.

    There are better images of his paintings in books though. These were (largely) painted pre-Apollo when we thought the mountains were more “sharp pointed” than smooth and rounded as they’ve (mostly?) turned out to be.

  26. Messier Tidy Upper

    @1. Your Name’s not Bruce? : “TMA-1?”

    Well it is on Tycho and it’s an anomaly of sorts but is it magnetic? 😉

    We’ll have to go there and find out.

    @20. Anchor :

    Here’s a fun comparison to make: the Near-Earth Object, asteroid MD-2011 which sailed by Earth last Monday is – at an estimated 10-meters or so across – smaller than that ‘small’ but prominent boulder one sees immediately above the behemoth in that May 2010 image.

    Some lunar craters are larger than some planet’s moons :

    “If we could transport Phobos and Diemos to our own Moon, they would fit comfortably inside the wide crater Copernicus with room enough for two moons of similar size.”
    – Stephen James O’Meara, page 102 “The Demon Sprites of Mars” in ‘Sky & Telescope’ magazine, June 2001.

    @24. Grand Lunar : Please continue – and ideally get it recorded! I’d like to hear that! 😉

  27. Messier Tidy Upper

    Oh & some great Chesley Bonestell art work can be found on Youtube even too – take a look at this :

    A classic tribute to a superb artist who fired a lot of imaginations and evoked much wonder and thought. :-)

  28. Michael Suttkus, II

    I thought rocks could only be pushed onto the tops of mountains by global floods. Clearly, Noah’s flood was deeper than formerly suspected.

  29. Dirty Harry

    Besides the Boulder…there is this “Ridge Line” thats running at the base of the Mountain all the way…Fault Lines definitely not the Rift Valley in making…is it..or more Canali ala Mars :)

  30. Stan9fromouterspace

    In the large image, the smaller peak shows a very similar morphology, on a smaller scale: a number of protrusions almost resembling a volcanic caldera (although it’s not) and in the depression at the peak, there is a large boulder. On the smaller peak there are more smaller fragments littered around the big chunk. Hmmm.

  31. jennyxyzzy

    I have a question for all of the astronomy-types here. If the Moon’s albedo was more like new snow (0.9), rather than it’s actual sooty 0.12, how bright would a full moon be? Would it be just about daylight here on Earth? And more importantly, how would we calculate it?

  32. Skip Huffman

    Jennyxyyz. If you think about it a bit you can see that it won’t be as bright as daylight.

    If the moon were a perfect mirror, it would reflect all of the sunlight that hit it, but because it is a sphere that reflected sunlight will go all directions, most of it not to earth.

  33. Gary Ansorge

    Reminds me a bit of the Grand Tetons in Wyoming. All sharp edges and straight planes.

    Cool Pics.

    Gary 7


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