APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

APOD Robot · Post by **APOD Robot** » Mon May 07, 2018 4:07 am

The Unusual Boulder at Tycho's Peak

Explanation: Why is there a large boulder near the center of Tycho's peak? Tycho crater on the Moon is one of the easiest features to see, visible even to the unaided eye (inset, lower right). But at the center of Tycho (inset, upper left) is a something unusual -- a 120-meter boulder. This boulder was imaged at very high resolution <a hre="ap130104.html">at sunrise</a>, over the past decade, by the Moon-circling Lunar Reconnaissance Orbiter (LRO). The leading origin hypothesis is that that the boulder was thrown during the tremendous collision that formed Tycho crater about 110 million years ago, and by chance came back down right near the center of the newly-formed central mountain. Over the next billion years meteor impacts and moonquakes should slowly degrade Tycho's center, likely causing the central boulder to tumble 2000 meters down to the crater floor and disintegrate.

<< Previous APOD

This Day in APOD

Next APOD >>

Ann · Post by **Ann** » Mon May 07, 2018 4:24 am

My own interest in meteor impacts and the Moon is dramatically lower than my interest in blue stars.

So I tend not to be blown over by any facts or hypotheses about the Moon, although I do find myself fascinated by hypotheses about the formation of the Moon. But an unusual boulder on a lunar crater peak? How strange or significant is that?

Today's APOD did encourage me to google the formation of craters, and I found one Youtube video that gave me most of the information that I feel I need on the subject!

Click to play embedded YouTube video.

Ann

ta152h0 · Post by **ta152h0** » Mon May 07, 2018 5:34 am

There was ( still is ? ) something similar at Eros

heehaw · Post by **heehaw** » Mon May 07, 2018 9:18 am

"Over the next billion years meteor impacts and moonquakes should slowly degrade Tycho's center, likely causing the central boulder to tumble 2000 meters down to the crater floor and disintegrate." I'm so annoyed that I won't be around to see it! Just imagine it bouncing down!

JohnD · Post by **JohnD** » Mon May 07, 2018 9:51 am

There's no crater around it, which the impact from even a sub-orbital flight after this boulder was ejected from the surface by a larger impact, would have caused, probably destroying the boulder.
So a more likely origin is that this is the first stage in the degradation of Tycho's peak that the blurb describes. It was thrust up there by the original impact, has become dislodged and rolled/slid to where it now lies. More pictures needed, at different sun angles, to see if there is any evidence of its journey to here.
JOhn

orin stepanek · Post by **orin stepanek** » Mon May 07, 2018 11:36 am

If man is involved; the bolder will get moved long before that!

Well unless it gets declared to be a part of a Luna Park!

neufer · Post by **neufer** » Mon May 07, 2018 1:29 pm

https://en.wikipedia.org/wiki/Surveyor_7 wrote:

Photomosaic of a panorama taken by Surveyor 7 of its landing site.
<<Surveyor 7 was the fifth and final spacecraft of the Surveyor series to achieve a lunar soft landing. The spacecraft landed on the lunar surface on January 10, 1968, on the outer rim of the crater Tycho. It was planned to be visited by the cancelled Apollo 20 mission, however Skylab and subsequent budget cuts stopped this from happening. Operations of the spacecraft began shortly after the soft landing and were terminated on January 26, 1968, 80 hours after sunset. On January 20, while the craft was still in daylight, the TV camera clearly saw two laser beams aimed at it from the night side of the crescent Earth, one from Kitt Peak National Observatory, Tucson, Arizona, and the other at Table Mountain at Wrightwood, California. Surveyor 7 was the first probe to detect the faint glow on the lunar horizon after dark that is now thought to be light reflected from electrostatically levitated moon dust. Operations on the second lunar day occurred from February 12 to 21, 1968. The mission objectives were fully satisfied by the spacecraft operations. Battery damage was suffered during the first lunar night and transmission contact was subsequently sporadic. Contact with Surveyor 7 was lost on February 21, 1968.>>

Chris Peterson · Post by **Chris Peterson** » Mon May 07, 2018 1:40 pm

JohnD wrote: ↑Mon May 07, 2018 9:51 am There's no crater around it, which the impact from even a sub-orbital flight after this boulder was ejected from the surface by a larger impact, would have caused, probably destroying the boulder.

Why? Cratering requires speeds of kilometers per second. A bounced boulder could easily be traveling under a few hundred meters per second- nowhere near enough to create a crater or even a significant pit, and well inside the material strength range for a piece of solid rock, both at ejection and landing.

neufer · Post by **neufer** » Mon May 07, 2018 1:55 pm

https://www.smithsonianmag.com/smart-news/giant-intact-egg-extinct-elephant-bird-found-buffalo-museum-180968850/ wrote:

Click to play embedded YouTube video.
Click to play embedded YouTube video.
<<The Buffalo Museum of Science has been accruing its collection for well over a century and is currently in the process of updating its catalog, some of which still exists on cards and ledgers. While inputting catalog data into the museum’s computer system, Paige Langle, the collections manager of zoology, opened a cabinet that hadn’t been looked in for quite some time. Inside was an enormous, cream-colored egg. It measured 12 inches long, 28 inches in circumference and weighed more than three pounds. It was also labeled as a model. Langle, however, immediately suspected that the egg was “too realistic to be a model,” she tells Smithsonian.com. “I tried to shrug it off, but the more closely I looked at the surface of the eggshell and felt the weight of the egg, the more I kept thinking this has to be real.”

She was right. Searching deeper in the collections, she found a replica of the elephant bird egg that was obviously the model in question. Museum staff then looked through the institution’s archives and found records indicating that the museum had purchased a sub-fossilized elephant bird egg from a London purveyor of taxidermy specimens in 1939. They also found a letter written by a curator at the time, who listed various objects that he wanted to acquire for an exhibit on birds. One of those objects was a an elephant bird egg.

“From what we could tell, he mailed this list to all kinds of dealers all over the world, several of them in London,” says Kathryn Leacock, the museum’s director of collections. “A couple of them wrote back and said, ‘Oh no, you’re not going to get one of those. They’re kind of expensive.’ Fortunately he didn’t let that deter him.”

Museum staff sent the specimen to SUNY Buffalo State to be radiographed and authenticated. Conservation experts there not only confirmed that the egg was real, but were also able to determine that it had been fertilized. They could make out the yolk sac and, Leacock says, “white fragments” that may point to the beginnings of a developing bird.

The 40 or so elephant bird eggs that are owned by public institutions exist in varying states of completeness. The National Geographic Society in Washington, D.C., has an intact sub-fossilized elephant bird egg, and inside is an embryonic skeleton. But other institutions “just have fragments of the shell,” Leacock says. (It is hard to know how many elephant bird eggs are held in private collections; David Attenborough has one, and in 2013, another sold for $100,000 at a Christie’s auction in London.)

Leacock hopes that the newfound specimen at the Buffalo Science Museum will prove valuable to experts who are interested in the elephant bird. There were several species of this massive creature. The largest towered 10 feet high and weighed around 1,000 pounds. These magnificent creatures died out relatively quickly once humans came to Madagascar; the last sighting of an Aepyornis was in the 17th century.>>

neufer · Post by **neufer** » Mon May 07, 2018 3:07 pm

Chris Peterson wrote: ↑Mon May 07, 2018 1:40 pm
JohnD wrote: ↑Mon May 07, 2018 9:51 am
There's no crater around it, which the impact from even a sub-orbital flight after this boulder was ejected from the surface by a larger impact, would have caused, probably destroying the boulder.
Why? Cratering requires speeds of kilometers per second. A bounced boulder could easily be traveling under a few hundred meters per second- nowhere near enough to create a crater or even a significant pit, and well inside the material strength range for a piece of solid rock, both at ejection and landing.

If Tycho's peak was a volcano long after the impact crater was formed then this could be a lava boulder thrown up by that volcano (or a left residual piece from the collapse of a volcanic dome spire).

Chris Peterson · Post by **Chris Peterson** » Mon May 07, 2018 3:16 pm

neufer wrote: ↑Mon May 07, 2018 3:07 pm
Chris Peterson wrote: ↑Mon May 07, 2018 1:40 pm
JohnD wrote: ↑Mon May 07, 2018 9:51 am
There's no crater around it, which the impact from even a sub-orbital flight after this boulder was ejected from the surface by a larger impact, would have caused, probably destroying the boulder.
Why? Cratering requires speeds of kilometers per second. A bounced boulder could easily be traveling under a few hundred meters per second- nowhere near enough to create a crater or even a significant pit, and well inside the material strength range for a piece of solid rock, both at ejection and landing.
If Tycho's peak was a volcano long after the impact crater was formed then this could be a lava boulder thrown up by that volcano (or a left residual piece from the collapse of a volcanic dome spire).

Why would we think Tychos's central peak was ever a volcano?

FLPhotoCatcher · Post by **FLPhotoCatcher** » Mon May 07, 2018 4:14 pm

JohnD wrote: ↑Mon May 07, 2018 9:51 am There's no crater around it, which the impact from even a sub-orbital flight after this boulder was ejected from the surface by a larger impact, would have caused, probably destroying the boulder.
So a more likely origin is that this is the first stage in the degradation of Tycho's peak that the blurb describes. It was thrust up there by the original impact, has become dislodged and rolled/slid to where it now lies. More pictures needed, at different sun angles, to see if there is any evidence of its journey to here.
JOhn

I agree. There appears to be evidence of a landslide or slump from the top ridge of the central mountain (what's the name of the mountain?). The evidence is the parallel cracks near the boulder.

JohnD · Post by **JohnD** » Mon May 07, 2018 4:55 pm

Chris Peterson wrote: ↑Mon May 07, 2018 1:40 pm
JohnD wrote: ↑Mon May 07, 2018 9:51 am There's no crater around it, which the impact from even a sub-orbital flight after this boulder was ejected from the surface by a larger impact, would have caused, probably destroying the boulder.
Why? Cratering requires speeds of kilometers per second. A bounced boulder could easily be traveling under a few hundred meters per second- nowhere near enough to create a crater or even a significant pit, and well inside the material strength range for a piece of solid rock, both at ejection and landing.

I think we agree, Chris. I disaagree with the original caption, that " the boulder was thrown during the tremendous collision that formed Tycho crater about 110 million years ago, and by chance came back down right near the center of the newly-formed central mountain." This boulder didn't arrive at any astronomical velocity, but was deposited there by some other means. The picture gives no scale, -is it shed, house or office building sized? There might be a trail - this video from the South Tyrol shows two house sized boulders that crashed through some houses, leaving a significant trail behind of their rolling. That trail will not last long on Earth, even if the land were not vinyards, but on the Moon it will take millions of years to obliterate that sort of mark.
https://www.youtube.com/watch?v=-5SiQqSroIw
John

Chris Peterson · Post by **Chris Peterson** » Mon May 07, 2018 5:10 pm

JohnD wrote: ↑Mon May 07, 2018 4:55 pm
Chris Peterson wrote: ↑Mon May 07, 2018 1:40 pm
JohnD wrote: ↑Mon May 07, 2018 9:51 am There's no crater around it, which the impact from even a sub-orbital flight after this boulder was ejected from the surface by a larger impact, would have caused, probably destroying the boulder.
Why? Cratering requires speeds of kilometers per second. A bounced boulder could easily be traveling under a few hundred meters per second- nowhere near enough to create a crater or even a significant pit, and well inside the material strength range for a piece of solid rock, both at ejection and landing.
I think we agree, Chris. I disaagree with the original caption, that " the boulder was thrown during the tremendous collision that formed Tycho crater about 110 million years ago, and by chance came back down right near the center of the newly-formed central mountain." This boulder didn't arrive at any astronomical velocity, but was deposited there by some other means. The picture gives no scale, -is it shed, house or office building sized? There might be a trail - this video from the South Tyrol shows two house sized boulders that crashed through some houses, leaving a significant trail behind of their rolling. That trail will not last long on Earth, even if the land were not vinyards, but on the Moon it will take millions of years to obliterate that sort of mark.
https://www.youtube.com/watch?v=-5SiQqSroIw
John

The boulder is described as being 120 meters across. That's similar to ejecta seen for many kilometers around the crater (some quite closely by Apollo 16). It appears to be in a shallow depression near the top of the central peak. It need not have landed exactly there- anywhere in the surrounds and it would have rolled to its current location. 100 million years isn't long enough for major erosion or slumping of the crater, but is certainly long enough that new regolith would have covered shallow tracks.

The uplift of the central mountain of a complex crater is a relatively gentle event in comparison with the formation of the crater as a whole. Rocks that rose with the center might have been tossed no more than a few thousand meters into the air, some of them nearly vertically. So I don't find it particularly implausible that one would have landed near the top and settled there.

Booduh · Post by **Booduh** » Mon May 07, 2018 5:23 pm

How Zen

[youtube]https://youtu.be/UfMP4Fy0KEQ[/youtube]

neufer · Post by **neufer** » Mon May 07, 2018 5:24 pm

Chris Peterson wrote: ↑Mon May 07, 2018 3:16 pm
neufer wrote: ↑Mon May 07, 2018 3:07 pm
Chris Peterson wrote: ↑Mon May 07, 2018 1:40 pm
Why? Cratering requires speeds of kilometers per second. A bounced boulder could easily be traveling under a few hundred meters per second- nowhere near enough to create a crater or even a significant pit, and well inside the material strength range for a piece of solid rock, both at ejection and landing.
If Tycho's peak was a volcano long after the impact crater was formed then this could be a lava boulder thrown up by that volcano (or a left residual piece from the collapse of a volcanic dome spire).
Why would we think Tychos's central peak was ever a volcano?

Tycho has a radius of 43 km whereas the near side lunar crust is only about 35 km thick.

https://en.wikipedia.org/wiki/Moon#Volcanic_features wrote:
Evidence of young lunar volcanism
<<The dark and relatively featureless lunar plains, clearly seen with the naked eye, are called maria; they are now known to be vast solidified pools of ancient basaltic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water. The majority of these lavas erupted or flowed into the depressions associated with impact basins. Several geologic provinces containing shield volcanoes and volcanic domes are found within the near side "maria". Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side. This is thought to be due to a concentration of heat-producing elements under the crust on the near side, seen on geochemical maps obtained by Lunar Prospector's gamma-ray spectrometer, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt. Most of the Moon's mare basalts erupted during the Imbrian period, 3.0–3.5 billion years ago. Until recently, the youngest eruptions, dated by crater counting, appeared to have been only 1.2 billion years ago.

In 2006, a study of Ina, a tiny depression in Lacus Felicitatis, found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old. Moonquakes and releases of gas also indicate some continued lunar activity. In 2014 NASA announced "widespread evidence of young lunar volcanism" at 70 irregular mare patches identified by the Lunar Reconnaissance Orbiter, some less than 50 million years old (compared with 108 million years old for Tycho). This raises the possibility of a much warmer lunar mantle than previously believed, at least on the near side where the deep crust is substantially warmer because of the greater concentration of radioactive elements. Just prior to this, evidence has been presented for 2–10 million years younger basaltic volcanism inside Lowell crater, Orientale basin, located in the transition zone between the near and far sides of the Moon. An initially hotter mantle and/or local enrichment of heat-producing elements in the mantle could be responsible for prolonged activities also on the far side in the Orientale basin.>>

Chris Peterson · Post by **Chris Peterson** » Mon May 07, 2018 5:40 pm

neufer wrote: ↑Mon May 07, 2018 5:24 pm
Chris Peterson wrote: ↑Mon May 07, 2018 3:16 pm Why would we think Tychos's central peak was ever a volcano?
Tycho has a radius of 43 km whereas the near side lunar crust is only about 35 km thick.

Sure, the crater is large enough to get basaltic flows in its base. Nothing unusual there. That's very different from suggesting that the central peak is a volcano, or there was ever any volcanism that could throw 120 meter boulders around!

neufer · Post by **neufer** » Mon May 07, 2018 6:42 pm

Chris Peterson wrote: ↑Mon May 07, 2018 5:40 pm
neufer wrote: ↑Mon May 07, 2018 5:24 pm
Chris Peterson wrote: ↑Mon May 07, 2018 3:16 pm
Why would we think Tychos's central peak was ever a volcano?
Tycho has a radius of 43 km whereas the near side lunar crust is only about 35 km thick.
Sure, the crater is large enough to get basaltic flows in its base. Nothing unusual there. That's very different from suggesting that the central peak is a volcano, or there was ever any volcanism that could throw 120 meter boulders around!

Which is why Ieft open the option of it being a "residual piece from the collapse of a volcanic dome spire."

Chris Peterson · Post by **Chris Peterson** » Mon May 07, 2018 7:05 pm

neufer wrote: ↑Mon May 07, 2018 6:42 pm
Chris Peterson wrote: ↑Mon May 07, 2018 5:40 pm
neufer wrote: ↑Mon May 07, 2018 5:24 pm
Tycho has a radius of 43 km whereas the near side lunar crust is only about 35 km thick.
Sure, the crater is large enough to get basaltic flows in its base. Nothing unusual there. That's very different from suggesting that the central peak is a volcano, or there was ever any volcanism that could throw 120 meter boulders around!
Which is why Ieft open the option of it being a "residual piece from the collapse of a volcanic dome spire."

But I don't think there would be any volcanic dome spires in a crater or on a crater central peak.

Boomer12k · Post by **Boomer12k** » Mon May 07, 2018 9:59 pm

Very interesting image, and very interesting boulder...at nearly 394 feet big, (nearly FOUR times the size of my mobile home at 90 feet long), with some appreciable Mass, and even if at 50 miles an hour...there is going to be SOME cratering, I would think... I think it was already THERE, when the "Mountain Building" after the impact occurred.... Meteor hits...goes deep...matter splays out...some molten... as WITH SOME VOLCANOES. there is an uplift of new rock, from pressure pushing up as Mass has been released from that spot..."mountain building"...this boulder, had landed where it was already...after the impact...then DURING the mountain building...rose with it... just my opinion... In Ann's Video... Meteor Crater does not have a central mountain... maybe it was just not over the right type of rock, or did not go deep enough, no hot spot. None of the projectile shots formed a mountain, though vaporized, and melted the sand. Many craters on the moon have no mountains... some of the larger ones do... my opinion, they had to go deep enough to hit some lava, or light rock, that could then rise to the surface...this is going on, on Earth. The Himalayan Mountains rise as rock and debris are sloughed off, and rinsed off the mountains... As the mass gets lighter...they rise. I don't think Tycho Crater's process was instant mountain... splash...up comes the liquid rock, and solidifies all at once, forming a mountain, then this boulder lands there... I think the process was slow lifting, and the rock WAS there.
In MY image... there are other, larger craters, and caldera with no central mountains, even very close by...there is a large crater at 5 o'clock with 2 smaller craters...one with a central mountain...so it does not have to be a "big, deep shot" to get mountain building...OR THERE IS ANOTHER PROCESS.

The Moon has always reminded me of cooking a Pancake. Bubbles rise...break, and you are left with cratering as the pancake solidifies from cooking, as it dehydrates from heat... you have a molten stage of the Moon...it bubbles...and like some Lava Tubes...they collapse...(but these are round "sink hole" areas, that become Craters and caldera)... as the surface cools, and solidifies... sometimes, there is still pressure from below to push up rock, or make rock. Also..."some" of these bubbles don't just collapse...they BLOW... POP!!! spewing material...collapsing, filling in...and some flooring, and mountain building, not always in the direct center, see my image.... Just my analogy....void where prohibited.

Unless, of course, you want to hear my OTHER theory...

MY Tycho Crater shot for the other week with my 6" Celestron Evolution, and my Zwo LP camera... this is one of my finest images ever...I think it is pretty perfect, and you can see wall details... so cool...

:---[===] *

Chris Peterson · Post by **Chris Peterson** » Mon May 07, 2018 11:40 pm

Boomer12k wrote: ↑Mon May 07, 2018 9:59 pm Very interesting image, and very interesting boulder...at nearly 394 feet big, (nearly FOUR times the size of my mobile home at 90 feet long), with some appreciable Mass, and even if at 50 miles an hour...there is going to be SOME cratering, I would think...

Material which was thrown into near orbit would come back down with enough speed (on the order of 2000 m/s) to produce minor cratering. But anything thrown upwards from the central peak uplift would likely have been much slower, not over a few hundred meters per second, which is nowhere near enough to produce a crater. On soft ground it could produce a pit (very different from a crater), but this was uplifted rock it landed on, not regolith.

I think it was already THERE, when the "Mountain Building" after the impact occurred.... Meteor hits...goes deep...matter splays out...some molten... as WITH SOME VOLCANOES. there is an uplift of new rock, from pressure pushing up as Mass has been released from that spot..."mountain building"...this boulder, had landed where it was already...after the impact...then DURING the mountain building...rose with it... just my opinion...

Anything near the impact would have been vaporized, down to a depth of a kilometer or more. Underneath that was solid rock, which would have been fragmented by the impact and ejected mainly outwards, forming the rays and ejecta fields surrounding the crater. The central peak would have uplifted very fast- too fast I think for a fragment to ride it up. Loose material on top would have been thrown upwards and come back down near the peak. Or on it. Note that uplift isn't a rebound process. It occurs with sufficiently large impacts where energy is directed outwards, producing a basin rather than a concave pit, and a kind of ring of pressure pushes the middle upwards, forming the central peak. It has no connection with reaching underlying molten material. Basins are filled with impact melt, and under the right circumstances there may be leakage of magma from fissures, but the central peak is much more solid, and is not formed from any kind of melt.

In Ann's Video... Meteor Crater does not have a central mountain... maybe it was just not over the right type of rock, or did not go deep enough, no hot spot.

Nothing to do with depth or type of rock. It was simply too small an impactor. The smallest craters we see on Earth that have central peaks are about 2 km in diameter, twice the size of Meteor Crater. Really large craters, over about 25 km across (on Earth), don't form central peaks, but central peak rings.

MarkBour · Post by **MarkBour** » Tue May 08, 2018 1:19 am

I wonder about the use of the description "Unusual Boulder" in the APOD title. Provocative. Perhaps just because of the locaton that looks a bit unexpected at first? I don't see any evidence that the boulder is itself really unusual. Looking at the fourth link in the APOD caption (center of Tycho), or the version on Wikipedia at: https://en.wikipedia.org/wiki/Tycho_(lu ... k_0.25.jpg.

Those images appear to show that this boulder is really not at all alone. There are a vast number of similar boulders all around, from smaller to larger sizes, and although most of them are buried more, some of them are as exposed as is this one. Look at the other nearby peak, for example.

Agent Buchwald · Post by **Agent Buchwald** » Tue May 08, 2018 10:50 am

Reminds me of Clarke's "The Sentinel".

GoshOGeeOGolly · Post by **GoshOGeeOGolly** » Tue May 08, 2018 5:32 pm

Looks like it disturbed a bed or semi-liquid something when it landed, or perhaps its landing created a very short term semi-liquid bed. Certainly is a curiosity.

GoshOGeeOGolly · Post by **GoshOGeeOGolly** » Tue May 08, 2018 6:30 pm

Ann wrote: ↑Mon May 07, 2018 4:24 am My own interest in meteor impacts and the Moon is dramatically lower than my interest in blue stars. So I tend not to be blown over by any facts or hypotheses about the Moon, although I do find myself fascinated by hypotheses about the formation of the Moon. But an unusual boulder on a lunar crater peak? How strange or significant is that?

Today's APOD did encourage me to google the formation of craters, and I found one Youtube video that gave me most of the information that I feel I need on the subject!

Click to play embedded YouTube video.

Ann

Here's some interesting craters. https://www.google.ca/search?q=gas+bubb ... &ie=UTF-8

Starship Asterisk*

APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)

Re: APOD: The Unusual Boulder at Tycho's Peak (2018 May 07)