Dark haloed craters are windows to the volcanic history of the Moon. This blog entry was inspired by Thomas’s choice of Image of the Week where he highlights impact craters that have dark material surrounding the crater hole itself.
Dark haloed craters provide us with key insights into what must have been a dramatic and violent volcanic period of lunar history. To probe a little further here is a little background about eruptive volcanism on the Moon:
Between about 4 billion years ago and 3 billion years ago the lunar mantle underwent a period of partial melting where magma was generated at depth and then propagated up through fracture networks and magma conduits towards the lunar surface. It has been proposed that some of this lava was very rich in gases like carbon monoxide that may have caused rapid upward movement (maybe on the scale of one to several days) and caused dramatic pyroclastic eruptions at the lunar surface. These fire-fountaining events are similar to, but on a much larger scale than, eruptions witnessed at volcanoes in Hawaii, with some plumes of lava being thrown up to 40 km in height above the surface of Moon!
Other lavas that were less gas-rich would have migrated to the lunar surface more slowly, and could have erupted more gently, forming long lava flows that travelled great distances from their volcanic vent site. These lava flows are thought to have the consistency of runny motor oil and easily flowed into topographic lows like impact craters. Sometimes large quantities of lava must have flowed in channel networks – forming rivers of fire across the lunar surface. It must have been a dramatic time, but as available heat sources were diminished in the lunar interior, less magma was generated and by about 1 billion years ago we believe the Moon’s eruptive volcanic history came to a close.
So how do dark haloed craters fit into this story? Well they actually help address two separate lunar science questions as there are two types of dark haloed craters to keep an eye out for in Moon Zoo images (although we would please like you to classify them using the same button!)…
1. Volcanic eruption sites – these are rare places where pyroclastic beads, the ‘airfall’ deposits of lunar volcanoes, are concentrated on the lunar surface and form mantles around their source vents. These beads are a little bit like the volcanic ash or the Pele’s tears glass that gets erupted from volcanoes on Earth and you can read more about these types of dark halo mantles at:
- Explosive Volcanic Eruptions on the Moon.
- The Pyroclastic Volcanism Project at the US Geological Survey.
- Moon Zoo Thomas’s guide to pyroclastic craters.
- Pyroclastic bead features seen in LROC NAC images.
2. Crater excavation sites – you are far more likely to spot these types of dark haloed craters in Moon Zoo images. The dark haloed craters provide us with a neat view down through a series of geological layers. These are formed when an asteroid or comets smashes into the Moon, punches through an overlying light coloured layer (probably an ejecta blanket material from a nearby highland impact crater) and excavates material from below that is darker in colour. This darker material is likely to be a lava flow that was buried at depth and that is now revealed by the impact cratering process.
Here’s a nice diagram of this process can be seen at where the lower image shows a schematic of what two dark haloed impact craters look like from side-on. You can also view a 3D perspective of this process.
We call these types of buried lava flows cryptomaria as they would otherwise be hidden from view if we had not have spotted the tell tale signs of dark haloed craters. By mapping the location and extent of dark haloed craters we can therefore map out the distribution of buried lava flows at depth across the Moon and get a much better idea of the amount of ancient volcanism on the Moon. This in turn helps to shed new light on the Moon’s thermal and magmatic history, helping us to understand geological processes on small rocky planetary bodies.
Good examples of these types of impact formed dark-haloed craters spotted by Moon Zoo users include:
- http://www.moonzoo.org/examine/AMZ100185s (top right)
- http://forum.moonzoo.org/index.php?topic=209.msg4111#msg4111 (lovely collection of small craters at left centre)
- http://forum.moonzoo.org/index.php?topic=209.msg4270#msg4270 (right centre)
- Other good examples are provided on the Moon Zoo How to Take Part Tutorial.
So please do keep an eye our dark haloed craters on your Moon Zoo lunar exploring! Thanks to Irene Antonenko for providing helpful guidance about this topic.
We are used to seeing different kinds of craters on the Moon Zoo forum. In particular we collect dark haloed craters and fresh white craters. Impacts can excavate rocks and material beneath the lunar regolith and this “fresher” material forming the ejecta blanket sometimes looks a very different colour to the rest of the surrounding area due to its higher or lower albedo.
Forum member kodemunkey recently found a couple of impacts which at first glance were hard to classify – you could say they were impacts of two halves. Are they fresh whites or dark haloed? Or is it just a trick of light and shadow? I think that’s exactly what we are seeing in the first crater. The combination of a high Sun, uneven terrain and a deep impact has produced an image of a crater half in shadow. The second crater is slightly more difficult to call. Both make striking images. Why not have a closer look and see what you think.
Here’s a reminder the Moon Zoo science goals- and what our clicks are being used for.
1. To improve our knowledge of the production of small lunar craters by gathering information about their numbers and dimensions. This can be used to improve lunar maps and coordinates.
2. To calculate the age of different lunar surfaces (e.g., mare, impact melt sheets, highland crust) by comparing the number and sizes of impact craters. The more cratered a region is the older it is. Knowing the age of different surfaces allows us to build up a history of the geological processes on the Moon, in particular its temporal thermal and magmatic history. What we learn about these processes on the Moon we can then apply to other small rocky planetary bodies.
3. Results from Moon Zoo could also assist in the development of automated computer crater counting systems, and to help understand how image viewing geometries influences crater counting studies.
4. To determine variations in lunar regolith thickness by assessing the presence of boulders around crater rims.
5. To identify unique and unusual morphological features that help us to better understand the geological diversity of the Moon. Recording these featured will help to develop a database of interesting morphological features (for example, boulder tracks, fresh white and dark haloed craters, crater chains, elongate craters and pits etc) for the lunar science community to use.
To produce a boulder density hazard map to assist in identifying suitable landing sites for future human or robotic lunar missions.
- To produce peer-reviewed science.
- To promote lunar and planetary science through using Moon Zoo as an educational and public outreach tool.
- To identify small, highly elliptical craters that may have preserved meteoritic material.
- To assess degraded craters according to variations in user measurements and produce maps of crater degradation states.
This week forum regular kodemunkey has chosen to highlight the lunar “black stuff” we have been looking for since Dr Tony Cook asked us to post examples. Often difficult to distinguish from shadows this black deposit might be volcanic in origin or just a dark albedo feature. Whatever it is we now have quite a collection to study. Over to kodemunkey to explain further.
Hello once again moon fans, this week I have a strange one for you, Lunar “Black Stuff.”
Of all the sub-topics on the forum, I think this one is the most mysterious and it’s certainly caught my attention.
To quote Anthony Cook on the subject:
“Description: Dark slightly branching features, often on the shaded side of slopes. Boulders associated with these. Also appears as an exposed strata layer in a nearby rill rim.
Interest: Is this “dark stuff” an exposed dark material black volcanic glass, a deep branching crack with shadow, dark boulders, or a combination? Either way we need to find more of these and their geographical distribution. Could be worth monitoring these from orbit and at different sun angles to see if the darkness is related to shadow.”
I, like many people, enjoy both a good mystery and a chance to be nosey, so this was one project that suited me down to the ground (or regolith if you prefer!)
Where has it been found so far?
During my time on the forum, I’ve found examples of “Black stuff” in the following locations:
Marius Hills (Perhaps ejecta from Aristarchus / Kepler?)
Schroter, Fauth, Bode, Sommering and Gambart (Ejecta from Copernicus perhaps?)
As well as various dark haloed craters and other unnamed crater ejecta blankets.
This section is a guide to where you might find examples of Black stuff:
On the edges of rille systems
Vallis Alpes Rille
On crater rims
Unamed impact, Taurus-Littrow region
Unnamed far side impact
Occasionally in the ejecta blankets of small impacts
Minor impact within Michelson crater on the far side.
Unnamed near side impact
Covering the landscape
Taking into account the number of impacts, both large and small, why isn’t there more black stuff laying around, and why is it seemingly more prevalent on the near side more than the far side?
WMS Browser: http://wms.lroc.asu.edu/lroc#damoon
Act – React tool: http://target.lroc.asu.edu/da/qmap.html
Moon Zoo Thread “TLP – Black Stuff”: http://forum.moonzoo.org/index.php?topic=264.0
Special mentions go to forum moderators Jules, Geoff, Ireneant and forum members Astrostu and Tom128, who i imagine i drove to insanity badgering them with my own inane ramblings on the subject.
This iconic image was taken 38 years ago today. It shows Apollo 17 astronaut Harrison “Jack” Schmitt next to the Lunar Rover during an EVA on December 13th 1972 with the crescent Earth hanging in the sky.
This week marks the 38th anniversary of the Apollo 17 mission to investigate the Taurus Littrow valley region of the Moon. The mission launched at 12.33am EST on December 7 1972 and ended on 19 December when the 3-man crew splashed down in the Pacific Ocean just 640 meters from the target point.
Apollo 17’s mission plan was for the spacecraft to land in the Moon’s Taurus-Littrow region near the rim of the Serenitatis Basin as this region was rich in a variety of lunar geological features such as volcanic cinder cones, highland mountains and many large boulders which had rolled down the North and South massifs. This meant that the crew could investigate young volcanic rock as well as older highland material at the same location. Debris from Tycho Crater’s rays also extended this far. The Apollo 17 crew collected 111 kilograms of lunar soil and rock, 741 individual samples, including a 3 metre deep drill core. This was the biggest and most varied collection of lunar materials returned by any Apollo crew. The mission had the experience of the whole Apollo programme to draw on and from lift off to splashdown it was flawless. A fitting end to an inspirational space programme.
One of the outcomes of the Apollo 17 mission was the distribution of so called “Goodwill moon rocks” – portions of a rock that Jack Schmitt picked from the floor of the Taurus-Littrow valley (since labelled sample 70017.) In Eugene Cernan’s words:
|“Jack has picked up a very significant rock, typical of what we have here in the valley of Taurus-Littrow. It’s a rock composed of many fragments, of many sizes, and many shapes, probably from all parts of the Moon, perhaps billions of years old. But fragments of all sizes and shapes — and even colors — that have grown together to become a cohesive rock, outlasting the nature of space, sort of living together in a very coherent, very peaceful manner. When we return this rock or some of the others like it to Houston, we’d like to share a piece of this rock with so many of the countries throughout the world. We hope that this will be a symbol of what our feelings are, what the feelings of the Apollo Program are, and a symbol of mankind: that we can live in peace and harmony in the future.”
Jack Schmitt continued:
Three months after Apollo 17 returned home fragments from the rock that Cernan and Schmitt collected were distributed to 135 foreign heads of state, the 50 U.S. states and its provinces. Each rock encased in acrylic was mounted to a plaque with the recepient’s flag (which was also flown to the Moon.) The samples to the 135 foreign heads of state also included a letter signed by President Nixon. In all nearly five hundred tiny pieces of the sample have been distributed to museums and researchers around the world though NASA still has about 80% of the rock. There is an analysis of sample 70017 here.
Apollo 17 has been a popular topic on the Moon Zoo forum. Forum regular Caro was the first to post a couple of images of the Apollo 17 landing site back in May which together show the Challenger descent stage (visible in the left image, surrounded by trails made by astronaut feet and the wheels of the lunar rover which is visible as a dark spot on the left edge. The US flag is just below Challenger and scattered around the site is various ALSEP debris (Apollo Lunar Surface Experiments Package.) Many other forum members have “rediscovered” the Apollo 17 landing site since.
|Further forum resources:
Apollo 17 resources thread
Dark Haloed Craters
Transient Lunar Phenomena
The UK Goodwill Rock Hunt
|Apollo 17 Internet resources:
Apollo 17 Image Library
LROC site and video of the landing site
Apollo 17 Lunar Surface Journal
LROC NAC image
Forum member NGC3172 (Nathaniel Burton-Bradford) produced this 3D anaglyph of the landing site:
Ronald E. Evans (Command Module Pilot), Harrison H “Jack” Schmitt (the only geologist to have walked on the Moon) and Eugene A. Cernan were the 3 Apollo 17 crew members. Just before he returned to the Lunar Module for the last time Eugene Cernan said:
“ As I take man’s last step from the surface, back home for some time to come — but we believe not too long into the future — I’d like to just [say] what I believe history will record — that America’s challenge of today has forged man’s destiny of tomorrow. And, as we leave the Moon at Taurus-Littrow, we leave as we came and, God willing, as we shall return, with peace and hope for all mankind. Godspeed the crew of Apollo 17.”
But despite the hope and optimism of Eugene Cernan’s words the thrill of landing a man on the Moon had passed. The Apollo mission had finally ended and the prospect of further funding and support for manned space exploration looked bleak. 38 years later Eugene Cernan is still the last man to have walked on the Moon.
Thanks to forum member Tom128 for the Goodwill Moon rock links.
jules is a volunteer moderator for the Moon Zoo forum
Forum member jaroslavp was presented with this Moon Zoo image a few weeks ago:
ID: AMZ1001i8l (Nr Apollonius on the edge of Mare Spumans / Mare Fecunditatis)
Intrigued by the elongated shape of the crater he went on to investigate and what he found posed us all with an interesting crater conundrum. jaroslavp commented that the marked crater looked very different under different solar illumination. In one image it looks like any other round crater. In the other it looks very elongated and is surrounded by bright material.
|NAC image: M111219210LE Incidence angle 35.13
||NAC image: M119482862RE Incidence angle 57.64
Moon Zoo Team Science member astrostu was impressed and thought this was an excellent example to use to highlight the effect that different angles of solar illumination can produce.
jaroslavp wondered if the round crater was actually new, maybe a recent meteorite impact: He said:
“Maybe the crater wasnt there before? When I look on the dark spot there is no sign of the crater we can see on the second picture. And maybe the sun 45° from the surface makes many things invisible that you can see on the dark picture for example fresh white and dark-haloed craters.”
After some forum discussion it became clear that this really is just the result of viewing the same crater under different illumination but it certainly got us thinking and it is the best example yet we have had on the forum of just what a difference lighting can make as this animation jaroslavp put together shows:
Now on a roll, jaroslavp then found another strange crater containing a chain of 4 smaller craters and noticed something on the right hand slope of the crater wall:
ID: AMZ10018h5 (Taurus Mountains region)
So – is the small chain of secondary craters overlying the featured crater from a different crater impact or from the same impact that created the host crater?
Every day something intriguing is posted on the forum. It’s a great place to discover the Moon!
Jules is a volunteer moderator for the Moon Zoo forum