Dear MoonZoo aficionados,
Our next surveying exercise will be centred on the Apollo 12 landing site.
Your previous and successful endeavour saw hundreds of thousands of craters and interesting features noted in the region of the Apollo 17 landing site in the Taurus-Littrow valley. Here we witnessed a chaotic and highly scarred terrain, squeezed between tall mountains and crossed by a deep fault (the Lee-Lincoln Scarp): a rather complex geological setting. Indeed, the landing site was selected based on its geological diversity, with the aim of collecting pre-Imbrian age highland material, mare basalts, and igneous products from potential volcanic edifices.
Now we are turning our attention to the Apollo 12 landing site, and from 9 May all the Moon Zoo images relate to this site. In November 1969 Apollo 12 landed within a vast lunar mare (lava plains) region called Oceanus Procellarum (Ocean of Storms), and in particular an area baptised as Mare Cognitum (Known Sea), so called given that it had already been visited by three unmanned lunar missions (Luna 5, USSR, Surveyor 3 and Ranger 7, US). The landing region was estimated to be younger than the Apollo 11 site based on kilometre-size craters census (2.37 times fewer craters). In the following years, returned sample analyses (i.e. Stöffler and Ryder, 2001; Barra et al., 2006) estimated ages of 3.58 ± 0.01 and 3.80 ± 0.02 Gyr (both Late Imbrian Epoch), for Apollo 11, against 3.15 ± 0.04 Gyr for Apollo 12, (Eratosthenian Period). It will be very interesting to compare these direct age estimates with your high resolution/volume crater count survey, AND also compare them with the results from the Apollo 17 blitz (samples’ age: 3.75 ± 0.01 Gyr).
Obviously, as before we are also going to harvest data generated by the Moon Zoo users regarding bouldernyness and shape of the noted craters in order to build a fuller picture of the impact record in the region. As it happens, the lunar science team based at Birkbeck/UCL, UK, has been looking at the Apollo 12 region for quite sometime, both in terms of geological mapping and analysis of returned samples. We are particularly interested in the different lava flows found in the region and the mapping of small craters; the associated boulder distribution will be employed to estimate the different ages and thickness of these lava flows. Your Moon Zoo measurements of the Apollo 12 site will therefore be greatly appreciated, and they will potentially be incorporated in future scientific publications.
So, let’s start this new and exciting journey together: I will keep you posted on both results from previous efforts (A17, etc.) and the ongoing ones. Go and explore!
Barra F., et al., 2006. 40Ar/39Ar dating of Apollo 12 regolith: Implications for the age of Copernicus and the source of nonmare materials, Geochimica et Cosmochimica Acta 70, 6016-6031.
Stöffler D. and Ryder G. 2001. Stratigraphy and isotope ages of lunar geologic units: chronological standard for the inner solar system. Space Science Reviews 96: 9-54.
The MoonZoo science team would like to extend a gigantic thank you to all 20,627 users who contributed in counting craters (and more!) relating to the Apollo 17 landing site (Taurus-Littrow)!
Let’s ponder on some astonishing numbers: to date, around 8.5 million craters in total have been marked by MoonZoo citizen scientists, with around 670,000 (~8%) relating to the A17 region (from 21 selected NAC images, Figure 1); further, 3.3% (22,063) of these craters have been classified as containing boulders and 6.9% (45,893) were found to be non-circular.
Our next step is to compare your input with the ‘expert’ count looking to validate and quantify your contributions. The ‘expert’ in question is a professional lunar scientist who has published research including the statistical occurrence of impact craters on planetary surfaces. The logical assumption is that given a more or less constant collision rate of interplanetary bodies (asteroids and comets), a surface will carry the record of impact products (craters and pits) as a function of time, i.e., from the time of resurface (maybe a lava mare flow) the scarring would be proportional to the length of exposure.
As most things in geology, this scenario is true but with caveats… : first, the resurfacing by lava flow or ejecta mantling might have only partially buried ancient craters, or, more probably, only the smaller ones, thus skewing the crater-size statistical record; crater rims erode with time, even on an airless body like the Moon, at a rate of around 0.06-1 cm per million year. This might not seem much, but in the lunar chronology scale, measured in billions of years, this factor becomes significant; in reality, the biggest source of uncertainty is represented by secondary craters: most impacts generate coherent distal ejecta that, when landed, produce smaller craters virtually indistinguishable from space-born ones. And this is fractal, i.e. scaled: big impacts will generate hundreds of smaller craters that will overlap with similar ones from nearby big impacts…
The hard reality is that there are no cast-iron methods to establish the origin of each excavation (although it has been advocated that a secondary crater might be somewhat shallower in comparison to a similarly-sized primary one). So, an ‘expert’ becomes so by developing a ‘sense’ or instinct on what ‘feels’ a statistically significant crater against one that is not. This approach is more akin to ‘artistic interpretation’ than ‘hard’ science, but qualitative investigation of certain geological features is an acceptable compromise when a physical method is either not yet available or even impossible to develop.
These considerations do not stop the development of alternative methodologies though; indeed, we are working closely with a research group at Manchester University which is building an automated pattern recognition software of circular features (and others) based on theoretical models, and actual data: ‘expert’ counts, AND MoonZoo users’ data.
Now, whatever approach brings us closer to a reliable crater counting method this cannot be easily accomplished by even a troupe of crater-counting planetary scientists: the 8.5 million craters noted by the MoonZoo community would have taken years to harvest otherwise!
So, what is going to happen now? Well, the ‘expert’ and pattern recognition software data will be compared with the MoonZoo output, uncertainties and limitations of all approaches established and, hopefully, develop a method that will represent the basis for ‘trusting blind’ the MoonZoo craters stats. In practice this will translate into something like “MoonZoo crater data are consistent with other methods for crater of sizes ‘x’ to ‘y’, in images with resolution higher than ‘z’ meters, and illumination of ‘n’ degrees or higher”.
Ultimately, the crater statistics (Cumulative Crater Frequency) plotted against known crater accumulation functions (i.e. Neukum, 1983, 2010) give us an estimate of the age of the lunar region. Using these data from landing sites allows for comparison with returned samples whose age has been established in the laboratory.
Our next journey will focus around the Apollo 12 landing site, in Mare Cognitum. The geology of this region is radically different from the Apollo 17 and it should serve as a perfect complement to our work so far. Elsewhere my colleagues will discuss and introduce the region in more detail, including ulterior scientific reasons behind the choice of this landing site.
We shall keep you informed of all further developments and new projects, and, once again, thanks for your patient and enthusiastic contribution to planetary science!
Michael G.G., Neukum G., Planetary surface dating from crater size-frequency distribution measurements: Partial resurfacing events and statistical age uncertainty, Earth and Planetary Science Letters, 2010, DOI: 10.1016/j.epsl.2009.12.041.
Neukum G., Meteoritenbombardement und Datierung planetarer Oberfl�chen. Habilitation Dissertation for Faculty Membership, Univ. of Munich, 186pp, 1983.
A puzzle for you this week. Can you tell the difference between a moon, a planet and minor planet? Below are images of craters on our Moon, Vesta and Mercury but which is which? Superficially very similar but there are differences. Click on the letters below for links to reveal the answers.
Don’t peek until you have had a guess!
Forum member Ewan, otherwise known as Dynamo Duck, found some strange looking craters on the South-East edge of Mare Crisium at Latitude: 12.275° Longitude: 62.1034°. They appear to have unusually high albedo floors and possibly some ejecta of the same high albedo material.
Searching around the area I found some more of these “strange whites.”
|Here are two.
And then they were everywhere.
At the moment they remain a puzzle. They look like bench/concentric craters but why are the floors so “white”? What is this high albedo material and why are there so many of these craters in this region of Mare Crisium?
While we work out the answers here are some NACs for you to peruse showing the “strange whites” under different illumination.
How the voting went:
Picture 1 is Mercury 15.6%
Picture 2 is the Moon 15.6%
Picture 1 is the Moon 34.4%
Picture 2 is Mercury 34.4%
So how did you do? As you can see most people got this wrong! I managed to find a region of the Moon that didn’t look too obviously Moon-like so don’t feel too bad if you got them the wrong way round. The coordinates are the same for both Mercury and the Moon at lat –45 : long 125. This takes us to the lunar region around Planck and Van der Waals craters on the far side which looks very much like Mercury. At first glance the two bodies do look very similar but there are some differences – though not all obvious from the two pictures.
- Mercury has more intercrater plains (its oldest surface) than the Moon.
- Ejecta deposits and secondary craters are less extensive on Mercury due to its higher gravity field. The region of Mercury chosen is atypical in this respect though there are some clues.
- There are more tectonic features on Mercury than on the Moon (rupes, ridges, troughs etc). The lunar region I chose highlights some lesser-known tectonic features.
- The Moon (particularly the nearside has expanses of bright highland terrain and dark basaltic maria. Mercury does not, though it does have splashes of bright relatively fresh craters against the darker terrain and in this respect has more in common with the lunar far side.
- Mercury has a magnetic field indicating it still has a molten core whereas the Moon has pockets of magnetism but no global magnetic field.
Well done to those who got it right. It wasn’t easy!
So after all the clicking on Moon Zoo you should know what the lunar surface looks like! But do you? Are you a true lunarphile? Like the Moon, Mercury is also rocky and heavily cratered. Can you spot the difference?
Study the two pictures below and decide which shows lunar craters and which shows craters on Mercury. You can vote on the Moon Zoo forum.
Voting ends Sunday 16 October. Answer next week!
Something is puzzling us on the Moon Zoo forum. Ever since Tony Cook set us a challenge last year to find craters with floors cleared of boulders we have been collecting these boulder repellent craters with melt pool floors. Tony Cook said of one of the examples:
“Why have the numerous boulders within this crater avoided filling the centre of this crater? Why is the central area so featureless – presumably it is younger than the main crater? Or is it that the solar altitude of 56° is preventing us from seeing craterlets on the floor of the flat patch. Is this central patch the reverse of a central peak, perhaps a central dimple and was filled with impact melt?”
So why is this a feature of just some craters and not others? Discussions on the forum have raised several questions. Some of these melt pools appear to show signs of impacts before the melt had solidified. So did the melt pool solidify at a slower rate so that some of the boulders that did roll into the centre sank from view? Although lunar temperatures suggest that melt pools would have solidified quickly. Are these cleared areas just very flat so the boulders stop rolling when they meet it? Does this feature correlate with a particular size of crater, impactor or type of rock being hit? And what role does space weathering play?
Some guidance was provided by a forum member xitehtnis whose work includes boulder clustering on Mars. He advised us that there are similar craters on Mars and offered some current thinking stating that different reasons applied depending on the age and environment of the craters:
“ For fresh craters, some amount of melt is generated in the course of an impact that takes diffusivity dependent cooling timescales for different depths of melt (which scales to crater size) (see Melosh, 1989).
For highly degraded craters it is likely the regolith has all been broken up to pieces beyond the limit of resolution due to impact gardening (very small impactors break up boulders and generally resurface the moon at small scales) ……..
For craters in the middle there could be a wide array of things going on. My preferred hypothesis comes from previous studies I worked on regarding glacial moraines. Basically, the idea is that fine particles are more easily mobilized during any erosive process. Since most erosive processes are gravity driven and craters generate slopes you would expect small particles to migrate to the lows in slopes while leaving the large particles (boulders) behind (check out Putkonen, Connolly, and Orloff 200?).”
xitehtnis also pointed us to this paper Impact Melt In Small Lunar Highlands Craters (Plescia et al, 2011) which notes that such melt deposits are very rare in small (km to sub-km) simple craters and concludes that:
“It may be that the small craters for which well defined melt pools are observed represent a special case – a vertical or near vertical impact.”
Could this also be the case for larger craters? OK we have more questions than answers right now! But that’s good. It allows us to research and learn – the forum is a great place for that. So we will continue to look for these intriguing craters, maybe map them out – and continue to debate their formation.
With thanks to the following forum members for their contributions: Tom128, JFincannon, astrostu, xitehtnis, Geoff, IreneAnt, Caro, matt.vader, jules, Half65, ElisabethB, Cruuux, Aliko, Thomas J, claymore, khearn. Read more and contribute here.
jules is a volunteer moderator for the Moon Zoo forum
This week, Moon Zoo celebrates its first year since launch back in May 2010. Initially designed as a way to count and measure craters, the simple ‘point and click’ interface was an inspired idea allowing users to mark out craters seen in high resolution images of the lunar surface. The addition of a tool to ‘flag’ interesting features, objects and locations has provided some great discussion and superb image posts to our forum.
We’ve hunted down and rediscovered the ‘Apollo’ and ‘Lunar’ landing sites in unprecedented detail, searched for lost spacecraft debris and followed miles of boulder tracks. Our hunt for the ‘weird and wonderful’ has revealed stunning volcanic vistas, beautifully defined features and intricate crater chains. Recent work on the forum, using new tools and techniques, has allowed us to study the lunar surface at oblique angles revealing yet more lunar mysteries and, equally, more questions.
For this special ‘Image of the Week’/Blog I have decided to take a retrospective look at the last year, recounting some of the amazing features and locations posted on the forum. I would like to post every image from our weekly slot but I’ll choose one of my personal favourites from each month.
I hope you enjoy them as much as I do.
From our first Image of the Week in May 2010 The volcanic caldera ‘Ina’.
Ina (named after a lunar goddess in Polynesian mythology) is an odd looking “D shaped” lunar geological feature about 2 kilometres wide which was first spotted by the Apollo Astronauts. (Jules)
Moon Zoo image
June 2010 Caro’s Tadpole.
Posted by Caro as something odd and maybe a possible crater chain, it is rich in detail and looks a little like a tadpole complete with a tail. (Thomas)
July 2010 Great Fresh Whites.
Fresh white impact craters are the most recent impacts on the Moon. Anything less than a billion years old (which means it is from the current Copernican era), is considered young in lunar terms. (Jules)
August 2010 Deep Seated Fractures.
Could they help us in the hunt for Transient Lunar Phenomena (TLP)?
September 2010 Moon Bridges
This is the King Crater Bridge from LROC image number M113168034R (Jules)
October 2010 The Aristarcus Region.
Aristarchus crater was named after the Greek astronomer Aristarchus of Samos by an Italian mapmaker called Giovanni Riccioli. The crater is relatively young, being formed approximately 450 million years ago and is one of the brightest craters on the nearside with an albedo almost double that of other similar features. (Geoff)
November 2010 Awesome Crater.
This crater was found by user mercutin and posted in the Crater Questions thread on 4th November 2010. I downloaded the LRO strip containing the crater and extracted the following image. (Geoff)
December 2010 Dark ejecta from Daguerre Crater.
A stunning picture of the dark material spreading out in a ray pattern and also cascading over the crater wall towards the crater floor. (Tom128)
January 2011 South Ray Crater
South Ray crater is about 2 million years old and the Apollo 16 astronauts returned samples from this area for analysis back on Earth. (Geoff)
An image stitched together by Moon Zoo forum member Bunny Burton Bradford
February 2011 Stratified Ejecta Blocks.
Another hunt….and this time it’s stripy! (jules)
Katie Joy from the Moon Zoo team says: We would like you to take a closer look at large boulders in Moon Zoo images. We want people to spot boulders that have layers cutting across the rock.
Forum members Half65 and Tom128 found these examples of stratified bouders in Aristarchus.
An example posted by Geoff
March 2011 Tycho.
Appropriately named after one of the most colourful characters in astronomy, Tycho Brahe, Tycho is one of the most prominent craters on the Moon with its large, bright ray system dominating the southern hemisphere. (Jules)
And here’s a close up of the rugged crater floor. (Jules)
April 2011 Potential Caves and Sink Holes in Copernicus Crater.
I came across one good candidate on the floor of Copernicus Crater (JFincannon)
Moon Zoo users have now classified 2,087,029; an area of 48,348 square miles or 206.6 Chigacos within the first year. With more images to come and fresh locations to search, I look forward to another successful year of discovery and learning as we reveal more of our closest neighbour.
HAPPY BIRTHDAY MOON ZOO!
Have fun and happy hunting.
Additional news links:
Thomas J is a volunteer moderator for the Moon Zoo forum.
Moon Zoo team member Dr Tony Cook sent me a link to Censorinus Crater which is south-east of Mare Tranquillitatis. At first glance it looks like one of the many craters we see in shadow. But this one is different. As Tony says:
“Despite the floor being almost shadow filled, plenty of interior detail is visible, including some shadows off boulders and craters. Presumably the source of illumination is from the sunlit side of the rim just out of the image field of view.”
The above image is just a taster. Better still have a look at the NAC image: M117277348RE and zoom in to see landslides and boulders clearly visible in the shadows. Stare into the depths – the more you stare the more you’ll see. You will come across these shadowy images from time to time so have a good look around them when you do but be careful to interpret what you see correctly. As Moon Zoo team member astrostu points out even though there are some features that can be clearly seen in shadowed areas, we must be careful about reading too much into image artifacts. Moon Zoo images have been compressed and will display blocky-looking features in regions of lower contrast.
Dr Tony Cook is a research lecturer at the Institute of Physics and Mathematics at Aberystwyth University. He researches into automated planetary cartography, and impact flash and change detection on the lunar surface. He is also Assistant Director of the British Astronomical Association Lunar Section.
Lunar caves are very interesting for the standard reasons (they offer possible locations for radiation-proof, thermally-benign bases for future astronauts). Another reason of interest is that there are so few of them… there are only three officially recognized ones! The Japanese Space Agency’s Kaguya lunar orbiter had found these three caves using its imager and these were later confirmed by LRO images. LRO, having better resolution than Kaguya, provides the possibility of finding other smaller caves or simply caves illuminated at different sun angles.
I am a NASA engineer who works the design of space power systems and have done some lunar polar illumination analyses (papers here, here, and here) supporting the Constellation Lunar Surface Systems program. These analyses are used to optimally size the solar arrays and energy storage systems for spacecraft including landers, bases or rovers near the poles. During the acquisition of LRO NAC images to enhance the polar illumination analysis (by supplementing the LRO laser altimeter data), it occurred to me that it would be feasible and relatively easy to use the same set of images I was downloading to search for caves (essentially a spin-off of the illumination activity). Examining images of the three known caves, I devised a cave “fingerprint” and wrote a FORTRAN program to search all the LRO NAC images for features which matched this fingerprint.
After a number of false positives, I came across one good candidate on the floor of Copernicus Crater (I call it H1).
It is in LRO NAC image M135324446LC:
Another image at a slightly different sun angle is in M135317661RC
Wondering if it could have been captured during the old Lunar Orbiter days (~60s), I found it shown in the center of the following image (vhr_5154_h2), but not clearly enough to determine if it was a cave or hole.
The size of H1 is about 86 m across at its furthest points, 40 m at its closest and seems somewhat triangular. I estimate the depth to be 20m. Clearly, this feature seems like a collapse, certainly not a crater. It almost seems like a fissure/crack, but by not being “near” any rille or lava tube or other features normally associated with a crack, it seemed very odd. It’s as though there was some void under the surface and a weak spot collapsed for some reason, leaving a hole.
Looking around this cave-like feature, I tried to find any other feature that could help to explain it. The entire Copernicus floor does have a lot of cracks and ledges, but they did not seem to be directly associated with H1. One odd feature looked somewhat like a crater but had some unique aspects which tended to imply a sink hole or some other type of circular collapse. The characteristics of this feature include sharply defined edges, somewhat flat bottom, boulders inside the circular area but not outside. The implication is of a sheet of lava or rock which had a void underneath which at some time collapsed, possibly due to dust accumulation. The thickness of the rock sheet in these features seem substantial. The void could have been either under the flat surface or possibly the void was inside/under a dome/hill-like feature which also occur on the Copernicus crater floor. While the diameters range from 150-300, the depth of the sink hole-like features are hard to estimate, possibly 5-10 m. The height of the original voids are also difficult to estimate based on a collapse of flat surface or dome/hill surface (possibly 10-30m). In any event, the features differ from typical impact craters because they have more smooth edges, bowl-like shape and characteristic rock/debris distribution.
Examples of these include:
From LRO NAC image M104648293R (I call the sink hole feature C1)
From LRO NAC image M111728277R (C2)
From LRO NAC image M104648293L (C3), which shows the sharp edge of the feature on one side but dust/regolith drifting into the other side.
From LRO NAC image M104648293L (C4), which also shows a sharp edge on one side but dust/regolith drifting into the other side. Are C4 and C5 suggestive of a contributing cause of the collapse, namely dust accumulation?
From LRO NAC image M102293451L (C5), the excerpt shows not only the sink hole but a suggestive dome/hill-like feature. Could the hill hold an un-collapsed void?
Lunar scientists have made some observations about these images. IreneAnt commented (here and here) that the floor of Copernicus is covered by impact melt and when the melt sheets cool, they crack, which is why this floor has a number of them. But, the H1 feature is odd in that it does not align with a crack. Referencing Giordano Bruno crater it was suggested that if the melt drained away in a similar fashion in the Copernicus crater, then voids may occur under the melt sheet. Regarding the sinkhole features, this lunar scientist confirms that they were not craters since the features were bigger and fresher than other craters in the area, have no ejecta and have a spherical morphology (not conical).
Other cave-like features:
These were found in the course of the work on the Copernicus crater floor:
M122339925R (11m diameter, called H2).
M119978417L (25 m diameter, called H3)
M109358669L (H3 at a different sun angle)
M124708491L (9m diameter, called H4)
M109365462R (H4 at a different sun angle)
M124701702L (H4 at a different sun angle)
M109365462L (7 meter diameter, called H5), this seems associated with a tube, crack.
Map of the Features:
The following map shows the relative location of each of the above discussed features. Most seem in a particular area, but note that the entire floor of the crater has not yet been imaged with the high resolution camera.
In my free time, I am working to document and publish these results in a NASA report. It is my hope that these results can assist in finding caves in other locations on the Moon.
JFincannon is also a member of the Moon Zoo forum