At Moon Zoo, they have asked for your help in identifying linear features on the Moon, some of which are likely to be faults. So, what are faults? Faults are fractures in a planet or moon’s crust that accommodate some movement along them. If the movement along a fault is great enough, a quake can be felt.
On Earth, the majority of faults occurs at plate boundaries, like the San Andreas fault which separates the North American and Pacific plates (Figure 1) or along the boundary between the Indian and Eurasian plates which forms the Himalaya Mountains.
Figure 1. San Andreas fault in California. A) Aerial view of the Carizzo Plain. Note the offset drainages. B) Annotated image showing the fault trace (black line) and the arrows denote the direction each side of this strike-slip fault moved. Image A: IPGP, Paris.
However, a planet or moon does not need to have plate tectonics (as on the Earth) in order to have faults. Faults can form anywhere where there is enough stress (the amount of force distributed over an area) in the crust to make it break – or fault.
There are several ways in which faults form. On the Moon, the source of stress is most commonly associated with impact basins, so most of the faults are found in and around the large impact basins on the lunar nearside.
There are two types of faults found on the Moon. Normal faults occur where there is tension (stretching) of the crust. When this occurs, the crust in that area gets thinner and longer, which means that one side of the fault must move down relative to the other (Figure. 2). This happens when the weight of the mare in the basins pulls the crust apart as the middle of the basin subsides.
Figure 2. Cartoon showing cross-sectional and map views of a pair of inward dipping normal faults, resulting in the formation of a graben. The red arrows show that the crust is being pulled apart and white arrows show the movement directions along the faults. Image: Sue Selkirk/ASU.
Normal Faults: on the Moon, there are several types of normal faults: straight rilles normal faults and thrust faults.
1. Straight rilles are long, narrow troughs and they exhibit two fault-related surface morphologies: linear (Figure 3) and arcuate. These are formed by faults and are found in the highlands near mare basins as well as near their margins. They have steep sides, which are interpreted to be the normal faults, and flat floors. These structures with two inward sloping walls are called graben (meaning trench in German) (Figure 3).
Figure 3. Linear rilles or graben of Rima Ariadaeus is about 300 km in length and is located between Mare Tranquillitatis and Mare Vaporum. Image: WAC M116222025MC NASA/GSFC/Arizona State University.
2. Isolated normal faults also exist, but are rare compared to rilles (graben). Like some normal faults on Earth, these tend to be very linear as shown by the Rupes Recta (“Straight Wall or Cliff”) in Mare Nubium (Figure 4).
Figure 4. The Rupes Recta normal fault (shown by black arrows) is ~110 km long and is located in the southeastern part of Mare Nubium on the nearside of the Moon. The fault scarp is a few km high and is in shadow. Image: JAXA/NHK.
3. Thrust Faults: When stress acts in an opposite sense, compression of the crust occurs and thrust faults are formed. In this case, the crust gets thicker and one side of the fault moves upward over the other (Figure 5).
Figure 5. Cartoon showing a thrust fault. U: up, D: down. Large black arrows show compression direction and small half arrows show movement directions along the faults. The surface trace of the fault is what geologists would map. Image: American River College.
On the Moon, this happens most often in impact basin interiors where the weight of the mare causes the basin to subside, or bend downwards, causing compression in the mare. Thrust faults on the Moon have two morphologies: wrinkle ridges and lobate scarps. Wrinkle ridges (Figure 6) are found in the mare in the basins and are very complicated structures. They consist of a broad arch (the ‘ridge’ in wrinkle ridges) with narrow, often sinuous ridges superimposed (the ‘wrinkle’). Lobate scarps, which are much simpler in their morphology (Figure 7), are almost exclusively found in the lunar farside highlands far from the influence of basin subsidence. These structures are instead thought to have formed from the slow cooling of the lunar interior that led to a small amount of global contraction.
Figure 6. Wrinkle ridges in Mare Serenitatis. Note also that normal faults are present at the basin margin in the lower corners. Both wrinkle ridges and normal faults are primarily concentric to the basin. Image width is ~280 km. Image: mosaic of Apollo Metric camera frames AS17-450 and AS17-454. NASA.
Figure 7. Lee-Lincoln scarp in the Taurus-Littrow valley (Apollo 17 landing site). Image is 1.6 km across. Image: NAC frame M104318871LC. NASA/GSFC/Arizona State University
Why are faults important to lunar and planetary scientists? On the Moon, since most faults form in response to stresses from the lunar basins, they can tell us about the geologic and tectonic evolution of these basins, particularly the mare-filled ones on the lunar nearside. Wrinkle ridges and rilles can be used to determine the structure of the basin and in some cases how thick the mare are. The fact that lobate scarps are found primarily in the lunar highlands and wrinkle ridges are found only in the lunar mare suggests that these materials behave differently under stress, which is important when trying to puzzle out the geologic history.
The tectonic evolution of a planet or moon can also give us important information about what the interior is like since directly accessing the deep interior is nearly impossible. For example, the lobate scarps (along with the presence of mare) tell us that the Moon was initially hot and that it cooled some finite amount over its lifetime. This has been determined from the offsets along the faults to be about 70 m.
This post was written for Moon Zoo by by Amanda Nahm at the Lunar and Planetary Institute.
One of the great things about the Moon Zoo forum is the way you can learn new things from questions posed by users.
At the end of May 2010, Darrin Cardani started a thread called What causes erosion on the Moon?.
This is an interesting question! There is no weather on the Moon (as we Earthlings define weather) as there is no atmosphere and no liquid water.
When the Moon was young, erosion was mainly due to impacts (from comets, asteroids and meteorites) and volcanism. Today the main causes of erosion are micro-meteorites, the solar wind, moonquakes and degradation of rocks by the temperature change as the surface alternately heats up and cools down.
Recently, a new user to the Moon Zoo forum, astrodel, posted in the “What causes erosion on the Moon?” thread with a reference to an article in Nature about superficial weathering on the Moon. I couldn’t access the original article as it requires payment but dug around a bit and found a reference to “Lunar Swirls”!
The term Lunar Swirls describes unusual sinuously-shaped features on the lunar surface. They have been described as looking like the swirls on the top of a mug of coffee when cream is poured in and slightly stirred! The following image shows an example of a lunar swirl in Oceanus Procellarum and is the largest and longest swirl on the near side.
All the lunar swirls found so far appear to be associated with magnetic anomalies on the lunar surface but their formation is still a bit of a mystery. There are three different models for swirl formation according to “The Lunar Swirls” document (see References at the end of this posting).
- The solar wind deflection model.
- The cometary impact model.
- The meteoroid swarm model.
A short quote from this document may help explain what swirls actually are:
At the resolution of current data, the swirls appear to overprint the topography on which they lie, indicating that they are quite thin or a surface manifestation of an underlying phenomenon that is manipulating normal surface processes. Swirls on the maria are characterized by strong albedo contrasts and complex, sinuous morphology, whereas those on highland terrain may be less prominent and exhibit simpler shapes such as single loops or diffuse bright spots. – [The Lunar Swirls; A White Paper to the NASA Decadal Survey]
Two of the swirls on the far side of the Moon are directly opposite the centres of two large near side impact basins, Mare Imbrium and Mare Orientale, so there appears to be some connection with a large impact causing a swirl to appear on the opposite side of the Moon.
Swirls show up because they “weather” a lot slower than surrounding terrain. If the original impacts that formed the near side impact basins also somehow caused the magnetic domains on the antipodes to form with swirls above them then these swirls are very old. Mare Imbrium formed about ~3.8 billion years ago so the swirl on the opposite side (“butterfly” swirl) must have been formed then and is still protecting the surface from weathering. This is one of the many mysteries of lunar swirls.
In the early 1970s NASA put two small satellites in orbit around the Moon to measure Earth’s magnetic tail (the solar wind blowing against Earth’s magnetic field creates a “tail” that stretches more than a million miles away from Earth) and these satellites also measured the magnetic field of the Moon. To the scientists’ surprise they found that there were strange magnetic domains all over the Moon in no particular order. They also found that the strongest magnetic fields were above lunar swirls.
These magnetic domains may help to prevent the solar wind from weathering the surface so the albedo remains high.
If you happen to spot a lunar swirl please post it here: TLP Project – Lunar Swirls
“Butterfly swirl” in Mare Ingenii (directly opposite Mare Imbrium).
[LROC WAC M103439292MC]
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.
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. Some may be very young indeed. There are very few large craters with the bright ray systems associated with fresh craters. Tycho is thought to be the youngest large crater unless a group of 12th century astronomers were right and this accolade should go to the far side crater Giordano Bruno.
They are important because their ejecta blankets are as fresh as they were on the day of the impact and have not been disturbed by micrometeorites. Many of these craters have extensive ray systems and in some cases ejecta was flung out for hundreds of kilometres (in Tycho’s case 1500 km stretching to the Apollo 17 landing site in the Taurus-Littrow region.) Landing sites for robotic or manned missions can, therefore, be chosen to take advantage of this to maximise the different types of rock available to analyse. You don’t have to go to Tycho to see what Tycho is made of. Analysis of the Tycho ray samples brought back by the Apollo 17 crew show Tycho to be around 100 million years old.
The rays of a fresh crater can be spectacular to view through binoculars or a telescope when the sun is overhead with respect to the crater so full Moon is the best time to observe them. The rays look white not because the rocks excavated are bright white in colour but because their newly exposed and broken surfaces are clean and shiny and have a relatively high albedo in comparison to the mature, darker mare material they lie on top of which has been battered and dulled by micrometeorite impacts.
So why is Moon Zoo interested in them? There are several reasons.
- By counting the number of fresh impact craters the team can calculate the current impact rate of the Earth-Moon system which is of interest for assessing the risk of asteroid and meteoroid impacts.
- Also small fresh, impact craters of of just a few kilometres in diameter are the most likely locations from which lunar meteorites found on Earth have been ejected and pinpointing the source of these meteorites is the subject of much research.
- And because fresh craters are undisturbed their crater walls, interior features and secondary craters can be studied in detail.
Forum member Tom128 developed an interest in freshly formed craters and started a forum thread to collect “Great Fresh Whites.” Here are some of the early finds:
And there is more information in the Fresh White Crater Reference Resource here.
Jules is the volunteer Moderator of the Moon Zoo Forum
For centuries Earth-based astronomers have reported seeing transient changes on the Moon’s surface, known as Transient Lunar Phenomena, or TLP. These have taken the form of short term brightness changes, coloured and non-coloured glows, obscuration of detail, shadow anomalies and flashes of light. The duration of TLP can be from a fraction of a second up to several tens of minutes; then everything returns to normal as far as we can tell from Earth. Unfortunately many of these so called TLP are from inexperienced observers, or made under poor observing conditions, however some TLPs are more intriguing as they are confirmed by more than one observer.
Although the Moon is widely believed by planetary scientists to be effectively geologically dead, there are four currently accepted theories that could explain some of these mysterious TLP reports: (1) Flashes of light seen on the night side are simply due to energy released at optical wavelengths from meteorite impacts – these are being studied by project ALaMO at NASA’s Marshall Space Flight Center and also by amateur astronomers at the Association of Lunar and Planetary Observers (ALPO). (2) Eruptive out-gassing from residual radiogenic gases such as Radon and Argon that accumulate in deep seated cracks and are released during Moon Quakes – we would effectively see the dust kicked up from this out-gassing. A robotic telescope at Cerro Tololo, Chile, is being used to look for white light changes on the Moon every few tens of seconds, and amateur astronomers at ALPO and the British Astronomical Association (BAA) are searching for coloured events, and TLP in Earthshine or more shaded areas not easily accessible by the Cerro Tololo scope. (3) Electrostatic levitation of dust particles forming dust clouds in electric fields that build up around sunrise in the form of Moon dust fountains. (4) Internal reflectance off volcanic glass beads – analogous to rainbows. However the only attempt to prove a TLP was caused in this way, in Torricelli B crater, was unsuccessful at reproducing this effect.
Figure 1. (Left) part of an LROC image (M116282876RC) of the Ina formation with an enlarged inset (right) showing craters on the chaotic terrain
Here at Abewrystwyth University we have been analysing some of the statistics of past TLP reports. A preliminary report was given at the Lunar and Planetary Science Conference in Houston in 2009 and we will provide an update in September 2010 at the European Planetary Science Congress in Rome. However we are also very interested to hear from Moon Zoo users, via the on-line forum (e.g. Picture of the Week) of any interesting surface features that they think might have been freshly disturbed or perhaps a vent from which out-gassing has come from. You may find such features as you go through “Boulder Wars” or the “Crater Survey”. However for those really keen to find additional interesting objects, then they can dip into the Apollo Metric and Panoramic Camera or higher resolution LROC image archives, though the latter has a bit of a learning curve. Things to look out for include small craters which are completely shadow filled, whereas their neighbours are not – these could be ceiling vents into underground lava tubes. Also unusual disturbed surfaces that do not look like anything elsewhere in the vicinity such as Figures 1-4. We do not propose that any of these are examples of where out-gassing may have occurred, but they are the kinds of unique features that we would like to know about, just in case.
Figure 2 (Left) M104476560LE LROC image of a small part of the floor of Hyginus Crater containing some geologically young sunken areas. (Right) M111972680LE LROC image of bright ray crater (east of Reiner Gamma) with a remarkably featureless central floor patch.
Figure 3(Left) Unusual dark shaded depressions, or dark textured material, to the north west of Vallis Alpes from LROC image M122218486RE. (Right) deep seated fractures on the floor of Tycho from LROC image M114031031LE.
So as Jules says in an earlier Moon Zoo blog, please get out there, looking at the Moon close up and report your findings to the Forum. Just maybe you will be the first to identify a true TLP site, and if not then I am sure that your findings will interest the Moon Zoo geologists anyway!
People take the Moon for granted. It’s familiar. It’s always there. Since the 1950s small American and Russian spacecraft have been sent to orbit it, photograph it and crash into it. Some never made it and blew up on launch, others completely missed it and are now orbiting the Sun but some successfully orbited it or landed on it and took what were back in the day considered to be amazing images.
Landing a spacecraft on the Moon represented a very significant achievement. It showed that it was possible to land things on the Moon, that the surface would support the weight of spacecraft and, therefore, astronauts who wouldn’t disappear into lunar quicksand. Apart from these fact finding missions people had looked through telescopes at the Moon, photographed it and sketched it for years before Neil Armstrong took one small step and actually stood on it. This and the following 5 manned missions provided a wealth of data and information which is still being studied today. So several scouting missions, 6 Apollo landing missions and nearly 400kg of lunar rock later what more could there possibly be left to learn? Plenty!
Just looking up at the Moon we can see the familiar dark and light patches so it’s easy for everyone to see that the Moon has two different kinds of terrain. Look through binoculars and we can make out some craters, bright crater rays and bumpy bits and the Moon starts looking a little more complicated. Through even a small telescope the Moon is transformed into a land of mountains, hills, deep shadowy craters some with mountains in the centre, craters within craters, dark areas and incredibly bright areas. Anyone who has done this might then wonder what the mountains and craters look like up close. Now we can find out.
Moon Zoo gives us a chance to get up close and personal with the Moon using bite sized images from the Lunar Reconnaissance Orbiter Camera. The resolution of these images is staggering. Not only can we see craters as small as 1 metre in diameter we can also see individual boulders and rocks. The media has picked up on the fact that it is now possible to identify bits of spacecraft and there are many pictures in magazines, newspapers and on the internet showing the crash sites of various American and Russian spacecraft. Most of the debris has already been found and identified but it’s fun to spot it in the Moon Zoo images too.
What is quite unexpected and sometimes takes your breath away is the sheer variety of the lunar landscape. This is where the Moon Zoo forum comes into its own. Some of the images posted on the forum are just stunning. There is everything from mountain ranges and rugged boulder strewn regions to smooth plains and picturesque valleys. We have found evidence of boulders sliding and bouncing down slopes, volcanic activity and, yes, we have found spacecraft. Every click is contributing to science. We are providing data for lunar scientists to find out more about the Moon, its geology, its past and to help pinpoint areas for future exploration.
Here are just some of our recent finds:
|Ina – an unusual volcanic feature||A lunar tadpole||Boulders close up|
|Bouncing, sliding boulder tracks||Apollo 17||Lunar Alpine Valley|
So while you are clicking on Moon Zoo please consider contributing to the forum. That’s where you can discuss your finds, post your favourite images and learn more about the Moon. We have boards where you can post images and discuss them and we choose one each week to highlight in our Image of the Week feature. We even have a virtual cafe where you can chat and chill. Don’t let that image with a striking odd feature or the image you think one of the science team should really take a look at go unnoticed — the forum is the place to post it. That’s where the Moon Zoo science team go to look. That’s where you can learn about and discuss the science and that’s where discoveries of the strange and unusual are likely to be made. It’s a mixture of amateur clickers and lunar scientists all with one thing in common — a desire to learn more about the Moon. It’s informal, friendly, and there is no such thing as a silly question. Make one post or become a regular, it’s entirely up to you, but please come and join us — you’ll get a warm welcome!
Jules is the volunteer Moderator of the Moon Zoo Forum
Planetary scientist Ian Crawford presents the case for our return to the Moon.
After a long hiatus following the Apollo missions forty years ago, the scientific exploration of the Moon is undergoing something of a renaissance. In the last few years a flotilla of robotic spacecraft has been sent to orbit the Moon by the space agencies of China, Europe, India, Japan, and the United States. This international concentration of effort is unprecedented in the history of space exploration. In part it reflects a renewed scientific interest in the Moon in its own right, and in part the aspirations of new space-faring nations to demonstrate their growing technical capabilities.
The primary scientific importance of the Moon arises from the fact that it has an extremely ancient surface, mostly older than 3 billion (i.e. 3 thousand million) years, with some areas extending almost all the way back to the origin of the Moon 4.5 billion years ago. It therefore preserves a record of the early geological evolution of a terrestrial planet, which more geologically active bodies, such as Earth, Venus and Mars, have long lost. The ancient lunar surface also preserves a record of everything that has fallen on it throughout the history of the Solar System. This includes fragments of meteorites and comets, as well samples of the ancient solar wind and, possibly, samples of the Earth’s oldest crust, blasted into space by giant meteorite impacts on our planet and collected by the Moon. Taken together, this is potentially a very rich scientific record of Solar System history which, with the possible exception of the much less accessible surface of Mercury, is unlikely to be preserved anywhere else. And it lies only three days away with current spacecraft technology.
The idea that samples of the Earth’s earliest crust might be preserved on the Moon is particularly intriguing. Although we have strong grounds for believing that the Earth, like the rest of the Solar System, is 4.5 billion years old, the oldest actual Earth rocks found to-date are only 3.5 to 3.8 billion years old. All older rocks have been destroyed or buried by Earth’s active geology and climate. The oldest Earth rocks already show tantalising evidence for life having been present on our planet by that early time, but as we don’t have access to any older rocks we cannot be sure exactly how or when life first appeared on our planet. However, as noted above, ancient Earth rocks, blasted into space by meteorite impacts, may be preserved on the Moon. Perversely, therefore, our natural satellite may preserve fragments of Earth’s earliest crust, along with a record of the origin and evolution of life on our planet, which the Earth itself has destroyed. Finding such samples could become a holy grail of future lunar exploration.
The airless surface of the Moon has other scientific advantages as well. It is a superb site for some types of astronomical observation. The lunar far-side, in particular, is probably the best site for radio astronomy anywhere in the inner Solar System, as it is permanently shielded from artificial radio transmissions from Earth, and also shielded from solar radio emissions during the 14-day lunar night. Optical astronomy may also benefit from the establishment of lunar observatories. As the Moon lacks any obscuring atmosphere, the lunar surface is a much better site for astronomical telescopes than the surface of the Earth.
To fully exploit the scientific potential of the Moon, to access the geological record of early Solar System history it undoubtedly contains, and to establish astronomical observatories on its surface, will require us once again to land astronauts on the lunar surface – and this time to stay. This must be the next step in lunar exploration, hopefully in the context of a fully international exploration programme, and science will be a major beneficiary. The Apollo missions demonstrated that human beings are highly efficient as explorers of planetary surfaces, and it is difficult to see how we will ever learn all that the Moon has to teach us about the history of the Solar System, and of our own planet, until people are once again actively exploring its ancient battered surface. Looking to the longer term, the human exploration of the Moon will also help develop essential experience that will be required for the human exploration of other locations in the Solar System, not least the planet Mars which also has much to tell us about the evolution of the Solar System and our place within it.
By helping to identify scientifically interesting places on the Moon, which may be explored when people do eventually return its surface, Moon Zoo participants can make a significant contribution to these exciting future activities.
Ian Crawford is a planetary scientist in the Department of Earth and Planetary Sciences, Birkbeck College London, and a member of the Moon Zoo Science Team.
This post is a little off track from Moon Zoo images of the lunar surface, but I want to share some information about my particular favourite Moon related subject — lunar meteorites.
What are lunar meteorites?
Thousands of meteorites have been found all over the Earth — the vast majority are thought to have originated from the asteroid belt — but very rarely some are identified that come from bodies like Mars, the Moon, and large asteroids.
Lunar meteorites are chunks of the Moon that were blasted off its surface by meteorite impacts, that then flew through space from the Moon and were captured by Earth’s gravity. The rocks then fell through the Earth’s atmosphere — often losing some mass on the way — and then land here on Earth.
How many have been collected so far?
So far (as of 2010) Dr. Randy Korotev, a lunar meteorite researcher from Washington University in St. Louis, states that 136 individual lunar meteorite stones have been collected. As some fell through the atmosphere at the same time, these samples actually represent only 66 meteorites! It is likely that many many more lunar meteorites than this have fallen onto the Earth through time, but because of high weathering rates (wind, rain, organic disaggregation, etc.) they have most likely been weathered away and could no longer be identified as having a lunar origin. We are lucky to have the ones that we have!
How do we know they have come from the Moon (and are not just chunks of grey concrete!)?
Proof of lunar origin can be taken from several lines of evidence that often requires analysis in a laboratory.
- The presence of a glassy crust suggests that the sample is of meteoritic origin and has passed through the Earth’s atmosphere causing frictional melting of the surface.
- The rock does not have chondrules and therefore can be classified as an anchondrite.
- The rock is poor in metal and therefore is classified as stony.
- Typical bulk rock elemental ratios and mineral chemistries that are similar to those of the Apollo and Luna Moon samples.
- An oxygen isotope ratio corresponding that of the Earth-Moon trend.
- Typical mafic mineral Mn/Fe ratios are indicative of the volatile-poor nature of lunar samples that trend on a ‘lunar line’ distinct from terrestrial rocks and samples from Mars and asteroids.
When did they land on Earth?
All lunar meteorites are thought to have been launched from the Moon in the last 20 million years. As there are believed to have been no large craters generated on the Moon during this period, it is assumed that all lunar meteorites are launched from craters only a few kilometres in diameter (all craters in the last 1 million years or so are thought to be <3.6 km in diameter). This implies that lunar meteorites have been ejected from relatively shallow depths, and so represent the upper layer of lunar crustal material.
What do they tell us about the Moon?
Manned (Apollo) and unmanned (Luna) missions to the Moon have returned about 382 kg of lunar rocks and soils. These were all collected from rather atypical regions on the lunar near-side, within and around the central lunar nearside, or from equatorial latitudes on the eastern limb. Therefore interpretations of the nature of the lunar crust and mantle have been made from a dataset from geographically restricted areas of the Moon. Lunar meteorites, in contrast, are derived from random sample sites on the surface, and thus provide a wealth of new information about the nature of the Moon, even though their precise provenance is as yet unknown.
Some cool lunar meteorite findings:
- Lunar meteorite Kalahari 009 provides a sample of the oldest basalt (volcanic lava) found on the Moon — it is 4.35 billion years old.
- Lunar meteorite NWA 032 is the youngest basalt (volcanic lava) found on the Moon — it is 2.9 billion years old.
- Many lunar meteorites that are rich in a mineral called plagioclase are believed to have originated from the farside of the Moon. These important stones provide information about how the lunar crust formed.
Some good lunar meteorite resources you might like to check out:
We’ve added a couple of new features to Moon Zoo this week – which should help you learn more about the project and about the Moon itself. As well as testing the capabilities of the Zooniverse HQ coffee machine we have been trying to create new, useful tools that allow everyone to really explore the Moon.
Moon Zoo Live, and the new Examine tool, allow everyone to begin to understand what the LRO images show, and where they are on the Moon’s surface. On the Moon Zoo forum, users have been asking to know a bit more about the parts of the Moon they have classified and explored. We’re hoping that these new additions will help.
Every LRO image in our database now has its own ‘examine’ page that shows you more information about it. At present, you can access these from either the ‘My Moon Zoo‘ page or from the ‘More Information’ links on Moon Zoo live. There are some nice examples, here, here and here.
This powerful new tool lets you see each tile from our LRO dataset in context. You can zoom in and out, explore the surrounding area and see the entire LRO strip from which the tile originated. You can also see the same region of the Moon in other online Moon tools.
Moon Zoo Live shows a near real-time stream of Moon Zoo classifications on a pair of ever-updating maps. You can see not only where on the Moon everyone is busy clicking, but also where on the Earth they are clicking from! Moon Zoo Live connects these two worlds through the magic of the Zooniverse!
We hope you enjoy these new additions to Moon Zoo.
Moon Zoo launch has arrived! After over a year of planning, discussing and debating, Moon Zoo is finally being launched today. It is an exciting time for all the people who have been working hard on the project: from the geologists and planetary scientists who helped to conceive the scientific rationale behind the tasks, to the computer whizzes and Galaxy Zoo gurus who have made the whole thing possible.
We would especially like to thank all those at NASA, Goddard Space Flight Center and Arizona State University who planned, designed, built, calibrated and operated the Lunar Reconnaissance Orbiter Camera (LROC) and LRO mission. We are using LROC images that have been archived through the Planetary Data System. We are incredibly grateful that NASA and the LROC team is willing to share these images with the rest of the world so that we can all enjoy looking at the surface of our nearest neighbour. If you would like to know more about the LROC camera I suggest taking at look at their great website and more information about the LRO mission itself can be seen at here.
So, down to it. Why should you spend your time working hard on Moon Zoo tasks? Well there are several pages on this site that will help to explain the science behind Moon Zoo in more detail, but in short we hope that Moon Zoo data will provide new insights into the geological history of the Moon from volcanic eruptions to asteroid impact events. Studying LROC images of the lunar surface provides a close up view that has never been seen before and we want to use this powerful new dataset to investigate the nature of the lunar surface. We hope to collect a database of the size and dimensions of small (less than 2 km) lunar craters that will be helpful not only to understanding impact cratering processes on the Moon, but also that can help studying the history of impact bombardment throughout the inner Solar System from Mars, to Mercury and even here on Earth.
We want you to spot lunar geological features that we think are really interesting – from billion-year-old volcanic vent sites to curving lava channels, to brand new impact craters that might have formed in the last forty years. You can see examples of these types of things on the Moon Zoo tutorial page. We also want you to help find out which parts of the Moon are covered with boulders so that we can develop hazard maps that could be used by future spacecraft and human exploration missions to plan the best and worst sites to land on the lunar surface! There are a lot of things to do in Moon Zoo and we have more planned for the future. Most of all – just have fun looking at the amazing diversity of the lunar surface – I certainly have not got bored of looking through these images and hope that you are as equally excited to explore our Moon.
Hope that you enjoy helping out with the investigation and please do leave comments here on the blog, and on the Moon Zoo Forum if you have any feedback, suggestions or questions.