Tag Archive | Craters

Crater Chains

Crater chains are just one type of feature we are looking out for in Moon Zoo but they are proving to be rather elusive. A number of processes can leave a chain of craters (a Catena):

  • Boulders from a larger impact are flung out and form smaller secondary craters where they land. The larger the impact the further away the ejected boulders are thrown. In really large impacts ejecta can be hurled hundreds of kilometres away. Some boulders land on their own forming isolated small craters; a group of boulders landing together can form a ridged herringbone pattern and a string of boulders landing together can form a chain of craters which fall radially to their parent crater. Individual craters in the chain are also usually elongate in shape (due to the shallow angle of impact) with irregular rims and the ejecta appears ‘splashed’. Isolated secondary craters are often difficult to identify but craters in chains are easier to spot and can, therefore, be studied as secondary craters.
  • The impact of a fragmented meteorite or comet might also have created a crater chain.
  • Some crater chains are thought to be volcanic in origin but it can be difficult to distinguish between the two types of crater chains. Volcanic crater chains are lined up along a common fault or set of faults, and each crater produces a blanket of volcanic ejecta. As you would expect, volcanic crater chains are not assocated with a parent crater.

There are many – too many – examples of three or four small craters in a line and while these may well be secondary craters from a larger impact they are not especially noteworthy. Some of the more famous crater chains are very impressive and contain over 20 smaller craters. It would be quite something if we could find an example like that.

Catena Davy in 3D

Crater chain in Mendeleev

These are some of our contenders so far:

Posted by Forum member Caro:
AMZ4003mgz


Moon Zoo team member Irene Antonenko says:
“The wispy, feathery texture associated with crater chains is formed when the ejecta deposits of the craters in the chain interfere with each other during their emplacement (kind of like point-source waves interfering in a wave tank.)”

And Caro also found our lunar tadpole:

ID: AMZ4000mmj
Latitude: 1.82082°
Longitude: 23.2839°

Discussion on the forum concluded that the impact angle was so low that the top part of the impactor sheared off and bounced to form the “tail.”

If you want to read more about Crater Chains try these links:

Apollo Over the Moon: A View From Orbit
List of Lunar Crater Chains (Catena)
Crater Chains on the Moon: Records of comets split by the Earth’s tides?

Finding a good, clean example of a long crater chain, whether volcanic or impact in nature, is this week’s challenge!


Jules is a volunteer moderator for the Moon Zoo Forum.

Dark Haloed Craters

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!

hawaiilava

Fire fountaining: Volcanic eruption in Hawaii. Droplets of molten lava are thrown up into the air, where they rapidly cool to form glass beads called Pele’s tears. This is a good analogy to how volcanic dark haloed mantling deposits were formed on the Moon. Image: USGS.

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.

Lunar glass beads: Orange and black glass beads collected from a pyroclastic deposit at the Apollo 17 landing site. These types of beads form mantles around the volcanic vent site from which they were erupted, forming dark mantling deposits. Image: NASA.

Lunar glass beads: Orange and black glass beads collected from a pyroclastic deposit at the Apollo 17 landing site. These types of beads form mantles around the volcanic vent site from which they were erupted, forming dark mantling deposits. Image: NASA.

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:

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.

Impact revealing buried lava flows: This LROC NAC image (taken from M112183669LE) is a good example of a dark haloed impact crater that has punched through a light surface deposit and has excavated darker material from an underlying lava flow. Image: LROC/NASA.

Impact revealing buried lava flows: This LROC NAC image (taken from M112183669LE) is a good example of a dark haloed impact crater that has punched through a light surface deposit and has excavated darker material from an underlying lava flow. Image: LROC/NASA.

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:

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 Craters, the brightest things on the Moon

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:

AMZ20004r5 (Tom128)

AMZ20004r5 (Tom128)

AMZ20003g7 (DJ_59)

AMZ20003g7 (DJ_59)

AMZ1000j38 (Aliko)

AMZ1000j38 (Aliko)

AMZ100dn8 (Geoff)

AMZ100dn8 (Geoff)

Read more about craters here and watch a cool animation here.

And there is more information in the Fresh White Crater Reference Resource here.


Jules is the volunteer Moderator of the Moon Zoo Forum

Welcome 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.