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.
I searched the forum for something new to post in this week’s slot and I found an image posted by Tom128, yesterday. It’s an interesting feature in Franklin Crater and I believe Tom’s post is the first for this.
The direction of sunlight and the angle of the terrain make these bright areas really stand out but why are they so bright? Is it just the angle of light and topography? Or maybe there is something in the surface material, here.
Tom128 included the a link to the strip. This region can be found at bottom of the strip. You can also zoom further in from here: M111279662LE
The original post is in TLP project –Notched cavities in lava.
This week I’m concentrating on the Aristarchus 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. It has a diameter of between 40 and 45km and a depth of 3.7km.
The following image of the Moon was taken by Jules and shows Aristarchus as the bright spot in the top left quadrant. It can be seen by the naked eye.
The Aristarchus area of the Moon is one of the most interesting and diverse regions on the nearside. It consists of a rectangular shaped plateau about 200km across which is located in the middle of the vast Oceanus Procellarum mare. This plateau was probably uplifted and tilted when the Imbrium basin was formed and has experienced much volcanic activity. The largest sinuous rille known, Vallis Schroteri, is found here and is about 160km long and up to 11km wide. The second article at the end of this post has a very interesting description of the head of the Vallis Schroteri rille and some great images.
The Aristarchus region has had many transient lunar phenomena (TLP) reported. When the Apollo 15 lander passed over this region in 1971 it recorded a significant rise in alpha particles which was believed to be caused by the decay of Radon-222. This radioactive gas has a half-life of only 3.8 days and is thought to be released through tidal stresses.
The following image shows the Aristarchus region. Aristarchus crater is on the left with Herodotus crater on the right and the Vallis Schroteri rille starting below it.
Nasa image from the Apollo 15 Mapping Camera
Some images of the Aristarchus area posted by users of the Moon Zoo forum:
Part of the collapsed walls of Aristarchus. Geoff
Latitude: 24.199° / Longitude: 312.434°
Impact melt in Aristarchus crater. Tom128
# ID: AMZ10036sv
# Latitude: 24.3744° / # Longitude: 312.405°
Interesting terrain in Aristarchus area. DJ_59
Latitude: 23.9853° / Longitude: 312.908°
More interesting terrain. Thornius
# ID: AMZ2000985
# Latitude: 23.5672° / # Longitude: 312.451°
An article from LROC about the geology of the central peak of Aristarchus crater and how the different rock types exposed by the impact help geologists to see what the interior of the Moon is made from.
An article from the Space Fellowship site discussing the Cobra Head feature which is thought to be the source vent of a tremendous outflowing of lava that formed the Vallis Schroteri rille.
One thing that I have learned here at Moon Zoo as a full member-newbie is that when considering the lunar landscape what is dark may not be black and what is light may not be white. A case in point is this photograph that stumped me shortly upon arrival at Moon Zoo.
Luckily, Forum moderator Thomas J introduced me to a term called albedo. He said:
“There are a number of reasons for this change in shade. The reflectivity of the surface material is known as its albedo; material that is highly reflective will have a higher albedo than that which is not as reflective. In some situations certain areas may display high albedo material due to geological activity such as impact effects, volcanic effects and even Moon quakes. It is, therefore, not uncommon to see two contrasting shades in adjacent regions. Also, the Moon’s surface is not flat, the topography rises and falls with slopes, hills and mountains. When the Sun is low in the sky a slight slope downward can leave an area in shade. So, in this image it may be that the material on the right has a higher albedo, or it may be a downward slope on the ground level to the left with a rise to that on the right.”
Why do the tracks of the astronauts on the lunar surface appear darker than the surrounding area? One answer from spacefellowship.com is:
” This effect is most likely due to compaction of a very loose surface powder by simply walking around. The more walking in a given area, the more compaction that takes place, and thus the lower the albedo.”
We know certain areas of the lunar surface have coloration due to crater impacts and lava flows such as the famous orange soil of Apollo 17 near Shorty Crater but generally the lunar landscape was described by the Apollo astronauts as concrete, mouse grey and/or light brown in color.
This brings me to the Apollo 12 lunar sample 12047,6 that is now on loan from NASA to the Seattle Museum of Flight.
Apollo 12 astronauts Pete Conrad and Alan Bean collected this specimen while at the mare region called Ocean of Storms. It is an Ilmenite Basalt sample. From the black and white photograph you can tell that it is a concrete like color not unlike many of the photographs we view here at Moon Zoo. What is interesting is that there is more to this specimen than what you see here and read about in the paper linked to above and that is the albedo effect and color change.
I happen to be lucky and live about 15 miles from the Seattle Museum of Flight. However, it was not until I viewed an online photograph of NASA 12047,6 taken by an amateur photographer visiting the museum that I found out that the sample was on display there. On my first visit I was perplexed as the sample did not look quite like the beautiful one in the photograph but more like the concrete colored black and white photograph, though not quite as drab looking. For a month or so this mystery nagged on me and I went so far as to question the on site guides about the authenticity of the display item. Maybe it was another sample or a copy. However, I was told that it is a genuine lunar sample.
Searching the internet I found reference to color change on the lunar surface:
“The orbiting Apollo astronauts noticed a peculiar phenomenon when they observed the lunar surface at a small angle related to the sun’s light. At such small angle, the lunar surface appeared warm brown colored.”
Yes, the light bulb went on in my head and I returned to the museum several months later. When moving as close to the display case as possible and viewing the lunar rock at a sharp angle, the brown color showed up. So, here is a photograph of NASA 12047,6 taken at the Seattle Museum of Flight by amateur photographer Svacher. Just as the astronauts did, we can see the brown color of the lunar surface when the sun or in this case the viewer is correctly positioned.
Here’s some more related reading:
And thanks to Moon Zoo Team member Katie Joy for providing the following additional information and links:
Lunar Sample Atlas
Katie says: “Thin or polished samples of lunar rock can be quite pretty. Some have hints of orange (glass), others bright green (the mineral olivine), some pink (the mineral spinel.) When you view them under the microscope using polarized light rather than direct light then all the minerals appear as a really bright range of colours and look like a stain glass window.”
A Final Thought:
Being one of many amateur scientists here at MZ, the notion of albedo and color change as it applies to larger natural occurring and unaltered geology samples comes to mind such as the Apollo 12 lunar sample above. Here the surface of the sample is in its natural state showing the color change in the visible light spectrum similar to what the Apollo astronauts would have seen in similar lighting conditions.
Analyzing existing samples at the Johnson Space Center in their natural-unaltered state (if not already performed) while replicating the effect of a lunar sun at all possible angles may provide valuable information about the lunar landscape – a more holistic perspective. It may also give clues to color change of lunar formations helping to explain some anomalies associated with transient lunar phenomena.
Mapping color change of the lunar landscape at specific areas may be a helpful tool to acclimate astronauts as they once again walk on the Moon.
Tom128 is a Moon Zoo participant and a regular contributor to the Forum.