Wednesday, November 30, 2011

LROC: Layered basalt on the wall of Marius A

Layered basalt on the wall of Marius A crater partially covered by debris flow. The crater rim is to the right and the crater floor is to the left. LROC Narrow Angle Camera (NAC) observation M137848463R, LRO orbit 5448, August 30, 2010; field of view of the original LROC Featured Image (HERE) 460 meters, at an illumination incidence angle of 33° from an altitude of 44.37 kilometers [NASA/GSFC/Arizona State University].
Sarah Braden
LROC News System

Marius A (12.58°N, 46.05°W) is an approximately 15 kilometer crater located in Mare Insularum. The Featured Image shows basalt layering partially covered by streaks of granular material that slid down from higher up on the wall. Craters with visible basalt layers like Marius A are windows to the history of basalt deposition. 

Each thin layer seen in the wall of Marius A is probably a single flow or flow lobe, each spreading out across the lunar surface due to the low viscosity of mare basalt (basalt has a viscosity similar to that of ketchup). How much time passed between each layer is still an unanswered question. By studying many craters with visible basalt flows, however, scientists may be able to piece together a more detailed, local history for the various mare on the lunar surface. Not all craters in the mare have visible mare basalt layering, though. Additionally, over time post-impact processes like the debris in today's Featured Image and slumping of the crater walls reduce the visibility of basalt layers.

Marius A at 62 meters resolution from LROC Wide Angle Camera (WAC) observation M135493956C, orbit 5101, August 3, 2010 in a field of view roughly 42 km across; incidence angle 57.09° from 44.1 km above. The much small field of view shown in detail in the Featured Image released November 29, 2011 is located at just shy of "3 o'clock" on the east crater rim wall [NASA/GSFC/Arizona State University].
LROC WAC context image of Marius A crater. The image is 59 km across and the rectangle indicates the area of the whole NAC frame from which the Featured Image is taken. View the full size and original LROC WAC context image HERE [NASA/GSFC/Arizona State University].

There are many craters with visible basalt layers and LROC has given us our first look at these incredible details of the lunar surface. Check out the NAC frame of Marius A and then explore the rest of the lunar maria!

Related Posts:
Layering in Euler Crater
Lava Flows Exposed in Bessel Crater
New Views of Lunar Pits

Marius A in a wider oblique context view from a virtual point 254 kilometers over the bright landmark crater Kepler, showing some of the more famous landmarks also nearby. One of the wispy rays of material and reflective secondary craters, superimposed upon Marius A by the Kepler impact event crosses directly upon Marius A and beyond, a distance of 280 kilometers from crater center to crater center [NASA/LMMP/GSFC/ARC/ASU].

Tuesday, November 29, 2011

LROC: Dionysius Detour

A high albedo granular flow traveled down the wall of Dionysius crater. Why is the flow curving around the crater floor? LROC Narrow Angle Camera (NAC) M111484008R, orbit 1563, October 29, 2010; incidence angle 26.934° with a resolution of 0.51 meter per pixel from 48.11 kilometers. Image filed of view is 500 meters. View the full size LROC Featured Image HERE [NASA/GSFC/Arizona State University].
Drew Enns
LROC News System

Craters on the Moon often develop granular flows on their walls as loose material slides towards the bottom.

As this process occurs the granular flows must overcome any obstacles in their path to reach the crater floor.  Dionysius, an 18 kilometer crater on the western edge of Mare Tranquillitatis, is no exception.



The curved termination of the talus is the result of series of granular flows with an impact melt mound blocking the immediate path of the flow.

LROC Wide Angle Camera image (604 nm) of Dionysius with the subject impact melt marked with the small yellow arrow. LROC WAC observation M148871990C, orbit 6778, December 13, 2010; resolution 59.4 meters per pixel from 43.19 kilometers altitude [NASA/GSFC/Arizona State University].
Because the granular flow cannot go over the mound, it is being redirected along the mound's slope until it reaches the crater floor. The result is a spectacular arc that acts as a geologic contact between the granular flow on one side and impact melt on the other!

Are any other geologic features redirecting the granular flow in the full NAC frame?

Related Posts:
Lunar landslides!
Dichotomy
Impact melt in Anaxagoras crater

Thursday, November 24, 2011

LROC: Polka-dot ejecta

A small fresh impact crater, among a number of others equally juvenile (yellow arrow) has saved future explorers a lot of expensive excavation work among some far older heavy-hitters in the west farside lunar highlands, just south of the equator and north of the vast 4 billion year-old South Pole-Aitken (SPA) basin. Notional oblique view courtesy of the LMMP and LROC Wide Angle Camera 100 meter Global Mosaic [NASA/GSFC/LMMP/Arizona State University].
LROC QuickMap NAC and WAC mosaic (reproduced from 16 meter per pixel resolution level) shows a distinctive low optical maturity characteristic of youthful craters [NASA/GSFC/Arizona State University].
A blanket of fresh ejecta from a relatively new crater (9.083°S, 161.337°E) on the floor of farside landmark Keeler, dotted with smaller low albedo craters. LROC Narrow Angle Camera (NAC) observation M123513537R, LRO orbit 3335, March 18, 2010; incidence angle 15.16° on a field of view 560 meters wide, resolution 56 cm per pixel from 54.87 kilometers. See the full size original LROC Featured Image HERE [NASA/GSFC/Arizona State University].
Drew Enns
LROC News System

Impact crater ejecta is usually distributed semi-uniformly around an impact crater. Immature ejecta from a fresh crater has a higher albedo than the mature material on the surrounding surface, and so fresh craters easily stand out against the mature background.

So why do the smaller craters in today's Featured Image have a lower albedo? On the Moon this is often due to a cryptomare located underneath the bright ejecta blanket. 

Taking a step back and looking at this area in the WAC context image gives us a better idea of how to interpret this scene.

LROC Wide Angle Camera context for their Featured Image, November 23, 2011, of ejecta from a fresh impact crater located within much larger Keeler crater (8.75°S, 161.37°E). The subject crater is two pixels left of direct center of the above 50 km-wide field of view at the full 87.86 meter per pixel resolution of LROC WAC observation M134130438C (604 nm), LRO orbit 4900, July 18, 2010 [NASA/GSFC/Arizona State University].

This fresh crater is actually located in the much larger 160 km diameter Keeler crater. Keeler crater is located in the highlands and instead of having a mare flooded floor, Keeler's floor is covered in impact melt. It is possible that the small craters are exposing buried impact melt under the immature ejecta. However, it is more likely that the small craters expose the mature regolith that is only thinly covered by the bright ejecta. The end result is a polka-dot laden ejecta blanket.

How many low albedo craters are there in the full NAC frame?

Related Posts:
Dark Craters on a Bright Ejecta Blanket
Dark halo crater
Intricate young ejecta blanket in ancient Murchison Crater

Wednesday, November 23, 2011

LROC: Shades of Grey

Virtual ILIADS/LMMP perspective from an imaginary point high over the farside lunar highlands looking southeast past the equator to Mare Orientale on the horizon, clearly the most broadly influential "impact event" affecting the topography of this area of the Moon. The LROC Featured Image, November 22, 2011, focuses on one of the more prominent and more recent superpositioned impact craters (yellow arrow, below center), and what its creation returned to the surface [NASA/GSFC/ARC/Arizona State University].
Focusing in on the northwest quadrant of the relatively fresh, optically immature unnamed crater, seen HERE at the 32 meter per pixel level of resolution using the LROC QuickMap. The yellow arrow indicates the location of the huge boulder in the Featured Image. [NASA/GSFC/Arizona State University].
Two streaks of high and low reflectance blocky ejecta from the same crater. A large boulder rests in the low reflectance deposit. LROC Narrow Angle Camera (NAC) observation M168862555R,, LRO Orbit 10019, August 24, 2011; image field of view 500 meters. See the full size LROC Featured Image HERE [NASA/GSFC/Arizona State University].
Drew Enns
LROC News System

This unusual ejecta is blocky, and exhibits high and low reflectance, and is from a very fresh crater located in the lunar highlands at 3.348°N, 259.724°E

Blocky craters can happen when an impact occurs in a more coherent target material, but what about the difference between the reflectance?

The reflectance difference has two possible causes. The two ejecta streaks could be from separate craters, or the ejecta could be the result of compositional differences in the target rock.

Local mid-morning over the Lends crater group region and the unnamed crater at center, subject for the LROC Featured Image released November 22, 2011. LROC Wide Angle Camera (WAC) mosaic, field of view 140 kilometers. View the full size LROC WAC context image HERE [NASA/GSFC/Arizona State University].
An additional 76 meter per pixel LROC WAC mosaic demonstrates how the appearance, revealing composition and morphology that might otherwise remain hidden can change dramatically under different angles of incidence; here the region of interest, with the subject crater at center, is seen under early evening illumination. One aspect of young, less weathered (and thus brighter than average) crater wall interiors can be that their reflective surfaces are sufficiently bright to illuminate that crater's otherwise darkly shadowed interior. LROC WAC mosaic (604 nm) from four orbital passes averaging 54.4 kilometers altitude during LRO orbits 4804 through 4807, July 11, 2010. Field of view 40 kilometers [NASA/GSFC/Arizona State University].
Since both ejecta streams point back to the unnamed crater, the ejecta contrast is most likely the result of a compositional difference in the subsurface. Since the context views show that the higher reflectance ejecta is much more prevalent, a small lower reflectance rock layer is probably the culprit.

For perspective, scale is vital on the Moon, as NASA discovered early on, during the Ranger impact probe missions. The blocky ejecta may look like simple "reject" pebbles, like those used for gravel roads here on Earth, but that large block described by Drew Enns further above is slightly larger than a city block in length. Once again the multi-storied, apartment-building-sized block, ejected more or less intact from beneath the surface by the relatively recent nearby impact event, is shown under not just two but four kinds of lighting conditions by the LROC Narrow Angle Cameras. Over the course of more than two years the subject probably doesn't change measurably but it clearly takes more than a single good photograph to obtain our best notion of the true shape of this huge resting boulder. LROC NAC observations M114613684L, orbit 2024, December 5, 2009; M135847041L, Orbit 5153, August 7, 2010; M160607763L, Orbit 8803, May 21, 2011 and M168862555R, Orbit 10019, August 24, 2011 [NASA/GSFC/Arizona State University].
Can you find any other low reflectance boulders or ejecta in the full NAC frame?

Related Posts:
Rubble Pile on Fresh Crater Floor
Dark streaks in Diophantus crater
Two-toned Impact Crater in Balmer Basin: A Reflection of the Target?

Monday, November 21, 2011

Apollo Metric Camera maps completed

The final three Apollo "J" missions as planned were devoted to science, and each of their Service Modules were equipped with an array of equipment that remained in orbit as their surface expeditions were carried out. Mapping Metric and Panorama Cameras operated over the sunlit surface over multiple orbits as part of the Apollo 15, 16 and 17 missions. Film canisters for these cameras were retrieved in spacewalks during the long cruise home. Until recently, the orbital corridors under the orbital plain of these last missions were the most well-understood detailed portions of the lunar surface [NASA/Google Earth].
Dr. Terry Fong
Director, Intelligent Robotics Group
NASA Ames Research Center

It gives me great pleasure to announce the release of the "Apollo Zone" Digital Image Mosaic (DIM) and Digital Elevation Model (DEM). These maps cover approx. 18% of the Lunar surface at a resolution of 1024 pixels per degree (approx 30 m/pixel). The maps are the result of 3 years worth of work by the NASA Ames Intelligent Robotics Group (IRG) to align and process more than 4,000 images from the Apollo Metric Camera (AMC), which flew aboard Apollo 15, 16, and 17. The AMC images were provided by the Apollo Image Archive at Arizona State University.

To preview the "Apollo Zone" maps, download the following "KML" file for viewing in Google Earth:

http://byss.ndc.nasa.gov/stereopipeline/dataviz/apollo_metric.kml

Once you open that file in Google Earth you will have options to view these "Apollo Zone" maps overlaid on Google Earth's "Moon mode". The full maps (in GeoTIFF format with complete metadata) have also been uploaded to the Lunar Mapping and Modeling Project (LMMP) portal (http://lmmp.nasa.gov) and will soon be available for visualization and download via that site.

The "Apollo Zone" maps cover the following sites of interest: Apollo 15, Apollo 16, Alphonsus Crater, Rima Prinz, Aristarchus Plateau-2, Ina D Caldera, Sulpicius Gallus, Mare Crisium, Mare Smythii, King Crater, Tsiolkovskiy Crater, Aitken Crater, and half of Van de Graaf Crater.

The terrain model has an average vertical accuracy of 40 m/pixel and standard deviation of 37 m (compared to LOLA laser altimetry tracks). Over 46% of the covered surface has vertical errors lower than 25 m.

The "Apollo Zone" maps (image, elevation, hillside, colorshade, confidence and precision) were automatically generated using new computer vision algorithms developed by IRG:

 - robust statistical sub-pixel stereo correspondence
 - robust bundle adjustment and radiometric corrections for large-scale
   image mosaics
 - orbital camera position/orientation estimation using interest point
   extraction
 - photometric correction of exposure time, shadow removal and generation of
   seamless large-scale image mosaics.
 - photometric method for reconstructing lunar albedo
 - photoclinometric terrain reconstruction method that improves lunar
   DTM precision
 - statistical method for multiple stereo digital terrain model mosaicking
 - multi-view 3D terrain reconstruction
 - DTM / LOLA alignment and lidar / image matching

These algorithms have been released as NASA open-source (Ames Stereo Pipeline, Neo-Geography Toolkit, and NASA Vision Workbench). Map processing was performed using the NASA Pleiades supercomputer. In addition to the Apollo Metric Camera images, the fully automatic map processing pipeline has also been used with data from the Lunar Reconnaissance Orbiter Camera (LROC) and by several planetary science groups.

This work was funded by the Lunar Mapping and Modeling Project (LMMP). We gratefully acknowledge the support of our collaborators at NASA MSFC, NASA GSFC, JPL and USGS. We sincerely thank Mark Robinson and the Apollo Image Archive at ASU for restoring and bringing the AMC data to "digital life". Our special thanks go to Ray French and Mark Nall for their support and leadership of LMMP.

If you have any questions, or would like more information, please let me know.

Cheers,

Terry Fong

Friday, November 18, 2011

LROC: Shiny Mound

Northeastern edge of a high-reflectance mound within "driving distance" of the Apollo 15 landing site on the southeastern frontier of Mare Imbrium. Downslope is to the upper-right. (Field of view 1512 meters across). LROC Narrow Angle Camera (NAC) observation M106869873R, LRO orbit 890, September 6, 2009; resolution 1.26 meters per pixel, incidence angle 36.72° from an altitude of 153.64 kilometers. View the much larger, full size LROC Featured Image HERE [NASA/GSFC/Arizona State University].
Hiroyuki Sato
LROC News System

At the southeastern edge of Mare Imbrium, about 25 km west of Rima Hadley, there is a small shiny mound on a dark and flat mare basalt plain which looks like a white sand island in the middle of a black ocean. This mound is about 2.7 by 2.2 km across. 

Normally fresh slopes and fresh ejecta have high reflectance due to less space weathering but this mound is brightest at its highest elevations and not down the slopes, brighter than nearby ejecta implying the mound is composed of higher-reflectance materials than mare basalts. Then how was this shiny island was formed?

Whole view of high-reflectance mound centered at 25.482°N, 1.684°E (Field of view about 5.3 kilometers. See the original LROC context image HERE, also from LROC NAC frame M106869873R [NASA/GSFC/Arizona State University].
Most likely, the mound is a remnant of highlands sticking through the mare, a hummock of plagioclase-rich highlands materials was embayed by mare basalt volcanism, burying all except its summit. If so, mare basalt is overlapping the mound's skirt. 

Can you see the an overlap contact in today's Featured Image?

An oblique view from a simulated low altitude looking northeast over the LROC WAC 100 m monochrome Global Mosaic affixed to LOLA topography, using NASA's ILIADS program. The bright mound is near the center of the view, with the Hadley Rille Valley and the landing site of Apollo 15 in the background. Does the angle of this view seem familiar? [NASA/GSFC/Arizona State University].
Unfortunately, the contact is not clear or sharp. Over time such sharp contacts are blurred by micrometeorite bombardment. If we are lucky, in the future, a small impact may occur right at the contact once again revealing the sharp contact. Or perhaps a future explorer might take a shovel to this spot and settle the question!

Explore this shiny mound in the full NAC image!

Related posts:
Farside Highlands Volcanism!
Up from the depths
Hortensius Domes - Constellation ROI

Slopes, Streaks and Flows

A granular debris flow on the wall of Stevinus A (downhill to the bottom and to the right, in the original full-size LROC Featured Image). A 7 meter boulder impedes the progress of the flow, which bifurcates and reconnects about 10 meters further downhill. LROC Narrow Angle Camera (NAC) observation M154893929R, LRO orbit 7960, March 16, 2011. Detail from LROC Featured Image Dry debris or liquid flow? by Lillian Ostrach, June 3, 2011 [NASA/GSFC/Arizona State University].
Paul D. Spudis
The Once & Future Moon
Smithsonian Air & Space

Although the Moon’s gravity is low, only about 0.165 of the Earth, rock and soil move down slope over time.  In geology, such processes are called mass wasting and is one of the principal sources of erosion on the Moon (the other being meteorite bombardment).  Mass wasting includes both gradual, infinitesimally slow soil creep on slopes and rapid, catastrophic mass movements, called landslides.  Long trains of rock debris can form scree slopes, loose fragments lying precariously at the critical angle beyond which they move, the angle of repose.  Because impact craters make steep walls and the larger ones bring up peaks in their centers, most mass wasting on the Moon is found in and around impact craters of all sizes.

Dark and light streaks on crater walls on the Moon. (click HERE to enlarge) [NASA/GSFC/Arizona State University].
As the number of high resolution images taken from the LRO mission continues to proliferate, several interesting and under-appreciated lunar surface phenomena are becoming more apparent.  Among the fresh craters of the Moon, we find light and dark steaks on the walls of the ubiquitous craters of the Moon.  Although it is not surprising that material might move or flow down steep slopes on the Moon, the appearance of these flows can be startlingly similar to those seen on other planets, particularly Mars, where such streaks have been cited as evidence for the presence of subsurface water.

The new narrow angle LRO camera can see objects on the surface smaller than one meter (typically, 50 cm per pixel resolution).  These new views have shown us a wide diversity of new features within impact craters and have given us a new appreciation for mass wasting.  Larger crater walls are slumped, with stair step-like wall terraces, concentrically arranged around the crater between rim and floor.  In detail, these terraces show ponds of dark material that seem to collect in low areas.  Most of this material looks like it was once molten but now congealed; it is probably solidified impact melt.  Flows of melt may cascade down and over the walls of fresh craters.

However, many “flows” of both dark and light material on the Moon seem to consist of loose fragments of rock debris lying on steep slopes.  These debris flows show a variety of morphologies, including simple flow shapes, cascades, ponding, and fan-like termini.  Sometimes the dark and light flows intermingle within a single crater while others show only one type.  These debris flows can usually be traced back to outcrops of bedrock in the upper portions of the crater wall.  As the bedrock erodes (usually by meteorite erosion and disaggregation due to the intense fracturing induced by the original impact that formed the crater), it sheds small fragments that train down slope, forming flow-like landforms.

Because crater walls are uneven, undulating surfaces, the rates of down slope movement can vary widely over small distances.  This sometimes results in multiple, overlapping flows of debris.  Factors that control the albedo (reflectivity) of the debris flows are not well understood.  It could be related to composition (for example, dark, iron-rich mare basalt vs. white, anorthositic highland rocks).  Another factor might be particle size; small pebble-sized rock flows could be bright as new, fresh surfaces are constantly exposed.  Flows that contain mixed soil might be darker than normal, as this soil could cover the fragments and reduce its average reflectivity.  But while all these factors may be of significance to one degree or another, the brightness of a streak is not particularly indicative of origin.

Dark streaks on crater walls, Mars. (click HERE to enlarge)

On Mars, many dark streaks are evident on crater walls and, as on the Moon, come in a wide variety of forms and occurrences.  Martian dark streaks have been variously interpreted as being caused by compositional and particle size differences, but the most popular idea is that the dark streaks are wet soil, i.e., they represent areas where liquid water is seeping out from the planet’s subsurface and moistening the surface.  One observation supporting this idea is an apparent correlation of some of the dark streaks with surface temperature, with warmer slopes showing more.  As liquid water is not stable on the martian surface, salt-rich brines (which would have much lower melting points than pure water) have been invoked as the possible liquid phase.

The dark streaks on the crater walls of the Moon call water-related interpretations of similar features on Mars into question.  The nature of down slope movement on Mars is likely to be controlled by even more diverse factors than the lunar case.  For example, large landslides partly cover the floor of the Valles Marineris, the large canyon system on Mars.  These landslides can extend tens of kilometers across the valley floor and the mass flow might have been lubricated by trapped atmospheric gas; this “cushioning” effect occurs within some landslides on the Earth.  Such a process would not occur on the Moon.  The diversity of geological processes on Mars suggests that explanations for dark wall streaks could encompass many more possibilities than simple wetting of the surface.

Although the existence of dark lunar streaks does not negate water-related interpretations of similar features on Mars, they do call attention to the need to keep alternative hypotheses in mind.  For many years (and with some success), planetary geologists have extrapolated landforms and processes (thought to be understood) on Earth, to similar appearing features on the planets.  In the case of the dark streaks, terrestrial water seepages in the desert can be darker than surrounding desiccated terrain.  A wide variety of evidence indicates that water is present in the subsurface on Mars but sometimes other effects such as rock composition or particle size are responsible for the streaks and alternatives to seepage should always be kept in mind.

Originally published November 17, 2011 at his Smithsonian Air & Space blog The Once and Future Moon, Dr. Spudis is a senior staff scientist at the Lunar and Planetary Institute. The opinions expressed are those of the author and are better informed than average.

Thursday, November 17, 2011

LROC: Nature's Art

Western half of an unusual unnamed crater and its ejecta near the center of Mare Serenitatis. LROC Narrow Angle Camera (NAC) observation M139795376L, LRO orbit 5735, September 22, 2010; field of view 600 meters, incidence angle 28° from an altitude of 43.91 kilometers. View the full size LROC Featured Image HERE [NASA/GSFC/Arizona State University].
Hiroyuki Sato
LROC News System

In many cases crater ejecta patterns on the Moon result in natural art.

Unlike the ejecta on the Earth and Mars, ejecta on the Moon does not interact with an atmosphere.

Thus the final pattern on the ground is solely a reflection the dynamics of impact cratering. Today's Featured Image highlights the western half of an unnamed crater located in the middle of Mare Serenitatis. The crater diameter is about 470 meters.

Context view of today's Featured Image, showing a wider view of the unnamed crater ejecta. Field of view close to the full 2.2 kilometer width of LROC NAC frame M139795376L. See the larger context image accompanying the image release HERE [NASA/GSFC/Arizona State University].
As seen in the second picture (a zoom-out of the same NAC frame), one third of the ejecta blanket (the western portion) is missing, probably due to an oblique impact from west to east. In the top image (near the crater center), almost all of the boulders are ejected in the northwest and southwest direction. The fine particles, however, extend out to the west in patterns not unlike a delicate lace. Studying the full variety of craters with distinctive ejecta patterns is key to understanding the dynamics of oblique impact events.

LROC Wide Angle Camera (WAC) 100 meter per-pixel monochrome mosaic of the center of the Mare Serenitatis basin. The yellow arrow and blue square show the location of the LROC Featured Image and the full NAC observation's footprint. See the larger WAC context image HERE [NASA/GSFC/Arizona State University].
Explore this beautiful ejecta blanket in the full NAC frame!


Another very familiar crater famous for its asymmetric ejecta and as a nearside landmark of the Moon in an evening sky is bright Proclus - with lighthouse rays guarding "the gates" separating distinctive Palus Somni from Mare Crisium. View of the crater from Earth on March 29, 2010 from a spectacular full lunar disk mosaic by Astronominsk compared with LRO Nominal Mission LROC WAC image[Aстроноmинск (Луна) - NASA/GSFC/Arizona State University].
Related posts:
Ray of boulders
Slice of Mare
How did I form?
Asymmetric Ejecta

Wednesday, November 16, 2011

LROC's new Global Lunar Topography

Full hemisphere example of the newly released Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) color-shaded relief of the lunar farside, derived from their global Digital Terrain Model. View the larger image accompanying their November 16 announcement, HERE [NASA/GSFC/DLR/Arizona State University].
Mark Robinson
Principal Investigator
Lunar Reconnaissance Orbiter Camera (LROC)
Arizona State University


Global topography -- a boon to lunar scientists and explorers around the world! Today the LROC team releases Version 1 of the Wide Angle Camera (WAC) topographic map of the Moon. This amazing map shows you the ups and downs over nearly the entire Moon, at a scale of 100 meters across the surface, and 20 meters or better vertically. Despite the diminutive size of the WAC (it fits in the palm of one's hand), it images nearly the entire Moon every month. Every month? Yes! Redundant data? No! Each month the Moon's lighting changes, so the WAC methodically builds up a record of how different rocks reflect light under different conditions, and adds to the LROC library of stereo observations. The WAC really is the little camera that could! It was built by Malin Space Science Systems (MSSS) in San Diego CA, and is very similar to another MSSS camera (MARCI) now in orbit around Mars.

Left: LROC Wide Angle Camera attached to a test setup shortly before mounting on the spacecraft. Right: WAC being handed up to engineers for integration with LRO. View the released image HERE (photos M. Robinson).
The WAC has a pixel scale of about 75 meters, and with an average altitude of 50 km, a WAC image swath is 70 km wide across the ground-track. Because the equatorial distance between orbits is about 30 km, there is nearly complete orbit-to-orbit stereo overlap all the way around the Moon, every month. Using digital photogrammetric techniques, a terrain model was computed from this stereo overlap. The new topographic model was constructed from 69,000 WAC stereo models. Due to persistent shadows near the poles it is not possible to create a complete WAC stereo map at the very highest latitudes. Fortunately, the LRO Lunar Orbiter Laser Altimeter (LOLA) excels at characterizing the topography of the poles. Since the LRO orbits converge at the poles and LOLA ranges to the surface with its own lasers, LOLA provides a very high resolution topographic model of the poles. This LOLA map can fill in the WAC "hole at the pole".

Detail from WAC topography model, shades of gray represent elevation. Darker values are lower terrain and brighter values are higher points. (Image center is near 19.1°N, 175.3°E) View the much larger demonstration image HERE [NASA/GSFC/DLR/Arizona State University].
How is a digital topographic map created from stereo images? The WAC stereo images were compared one against another by pattern-matching a moving box of pixels until the best fit was found between two images with different viewing angles. Best fit pixel positions are combined with the LRO orbit position and the WAC viewing angles to define two 3D rays (lines of sight). The intersection point of these rays defines the location and the elevation of the point on the surface. Since the correlation box is bigger than 100 meters, surface details at the 100-meter scale are not fully resolved in a single stereo pair. However, each 100 meter square has an average of 26 stereo points within it (for a planet-wide total of 100 billion points), which helps to sharpen the elevation estimate. The resolution, in a formal sense, is probably close to 300 meters, and the accuracy of the elevations is estimated to be about 10 to 20 meters. This new map is called the Global Lunar DTM 100 m topographic model, or “GLD100”,  and covers 79°S to 79°N latitudes, 98.2% of the entire lunar surface. The WAC topography was produced by LROC team members at the German Aerospace Center (DLR).

Color-shaded relief detail of the same region in the figure above. View the spectacularly detailed and larger release image HERE [NASA/GSFC/DLR/Arizona State University].
Shaded relief images can be created from the GLD100 by illuminating the surface from a given Sun direction and elevation above the horizon, and to convey an absolute sense of height the resulting grayscale pixels are painted with colors that represent the altitude. Visualizations like these allow scientists to view the surface from very different perspectives, providing a powerful tool for interpreting the geologic processes that have shaped the Moon
.
And the LROC WAC Global monochrome mosaic also corresponding to same area, with the accompanying larger and more detailed release image available HERE [NASA/GSFC/DLR/Arizona State University].
The large irregularly shaped Buys-Ballot crater, seen in the three images above, is about 47 km by 62 km. The WAC topography shows the flat floor to lie some 3100 meters below the western rim and 4600 m below the eastern rim. The central peak rises about 800 m above the floor. For comparison the width and depth of this crater are larger than those of the Grand Canyon, AZ.

Topographic profile (highly exaggerated) across Buys-Ballot crater, note the flat floor [NASA/GSFC/DLR/Arizona State University].

Why is the floor of the crater so flat? The WAC mosaic holds an important clue -- note how dark the floor is. On the Moon, dark (low albedo) material is typically basalt, which is dark because it is relatively rich in iron (mafic minerals). On the Moon, basalts are erupted as very hot lavas, making them very fluid, thus they tend to spread out and flood local topographic lows. From the topography and WAC image data, one can make a confident interpretation that the floor of this unusual crater is most likely flooded with basalt. But why such a small eruption? Most flood basalts on the nearside cover vast expanses of lunar terrain, but why not on the farside? Another mystery for future lunar explorers to unravel!

The area shown here is only a tiny portion of the Moon: see if you can find Buys-Ballot in the full resolution hemispheric view.

What improvements can be made over this first release of the LROC WAC GLD100? The current model incorporates the first year of stereo imaging, and there is another year of data that can be added to the solution. These additional stereo images will not only improve the sharpness (resolution) of the model but also fill in very small gaps that exist in the current map. The LROC team has made small improvements to the camera distortion model, and the LOLA team has improved our knowledge of the spacecraft position over time. These next generation steps will further improve the accuracy of Version 2 of the LROC GLD100 topographic model of the Moon.

Explore the new LROC GLD100!

And here are Direct links to color shaded relief visualizations (relatively large *.tif image files*):



Orthographic projection centered at 0° longitude and 0° latitude.
Orthographic projection centered at 60° longitude and 0° latitude.
Orthographic projection centered at 120° longitude and 0° latitude.
Orthographic projection centered at 180° longitude and 0° latitude.
Orthographic projection centered at 240° longitude and 0° latitude.
Orthographic projection centered at 300° longitude and 0° latitude.
Orthographic projection centered at 0° longitude and 90° latitude.
Orthographic projection centered at 0° longitude and -90° latitude.

Color scale legend for LROC Color Shaded Relief
. View the full size graphic, HERE [NASA/ GSFC/ DLR/ Arizona State University].
*NOTE: OS X (and many other) users may prefer opening these large TIFF files directly within a browser. Please select and "Save" to local storage media, allowing the option of opening these files in an image viewer or editing program.

Tuesday, November 15, 2011

LROC: Boulder mound high on Dawes rim

Boulder rich mound on the northeastern rim of Dawes crater. Image field of view is 290 meters, under a high early afternoon Sun. LROC Narrow Angle Camera (NAC) M139734469L, LRO orbit 5726, September 21, 2010; incidence angle 20.59° with a resolution of 49.4 centimeters per pixel from 44.12 km. See the full 500 meter field of view HERE [NASA/GSFC/Arizona State University].
Hiroyuki Sato
LROC News System

Today's Featured image focuses on an extremely boulder rich mound, located about 100 m east of the rim of Dawes crater. Dawes crater is 18 km in diameter and located at the boundary between Mare Serenitatis and Mare Tranquillitatis.

The diameter of the mound is about 150 meters. From the appearance of relatively fresh fragments clustering within a circular area, one gigantic boulder likely hit the ground and fragmented to make this mound. But it did not hit hard enough to make a crater, so we can infer that the impact velocity was low. Then the question is, where did that gigantic boulder came from?

LROC Wide Angle Camera (WAC) 100 meter monochrome mosaic affixed to LOLA 128 topography in ILIADS simulated oblique perspective from the south and 18 km altitude. The boulder mound seen in the LROC Featured Image rests in a conspicuous interruption in the off-center rise in elevation along the northeast rim [NASA/GSFC/Arizona State University/ILIADS].
Fifty kilometer field of view of oddly-shaped Dawes, LROC WAC 100 meter Global Mosaic on LOLA topography, also from ILIADS, perspective from high above the center of the familiar landmark crater, along the Serenitatis and Tranquillitatis frontier [NASA/GSFC/Arizona State University/ILIADS].
LROC WAC 100 meter monochrome Global Mosaic showing Dawes in the context of the boundary zone, between Mare Serenitatis and Mare Tranquillitatis. Image center is latitude 17.226° N, 26.414° E, and the yellow arrow and blue rectangle indicate the location of the area of interest in the LROC Featured Image, November 15, 2011 and the NAC footprint of M139734469L [NASA/GSFC/Arizona State University].

Since this bouldery mound is beside an 18 km diameter crater, huge boulders could have been thrown out as a part of its ejecta. But in the case of this mound, the landing must have been at the end of the ejecta emplacement, otherwise it would have been buried. Why did it land late in the sequence of ejecta emplacement? Another source crater might have supplied this huge boulder. If so, that second crater must be nearby to keep the impact velocity low.

Explore other boulder rich mounds and search for a possible source crater in the full NAC frame yourself!

Related posts:
Zebra Stripes
Impact melt in Anaxagoras crater
Bright ridge near Mons Hansteen
Buckland Boulders
Fragmented Impact Melt
Mounds in a melt pond

Monday, November 14, 2011

Even a mere passing glance...

The familiar face of our nearest neighbor and its magnificent desolation, as introduced by Galileo through even minimal magnification barely four centuries ago, captured by Mikael Sundberg [500px]

Scientific Preparations for Lunar Exploration Workshop

Notional (2010) node of the International Lunar Network (ILN) NASA/MSFC
ESA Conference Bureau

We are pleased to announce, on behalf of the organisers, that the Scientific Preparations for Lunar Exploration Workshop will take place on 6 and 7 February 2012 at ESA/ESTEC, Noordwijk, The Netherlands.

Objective: The objective of the workshop is to explore the scientific challenges associated with enabling future exploration of the Moon and the ways in which these challenges can be addressed through:

       - Terrestrial research activities
       - Experiments in Low Earth Orbit and in reduced/micro gravity
       - Investigations on in situ precursor missions

Call for papers
Authors are kindly invited to submit their abstract by using the online abstract submission form, posted on the workshop website http://www.congrex.nl/lunarexplorationws/

More relevant information can be found on the above mentioned website.

We are looking forward to welcoming you at ESA/ESTEC.

Friday, November 11, 2011

New view of the Sinas pit crater

Latest publicly available close-up of the Tranquillitatis pit crater (8.337°N, 33.219°E), LROC Narrow Angle Camera (NAC) observation M155016845R, LRO orbit 7979, March 17, 2011; whose interior is finally seen under a high Sun (incidence angle 10.58°) at a resolution of 47.4 centimeters per pixel from 39.67 kilometers. LROC QuickMap link [NASA/GSFC/Arizona State University].
Joel Raupe
Lunar Pioneer

Since its arrival in lunar orbit in June 2009 every three months LRO investigators have made available data collected by their respective instrument teams during the 90-day period between six and three months prior.

On September 15, for example, the LROC team, led by Dr. Mark Robinson at Arizona State University (and by far the most consciencious of these admittedly very busy science teams), released to the PDS (Planetary Data System) photography collected by their Wide and Narrow Angle cameras (WAC and NAC) between mid-March through  the middle of June 2011. The LROC team has also continued to make improvements to their already impressive set of web-based tools, created for sorting through these vast stores of data, most recently marked improvements to the ACT-REACT QuickMap interface.

So, every ninety days "lunatic" investigators, even rogue investigators like ourselves, everywhere on Earth jump on these data and begin scrambling through an ever-growing list of favorite targets, anxious for any new views or improved resolutions, even a different degree of illumination. Though it's rare when a new high resolution NAC view of a previously imaged location on our list becomes available it's difficult to complain when remembering more than a third of the Moon's surface has now been mapped at a half-meter per pixel resolution or better, or that the entire Moon has, by now, been photographed at 50 to 60 meters resolution several times over, at a respectable variety of illuminations.

After September 15, the date that a seventh batch of LROC observations were released, nearly two months passed before we finally reached the Moon's now-famous "skylights" on our list, in particular the now-famous pit craters at Marius Hills, Mare Ingenii and Mare Tranquillitatis.

No new LROC NAC views appears to have yet been processed of the "Haruyama pit," in the upper stretches of the Sinuous Rille A in the Marius Hills (14.094°N, 303.224°E). A low angle, very detailed image of the huge pit in the Mare Ingenii basin (35.95°S, 166.06°E), captured in 2010, will be hard to improve upon, though perhaps a view revealing more of that formation's boulder-strewn floor under a high sun would help expand our understanding of its extent.

And we've still not had the time to look for any better views of the natural bridge north of King crater, nor what appear to be small pits on the floor of Messier A.  There does not seem to be anything new to add to the little we know about the other, much smaller and far less dramatic "pit" north of the skylight pictured above (and below).

The LROC Science Operations Center at Arizona State University has taken advantage of at least five separate opportunities to capture the Tranquillitatis pit crater, surrounded by the Sinas crater group . All five close-ups are reproduced here in an animated gif, including one "double exposure," positioning the second observation with the third to obtain a better look at the interior before a fifth observation swept up on St. Patrick's Day. A fourth oblique view offered a breathtaking view of subsurface layers, and thus the long and apparently very eventful early history of Mare Tranquillitatis [NASA/GSFC/Arizona State University].
The Sinas group pit crater captures our imaginations perhaps primarily because, like all great discoveries, it raises so many more questions than it answers. These initial historic surveys will be among those things 100 years from now LRO investigators will be credited for as paying the treasure and devotion paid to the entire LRO mission all by themselves.