Another look at the effusive dome west of Rima Yangel

Effusive dome on the southern rim of a  ghost crater situated on the northern shore of Mare Vaporum, in a 11.48 km-wide field of view west of Rima Yangel. LROC NAC mosaic M1111791664LR, LRO orbit 16100, January 2, 2013; 71.03° angle of incidence, 1.19 meters per pixel resolution from 118.91 km [NASA/GSFC/Arizona State University].

Follow-up LROC Narrow Angle Camera (NAC) observation swept up by the orbiter in January and released to the Planetary Data System (PDS) in June. This effusive dome on the north bank of Mare Vaporum was the subject of two extensive posts in February and March.

Follow-up research on the effusive dome near Rima Yangel (March 26, 2013)
A fascinating effusive dome in Mare Vaporum (February 19, 2013)

The mosaic above can be viewed at full and at a variety of medium resolutions, HERE. The dome has bow been imaged from LRO from high and low altitudes, under a range of illumination angles, and many of those observations are referenced in the posts from earlier in the year, linked above.

Convergence

Debris flows converge at the bottom of a youthful crater on the northern frontier of the Moscoviense basin (32.660°S; 143.668°E). LROC Narrow Angle Camera (NAC) frame M1107331321R, spacecraft orbit 15474, November 12, 2012; 62.63° incidence, 1.45 meters resolution from 145.44 km. Field of view approximately 1.4 km across [NASA/GSFC/Arizona State University].

James Ashley
LROC News System

Small crater floors are places where slopes facing different compass directions (azimuths) naturally approach each other.

Steep, recently formed slopes will often produce debris flows that migrate part way or completely to the floor.

The resulting zones of debris convergence can present interesting juxtapositions of coarse and fine deposits with variable light and shadow effects. On an airless body like the Moon, the patterns are frequently striking, and make for studies in artistic composition. The play of sunlight on these surfaces often create some surprising textural patterns and relationships.

Context for the LROC Featured Image within a 7 km field of view [NASA/GSFC/Arizona State University].

This small, unnamed farside crater in the lunar highlands presents a nice example. High-reflectance ejecta in the WAC context image shows it to be the result of a relatively recent impact. Mass wasting events have generated debris flows that have different textures by the time they come to rest at or near the crater floor. Their different slopes produce different angles of illumination and different intensities of reflection.

Roughly 9.2 km-wide field of view from LROC NAC mosaic M187306990LR, LRO orbit 12672, March 25, 2012; 31.65° angle of incidence, resolution 105 cm per pixel from 161.18 km over 32.67°E, 143.77°E [NASA/GSFC/Arizona State University].

 Slightly less than 40 km-wide field of view from LROC Wide Angle Camera frame M167260236CE, orbit 9783, 56.55° angle of incidence, 67.4 meters per pixel resolution from 50.4 km [NASA/GSFC/Arizona State University].

There are also examples of impact melt visible in the debris, best seen in the full NAC frame just south of the Featured Image boundary. What clues would you look for to help distinguish impact melt from fine-grained debris flows?

The bright ejecta from the small crater (arrow) contrasts sharply from its far more 'optically mature' surroundings, allowing the eye to easily pick area of interest in small scale albedo maps and this segment of the LROC GLD100 mosaic showing the crater's location with respect to Mare Moscoviense [NASA/GSFC/Arizona State University].

Explore additional details in the full NAC frame HERE.

Similar Featured Image posts have been presented as "Diversity," "Complicated Crater," and "Rubble Pile on Fresh Crater Floor."

Project Morpheus tether test #28

Morpheus Bravo vehicle executed a successful tether test on August 7, 2013 at Johnson Space Center. The combined Morpheus/JPL team met all test objectives including engine ignition, ascent, a 3 meter lateral translation over simulated Mars soil provided by JPL to help them with a plume study, 40 seconds of hover at the apex, and a slant descent to "landing" using free flight guidance. The entire flight duration was ~80 seconds. All though the Mars soil simulant is not typical for Morpheus test fires, it sure made for a spectacular show.

Project Morpheus Tether Test 21 (May 24, 2013)
Morpheus Unit B first fully integrated hot fire test (May 6, 2013)
Morpheus and ALHAT teams, still hard at work (February 11, 2013)
Morpheus employs ALHAT in teather test #16 (June 13, 2012)
Project Morpheus lander - Soft Abort Test (May 11, 2012)
Morpheus Tether Test #10 (April 9, 2012)
Morpheus Tether Test #8 (March 14, 2012)
Project Morpheus methane Hot Fire Test #5 (February 29, 2012)
Morpheus lander in tethered flight tests (May 7, 2011)  

Symmetry in Asymmetry

A beautiful example of an asymmetric impact feature (27.674°S; 125.465°E). LROC Narrow Angle Camera (NAC) frame M110771566R, LRO orbit 1458, October 21, 2009; illumination angle of incidence 31.51° from the northeast, image field of view roughly 1.2 km across, resolution 63 cm per pixel from 60.63 km [NASA/GSFC/Arizona State University].

James Ashley
LROC News System

While the total energy of an impact depends on the projectile velocity and mass, low-angle (oblique) impacts can distribute this energy in ways that differ from that of a higher angle trajectory.

By definition oblique impacts strike at an angle of 15° or less, producing something more akin to a 'glancing blow' rather than a 'hard smack,' and often result in asymmetrical 'wing-shaped' ejecta patterns.

Based on the ejecta surrounding this small feature in Neujmin crater in the lunar farside highlands, a case can be made for a southwestern approach from the impacting object. Debris was tossed in the down-track direction and splayed at right angles to the flight path on either side. The ejecta is actually quite symmetrical with respect to this flight axis (axial symmetry). The notion of asymmetry really applies to rotational symmetry in the case of many oblique impacts.

One of three dark halo craters (DHC) on the floor of Deutsch crater and recently proposed as one of many newly surveyed potential landing sites picked to fulfill high-priority science goals. A 4-km-wide field of view from LROC NAC observation M185169501R,  spacecraft orbit 12373, February 29, 2012; angle of incidence 29.7° resolution 1.46 meters per pixel from 148.15 km [NASA/GSFC/Arizona State University].

Smaller impacts created markings on the ejecta blanket, and these events excavated through the high-reflectance ejecta bringing up lower reflectance, mature materials -- producing dark-haloed craters. These small dark halo craters likely formed seconds after the high reflectance material was emplaced as slower, larger pieces of ejecta landed.

LROC Wide Angle Camera (WAC) GLD100 mosaic of the ancient, possibly highly "disrupted" terrain in and around Neujmin crater, southeast of the more distinctive farside landmark Tsiolkovskiy crater, presented as context for the 'winged' crater in the LROC Featured Image, released August 6, 2013. It's location is marked by the arrow [NASA/GSFC/Arizona State University].

The full NAC frame can be explored HERE.

Additional examples of oblique impacts are available in the Featured Image browse gallery, including "Not Your Average Crater," "A Tiny, Glancing Blow," and "Crash or Coincidence?"

Melted Moon

The fresh lunar crater Giordano Bruno -a wealth of fascinating landforms to study. (click image for full resolution view, or HERE for a wider, medium resolution field of view showing the entire crater) [NASA/GSFC/Arizona State University].

Paul D. Spudis
The Once and Future Moon
Smithsonian Air & Space

Prior to the Space Age, one of the longest running controversies in lunar science was over the origin of the Moon’s craters.  Two camps emerged, one favoring an internal (volcanic) origin and the other an external (impact by solid bodies) origin.  Although this debate was finally resolved in favor of impact, the argument was long and vehement, reigniting at one point during the flight of the last of the robotic precursor probes to the Moon, prior to the Apollo landings.  Although the basic physics of impact were well understood by the mid-1960s, this newest argument centered around high-resolution pictures obtained by Lunar Orbiter 5 (1967) of the fresh (and therefore young) crater Tycho.  These spectacular images showed a multitude of flows, smooth ponds, and fluid rock, seemingly draped over hills and hummocks (like a chocolate shell coating over a scoop of ice cream).

An asteroid possesses an enormous amount of kinetic energy when it strikes a planetary body at very high speeds.  On contact, the asteroid vaporizes and the surface target rocks are intensely compressed.   After the shock wave has passed, these rocks decompress and the release of this energy totally melts part of the crustal target.  This material is said to be shock melted, with the resulting liquid called impact melt.  Impact melt was first described from craters on the Earth, particularly some of the very large impact craters found on the ancient Canadian Shield.  These rocks superficially resemble some volcanic rocks, having both fine-grained textures and partly melted inclusions.  But unlike volcanic rocks, they have high concentrations of siderophile (“iron-loving”) elements, such as iridium.  These elements are extremely rare in the Earth’s crust, but are more abundant in meteorites and asteroids.  It is thought that they are added to the melt from the incoming projectile.

The newest chapter in the argument about the origin of craters came about because some landforms around Tycho look similar to small-scale volcanic features on Earth.  The idea proposed was that the craters had been formed by impact, with those collisions triggering volcanic activity and producing multiple episodes of eruption at Tycho and other craters.  At first glance, such a scenario seems plausible.  After all, impact is a catastrophic event and one can imagine churning seas of subsurface liquid rock, released suddenly through the creation of fractures deep in the crust.  But the Moon’s interior is relatively cool.  If interior melt exists, it is at a level much too deep for any reasonably sized impact to tap.  But these amazing landforms needed to be explained.  What might they represent?

We found abundant physical and chemical evidence for impact (including shock-melted rocks) by studying the Apollo samples.  They appear similar to volcanic lava, with inclusions, melt textures and even vesicles (holes), comparable to the ones produced by magmatic volatiles coming out of solution in basaltic lavas on Earth.  Although it took a bit of study (and many more arguments) to establish their origin, shock melting became recognized as an important lunar (and Earth) impact process.

Breech in the northwest rim of Tycho connects to the spectacular melt ponds inside out outside of the 109 million year old landmark crater. Illustration originally from "Landing Site at Tycho North," March 20, 2013 [NASA/GSFC/Arizona State University].

The images of the flows and ponds seen around Tycho and other fresh lunar craters led to a better understanding of how these rocks formed.  Although we knew about impact melting from the study of Earth’s craters (and had found evidence of the same in lunar samples), some researchers still weren’t convinced that we were seeing flows of liquid impact melt on the Moon.  The leading non-volcanic alternative was that these features were flows of dry, fine-grained granular debris.  In part, this interpretation proceeded from the observation that the thermal signatures of some of these melt-like flows suggested the presence of fine debris rather than bare, jagged rock.  Yet other data, such as radar backscatter, suggested that rough surfaces were common, while extremely high-resolution images showed abundant blocky craters on the surfaces of the flows, suggesting they were composed of solidified rock.

Landing site of Surveyor 7 (arrow) in relation to it's hoped for target, the kilometer-sized impact melt pond immediately to the northeast, part of the spectacular melt throughout the vicinity of Tycho [NASA/GSFC/Arizona State University].

Images from the robotic Surveyor 7 (1968) spacecraft, which landed on the rim of Tycho, revealed the thinnest regolith (soil) covering of any site on the Moon.  Visible in the surface panoramas were flow features covering the distant hills.  It took a great deal of painstaking, detailed work to establish that these flows and ponds were composed of liquid rock, created simultaneously with their host crater and likely originated by impact melting and subsequent solidification.

For the last several years, NASA’s Lunar Reconnaissance Orbiter (LRO) has been sending us new and astonishing views of the Moon’s impact melt flows.  Whereas fresh craters like Tycho, Aristarchus and Copernicus were well known from previous Lunar Orbiter frames, far side craters like the spectacular Giordano Bruno can now be seen with incredible clarity.  G. Bruno is one of the very youngest craters on the Moon.  A low density of craters overlying G. Bruno suggests an age of less than a couple million years (extremely young on a planet where most features count years in the billions).  It is an astonishing spectacle of melt shapes and deposits (cracked floors, pools, flow festoons and lobes); the crater floor has an amazing whirlpool of solidified melt. All these features indicate that after the crater formed, the impact melt was mobile, flowing and collecting, and ponding in low areas.

Impact melt forms a swirled feature in Giordano Bruno crater. Field of view 1 kilometer. From LROC Narrow Angle Camera (NAC) observation M143947267L LRO orbit 6347, November 9, 2010; 53.08° angle of incidence, 57 centimeters per pixel resolution from 54.50 km. Illustration from "Giordano Bruno Whorl," June 8, 2013 [NASA/GSFC/Arizona State University].

Impact melts are of great interest to geologists.  Unlike other crater ejecta, the radiometric clocks of impact melts are completely re-set by the melting.  Thus, if a sample can be obtained first-hand, directly from an observed flow or pool of melt around a host crater, the age of that rock specifically and unambiguously dates the impact event.  Unfortunately, we did not visit such deposits during the Apollo explorations.  What we do have are loose samples of lunar impact melt but not their scientifically important corresponding geological context.  It is for this reason that the age and sequence of early lunar history is so contentious – we must make educated guesses about where certain melt rocks come from.  If we get the context wrong, then our conclusions about the history of the Moon are incorrect.

Increased understanding of the generation and deposition of impact melt comes from the new images obtained by the LRO camera of the geologic setting of impact melts.  Future sample return missions to the Moon can be directed to landing sites that will provide us with samples of clear geological context (that they were from that area and not just flung there by an impact occurring elsewhere on the lunar surface).  As features age on the Moon, subsequent geologic events (such as superposition of new units) bury or erase the original event making the context less clear.  This problem is particularly acute for the oldest features on the Moon (multi-ring impact basins).  By studying the geology of the freshest lunar features (such as Tycho and other fresh craters), we understand how the older impact features looked immediately after their formation.  Thus, they serve as a guide to the interpretation of the older features.  On the Moon, as on the Earth, as Charles Lyell, the 19th century author of the classic Principles of Geology aptly put it:  The present is the key to the past.

Collection of spectacular impact melt features from LRO:
Giordano Bruno high-resolution full view
G. Bruno sunset
G. Bruno flows
G. Bruno cracked melts
Tycho oblique
Tycho floor
Tycho river of rock

Originally published July 31, 2013 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 but are better informed than average. 

ESA prepares for LADEE

Artist's view of NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) observatory as it approaches lunar orbit [NASA].

An advanced laser system offering vastly faster data speeds is now ready for linking with spacecraft beyond our planet following a series of crucial ground tests. Later this year, ESA’s observatory in Spain will use the laser to communicate with a NASA Moon orbiter.

The laboratory testing paves the way for a live space demonstration in October, once NASA’s Lunar Atmosphere and Dust Environment Explorer – LADEE – begins orbiting the Moon.

LADEE carries a terminal that can transmit and receive pulses of laser light. ESA’s Optical Ground Station on Tenerife will be upgraded with a complementary unit and, together with two US ground terminals, will relay data at unprecedented rates using infrared light beams at a wavelength similar to that used in fiber-optic cables on Earth.

“The testing went as planned, and while we identified a number of issues, we’ll be ready for LADEE’s mid-September launch,” says Zoran Sodnik, manager for ESA’s Lunar Optical Communication Link project.

“Our ground station will join two NASA stations communicating with the LADEE Moon mission, and we aim to demonstrate the readiness of optical communication for future missions to Mars or anywhere else in the Solar System.”

Read the illustrated ESA article, HERE.

ESA's Optical Ground Station (OGS) is 2400 meter above sea level on the volcanic island of Tenerife, in the Canary Islands. Visible green laser beams are used for stabilizing the sending and receiving telescopes on Tenerife and neighboring La Palma. The OGS facility is utilized for extensive experiments with entangled photons, quantum communication and teleportation. OGS is also used for standard laser communication with satellites, tracking space debris and finding new asteroids. The image above includes Tenerife's Teide volcano with the Milky Way in the background [ESA/IQOQI Vienna, Austrian Academy of Sciences].

Related Posts:
LADEE arrives at Wallops Island (June 5, 2013)
LADEE ready to baseline dusty lunar exosphere (June 5, 2013)
First laser comm system ready for launch on LADEE (March 16, 2013)
LADEE project manager update (February 6, 2013)
The Mona Lisa test for LADEE communications (January 21, 2013)
Expectations for the LADEE LDEX (March 23, 2012)
LADEE architecture and mission design (July 6, 2010)
NASA applies low cost lessons to LADEE (January 18, 2010)
LADEE launch by Orbital from Wallops Island (April 14, 2009)

Orientale Sculpture

An oblique view of ejecta over 400 km south of the Orientale basin rim, a scene approximately 5 km across, centered at 51.8°S, 264.8°E, LROC Narrow Angle Camera (NAC) mosaic M1127819355LR, LRO orbit 18355, July 7, 2013; native resolution 1.9 meters per pixel [NASA/GSFC/Arizona State University].

Brett Denevi
LROC News System

Today's featured image is located near the center of the ancient 600-km Mendel-Rydberg basin. Its degraded state means Mendel-Rydberg's presence is not obvious in the WAC context image below (in fact, its existence was only confirmed with Clementine (1994) topography data), but its western rim is near the crater Mendel, and Rydberg and Guthnick craters are near the center of the basin.

However, it was not the Mendel-Rydberg impact that was responsible for the ups and downs in the hummocky deposits seen in today's Featured Image, but the Orientale impact event, hundreds of kilometers away to the north.

Ejecta from impact basins is both erosional, gouging out long valleys and leaving strings of large secondary craters (along the arrows in the image below), and depositional, blanketing even distant terrain with material excavated from the impact site. Basin ejecta plays such a large role shaping the lunar surface that these ups and downs are often referred to as "basin sculpture," and the ejecta from Orientale certainly sculpted the terrain in today's image.

LROC Wide Angle Camera (WAC) mosaic context views of the southern Orientale region. The blue box in the image at bottom shows the field of view at top, where a yellow box shows the approximate field of view shown in the LROC Featured Image. Click to enlarge [NASA/GSFC/Arizona State University].

The hummocky deposits that cover low-lying areas in the top image, and the image below, are likely ejecta from the Orientale basin. These low-lying regions may have once been exposures of smooth mare basalt, some of which is still exposed on the surface in nearby regions, but are now hidden under a blanket of debris from Orientale. Buried volcanic deposits such as these are known as "cryptomare" and tracking down the locations of these ancient sites of volcanic activity is key for understanding the extent of early volcanism on the Moon.

A wider (and reduced-resolution) view of the LROC NAC mosaic from which the LROC Featured Image within the Mendel-Rydberg basin was cropped. LROC NAC M1127819355LR [NASA/GSFC/Arizona State University].

You may also note that the hills in the southern portion (right side) of the image above have a lumpy texture, also visible in the WAC context image. This is also likely due to Orientale's influence - the result of a massive ground hugging flow of ejecta that piled up on the sloped terrain. This oblique view of the region gives a great perspective on its complex history that would have been compelling enough with just the ancient Mendel-Rydberg basin and early lunar volcanism, but the spectacular basin ejecta flows captured here are just icing on the cake (so to speak).

Click HERE to see the full-resolution view.

Related LROC Featured Images:
Amazing Orientale Peaks and Valleys
Regolith Patterns in Mendel-Rydberg
Window to the Farside Mantle
Two-toned Impact Crater in Balmer Basin: A reflection of the Target?
Dark Craters on a Bright Ejecta Blanket

Snapshots from the Moon and Cislunar Space

Apollo 17 commander Eugene Cernan (UR, LR), CM pilot Ron Evans (UL, LR) and LM pilot and geologist Harrison "Jack" Schmitt (LL) relaxing in the Apollo 17 Command Module America after Cernan and Schmitt returned from three days of exploring the magnificent Taurus Littrow valley, the last manned expedition to the lunar surface 40 years ago, December 1972 [NASA/ Arizona State University].

Mark Robinson

Principal Investigator

Lunar Reconnaissance Orbiter Camera

Arizona State University

This year, we commemorate the forty-fourth anniversary of the first human lunar landing. By now, the whole world is very familiar with the high-quality Hasselblad snapshots taken by the Apollo astronauts during their voyages. However, 35-mm cameras were also carried on some of the Apollo missions for both surface and orbital imaging. Most of the surface 35-mm images are extreme closeups of the lunar regolith from the Apollo Lunar Surface Closeup Camera (ALSCC; Apollo 11, 12, 14); sometimes called the Gold Camera after its Principal Investigator Thomas Gold.

The Nikon camera used on board the Apollo Command Module was equipped with a 55-mm lens and was loaded with either black-and-white or color film. During Apollo missions 16 and 17, black-and-white film was used for dim-light photography of astronomical phenomena and lunar surface targets illuminated by Earthshine. During Apollo 17, color film was used for documenting various activities in the Command Module.

The 35-mm frames are now scanned as part of a joint project between Arizona State University and the NASA Johnson Space Center to scan all of the original Apollo flight films.

Boot print anaglyph - Stereo anaglyph (get out your red-blue stereo glasses!) AS14-77-10369a,b from the ALSCC showing extreme detail of an astronaut bootprint in the fine-grained lunar regolith. The original field of view is about 3 inches on a side [NASA/Arizona State University].

The Apollo 17 crew seems to have had the most fun with the 35-mm format! Gene Cernan, Ron Evans and Jack Schmitt snapped quite a few spectacular black-and-white images showing the view out of the window of their Command Module, the America. Some of these images are a bit grainy, resulting in a very different feeling than the crisp Hasselblad photographs. They also took numerous color candid shots inside the Command Module. It is rare to see such carefree moments during the Apollo missions, but you can feel the relief and happiness after the astronauts so successfully fulfilled their surface mission!

Reiner Gamma illuminated solely by earthshine (35-mm Apollo 17) - Reiner Gamma, one of the enigmatic lunar swirls; their origin is related to localized magnetic fields within the crust AS17-158-23894 [NASA/Arizona State University].

Many of the window shots present an oblique view across lesser known regions of the Moon. The terminator (boundary between night and day) scenes are always captivating. Look closely at the scene below; near the center is a shallow-sloped scallop-shaped rise. Just below and to the right are two other smaller rises - perhaps these are low shield volcanoes? You can dig deeper by visiting the LROC QuickMap browser and see if the NAC images can elucidate what is seen here (Natasha crater is at 19.973°N, 328.843°E).

Mare Imbrium meets Mare Procellarum (Apollo 17 35-mm frame) a complex region composed of nearly buried peaks that are part of the Imbrium rim, impact craters, and volcanic forms. Annotated AS17-160-23992 [NASA/Arizona State University].

Relive the incredible adventure that was Apollo, browse the Apollo 35-mm archive and the rest of the Apollo scans (Metric, Pans; Hasselblads to follow next year). While browsing, map out your own next mission to the Moon! The hard part is figuring out where to visit next. Enjoy!

Related Posts:
Project Mercury Photography Now Online
Project Gemini Comes to Life
Reiner Gamma Constellation Region of Interest
Mare Ingenii Swirls

The View Inside a Tilted Crater

Oblique view of the chaotic interior of 30-km Wiener F crater. LROC Narrow Angle Camera (NAC) mosaic M1113262343LR; LRO orbit 16307, January 19, 2013, spacecraft and camera slewed 52° west from 160.39 km over 41.84°N, 140.28°E, subsampled from a scaled 2.78 meter per pixel resolution. Scene width approximately 13 kilometers from left to right, centered at 41.1°N, 150.0°E. [NASA/GSFC/Arizona State University].

Brett Denevi
LROC News System

Impact melt is commonly found in and around fresh lunar craters and can be spotted as ponds, flows, and ejecta.

This oblique view of the farside crater Wiener F highlights one of the more spectacular examples of what happens to the melt when a crater forms on a slope.

In the image above, you have a great perspective view of the chaotic crater interior, where material slumping into the crater interacted with the fluid melt, creating rough, hummocky mixtures in some regions and smoother pools of melt in others. But what is really interesting about this crater becomes clear when you zoom out to the full width of the image, below.

Thumbnail view of LROC NAC mosaic M1113262343LR, looking from west to east into Wiener F crater. For the full-resolution, zoomable view click HERE [NASA/GSFC/Arizona State University].

Wiener F formed atop a larger, older crater, so its northern rim, on the left in the picture above, ended up substantially lower than the southern rim. A profile across the crater, taken from the GLD100, shows the northern rim of the crater is over 2 km lower in elevation than the southern rim!

A profile from south to north across crater Wiener F, taken from LROC WAC-derived topography data [NASA/GSFC/Arizona State University].

So tilting the crater like this is like tilting a glass of water - it spills. In this case, the hot impact melt that would normally stay within the crater poured out, spilling over the northern rim and pooling outside the crater. Click on the image below to see this spectacular flood. You can find individual flows and places where the melt was still moving even as a crust of hard rock formed on top, resulting in cracks and wrinkles in the top layer.

View of the impact melt that escaped Wiener F, pooling outside the northern crater rim. Image subsampled from the original resolution [NASA/GSFC/Arizona State University].

Impact melt is a favorite target for LROC imaging because of its often complicated and bizarre features, and because of what it tells us about the impact process. The volume of melt can give clues as to how fast an impactor hit the surface (higher velocities mean higher shock pressures and more heat to melt rock), at what angle it impacted (melt is often thrown downrange of an impact), and how long ago the impact occurred (by observing how well preserved the melt morphology is, or by age-dating a sample of melt). Impact melt can also give insights into how portions of the crater moved and settled as the crater formed (for example, how did melt get up HERE?).

LROC Wide Angle Camera (WAC) contextual view of Wiener F crater, nested in the Farside Highlands [NASA/GSFC/Arizona State University].

Wiener F is another piece of that puzzle, showing what a dynamic environment an impact crater is shortly after formation. Click HERE for the full-resolution view of Wiener F.

Other Spectacular
Impact Melt Favorites:
Rumker E Impact Melt
Dynamics of Molten Rock
La Pérouse A Impact Melt
Rippled Pond
Breached Levee
Secondary Melt on the rim of Wiener F
Getting cracked in Wiener F
Giordano Bruno Whorl

Small-Scale Volcanism on the Lunar Mare

"Small Shield Volcanism on the Lunar Mare," (figure 1.) EPSC 2013-875 Plescia, Robinson & Joliff. Constructs in Mare Tranquillitatis. a: low-relief, low-slope with central crater; b "pancake-shaped"; c and d': hummocky, steep-sided , gc: ghost crater. LROC Wide Angle Camera high-angle incident mosaic, centered near 7.5°N, 37.5°E [NASA/GSFC/Arizona State University] .

Plescia, Robinson & Jolliff
Johns Hopkins APL
Arizona State University
Washington University of St. Louis

"Small shield volcanoes having low relief and gentle slopes are scattered across the lunar mare. These features represent the terminal phases of mare volcanism and are formed by short-duration, low-volume eruptions. Composition and eruption dynamics may have varied as the morphology and color of the shields vary. There appears to be regional correlations of morphometric properties indicating larger-scale organization of the eruptions.

"Data from LRO and other missions now provide the ability to characterize each dome in terms of areal extent, topography, morphology, and color properties in unprecedented detail allowing for an analysis of their origin.

"Here, a subset of the domes are interpreted to represent a volcanic style characterized by small volume eruptions that built low-relief constructs (Fig. 1). This style of volcanism has been termed plains volcanism [14] and is common in the Tharsis region."

Small Shield Volcanism on the Lunar Mare, European Planetary Science Conference 2013, Vol. 8, #875; J.B. Plescia, Johns Hopkins University Applied Science Laboratory; M.S. Robinson, Arizona State University; B. Jolliff, Washington University, St. Louis

Small-scale shield volcanic vent structure ("d." in WAC mosaic above) south of Rupes Cauchy in Mare Tranquillitatis, near 7.5°N, 37.5°E; Vent strongly presents features resembling those of the Ina structure. 6.2 km-wide field of view from LROC NAC mosaic M190351657LR, LRO orbit 13098, April 29, 2012; 41.95° angle of incidence, resolution 0.95 meters per pixel from 113.33 km. Full-size versions HERE [NASA/GSFC/Arizona State University].

An observation post on the rim of Posidonius

Deep interior of an unnamed Copernican crater (30.363°N, 30.705°E) notched on the south rim of Posidonius, the 95 km pre-Imbrium crater on the northeast edge of Mare Serenitatis. The slope of the impact zone and angle of attack resulted in a triangular melt pond at the exposed center. Photograph from a mosaic of mosaics stitched from four overlapping LROC Narrow Angle Camera (NAC) frames taken 177 days apart (M157391825RL and M172717111LR), field of view 1160 meters, resolution 48 cm [NASA/GSFC/Arizona State University].

Joel Raupe

Lunar Pioneer

Posidonius (95 km, 31.878°N, 29.991°E) is a well-known floor-fractured crater, and a grand sight even through small telescopes in early evenings before First Quarter or before dawn, four days after a Full Moon. It is also an enduring crater, a remnant of the Moon's surface before the basin-forming impacts creating Mare Serenitatis, Mare Crisium and Mare Imbrium.

With regard to the oldest of these three basin, Serenitatis, Posidonius clings to its inundated northeastern edge, carrying scars from each of these epoch-changing events as well as the continuous gardening of subsequent lunar bombardments, both large, small and microcosmic. 

A kind of ready-made construction site for an observation post is notched into the north-facing.southern wall of Posidonius, very near the rim, and it features more than just an excellent view of the southern interior of the ancient crater. In terms of superposition and strategraphy this "improvement," in the form of a relatively recent small Copernican age crater may also be an observation post into the Moon's deeper past and the history of our star system.

A full-resolution sample of the mosaic of mosaics shows a a straight contact between the wall and floor of "30-30" crater. The left (west) side of the 272 meter field of view shows part a flat triangular melt zone, with an upslope on eastern wall. If the crater's progenitor impacted in a relatively flat plain, presumably the contact would have been the border of an encircled melt pond. LROC NAC M172717111LR, LRO orbit 10587, October 8, 2011; 34.21° angle of incidence, resolution 47 cm from 39 kilometers [NASA/GSFC/Arizona State University].

"30-30" crater, informally named for its location near 30°N, 30°E (30.363°N, 30.705°E), is a bright and distinctive two kilometer notch excavated on Posidonius' wall, near the top of its south-southeastern wall, a result of a relatively recent impact in the past half-billion years or so, a youngster in the neighborhood and on the lunar timescale.

The oldest, or at least deepest, material a lunar impact tosses out ends up on the crater's rim. So this small younger impact did future geologists a service. Efficiently, "nature's dynamite" excavated material originally thrown up and out from the Posidonius impact event and, as luck would have it, ejecta from Chancornac, also a pre-Imbrium crater to the southeast and more or less sharing the same rim.

The interior and east side of "30-30," shows small intriguing exposures of "dark halo" material on the crater's east wall and deposited with it's southeastward ejecta. LROC NAC M172717111LR [NASA/GSFC/Arizona State University].

The entire region is characterized by intriguing hints of underlying features in addition to its more obvious scars from disrupting shocks. Posidonius and its vicinity are deeply faulted, its floor scoured, inundated and subsequently drained of catastrophic lava flows and was clearly, on more than one occasion, subject to energies powerful enough to buckle its underlying floor.

A distinctive sinuous rille circumscribes the interior wall of Posidonius pointing to a rapid disbursal of.heated flows into Serenitatis at some point in its busy past.

Old Posidonius is at a crossroads in space, between crater-saturated highlands and the deeper plains of Lacus Somniorum and Mare Serenitatis, and it also sits at a crossroads in time, being older than Serenitatis and carrying some of the same history as the Sculptured Hills near the landing site of Apollo 17, 300 km to the south.

To get below these scars to sample the material originally tossed up by Posidonius in the dim past, before Serenitatis we would need to dig its its rim. Fortunately, the progenitor of "30-30" already did the digging.

A thumbnail, very much a miniature 580 pixel-wide reduction of the 9600 sample-wide "mosaic of mosaics" high-resolution and finely detailed survey of the "30-30" excavation of the ancient rim of Posidonius. LROC NAC mosaic of M172717111LR and the overlapping NAC observation swept up 177 days earlier, M157391825LR, from LRO orbit 8329, April 14, 2011; 35.35° angle of incidence, 48 cm per pixel resolution from 41.18 km [NASA/GSFC/Arizona State University].

As "the Rosetta Stone of the Solar System," the Moon is a history of bombardment (in the inner Solar System and, more importantly for us, in the vicinity of Earth) at a frequency and magnitude supposed to have steadily fallen off from its beginning roughly 4.575 billion years ago. A question as enduring as Posidonius, perhaps, is whether the rate of this bombardment might once have increased for a time, perhaps as a consequence of a disrupting shuffle in the orbits of the outer planets somewhat "late" in our star system's history, within its first billion years. 

"LROC Quick Map" quick look at a three dimensional model of a 27 km-wide area of the lunar surface around the "30-30" crater on the south-southeast rim of Posidonius, derived from WAC global surveys [NASA/GSFC/Arizona State University/DLR].

From the Real Estate trade we borrow the all-encompassing Latin word Situs, familiarly translated (outside strict legal circles) as "location is everything," or "location, location, location." Though "30-30" may not perhaps be uniquely situated, it may, if little else at this point, illustrate one way to determine the relative value of places on the Moon as they might be chosen for their value to science.

The dramatic disruption inside Posidonius, even the bright "30-30" crater itself, can distract the eye away from deep fractures nearby. Note a long fault line running south away from the rim of Posidonius, easily mistaken for a photographic artifact. A 34 km-wide field of view from LROC Wide Angle Camera (WAC) monochrome (566 nm) observation M159752877C, LRO orbit 8677, May 11, 2011; 53.58° incidence angle, resolution 58.8 meters from 42.28 km [NASA/GSFC/Arizona State University].

"30-30" itself presents to us a fairly average Copernican crater, for its size, though its location (there's that word again) perhaps more than its progenitor's angle of attack, caused it to end up presenting an atypical interior.

Instead of a round interior melt pond, or disk of impact melt at the center, the melt at the exposed center of "30-30" ended up triangular, making it into a flat balcony on Posidonius' south wall. It's essentially missing north has left the triangular melt pond to the mercy of steady erosion, shedding boulders and other fine, bright material down onto the slumped terraces of Posidonius' walls.

It's bright ejecta is marked in a few places by a definitely darker material, what might be an exposed layer or vein of dark halo material or even cryptomare half-way down the small crater's southeast wall. Additionally, there are at least two patches of perhaps this same darker material to the small crater's southeast and southwest, on its "normal" ejecta.

All in all, what else has the "30-30" crater "dug up?"

A broader context view of Posidonius (our crater of interest hugging to a "Five O'Clock" position on its rim. The fault proceeding south from Posidonius' rim is readily seen, as a crack through Chacornac that seems almost contiguous with a long crack in floor of Posidonius. LROC WAC mosaic stitched from surveys over five sequential orbits from about 42 km on May 11, 2011 [NASA/GSFC/Arizona State University].

Japan's lunar orbiter Kaguya (SELENE-1) captured Posidonius, together with the bright "30-30" crater on it's south-southeast rim in this HDTV still of eastern Mare Serenitatis from polar orbit in 2007 [JAXA/NHK/SELENE].

Sunrise across Posidonius and the environs of northeastern Mare Serenitatis, early evening viewing before First Quarter Moon here on Earth.  Those with an anatomical eye can see the lucky location of "30-30" crater and its excavation.

Related Posts:

Meanders in Posidonius (February 13, 2013)
Geological mapping of another world (January 25, 2013)
Rimae Posidonius (December 1, 2010)