LROC: Impacts on the Impact Melts

Impact melt surface ejected from Necho crater. Field of view width is 620 meters, LROC Narrow Angle Camera (NAC) observation M134374642L, LRO orbit 4936, July 21, 2010; Sunlight from the west, angle of incidence 68.85° at 0.62 meters resolution from 59.98 km. View the larger original LROC Featured Image HERE [NASA/GSFC/Arizona State University].

Hiroyuki Sato
LROC News System

Today's Featured Image looks vaguely like a microscope picture of onion cells (complete with a nucleus and cell walls), but in reality this is an impact melt deposit that extends out of Necho crater (5.25°S, 123.24°E; see whole view of this melt sheet HERE).

In between the network shaped cracks (notice that the sunlight is from left of the image, thus lineations are negative relief), multiple strangely-shaped craters with a central dent surrounded by a flat moat about 15 to 40 m in diameter are observed. They resemble bench craters (e.g. Fresh Bench Crater in Oceanus Procellarum, Bench Crater in Plato), except that they are not quite circular in shape and no radial ejecta is visible. The relatively bigger one near the image center has deeper dent and a petal shaped system of exterior deposits.

Full size field of view in the LROC Featured Image in context with the larger NAC frame M134374642L at roughly 4 meters per pixel resolution, shows some of the complexity of the impact melt on the east flank of Necho [NASA/GSFC/Arizona State University],

Necho crater and its eastern side, dominated by its ejecta deposits,  in viewed on the digital terrain model available in the Google Earth application, overlaid with the 604nm monochrome data from LROC Wide Angle Camera observation M165041995C, LRO orbit 9456, July 11, 2011; resolution 86.15 meters from 61.3 km. The locations of full NAC frame (blue box) and the field of view, highlighted in the LROC Featured Image (yellow arrow, 4.79°S, 124.125°E) are indicated [NASA/GSFC/Arizona State University].

These strangely-shaped craters are probably self-secondary craters, formed after the emplacement of the impact melt deposit but before the complete solidification of the molten rocks. The physical properties of unsolidified target might have resulted in these distinctly-shaped craters.

Explore more strangely-shaped craters on Necho's impact melts in the full LROC NAC image, HERE.

Related Posts:
Splash Mark at Necho crater (July 31, 2012)
Fresh Bench Crater in Oceanus Procellarum (December 23, 2011)
Bench Crater in Plato (November 9, 2011)
Impact melt at Necho crater (September 1, 2010)
A molten flood (July 28, 2010)
Necho Crater (August 22, 2009)

LROC: "Splash Mark" at Necho crater

Meandering line of boulders at the bottom of Necho crater. Image width is 690 m, LROC Narrow Angle Camera (NAC) observation M167390131L, LRO orbit 9802, August 7, 2011; incidence angle 47.08° at 0.69 meters resolution, from 60.11 km. Sunlight is from west (left side) [NASA/GSFC/Arizona State University]

Hiroyuki Sato
LROC News System

Today's Featured Image highlights the southern edge of an impact melt pond, located on the floor of Necho crater. Necho is a relatively young, Copernican-aged crater (meaning, it formed between ~1.1 billion years ago and the present) with a diameter of 30 km, located on the farside of the Moon (5.25°S, 123.24°E).

As seen in the WAC context image below, the crater floor is filled by impact melts. The meandering line of boulders in the opening image was found near the bottom of a north to northeast facing slope. There is no clear relief or texture difference on the surface except this boulder line. How was it formed?

Necho crater as viewed on the digital terrain model available in the Google Earth application, overlaid with the 604nm monochrome data from LROC Wide Angle Camera observation M165041995C, LRO orbit 9456, July 11, 2011; resolution 86.15 meters from 61.3 km. The locations of full NAC frame (blue box) and the field of view highlighted in the LROC Featured Image (yellow arrow) are indicated [NASA/GSFC/Arizona State University].

Probably this line of boulders was formed as a splash mark or wave front coming from the melt pond, driven by secondary impacts or debris dumped into the melt pond. In fact, impact melt flows frequently retain similar boulder lines along the edge of each flow unit (see Scale-like Impact Melts, A molten flood). Also, discontinuous boulder marks at the upper part of this image extend downslope, near the relatively level melt pond area, which might be a side of the splash flow.

Explore the full NAC view of Necho's impact melt pond HERE.

Related Posts:
Necho Crater (August 22, 2009)
A molten flood (July 28, 2010)
Necho's terraces (August 31, 2010)
Impact melt at Necho crater (September 1, 2010)
The jumbled floor of Necho crater (September 2, 2010)
Impact melt in Anaxagoras crater (May 31, 2011)
LROC: Jackson Waves, (August 10, 2011)
Scalelike Impact Melts (April 19, 2012)

The jumbled floor of Necho

The chaotic floor of Necho crater attests to a dynamic environment immediately after the impact event. LROC Narrow Angle Camera (NAC) observation M115502787RE, LRO orbit 2155, December 15, 2009; alt. 59.85 km, resolution = 0.96, field of view width = 960 meters [NASA/GSFC/Arizona State University].

Brett Denevi
LROC News System

Wide Angle Camera monochrome full image of the 30 km far side crater Necho, 490 km northeast of Tsiolkovskiy (5°N, 123.1°E); arrow indicates approximate location of NAC detail above. LROC WAC observation M119048299ME; LRO orbit 2677, January 25, 2010; alt. 56.44 km [NASA/GSFC/Arizona State University].

Curious as to what's in the shadows? A more drastic stretch of the image can help.

A look into the shadows - close-up of the same NAC scene above, but "harshly stretched" to highlight shadowed terrain where boulders litter a dark slope in shadow, salvaging light scattered by the surrounding crater interior [NASA/GSFC/Arizona State University].

Browse the full-resolution image of Necho's interior here!

Stepping back to view the full width of the NAC frame, shows the interior of Necho exhibits a rich geologically-complex morphology, debris and melt deposits with substantial ponding. (NAC M115502787RE; field of view width = 2.4 km) [NASA/GSFC/Arizona State University].

Related posts:
Impact Melt at Necho Crater
September 1, 2010
Necho's terraces
August 31, 2010
A molten flood
July 29, 2010

Impact Melt at Necho Crater

Impact melt, eastward of Necho (5°N, 123.1° E) that once flowed from the rim for a brief time after the crater's relatively recent Copernican Age formation. Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) observation M134374642R, LRO orbit 4936, July 21, 2010; Full Resolution 62 centimeters per pixel, field of view = 620 meters [NASA/GSFC/Arizona State University].

Brett Denevi
LROC News System

This region of impact melt was highlighted in a past featured image, but just a few weeks ago it was imaged again with the LROC NAC, revealing impact melt flows that extend further to the east than previously seen.

A wider view of the broad flows of impact melt east of Necho. From mosaic of both the left and right frames of LROC NAC observation M134374642; Full-sized field of view = 6.2 km. [NASA/GSFC/Arizona State University].

Explore Necho's impact melt flows in the full resolution LROC NAC image!

Closer, again, with west at top, for a look at the mix of shocked terrain, ejecta and the down-grade flow of impact melt [NASA/GSFC/Arizona State University].

Related posts:
Necho Crater
July 29, 2010
Necho's Terraces
August 31, 2010

Necho's Terraces

Closeup view of the spectacular western terrace of Necho crater. LROC Narrow Angle Camera observation M134388215R, field of view is 660 meters; LRO orbit 4938, July 21, 2010 [NASA/GSFC/Arizona State University].

Brett Denevi
LROC News System

Necho is a Copernican Age 30-km complex crater in the far side highlands (5°S, 123°E). Necho displays beautiful terraced walls formed as a large section of the wall slumped into the crater interior shortly after the impact event.

Reduced resolution NAC mosaic of images M134388215L and R [NASA/GSFC/Arizona State University].

Terraces are typical for craters of this size, though in Necho's case the terraces formed only on the western side.

LROC Wide Angle Camera (WAC) monochrome image of Necho (30 km in diameter) showing the location of the NAC mosaic above. LROC WAC M119048299M [NASA/GSFC/Arizona State University].

What's causing this asymmetry?

It appears that Necho formed on the rim of an older, highly degraded crater. The western half of Necho formed rather normally but the eastern half was affected by this preexisting topography.

The walls on that side were lower, allowing huge flows of impact melt to spill from the crater as seen in the past Featured Image, July 29, 2010 (highlighted again in tomorrow's image.

Necho's serendipitous formation at this site resulted in an extra-beautiful lunar crater. Discover the beauty of Necho's terraces for yourself in the full LROC NAC mosaic.

Related posts: Necho Crater

A molten flood

A flood of impact melt swept away from the rim of Necho crater (5°N, 123.1°E). LROC Narrow Angle Camera observation M119041553, LRO orbit 2676, January 25, 2010; resolution 0.56 m/p, above field of view = 540 meters (see full image HERE) [NASA/GSFC/Arizona State University].

Brett Denevi
LROC News System

Large impacts are catastrophic events for the local area. Besides the huge craters they leave behind (this one is 30 km or 19 miles across), impacts heat portions of the crust to such high temperatures that rocks melt and flow like lava, as seen in today's featured image. These melts run downhill, cool and solidify, leaving behind beautiful flow features also highlighted in several past featured images.

A reduced resolution view of the impact melt outside the eastern rim of Necho, from a mosaic of M119041553L/R; field of view = 5.3 km [NASA/GSFC/Arizona State University].

The scene above is a wider view outside the eastern rim of Necho crater (the detailed view in the first image is in the upper left corner here). Almost everything you see is coated in impact melt, which flowed from the crater, moving boulders along with it and ponding in small topographic lows, which now look like smooth, frozen lakes. What a sight this must have been shortly after the crater formed!

A Wide Angle Camera (WAC) monochrome view of 30km Necho. The impact melt is concentrated outside the northeastern rim, approximate location of the NAC detailed views is indicated by arrow. Image M119048299M [NASA/GSFC/Arizona State University].

Impact melts play a key role in our understanding of when things happened on the Moon. As rock is melted and then cools and reforms, its internal radiometric clock is reset. By collecting a sample of impact melt scientists can very accurately determine when that crater formed. Since crater rays run out long distances we can determine the relative ages of rays, material that underlies rays, and rays that cross other rays. By sampling a few key craters scientists could easily unravel the absolute chronology of some key events on the Moon over the past billion years - a time not well sampled during the Apollo years. Sample return missions are a high priority for lunar exploration, and absolute age dating is only one of the many reasons why!

How many impact melt features can you see in the full NAC image of Necho?

From Lunar Pioneer 4

Necho Crater

Blasted Heath - The cracked impact melt sheet on the floor of 30 km wide Copernian Age (>100 million years before present) Necho Crater (123.0°E, 4.9°S LO I-136-M) on the Moon's far side, in this thumbnail from the Narrow Angle Camera (NAC) of the Lunar Reconnaissance Orbiter (LRO); full image 1000 pixel width=1.04 km [NASA/GSFC/Arizona State University].

Brent Gerry LRO News System

"The bright rays of the crater and lack of superimposed impacts is evidence that Necho is a young, fresh crater. Similar to other young impact craters the floor is flooded with massive amounts impact melt. Impact melt is instant lava, lunar rock melted in an instant as the tremendous energy of impact is released.The melt pools in the bottom of the crater,perches on terraces and flows down the flanks. Often times distinct flows can be found that look just like lava flows found on Earth. This portion of the NAC frame (above) shows cracks, 10 to 15 m wide, within the impact melt on the crater floor which formed as the melt cooled and the crater floor was readjusting. Scroll around in the whole image and see how many impact melt features you can find.

LROC NAC Image M103703826LE: Uncalibrated data; north is up
Explore a full Apollo metric frame (AS17-M-1142) of Necho Crater.
Read a research article by Gifford et al. (1979) on the geology of Necho Crater.