Thursday, April 3, 2014

A Small Clearing on the hazardous floor of Tycho

Mound littered with boulders on the floor of Tycho features a rare clearing, in the midst of the general rubble, of relatively low slope. The mound, east of the landmark nearside crater's spectacular central peaks, likely formed from squeezed up impact melt. LROC NAC observation M1144856403R, LRO orbit 20751, January 20, 2014, field of view 730 meters wide; illumination incidence angle 57.92° at 72 cm per pixel resolution from 59.2 km [NASA/GSFC/Arizona State University].
Raquel Nuno
LROC News System

Tycho is one of the most spectacular craters on the Moon. If you've never done so, next time you get access to a pair of binoculars and the Moon is near full, look at the Moon's southern hemisphere: you will see a very bright crater with spectacular rays emanating from it. That's Tycho!

It formed when an asteroid (or comet), going at roughly 20 km/s, hurled into the Moon around 109 million years ago. That age may seem old to you and me, but by lunar standards, that's young.

We think we sampled impact melt that originated from Tycho at the Apollo 17 landing site, but we can also tell it's young just by looking at it: it has a crisp morphology and its rays are seen as high reflectance streaks. With time, exposure to the space environment will fade the rays and erode the crater's sharp features into smooth curves.

Small mound with clearing, east of the more spectacular central peaks of Tycho, in the context of a wider cropped, 3 km-wide field of view from LROC NAC observation M1144856403R {NSA/GSFC/Arizona State University].
During an impact event, almost all of an impactor's kinetic energy gets deposited as internal energy into the target rock. The near-surface layers of the shock melted rock begin cooling relatively quickly, creating a hardened crust lining the crater floor. The subsurface melt, however, can take up to ~500,000 years to cool. This post-impact thermal structure sculpts the floor of many lunar impact craters.

LROC Wide Angle Camera (WAC) mosaic, context for the footprint of LROC NAC observation M1144856403L & R (blue rectangle), showing the 3 km crop and location of the clearing. LROC WAC monochrome (643 nm) mosaic of seven sequential passes over the region, February 21, 2011; rough incidence angle 57.78° at 63.4 meters resolution from 46.25 km; field of view roughly 36.8 km across [NASA/GSFC/Arizona State University].
Today's Featured Image is a ledge of a mound on the floor of Tycho crater. The mound is littered with meter-sized boulders, except for this smooth portion on this western ledge. Why is this portion so smooth? The two apparently identical looking 44 meter craters that dot the smooth region probably did not have enough energy to push the boulders aside, and they most likely did not excavate enough material to cover the boulders. The answer may be that still molten rock extruded from beneath the cooled crust, oozing onto the surface, leaving the boulders just out of sight.

Tycho (85.29 km, 43.295°S, 348.784°E) in a roughly 117 km-wide field of view from seven sequential LROC WAC monochrome (643 nm) observations from over the region on February 21, 2011; incidence angle 57.8°, about 63.4 meters resolution from 46.25 km [NASA/GSFC/Arizona State University].
Can you find other examples of effusive events and melt squeeze ups in the full resolution NAC? Hint: look along the floor fractures, HERE.

Related Posts:
Fractured melt rock on Jackson's terraced wall (October 22, 2013)
Melted Moon (July 31, 2013)
Landing Site at Tycho North (Science Concept 7) (March 20, 2013)
Rippled Pond on Tycho's Wall (September 13, 2012)
Breached Levee at Tycho (September 11, 2012)
America's last unmanned lunar lander (September 7, 2012)
Giant Flow of Impact Melt (August 14, 2012)
River of Rock (June 20, 2012)
View from the Other Side (May 21, 2012)
Impact Melt Fingers (May 8, 2012)
Melt on a Rim (May 3, 2012)
Jackson's Complexity (January 20, 2012)
Tycho's flash-frozen inferno (November 2, 2011)
Ejecta on slumped wall of Tycho (December 9, 2010)

When the Moon is full, Tycho's bright ray system is among the few lunar features visible to the naked eye. A testimony to its youth, a low degree of steady space weathering when compared to hundreds of similar but older crater,s from before the time when dinosaurs ruled the earth. The "miracle boys of Minsk" (Astronominsk) captured this local late morning image of Tycho, part of a full disk monochrome mosaic, captured from Belarus, September 20, 2010.  One of their fabulous color images of Тихо can be viewed HERE Above originally posted to illustrate "Landing Site at Tycho North (Science Concept 7), March 20, 2013 [Astronominsk].

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