Tuesday, April 24, 2012

LROC: Orion, Up Close

40 years parked on the Cayley plain northwest of the Descartes formation.
The second of two narrow periapsis orbital passes afforded the LROC team an opportunity to capture this astounding view of the Apollo 16 landing site, orbit 10950, November 6, 2011. LROC Narrow Angle Camera (NAC) mosaic M175179080; field of view above = 145 meters. See the 250 meter FOV in the LROC Featured Image, released on the 40th anniversary of the lift-off from the Moon of the Apollo 16 lunar module ascent stage Orion, April 22, 2012, HERE [NASA/GSFC/Arizona State University].

Mark Robinson
Principal Investigator
Lunar Reconnaissance Orbiter Camera
Arizona State University

The Apollo 16 Lunar Module Orion set down on the lunar surface 40 years ago (21 April 1972) after remaining in a holding pattern for six hours while technical issues with the Command Module Casper were resolved.

Here John Young and Charlie Duke undertook the first and only exploration of a highlands site; their main goal was to sample the enigmatic light plains deposits that geologists had interpreted as remnants of a large scale explosive volcanic eruption.

These proposed volcanic rocks were to be very different than the volcanic mare basalts sampled at previous sites (Apollo missions 11, 12, and 15).

Annotated version of the LROC commemorative Featured Image of the Apollo 16 landing site, full image release 250 meters field of view (M175179080) HERE [NASA/GSFC/Arizona State University].
Once Young and Duke started looking at rocks near Orion, it became clear that there were no strange highland volcanic rocks. What they found were breccias, breccias, and more breccias. Why breccias, and how did they form? The Apollo 16 rocks were most similar to those collected by Apollo 14 astronauts Al Shepard and Ed Mitchell. As it turns out, the breccias formed as part of massive flows of ejecta from the Imbrium and Nectaris basin-forming events. Young and Duke were sampling crushed rocks that flowed hundreds of kilometers from their source!

Enlargement of Apollo 16 site, the Lunar Portable Magnetometer (LPM) is in the center of the dark spot below the annotation, the arrow shows Sun glint off an electronics cable, M175179080 [NASA/GSFC/Arizona State University].
Similar to the other Apollo missions, the Apollo 16 crew set up science instruments to measure varied aspects of the Moon and its environment. Most science instruments were part of the Apollo Lunar Surface Experiments Package, or ALSEP. The Apollo 16 crew also carried with them on their geology traverses the Lunar Portable Magnetometer (LPM) that measured variations in the strength of the Moon's weak magnetic field. Some of the ALSEPs (Apollo missions 12, 15, 16) carried a stationary Lunar Surface Magnetometer (LSM) that provided a point measurement for the landing site as a whole.

On April 22, 1972, minutes before the end of their third and final EVA, John Young took this photograph from his vantage over the lunar rover, parked for the final time so it's color television camera, controlled from Houston, could capture the ascent stage lift off. The LPM is just outside the full-size picture (AS16-116-18716) to the right, and the ALSEP site is in the distance on the left. [NASA]. 
Still image from the televised feed, after nearly 21 hours out on the lunar surface, at Mission Elapsed Time (MET) 175 hours, 31 minutes, 49 seconds, Young and Duke lift off in the Orion ascent stage, headed for rendezvous with Tom Mattingly awaiting them in the Command Module, and home [NASA/Apollo 16 Lunar Surface Journal]. 
The LSMs showed that from site-to-site the magnetic field varied by about a factor of fifty, from a low of 6 gammas (Apollo 15) to a high of 313 gammas (Apollo 16). From the LPM station-to-station measurements within the Apollo 16 traverses, the magnetic low was 121 gammas and high the high was 313 gammas; a factor of nearly three over a distance of 7 km.

The Apollo 16 Lunar Portable Magnetometer in its final configuration beside the parked rover. Note lunar sample rock 60335 is  temporarily perched on the magnetometer for calibration purposes. AS16-116-18721 [NASA].
The magnetometer on Lunar Prospector (1998-99) mapped
what may be the most intense crustal magnetism on the Moon
80 kilometers south of the Apollo 16 landing site, associated
with the bright albedo north of ancient Descartes crater
[Richmond, et al., (2003)].

After setting up the LPM, a final experiment was performed by measuring the magnetic field before and while a small rock was perched on the experiment. This experiment returned two important results: a) the local rocks had a remnant magnetic field so weak that the LPM could not detect it, and b) that the LPM was still working as before launch. These results came from the fact that the astronauts brought the sample (60335) back to Earth, and it was measured by an identical LPM as well as well as even more sensitive instruments.

What did these varied magnetic readings tell us about the Moon? The Moon's magnetic field comes from crustal and mantle materials, has no dipole signature, and is very weak. 

This is a magnetic field very different from the dipole field generated in the Earth's core. Right now scientists do not understand the origin of the lunar magnetic field or its variations. Perhaps the signature of an early, but now extinct, dipole field was captured in ancient lunar rocks as they cooled from a magma ocean. 

Perhaps basin-forming impacts induced local fields in the crust. These Apollo area measurements do tell us that the interior of the Moon is heterogeneous and complicated: the Moon is not a simple body. The two GRAIL spacecraft, Ebb and Flow, that are now in orbit about the Moon will provide gravity measurements that geophysicists will use to deepen our understanding of the lunar interior; the Apollo era magnetic readings will be part of that unfolding story.

Find the LPM and the rest of the ALSEP hardware in the full NAC image, HERE.

Previous LROC Apollo 16 Featured Images:
Apollo 16, Footsteps Under High Sun
How Young is Young?
Apollo 16 First Look
Apollo 16 North Ray crater

Young put the Orion ascent stage into a slow roll so Tom Mattingly could photograph the buckled skin of the spacecraft first noticed after the lunar module was retrieved from the SIVB after trans-lunar injection. The damage was made much worse by the force of its lift-off from the Moon. Back in lunar orbit, the distinctive craters Messier and Messier A can be seen at right. AS16-122-19535 [NASA/JSC].
Previous Low Altitude LROC Image Releases:
Apollo 11
Apollo 12
Apollo 14
Apollo 15
Apollo 17, Shorty crater

A fanciful edit of AS16-107-17435, showing how the Orion descent stage may look forty years after the brief, but productive expedition of Apollo 16.

1 comment:

Anonymous said...

How about the mortar experiment in the ASLEP package? Are the mortar impacts visible in LROC images? Has anyone looked for them?