 |
| What may be a newly resolved "pit crater," similar to at least three other unique features found elsewhere on the Moon. This one is near the equator in Mare Fecunditatus (0.92°S, 48.66°E). The nearly circular 110 meter-wide opening may or may not narrow in diameter further into its interior. LROC Narrow Angle Camera (NAC) observation M1107960917R, (at 180%) LRO orbit 11562, November 19, 2012; angle of incidence 62.93° from 108 km [NASA/GSFC/Arizona State University]. |
Lunar Pioneer
It’s time to inventory the Moon’s “pit craters.” The first, the "Haruyama," or "Marius Hills pit crater" (
14.065°N, 303.224°E) is in a sinuous rille immediately west of the famous shield volcano range in Oceanus Procellarum.
A second and third have now been found and photographed from many angles, in Mare Tranquilitatis (
8.34°N, 33.22°E) and Mare Ingenii (
35.95°S, 166.06°E), respectively.
It appears the LROC team at Arizona State University uncovered another, over the past year, out on the vast equatorial plains of Mare Fecunditatis (
0.92°S, 48.66°E).
This is remarkable for a number of reasons, not least among them the mission’s elapsed time. As of this writing LRO has completed 17,801 orbits around the Moon. Without knowing the exact percentage of the lunar surface yet to be photographed by the LROC Narrow Angle Cameras – it’s remarkable a 110 meter wide target could have been missed until relatively recently.
That is it might
seem remarkable, until we consider some basic “beta angles,” so to speak, some basic mission priorities and logistics.
 |
| Location of a possible pit crater in a 155 km-wide field of view of northwest Mare Fecunditatis. LROC QuickMap 250 meter per pixel resolution [NASA/GSFC/Arizona State University]. |
The target is within a single degree south of the equator. Obviously a spacecraft in polar orbit is going to see its orbital pathways and targeting opportunities converge directly over the poles, conversely those same opportunities will be at their greatest distance apart at the equator.
 |
| A closer look through one particularly fine set of LROC Wide Angle Camera passes over target (arrow), the feature is just visible in this imperfectly merged monochrome (604 nm) WAC mosaic swept up during three sequential orbital passes; from 47.4 km altitude. Resolution roughly 55 meters, 63° angle of incidence; field of view a little over 40 km, from west to east [NASA/GSFC/Arizona State University]. |
Secondly, this has got to be one of the Moon’s great “
Rub’ al khali's,” an empty quarter, which must have seemed nearly void of inviting targets, with very inviting targets nearby, particularly to the west, where the fascinating Messier and Messier A craters reside. The east rim of Messier B is only a little over 20 kilometers directly to the west. The desire, even the need, to slew the spacecraft and camera’s off nadir to examine these and other nearby targets is reason enough for the pit to have been overlooked.
Then there’s the target itself, which brightens considerably between a 30° and 0° angle of incidence. Under the highest sun, near noon, and again, very near the equator, the target looks like what it may in fact be: an unusual but still rather commonplace nearly fresh crater.
It proves, yet again, that there are still great new discoveries yet to be made on the Moon.
 |
| Raw rendition of the LROC NAC observation which may have touched off further interest in a new "target of opportunity," in the months that followed. The pit crater in Mare Fecunditatis shows up on the very edge of this frame from orbit 13087, April 28, 2012. LROC NAC M190280022L, 62.93° angle of incidence, 1.09 meters resolution from 108.01 km [NASA/GSFC/Arizona State University]. |
Having to guess just what drew their interest, the target seems to have been photographed at high resolution April 28, 2012, in orbit 13087. Amazingly, the pit was nearly missed. You can see the north half of the target at the very top of LROC Observation M190280022L,
HERE.
By last fall it seems the pit was directly targeted under three lighting conditions, the first, last September, must have seemed disappointing. With the Sun only five degrees from directly overhead what little topography might be seen on target and in the region may have seemed washed out in shadowless albedo contrasts. If this was a pit crater the “ledge,” if any, was not overshadowing.
 |
| First full close-up released to the PDS shows a brightly lit interior, and little to no depth. But the Sun was high, and the location less than a degree south of the equator. LROC NAC M1103245601L, orbit 14902, September 25, 2012, angle of incidence 7.765° at 0.94 meters resolution, from 108.88 km [NASA/GSFC/Arizona State University]. |
 |
| A month later the Sun was a little more favorable. LROC NAC M1105602888L, orbit 15232, October 23, 2012; angle of incidence 35.18° at 0.93 meters resolution from 108.28 km [NASA/GSFC/Arizona State University]. |
 |
| After yet another month, the mid-morning Sun is at an even greater angle. Shown at its original resolution, this is the image at the top of the post. LROC NAC M1107960917R, orbit 15562, November 19, 2012; angle of incidence 62.93° at 1.1 meters resolution, from 108.01 km [NASA/GSFC/Arizona State University]. |
Related Posts:
Impact melt collapse pit (March 2, 2012)
Failed Skylights of Copernicus (January 24, 2012)
New view of Sinas pit crater (November 11, 2011)
Sublunarean Void (February 7, 2011)
New views of lunar pits (September 14, 2010)
How common are mare pit craters? (July 15, 2010)
