Wednesday, July 6, 2011

LOLA: Steepness of the Moon's polar slopes

The steepness of elevation changes, or slopes, in degrees rather than relative elevation heights, themselves are seen above north of the 75th parallel, as determined through millions of laser altimeter samples gathered in thousands of orbits of LRO since 2009 [NASA/GSFC].

The Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO) sends laser pulses down to the surface of the Moon from the orbiting spacecraft. These pulses bounce off of the Moon and return to LRO, providing scientists with measurements of the distance from the spacecraft to the lunar surface. As LRO orbits the Moon, LOLA measures the shape of the lunar surface, which includes information about the Moon's surface elevations and slopes.

LOLA's laser pulse is split into 5 separate beams that hit the lunar surface in a cross-shaped pattern. The reflected pulses from these beams provide 5 parallel profiles along the surface directly beneath LRO. This pattern allows scientists to calculate slopes on the surface of the Moon in a variety of directions on scales of approximately 25 meters.

This image shows the slopes found near the north pole of the Moon, poleward of 75 degrees North. The bright red to white areas have the highest slopes (25 degrees or more) while the dark blue to purple areas have the lowest slopes (5 degrees or less). The steepest slopes are found in impact crater rims, which appear as brightly colored circular features throughout the image.

References: [1] Smith, D. E., et al., 2010. The Lunar Orbiter Laser Altimeter Investigation on the Lunar Reconnaissance Orbiter Mission. Space Sci. Rev. 150: 209-241. [2] Rosenburg, M. A., et al., 2011. Global surface slopes and roughness of the Moon from the Lunar Orbiter Laser Altimeter. J. Geophys. Res., 116, E2, E02001.

>> small (South Pole) | large (South Pole) | high-res (North Pole) [PDF]

LOLA slope determinations in the vicinity of the lunar South Pole include sanctuaries of permanent shadow noted in the LROC Wide Angle Camera Global Mosaic at the bottom. Shackleton (1.) has a steeper inner rim to floor ratio than most simple craters nearby. The LCROSS impact in Cabeus (2.) seems surprisingly free of steeper inclinations at the resolution determined above, and Malapert Massif (3.) has wider slopes on its Earth-facing side (up) than its opposite side, facing south [NASA/GSFC/Arizona State University].

No comments: