J. J. Rennilson1 and D. R. Criswell2
(1)  Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, Calif., USA
(2)  The Lunar Science Institute, Houston, Tex., USA

Received: 13 August 1973 
Abstract  Each of the Surveyor 7, 6, and 5 spacecraft observed a line of light along its western lunar horizon following local sunset. It has been suggested that this horizon-glow (HG) is sunlight, which is forward-scattered by dust grains (~ 10µ in diam, ~ 50 grains cm–2) present in a tenuous cloud formed temporarily (lap 3 h duration) just above sharp sunlight/shadow boundaries in the terminator zone. Electrically charged grains could be levitated into the cloud by intense electrostatic fields (> 500 V cm–1) extending across the sunlight/shadow boundaries. Detailed analysis of the HG absolute luminance, temporal decay, and morphology confirm the cloud model. The levitation mechanism must eject 107 more particles per unit time into the cloud than could micro meteorites. Electrostatic transport is probably the dominant local transport mechanism of lunar surface fines.
This work was supported in part by the California Institute of Technology under Grant NGR 05-002-158, and in part by the Lunar Science Institute, which is operated by the Universities Space Research Association under Contract No. NSR-09-051-001 with the National Aeronautics and Space Administration. This paper is Lunar Science Institute Contribution No. 163.

Surveyor Observations of Lunar Horizon-Glow

Organization  NASA
Major contractors  Hughes Aircraft
Mission type  Lander
Launch date  January 7, 1968 at 06:30:00 UTC
Launch vehicle  Atlas-Centaur
Mission duration  65 hours
Decay  Landed on moon January 10, 1968, 01:05:36 UTC at 41.01° S 348.59° E
NSSDC ID  1968-001A
Mass  305.7 kg after landing

Surveyor 7 was the seventh and last lunar lander of the Surveyor program that explored the Moon.

    * Launched January 7, 1968; landed January 10, 1968
    * Weight on landing: 305.7 kg (674.0 lb)

A total of 21,091 pictures were transmitted to Earth.

Surveyor 7 was the fifth and final spacecraft of the Surveyor series to achieve a lunar soft landing. The objectives for this mission were to: perform a lunar soft landing (in an area well removed from the maria to provide a type of terrain photography and lunar sample significantly different from those of other surveyor missions);  obtain postlanding tv pictures; determine the relative abundances of chemical elements;  manipulate the lunar material; (5) obtain touchdown dynamics data; and, obtain thermal and radar reflectivity data. This spacecraft was similar in design to the previous Surveyors, but it carried more scientific equipment including a television camera with polarizing filters, a surface sampler, bar magnets on two footpads, two horseshoe magnets on the surface scoop, and auxiliary mirrors. Of the auxiliary mirrors, three were used to observe areas below the spacecraft, one to provide stereoscopic views of the surface sampler area, and seven to show lunar material deposited on the spacecraft. The spacecraft landed on the lunar surface on January 10, 1968, on the outer rim of the crater Tycho. Operations of the spacecraft began shortly after the soft landing and were terminated on January 26, 1968, 80 hours after sunset. Operations on the second lunar day occurred from February 12 to 21, 1968. The mission objectives were fully satisfied by the spacecraft operations.

The spacecraft landed near the large lunar crater Tycho, named for the famous astronomer. This crater is visible to the naked eye from Earth with luminous rays of impact ejected material emanating radially from it. Surveyor 7 was the final spacecraft in the Surveyor program. It landed perfectly, less than two miles (3 km) from the navigational target. The alpha backscattering instrument failed to deploy properly. Mission controllers successfully used the surface soil sampler claw to push the alpha backscattering instrument into the proper position to conduct its experiments. Battery damage was suffered in the first lunar night and transmission contact was subsequently sporadic. The spacecraft was last in contact on 20 February 1968.

Surveyor 7 was the first probe to detect the faint glow on the lunar horizon after dark that is now thought to be light reflected from electrostatically levitated moon dust.

Wikipedia - Surveyor 7

Tycho Crater Rim, January 1968

Surveyor 7 landed in the lunar highlands, near the north rim of the crater Tycho, at 40.86 S, Longitude 348.53 E. Scientists used the scoop on the spacecraft to weigh lunar rocks, based on how much current was needed to lift each rock. Images sent back from the spacecraft indicated, for the first time, that some of the lunar rocks had been molten at some time in their history. This panorama was scanned from a photographic print of a hand-assembled mosaic, then digitally reconstructed and cleaned of visual defects by Philip Stooke.

Surveyor 7

Successful lunar lander (USA)
Launched: Jan. 7, 1968
Lunar landing: January 9, 1968
Surveyor 7 landed in the lunar highlands near the crater Tycho. Scientists used the scoop on the spacecraft to "weigh" lunar rocks, based on how much current was needed to lift each rock. Images sent back from the spacecraft indicated, for the first time, that some of the lunar rocks had been molten at some time in their history. The mission was successfully completed on February 21, 1968.  

The Planetary Society: Missions to the Moon