YM COLUMN ARCHIVE

December 3, 2008

At the time of Ranger 7

Three spacecrafts, KAGUYA of Japan, Chang-e of China and Chandrayaan of India, are now going around the moon. New era of lunar exploration has begun. Particularly, KAGUYA is sending abundant detailed data so as to be renewing lunar science. As we look back at past, however, lunar exploration of mankind was succession of difficulties. In the earlier stage, rockets just couldn’t get to the moon.

Of course in earlier years, the countries to have aimed at moon were just two, USA and USSR. Especially, American challenge faced utmost difficulties of 14 failures in a row after the first trouble of explosion in the first stage rocket of lunar explorer Pioneer in 1958 until Ranger 7 in July of 1964. Among those attempts of lunar exploration, partly successful so to say were only Pioneer 4 (first artificial planet not fulfilling the intended objective, though) in 1959 and Ranger 6 in 1964. It’s rather strange for American people not to have claimed against those failures, but in a sense it might have meant heated hard competition of space race between USA and USSR at that time.

Ranger 7 weighted 366kg that was launched by Atlas-Agena Rocket on July 28, 1964 clashed into Mare Nubium (Sea of Clouds), but kept taking pictures while descending until the moment of collision and succeeded in transmitting 4,316 images to the earth. Two kinds of camera were used: one was a wide angle camera with view angle 25 degrees, aperture 25 milli and aperture ratio 1 while the other was view angle 8, aperture 75 milli and aperture ratio 2. As the images were taken from fast moving probe of 1.6km/sec, exposure time was set at 1/200 seconds ~ 1/500.

I would like you to look at the typical one. The image is Mare Nubium taken from 1,335km high.

http://master.redorbit.com/images/gallery/the_moon/guericke_
crater_as_ seen_ by_ ranger_7/16/10/index.html

Up is north and right is east. The sun was at 23 degrees high in western sky. Whole area is equivalent to the Kanto Plain and you can see the crater named “Guericke” in there. What appears whitish is land and dark is lowland areas called “sea”. With this picture in front of me, my imagination was expanding for a university student that I was then. The memory is so dear to my heart.

It is very interesting to let primary and middle school pupils to exchange their opinions by just showing them this image. What do you make out of this image? First of all, let us pay attention to Guericke Crater. Crater is usually, like a volcano outer rim on earth, is surrounded by lofty walls, but the walls of the crater in the image is washed away by some dark materials toward east and north so that north-eastern part of the crater looks like dark sea. To the west of crater located west-southwest of Guericke looks like sea materials are flowing in, and new small craters can be seen in Guericke, which could be understood some small matters might have collided in there after formation of Guericke.

Western part of Guericke is whitish upthrust landscape where are scattered many small craters. If small craters were made from collisions with lunar surface at constant rate every year, land area with more craters can be said older than the one with less. Why so is because there is no erosion or weathering by water or air on moon so that craters would have never disappeared.

All of this means that the upthrust landscape around Guericke Crater was already there before the sea was formed, and it can be presumed that washing away of walls at the north-east took place just at the time of sea formation. Small craters in the sea must have been made in there after the sea was formed. Children discuss this problem on the hints carefully given piece by piece from just one sheet of picture such as how three different landscapes of different ages, Guericke Crater, sea and land, were historically formed by what order. There is a class lesson to presume the ages from the hints how strata had been layered up, and so this kind of discussion could be good practical exercises.

I shall be very happy if you would kindly produce such teaching materials for educational training out of many images KAGUYA has sent to us. I would like to make such steady efforts together with you from all over Japan. I hope to be given full support of yours.

I welcome your opinions on this column to the following E-mail address.
matogawa@planetary.or.jp

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