I’ll See You on the Far Side of the Moon
The Soviets got to the far side of the Moon first, and the mystery they found remains.
Ponder something for a moment. Most of humanity, people living today and those who died over the last hundred thousand years, have never seen the far side of the Moon with their own eyes. In fact, before October 7, 1959, no human had ever seen the other side of the Moon, even in photographs.
Last week marked the 55th anniversary of the first photographs of the lunar far side, taken by the Luna 3 probe. Today we’re spoiled by the ubiquity of beautiful images from any number of spaceships exploring the Solar System, but in 1959, the entire field of space exploration was very new. The Soviet Union had only launched the first Sputniks two years before, with the United States’ Explorers following the next year.
The first photos from the far side of the Moon are singularly unimpressive to modern eyes. They are grainy, low-resolution black-and-white pictures, more scruff than science. However, when you realize how difficult it was to take those photos in 1959 and how new the images were to audiences on Earth, they become more moving. And not least, they were the first glimpse at a Moon mystery we still haven’t fully solved: Why is the far side so different from the side we see from Earth?
The Moon is “tidally-locked” to Earth: It always presents the same face to us. As a result, humanity can never see the other side of the Moon without going into space. The side we see contains the patterns of lighter and darker patches that form the “man in the Moon”, or “rabbit and tree”, or whatever shape your cultural heritage prefers. (I personally have never thought it looked like a face.)
Through even a small telescope or binoculars, you can see many of those patterns turning into mountains, craters, and darker regions known as “mares.” While the name means “seas” in Latin, the mares (pronounced “MAR-ays”) are solidified lava, the result of Moon volcanoes that flooded the surface in the past.
It’s a reasonable guess that the far side would be the same, but it’s not. As first seen by Luna 3 and confirmed by later missions, the far side of the Moon is more heavily cratered and almost completely without mares. Those two facts are likely related, if the volcanoes wiped out older craters on the near side, but why the terrain is so different is something we still don’t completely understand.
That’s the context of the Luna 3 photos from 1959. This was the third Soviet Moon probe, preceded by Luna 1, which failed and missed the Moon entirely, and Luna 2, which successfully crashed on the Moon’s surface. (A successful crash is not an oxymoron if you planned it!) Luna 3 had a different mission: to loop around the Moon and send pictures back to Earth.
The photographic technology on Luna 3 was simultaneously elaborate and primitive by modern standards. The probe carried a film camera with enough film for 40 pictures, which—since it didn’t carry a human—had to be developed automatically aboard the craft. The film itself was designed to be radiation-tolerant and resistant to high temperatures, since it would be exposed to direct sunlight without any atmosphere to block anything.
The Soviet engineers achieved something remarkable: they designed a mechanical apparatus capable of taking photos, developing and drying the film aboard an unpiloted spacecraft, and then scanning them for transmission. The scanning involved technology developed for television: sweeping a thin beam of light (itself produced by an electron beam) back and forth across the developed film. More light gets through where the film shows bright objects, and a detector converts the amount of light coming through the film into electric current. That in turn can be sent via radio wave back to Earth.
The photos Luna 3 took couldn’t be beamed directly back, but the spacecraft followed a looping orbit that carried it past the Moon and back toward Earth. As it turned out, the probe took 29 photos, of which 17 actually turned out. And again, while they were grainy and dominated by fuzz, they were the first views humanity ever had of the Moon’s far side.
Today, space probes use digital cameras, which are smaller, have fewer moving parts, and of course don’t need to scan the photos for return to Earth, since they’re already in digital form. As a result, the images can be much more detailed and the equipment less subject to mechanical problems. (And later film-camera images were better quality as researchers learned how to streamline the process.)
But the mystery first seen by Luna 3 remains, though we have many clues. Most scientists who study the Moon think it formed when a huge impact in the early Solar System broke a chunk of Earth off. Uneven heating during the Moon’s birth may have resulted in profound differences in the thickness of the crust, and therefore the amount of volcanic activity. Missions like the Gravity Recovery And Interior Laboratory (GRAIL) probes have helped by showing the difference between near and far sides go beneath the surface. So, think of those fuzzy, terrible pictures of the Moon’s far side as the beginning of the modern study of our closest celestial companion, and appreciate them.