This summer marks 50 years since NASA dispatched the Apollo 16 astronauts to Sudbury for field training ahead of their trip to the moon.
Commander John Young and pilot Charles Duke, whose spacecraft would launch from Cape Canaveral less than a year later on April 16, 1972, teamed up with experts from Inco to study Sudbury’s impact crater and its unique geological structures.
NASA hoped that the field training, which took place from July 7 to 9, 1971, would prepare the astronauts for lunar surface experiments.
It turns out, the excursion didn’t prepare them as much as they’d hoped.
“We were very interested, at the time, in trying to work up the geology of the moon. The great debate in the literature prior to our first moon landing was how much of the moon was formed by volcanic activity and how much of it was formed by impact structures,” said Michael Dence.
“That’s a question that goes back 400 years to Galileo. There was a lot of literature about that. That was the reason, in a sense, for my being employed by the government. There was this question of whether anything on Earth resembles the moon, and if so, how we could identify it.”
Dence, who is now considered an international expert in the subject, was one of the pioneers in the study of asteroid impact craters like the one in Sudbury.
He helped build what was called the Earth Physics branch of the Department of Energy, Mines, and Resources (now Natural Resources Canada) to study impact structures on Earth.
When Dence first immigrated to Canada from Australia, he worked as a field geologist for Falconbridge Nickel Mines (now Glencore) in Sudbury. He was also part of the team of geologists who worked with the Apollo 16 crew.
“One of the biggest things to emphasize is that, regardless of their backgrounds, the astronauts got very little out of this training except for maybe an excursion or a break from their routines,” said Dence.
“Because it turns out that the moon is covered with dust which has been building up for three billion years, so the idea of seeing fresh rock or any sort of rock was never really discovered by any of them.”
By the time of the Apollo excursions in the 1970s, Dence said that it was well-established that the Sudbury structure is “the deeply eroded remnants of an impact” that is roughly 1.84 billion years old.
“The rocks that are displayed on the surface are a good cross-section of many of the details of what an impact structure looks like, and it had the convenience of being easy to get at,” he said.
“You could walk around and see what we were talking about. That never applied on the moon, but nonetheless, it gave them an education in what a large, ancient impact can look like.”
As part of his research, Dence was studying the distinctive features of impacts that left imprints on the rocks that could be mainly identified under a microscope.
When astronauts retrieved lunar samples, these same features, described as very distinctive structures where the crystal structure had been partly obliterated by the shock of the impact, were identifiable.
“The one thing in Sudbury, which led to the recognition of it being an impact structure, was a peculiar thing that could be observed in the rocks. These fractures, which we call shatter cones, are sort of conical-shaped structures which appear on the surface of rocks when they are properly exposed,” he said.
It was the discovery of shatter cones in Sudbury by an oceanographer named Robert Dietz that led to it being declared an impact crater.
“He made a sort of hobby of looking for shatter cone structures around the world, and he had been successful in suggesting to the South Africans that a very large structure known as the Vredefort crater was the result of an impact,” he said.
“A year or two later, he decided to look at Sudbury. He went there and talked to the locals. Rocks that people had walked over for 70 years of geologists working in Sudbury, and they never recognized the existence of shatter cones. Once their eyes were tuned in to what to look for, it took only a week.”
The point of an impact, said Dence, is that it generates an immensely strong pulse of energy. The pressure is comparable to that of the centre of the Earth.
It lasts but a second or two, but it’s enough to melt rock at the highest temperatures and to develop these peculiar structures.
“The thing about the melting aspect of it is you have the outline of the Sudbury structure and in the rock, it has an igneous texture. It has the texture of a lava,” he said.
“That outlines the entire structure of Sudbury. That is entirely caused by the impact pressure being at a melting point, at the time. In other words, the projectile, which in this case was probably 15 km or so across, melted tens of thousands of cubic kilometres of rock in an instant.”
Of his experience working with the Apollo 16 crew, Dence said it was a pleasant experience and the crew members were “real characters.”
“Young was a very straightforward, outspoken sort of guy. He told me he had no liking at all for the official drink of astronauts – Tang,” he said.
“He really didn’t relish the idea of having to drink Tang for a week. He was also a really good astronaut. I certainly enjoyed the time I had with them, and I certainly could see their dedication.”
Dence and the Apollo 16 crew – and later the Apollo 17 crew that came up north a year later – were ultimately lucky to have had the chance to explore the Sudbury impact crater as it was in the 1970s.
“Most of that area has now been overgrown very considerably. It is now woods, and it’s very difficult to work out exactly where we went with the astronauts,” he said.
“The rehabilitation of the Sudbury landscape has gone that far – after 50 years, most of it is lost in the woods.”
The Local Journalism Initiative is made possible through funding from the federal government.
Colleen Romaniuk, Local Journalism Initiative Reporter, The Sudbury Star