November 8, 2020 - Meteor Crater, Arizona
Meteor Crater is considered the most famous impact site on Earth.
From the brochure: "50,000 years ago, out of the northeastern sky, a pinpoint of light grew rapidly into a brilliant meteor. This body was probably broken from the core of an asteroid during an ancient collision in the main asteroid belt some half billion years ago. Hurtling at about 26,000 miles per hour -- that's 7.2 miles per second -- it was on an intercept course with Earth. In seconds, it passed through our atmosphere with almost no loss of velocity or mass.
A huge-iron-nickel meteorite or dense cluster of meteorites, estimated at 150 feet across and weighing several hundred thousand tons, struck the desert with an explosive force greater than 20 million tons of TNT.
The result was a crater over 4,000 feet across, 2.4 miles in circumference and 550 feet deep. 20 football games could be played simultaneously on the crater floor with 2 million spectators around the sloping sides.
"The story begins in the early 1950s when a bright young geologist named Eugene Shoemaker paid a visit to Meteor Crater. .... By the time Shoemaker came along, a common view was that Meteor Crater had been formed by an underground steam explosion. Shoemaker knew nothing about underground steam explosions -- he couldn't: they don't exist -- but he did know all about blast zones. One of his first jobs out of college was to study explosion rings at the Yucca Flats nuclear test site in Nevada. He concluded, as Barringer had before him, that there was nothing at Meteor crater to suggest volcanic activity, but that there were huge distributions of other stuff that suggested an impact from space. Intrigued, he began to study the subject in his spare time." -- Bill Bryson --A Short History of Nearly Everything
A key discovery was the presence in the crater of the minerals coesite and stishovite, rare forms of silica found only where quartz-bearing rocks have been severely shocked by an instantaneous overpressure. It cannot be created by volcanic action; the only known mechanisms of creating it are naturally through an impact event, or artificially through a nuclear explosion. In 1960, Edward C. T. Chao and Shoemaker identified coesite at Meteor Crater.
But this was only the beginning for Shoemaker. "Working first with his colleague Eleanor Helin and later with his wife, Carolyn, and associate David Levy, Shoemaker began a systematic survey of the inner solar system. They spent one week each month at the Palomar Observatory in California looking for objects, asteroids primarily, whose trajectories carried them across Earth's orbit. ... What Shoemaker and his colleagues found was that there was more risk out there -- a great deal more -- than anyone had ever imagined." -- Bill Bryson
As if that wasn't enough, in 1993 the Shoemakers and David Levy discovered Comet Shoemaker-Levy 9 which was on a trajectory to impact planet Jupiter. "For the first time, humans would be able to witness a cosmic collision -- and witness it very well thanks to the new Hubble space telescope. ... The impacts began on July 16, 1994, went on for a week and were bigger by far than anyone -- with the possible exception of Gene Shoemaker -- expected." -- Bill Bryson. This was proof that a meteor collision could create the Chicxulub Crater at the top of the Yucatan Peninsula in Mexico and cause the extinction of the dinosaurs 66 million years ago.
Surprisingly, Shoemaker's genius was recognized. He was involved in the training of the American astronauts and was a CBS News television commentator on the early Apollo missions, especially the Apollo 8 and Apollo 11 missions, appearing with Walter Cronkite during live coverage of those flights. He himself was a possible candidate for an Apollo Moon flight.
Shoemaker spent much of his later years searching for and finding several previously unnoticed or undiscovered impact craters around the world. He died on July 18, 1997 during one such expedition in a head-on car collision on the remote Tanami Track, a few hundred kilometers northwest of Alice Springs, Australia.
On July 31, 1999, some of his ashes were carried to the Moon by the Lunar Prospector space probe. Shoemaker is the only person whose remains have been placed on any celestial body outside Earth. The brass foil wrapping of Shoemaker's memorial capsule is inscribed with images of Comet Hale–Bopp ("the last comet that the Shoemakers observed together"), the Barringer Meteor Crater, and a quotation from Shakespeare's Romeo and Juliet reading:
And, when he shall die
Take him and cut him out in little stars
And he will make the face of heaven so fine
That all the world will be in love with night
And pay no worship to the garish sun.
