Issue 2, December 2003

COMMENTARY
The Spirit and the Opportunity: Episodes of Science at its Best

Selby Cull, Senior Research Editor, Science Journalist
Planetary Sciences, Hampshire College
cull@jyi.org

Emanuel Swedenborg, the Swedish scholar who mastered every facet of science he could lay his hands on. His vacuum pump would lead to incredible discoveries centuries later. Source: Swedenborg Foundation.

One does not become a biochemist overnight, or a physicist, or an engineer, or a great inventor.

Today, the fields of science are vast, complicated, and so painfully detailed that it might take an entire lifetime of study and devotion to master even one.

There was a time, though — hundreds of years ago, in a world with less data — when a gifted and spirited individual had the opportunity to master many facets of science. Such a thing was never easy, and it required talent, dedication, and the spirit of a true lover of science. Such a spirit can make monumental discoveries — or small ones that grow monumental with time. Emanuel Swedenborg had such a spirit, and just such an opportunity.

The Last of the Universal Scholars

In 18^th-century Europe, a world innocent to the existence of the atom and only barely touched by Newton’s laws, Emanuel Swedenborg mastered every field of science he could lay his hands on: chemistry, engineering, physics, mathematics, mineralogy, geology, paleontology, anatomy, astronomy, metallurgy, cosmology, cosmogony, psychology. In war-torn Sweden, he founded the science of crystallography, localized brain functions 100 years ahead of anatomists, and developed a theory of the formation of the sun and the planets that would take hundreds of years to verify.

Swedenborg was also a spirited inventor, designing machines far ahead of his time. He designed a one-manned submarine, a crude calculator, the lock for raising ships, the jack (now used for raising cars), a new crane, a new air gun, a traction machine, an airtight hot air stove, drawbridges, an ear trumpet for those with deafness, and a machine for raising ore out of mines, to name a few.

One of Swedenborg’s least-recognized designs turned out to have a stunning effect a century later: a new type of vacuum pump. Since the invention of the vacuum pump by Otto von Guericke in 1654, vacuum technology had progressed slowly. The pumps did not produce much of a vacuum, a fact that did not escape Swedenborg. Combining Evangelista Torricelli’s mercury work of nearly a century before with von Guericke’s pump, Swedenborg designed an entirely new type of machine: a mercury vacuum pump.

By replacing von Guericke’s piston with a tube of mercury and alternately increasing and decreasing the volume of the mercury, Swedenborg had designed a vacuum pump that created an excellent vacuum. However, the design, published in 1722, caused little stir.

The Glassblower and the Physicist

Vacuum technology continued to progress slowly through the late 1700s and early 1800s, lacking any opportunity to advance. Then, in 1855, a German glassblower and instrument designer took an interest in Swedenborg’s mercury design. Heinrich Geissler, who preferred building over drawing designs, stumbled upon Swedenborg’s pump design and modified it by connecting the mercury reservoir to a glass bulb via a flexible tube. By attaching a two-way valve to the bulb and alternately raising and lowering the mercury, Geissler created the best vacuum yet invented.

Although a near-vacuum might have been mildly interesting to a glassblower, to a physicist it was a monumental opportunity. Hearing of the invention, the German physicist Johann Hittorf immediately purchased Geissler’s mercury pump for his experiments with electricity.

Hittorf hooked Geissler’s pump up to a primitive Crooke’s tube, a glass tube with two metal plates inside, one connected to the positive side of an electricity supply and one to the negative side. When Faraday had tried this experiment 40 years before with a weak vacuum pump, he had found a small dark space near the negative plate as electric discharges flashed across the tube. Now, in 1869, Hittorf and his excellent vacuum found something even more intriguing. As the amount of air in the Crooke’s tube decreased, the Faraday Dark Space widened to fill the whole tube, and the negative plate emitted rays that made the glass tube glow.

Rays and Radiation

Wilhelm Roentgen, the German physicist who discovered X-rays. Source: Pennsylvania State University.

Roentgen experimented obsessively with his new puzzle, and by 1895 he had reached an impossible conclusion: the Crooke’s tube was emitting some new type of radiation. To reflect his bewilderment, Roentgen dubbed the new rays “X-rays.”

Scientists on the Warpath

Marie Curie, the French chemist who, with her husband, discovered radiation in the late 1800s. Her discovery was fueled by Roentgen's discovery of X-rays. Source: Archives Curie et Joliot-Curie.

Within five years of Roentgen’s discovery of X-rays, the world of science was thrown into a frenzy of discovery. An entirely new facet of physics had suddenly opened to the scientists, and a new suite of elements and radiation types were discovered in rapid succession. Although physicists and chemists were the prime movers of the new revolution, all of science was affected. Doctors, surgeons, and anatomists were suddenly X-raying people (though the technique would not be refined for decades); mathematicians were thrown puzzles of radioactive decay rates. Geologists began to measure the ages of rocks and minerals for the first time, obtaining what were to them outrageous ages — rocks that were billions of years old on an Earth that they believed to be only a few hundred thousand years old. Astronomers joined the warpath as they found the rays raining down from space. Those most affected, though, were the physicists and chemists, who were beginning to glimpse the internal complexities of the atom for the first time.

The Turn of the Century and the Turn of Physics

The first X-ray photograph ever taken: Wilhelm Roentgen’s wife’s hand. The large glob you see on her finger is her wedding ring. Source: Pennsylvania State University.

Down the street from the Curies and their radioactive cauldrons, the French physicist Paul Villard was experimenting with the Curies’ radioactive elements. The elements all emitted a radiation of their own, puzzling Villard. Most dismissed the radiation as X-rays; however, the radiation from the Curies’ elements was much more penetrating than X-rays. Others thought them to be alpha or beta particles; however, they were unaffected by electric or magnetic fields. In 1900, after years of experimenting, Villard proclaimed that they were something new altogether: gamma rays.

X-rays caused an enormous public stir, but not gamma rays. The scientific community was already ray-crazed, and one more ray hardly fazed them. The public was unimpressed — gamma rays couldn’t give you photographs of your skeleton, after all. Rutherford, however, was intrigued and looked closer. By 1914, he had shown that gamma rays are part of the electromagnetic spectrum, and that they have higher energies and shorter wavelengths than X-rays.

Rutherford showed that radioactive elements emit gamma rays with alpha or beta particles from their nuclei as they decay. Over the next 30 years, physicists expanded this idea back into the structure of the atom. A gamma ray photon has momentum, so if an atom absorbs it, the atom jerks backward slightly in a recoil. The atom would experience an increase in energy from the gamma ray; however, this energy should be less than that of the ray, due to energy lost in recoil. The atom could then re-emit a gamma ray, but at a much lower energy. This interpretation was well established by the 1950s.

Probing the Gamma Ray

In the mid-1950s, a young graduate student named Rudolf L. Mossbauer began examining the gamma ray absorption theory described above in more detail. Through repeated experimentation, he discovered that, by placing the absorbing nucleus in a crystal lattice, no recoil occurred. The momentum of the incoming gamma ray was absorbed by the entire lattice, and the absorbing atom could then reemit the gamma ray at the same energy level.

This may not sound like much — but it won Mossbauer a Nobel Prize in 1961. The Mossbauer effect provides the opportunity to detect extremely small energy and velocity shifts within the lattice. In short, by rigging up a Mossbauer detector, minute differences in the energies of incoming gamma rays, X-rays, or alpha particles are easily detected. In the 1960s, several Harvard University astronomers used this technique to detect tiny differences in incoming radiation to detect gravitational red shifts as small as 1%.

The Mossbauer effect was quickly adapted for use in Mossbauer spectroscopy. This is the process of analyzing a material based on how it interacts with gamma rays, and it is used to reveals the properties of minerals. Mossbauer spectroscopy is especially useful for measuring the composition of iron minerals (such as hematite and magnetite), their abundances within rocks, and their oxidation states. Such measurements provide information not only on formation conditions but also on the sort of magnetism a rock has been exposed to. For a rock you can hold in your hand, there are easier ways to determine these qualities. But for a rock you can’t hold, for a rock that will never come within arms’ reach, a Mossbauer spectrometer and a small robot to run it is a great opportunity.

The Spirit and Opportunity

A drawing of the Spirit rover, set to arrive at Mars in late January 2004. Its twin, the Opportunity, will arrive at Mars in February 2004. Source: NASA.

In June and July of 2003, NASA launched its rover twins Spirit and Opportunity, bound for Mars.

Aboard each of the small rovers, a hand-sized Mossbauer spectrometer is waiting for the iron-rich Martian surface, where they will patiently measure the gamma rays leaving Martian rocks. Above each Mossbauer spectrometer is a head-like machine that will measure the X-rays and alpha particles emitted by the Martian rocks — determining their chemistry and composition.

This is a rare time in planetary exploration — two satellites orbit Mars, two more are on their way, and three rovers will arrive at the planet within months (the third will come from the European Space Agency). The data pouring in has already revealed ancient coastlines, where a Martian ocean once lay; evidence of glaciers on the sides of enormous volcanoes; astounding contemporary reservoirs of water just below the surface; young valleys and streambeds where liquid water once flowed; and deposits of the iron oxide mineral hematite the size of Oregon.

As the Mars rover twins and their Mossbauer and X-ray spectrometers hasten toward the Red Planet, astronomers and geologists are caught in very much the same spirit of discovery and excitement that accompanied Roentgen’s X-rays, in the same spirit of eclectic study that absorbed Swedenborg. Where once a single gifted scientist was all that was required to explore the world, or a small group all that was required to uncover the mysteries of the atom, an entire community of technicians, engineers, and specialized scientists is now reaching beyond the bounds of our planet, in the same spirit of the scientists before them, but with the opportunity for discoveries far beyond those who came before.