James' World 2

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As a young course instructor in seminars for medical students, I faithfully taught neurophysiology by the book, enthusiastically explaining how the brain perceives the world and controls the body. Sensory stimuli from the eyes, ears, and such are converted to electrical signals and then transmitted to the relevant parts of the sensory cortex that process these inputs and induce perception. To initiate a movement, impulses from the motor cortex instruct the spinal cord neurons to produce muscular contraction.

Most students were happy with my textbook explanations of the brain’s input-output mechanisms. Yet a minority—the clever ones—always asked a series of awkward questions. “Where in the brain does perception occur?” “What initiates a finger movement before cells in the motor cortex fire?” I would always dispatch their queries with a simple answer: “That all happens in the neocortex.” Then I would skillfully change the subject or use a few obscure Latin terms that my students did not really understand but that seemed scientific enough so that my authoritative-sounding accounts temporarily satisfied them.

Like other young researchers, I began my investigation of the brain without worrying much whether this perception-action theoretical framework was right or wrong. I was happy for many years with my own progress and the spectacular discoveries that gradually evolved into what became known in the 1960s as the field of “neuroscience.” Yet my inability to give satisfactory answers to the legitimate questions of my smartest students has haunted me ever since. I had to wrestle with the difficulty of trying to explain something that I didn’t really understand.

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Credit: Stefania Infante

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Nobel laureate Otto Hahn is credited with the discovery of nuclear fission. Fission is one of the most important discoveries of the 20th century, yet Hahn considered something else to be his best scientific work.

In 1921, he was studying radioactivity at the Kaiser Wilhelm Institute for Chemistry in Berlin, Germany, when he noticed something he could not explain. One of the elements he was working with wasn’t behaving as it should have. Hahn had unknowingly discovered the first nuclear isomer, an atomic nucleus whose protons and neutrons are arranged differently from the common form of the element, causing it to have unusual properties. It took another 15 years of discoveries in nuclear physics to be able to explain Hahn’s observations.

We are two professors of nuclear physics who study rare nuclei, including nuclear isomers.

The most common place to find isomers is inside stars, where they play a role in the nuclear reactions that create new elements. In recent years, researchers have begun to explore how isomers can be put to use for the benefit of humanity. They are already used in medicine and could one day offer powerful options for energy storage in the form of nuclear batteries.

On the hunt for radioactive isotopes

In the early 1900s, scientists were on the hunt for new radioactive elements. An element is considered radioactive if it spontaneously releases particles in a process called radioactive decay. When this happens, the element is transformed over time into a different element.

At that time, scientists relied on three criteria to discover and describe a new radioactive element. One was to look at chemical properties — how the new element reacts with other substances. They also measured the type and energy of the particles released during the radioactive decay. Finally, they would measure how fast an element decayed. Decay speeds are described using the term half-life, which is the amount of time it takes for half of the initial radioactive element to decay into something else.

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The discovery that the nucleus of an atom is made of both protons and neutrons allowed physicists to explain isotopes as well as uranium Z.PANGGABEAN/iStock via Getty Images

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You don’t really hear about Neptune, do you?

Not as often as the other planets, certainly. Space robots regularly provide snapshots of the surface of Mars and the clouds of Jupiter. Mercury is a frequent scapegoat for astrology-minded folks having a bad day (even though Mercury being in retrograde is actually just an optical illusion in our night sky). For 13 whole years, the Cassini spacecraft orbited Saturn before plunging into the planet, ending its glorious streak of observations. And planetary scientists recently announced that NASA should prioritize sending a probe to Uranus in the next decade. Indeed, Neptune’s brief foray into the news cycle last week, because of a new study about what makes Neptune so blue, was a rare appearance.

And even that finding was an accidental discovery, according to Patrick Irwin, a planetary physicist at Oxford University and the lead author of the study. Irwin told me that he and his team had set out to study the atmosphere of both Neptune and Uranus, not to investigate the specific mystery of Neptune’s lovely appearance. The two ice giants—so-called because scientists believe the planets were originally glommed together from icy materials—are often studied in this way, as a pair. They have so much in common: They’re about the same size—bigger than Earth, but smaller than Jupiter and Saturn. They are surface-less worlds, with atmospheres of hydrogen, helium, and a splash of methane. And deep in their interior, scientists suspect, the pressure is so intense that carbon atoms compress into diamonds.

Scientists already knew that Neptune and Uranus get their general bluish appearance from the methane in their atmosphere, which absorbs incoming sunlight’s red hues, leaving blues and greens for our eyes to see. But Irwin and his colleagues found that a particular layer of methane haze is twice as thick on Uranus as it is on Neptune. “These atmospheres are naturally blue if there were no haze,” Irwin told me. “Adding haze makes them paler.” The researchers suspect that Neptune, which has a more turbulent atmosphere, is better at churning up methane particles and thinning out this layer. That’s why Uranus is a soft aquamarine, and Neptune is cerulean, the bluest planet in our solar system—the perfect distinction for our most neglected planet.

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