A child’s partial skull adds to the mystery of how Homo naledi treated the dead

A child’s partial skull found in a remote section of a South African cave system has fueled suspicion that an ancient hominid known as Homo naledi deliberately disposed of its dead in caves.

An international team led by paleoanthropologist Lee Berger of University of the Witwatersrand, Johannesburg pieced together 28 skull fragments and six teeth from a child’s skull discovered in a narrow opening located about 12 meters from an underground chamber where cave explorers first found H. naledi fossils (SN: 9/10/15). Features of the child’s skull qualify it as H. naledi, a species with an orange-sized brain and skeletal characteristics of both present-day people and Homo species from around 2 million years ago.

“The case is building for deliberate, ritualized body disposal in caves by Homo naledi,” Berger said at a November 4 news conference held in Johannesburg. While that argument is controversial, there is no evidence that the child’s skull was washed into the tiny space or dragged there by predators or scavengers (SN: 4/19/16).

Berger’s group describes the find in two papers published November 4 in PaleoAnthropology. In one, Juliet Brophy, a paleoanthropologist at Louisiana State University in Baton Rouge and colleagues describe the youngster’s skull. In the other, paleoanthropologist Marina Elliott of Canada’s Simon Fraser University in Burnaby and colleagues detail new explorations in South Africa’s Rising Star cave system.

Researchers nicknamed the new find Leti, short for a word in a local South African language that means “the lost one.” Leti likely dates to the same time as other H. naledi fossils, between 335,000 and 236,000 years ago (SN: 5/9/17). Berger’s team suspects Leti died at about age 4 to 6 years based on the rate at which children grow today. But that’s a rough approximation as the scientists can’t yet say how fast H. naledi kids grew.

Lasers reveal construction inspired by ancient Mexican pyramids in Maya ruins

At Teotihuacan, near Mexico City, three giant pyramids rise above the ancient city’s main street, the Avenue of the Dead. The smallest of these is the Temple of the Feathered Serpent, which sits within La Ciudadela, or the Citadel, a massive sunken plaza with tall walls.

Now, more than a thousand kilometers away at the Maya capital of Tikal in what’s now Guatemala, researchers have found a smaller plaza and pyramid possibly modeled after La Ciudadela and its temple.

Teotihuacan is thought to have conquered Tikal in the year 378 (SN: 9/27/18). The finding adds to evidence of Teotihuacan’s influence over Tikal, the team reports September 28 in Antiquity.

“The architectural layout revealed by this study is stunning,” says anthropological archaeologist Nawa Sugiyama of the University of California, Riverside, who was not involved in the new research. “The very orthogonal city planning with specific orientation of the pyramids gives Teotihuacan a very characteristic architectural style, making it easy to identify any Teotihuacan influence abroad.”、
What’s more, the newfound structures had six construction phases, the researchers say, most dating to a time in Mesoamerica that archaeologists call the Early Classic period, which lasted from about 300 to 550. That means that the Tikal complex possibly predates the Teotihuacan conquest of the Maya city in 378. If true, that would add more evidence to an idea that scientists have worked on for decades — that these civilizations were in contact much earlier than the conquest of Tikal, possibly trading and making political connections with one another.

To uncover the pre-Columbian architecture, archaeologist Stephen Houston of Brown University in Providence, R.I., and colleagues at the Proyecto Arqueológico del Sur de Tikal along with the Pacunam LiDAR Initiative and the University of Texas at Austin used an airborne remote-sensing technique called lidar, or light detection and ranging.
“We knew this area in Guatemala was important to Teotihuacan culture,” says study coauthor David Stuart, director of the Mesoamerica Center of the University of Texas at Austin. But the place where the Citadel-inspired construction is located did not appear on old maps of the Tikal archaeological site because it is covered in vegetation. “As there was no visible stonework there, it was thought to be a natural hill,” Stuart says.

The team decided to look closer because the mound looked unusual for a Maya site. “Since the location was adjacent to an area in Tikal where many Teotihuacan-style artifacts were found in the 1980s, we thought it deserved more attention,” Stuart says. After reviewing the lidar mapping, Houston saw that the general plan of the buildings resembled the Ciudadela and its temple at Teotihuacan.

In her 2004 book The Ancient Maya: New Perspectives, Louisiana State University archaeologist Heather McKillop noted that the abundant presence of Teotihuacan-style architecture and pottery found in Tikal and a number of Maya sites across Guatemala is extensive evidence of the Teotihuacan influence across Mesoamerica from the year 400 to 700. The ancient city in Mexico thrived from about 100 to 750, but much about the people who lived there and why the city was destroyed and abandoned is still a mystery. The Aztecs gave the name Teotihuacanto the city centuries after its collapse.

“It is almost like Teotihuacan had installed their own neighborhood or embassy in Tikal,” says study coauthor and archaeologist Thomas Garrison, also at the University of Texas at Austin. Other research led by Sugiyama shows that “there was also a more permanent Maya presence in Teotihuacan before the conquest of Tikal as well, so influence probably went in both ways.”

Sugiyama studies the Plaza of the Columns Complex at Teotihuacan, where researchers have found Maya ceramics and evidence of Maya-style painted walls. “These murals were destroyed … before the 378 arrival event,” she says. “That makes us wonder whether the conquest [of Tikal] was one of the last chapters” in a long history of contact between the Mayas and the Teotihuacanos.

Eduardo Natalino dos Santos, a Mesoamerica historian at the University of São Paulo who did not take part in the study, agrees with Sugiyama. “The circulation of these ancient architectural styles show that the Mesoamerican Indigenous elites were connected. We used to see traces of one culture in a different region always as a result of a colonizing or domination process. Maybe this is not always the case,” he says.

Here’s the physics of why ducklings swim in a row behind their mother

There’s physics to having your ducklings in a row.

By paddling in an orderly line behind their mother, baby ducks can take a ride on the waves in her wake. That boost saves the ducklings energy, researchers report in the Dec. 10 issue of the Journal of Fluid Mechanics.

Earlier measurements of duckling metabolism showed that the youngsters saved energy when swimming behind a leader, but the physics behind that savings wasn’t known. Using computer simulations of waterfowl waves, naval architect Zhiming Yuan of the University of Strathclyde in Glasgow, Scotland, and colleagues calculated that a duckling cruising in just the right spot behind its mother gets an assist.

When a duckling swims on its own, it kicks up waves in its wake, using up some energy that would otherwise send it surging ahead. That wave drag resists the duckling’s motion. But ducklings in the sweet spot experience 158 percent less wave drag than when swimming alone, the researchers calculated, meaning the duckling gets a push instead.

Like good siblings, the ducklings share with one another. Each duckling in the line passes along waves to those behind, so the whole brood gets a free ride.

But to reap the benefits, the youngsters need to keep up with their mom. If they fall out of position, swimming gets harder. That’s fair punishment for ducklings that dawdle.

Here’s how ice needles sculpt patterns into cold, rocky landscapes

Neat rings, stripes and swirls embellish many cold, rocky landscapes. Although these beautiful stone patterns look like humanmade artwork, they’re all natural. Scientists have long known that such rocky patterns result from freezing and thawing. But precisely how they develop has been a mystery — until now.

New experiments reveal that so-called “ice needles” can sort and organize rocks into many patterns, Anyuan Li of the University of Tsukuba in Japan and colleagues report the Oct. 5 Proceedings of the National Academy of Sciences.

“The beauty of [our] experiments is that you can actually see direct information on how the patterns form,” says Bernard Hallet of the University of Washington in Seattle, who has studied natural patterns in surface rocks around the world.
The researchers spread pebbles atop a pan holding moist, fine-grained soil, then froze and thawed this mini-landscape over and over. When the moist soil had not yet frozen but the air temperature dropped below freezing, tiny, needlelike columns of ice sprouted up from the soil. These ice needles, each up to a few centimeters high, lifted any stones atop them. When temperatures rose again, the ice collapsed and the stones tumbled off. Because the ice needles curved as they grew, the stones tended to fall off their icy pedestals to one side.

Over many freeze-thaw cycles, the ice needles cleared patches of exposed soil. Since needles could more easily form in spots where there were fewer rocks in the way, they more efficiently cleared out any remaining pebbles. Stones were gradually shuffled into clusters between stone-free areas to form larger patterns. The pattern that builds on a landscape “strongly depends on its [local stone] concentration,” says study coauthor Quan-Xing Liu, a theoretical ecologist at East China Normal University in Shanghai.
In lab experiments, the team “was able to able to get patterns after 30 freeze cycles,” says Hallet. That could equate to 30 cold nights — or 30 years, if each freeze lasted a whole winter. In the real world, Hallet says, some patterns might take “thousands, if not tens of thousands, of years to form.”

Using observations from their soil experiments, the researchers built a computer simulation of ice needle landscaping. This simulation could predict stone movement in the open environment under a range of conditions. The simulation confirmed that the rate of pattern formation depended on how dense the stone cover was, among other factors. The shapes and formation rates of patterns were also related to how moist the soil was, how the ground sloped and how tall the ice needles grew.

“We see identical patterns in different systems, such as fluids,” Hallet says of the rock formations. Materials with different characteristics or sizes often start all mixed together but don’t stay that way (SN: 4/22/21). Phase separation is the process that morphs these mixes into patterns. The new study is among the first to show how phase separation applies to landscapes.

The combination of experiments and computer modelling in this study provides a new way to connect how natural landscapes form and how their materials behave, says Rachel Glade, a geologist at the University of Rochester in New York who was not involved in the work. This approach “is vital for our understanding of complex materials,” she adds, and it could help us understand how landscapes may evolve differently in a changing climate.

A new particle accelerator aims to unlock secrets of bizarre atomic nuclei

Inscribed on an Italian family’s 15th century coat of arms and decorating an ancient Japanese shrine, the Borromean rings are symbolically potent. Remove one ring from the trio of linked circles and the other two fall apart. It’s only when all three are entwined that the structure holds. The rings have represented the concepts of unity, the Christian Holy Trinity and even certain exotic atomic nuclei.

A rare variety, or isotope, of lithium has a nucleus that is made of three conjoined parts. Lithium-11’s nucleus is separated into a main cluster of protons and neutrons flanked by two neutrons, which form a halo around the core. Remove any one piece and the trio disbands, much like the Borromean rings.

Not only that, lithium-11’s nucleus is enormous. With its wide halo, it is the same size as a lead nucleus, despite having nearly 200 fewer protons and neutrons. The discovery of lithium-11’s expansive halo in the mid-1980s shocked scientists (SN: 8/20/88, p. 124), as did its Borromean nature. “There wasn’t a prediction of this,” says nuclear theorist Filomena Nunes of Michigan State University in East Lansing. “This was one of those discoveries that was like, ‘What? What’s going on?’ ”
Lithium-11 is just one example of what happens when nuclei get weird. Such nuclei, Nunes says, “have properties that are mind-blowing.” They can become distorted into unusual shapes, such as a pear (SN: 6/15/13, p. 14). Or they can be sheathed in a skin of neutrons — like a peel on an inedible nuclear fruit (SN: 6/5/21, p. 5).

A new tool will soon help scientists pluck these peculiar fruits from the atomic vine. Researchers are queuing up to use a particle accelerator at Michigan State to study some of the rarest atomic nuclei. When it opens in early 2022, the Facility for Rare Isotope Beams, or FRIB (pronounced “eff-rib”), will strip electrons off of atoms to make ions, rev them up to high speeds and then send them crashing into a target to make the special nuclei that scientists want to study.

Experiments at FRIB will probe the limits of nuclei, examining how many neutrons can be crammed into a given nucleus, and studying what happens when nuclei stray far from the stable configurations found in everyday matter. With FRIB data, scientists aim to piece together a theory that explains the properties of all nuclei, even the oddballs. Another central target: pinning down the origin story for chemical elements birthed in the extreme environments of space.

And if scientists are lucky, new mind-blowing nuclear enigmas, perhaps even weirder than lithium-11, will emerge. “We’re going to have a new look into an unexplored territory,” says nuclear physicist Brad Sherrill, scientific director of FRIB. “We think we know what we’ll find, but it’s unlikely that things are going to be as we expect.”
Exploring instability
Atomic nuclei come in a dizzying number of varieties. Scientists have discovered 118 chemical elements, distinguished by the number of protons in their nuclei (SN: 1/19/19, p. 18). Each of those elements has a variety of isotopes, different versions of the element formed by switching up the number of neutrons inside the nucleus. Scientists have predicted the existence of about 8,000 isotopes of known elements, but only about 3,300 have made an appearance in detectors. Researchers expect FRIB will make a sizable dent in the missing isotopes. It may identify 80 percent of possible isotopes for all the elements up through uranium, including many never seen before.

The most familiar nuclei are those of the roughly 250 isotopes that are stable: They don’t decay to other types of atoms. The ranks of stable isotopes include the nitrogen-14 and oxygen-16 in the air we breathe and the carbon-12 found in all known living things. The number following the element’s name indicates the total number of protons and neutrons in the nucleus.

Stable nuclei have just the right combination of protons and neutrons. Too many or too few neutrons causes a nucleus to decay, sometimes slowly over billions of years, other times in mere fractions of a second (SN: 3/2/19, p. 32). To understand what goes on inside these unstable nuclei, scientists study them before they decay. In general, as the proton-neutron balance gets more and more off-kilter, a nucleus gets further from stability, and its properties tend to get stranger.

Such exotic specimens test the limits of scientists’ theories of the atomic nucleus. While a given theory might correctly explain nuclei that are near stability, it may fail for more unusual nuclei. But physicists want a theory that can explain the most unusual to the most banal.

“We would like to understand how the atomic nucleus is built, how it works,” says theoretical nuclear physicist Witold Nazarewicz, FRIB’s chief scientist.
A fast clip
Accelerating beams of ions in FRIB is like herding cats.

In the beginning, “it’s just a gaggle of cats,” says Thomas Glasmacher, FRIB’s laboratory director. The cats meander this way or that, but if you can nudge the unruly bunch in a particular direction — maybe you open a can of cat food — then the cats start moving together, despite their natural tendency to wander. “Pretty soon, it’s a stream of cats,” he says.

In FRIB’s case, the cats are ions — atoms with some or all of their electrons stripped off. And rather than cat food, electromagnetic forces get them moving en masse.

The journey starts in one of FRIB’s two ion sources, where elements are vaporized and ionized. After some initial acceleration to get the ions moving, the beam enters the linear accelerator, which is what sets the particles really cruising. The linear accelerator looks like a scaled-down freight train — a line of 46 boxes the color of pistachio ice cream, each about 2.5 meters tall, of varying lengths. But the accelerator sends the beam moving much faster than a cargo-filled train — up to about half the speed of light.

Within the green boxes, called cryomodules, superconducting cavities are cooled to just a few kelvins, a smidge above absolute zero. At those temperatures, the cavities can accelerate the ions using rapidly oscillating electromagnetic fields. The chain of pistachio modules wends around the facility in the shape of a paper clip, a contortion necessary so that the approximately 450-meter-long accelerator fits in the 150-meter-long tunnel that houses it.

When the beam is fully accelerated, it’s slammed into a graphite target. That hard hit knocks protons and neutrons off the nuclei of the incoming ions, forming new, rarer isotopes. Then, the specific one that a scientist wants to study is separated from the riffraff by magnets that redirect particles based on their mass and electric charge. The particles of interest are then sent to the experimental area, where scientists can use various detectors to study how the particles decay, measure their properties or determine what reactions they undergo.
The energy of FRIB’s beam is carefully selected for producing rare isotopes. Too much energy would blow the nuclei apart when they collide with the target. So FRIB is designed to reach less than a hundredth the energy of the Large Hadron Collider at CERN near Geneva, the world’s most energetic accelerator.

Instead, the new accelerator’s potential rests on its juiced-up intensity: Essentially, it has lots and lots of particles in its beam. For example, FRIB will be able to slam 50 trillion uranium ions per second into its target. As a result, it will produce more intense streams of rare isotopes than its predecessors could.

For isotopes that are relatively easily produced, FRIB will churn out about a trillion per second; plenty to study. That opens prospects for scrutinizing isotopes that are more difficult to make. Those isotopes might pop up once a week in FRIB, but that’s still much more often than in a weaker beam. It’s like a case of low water pressure in the bathroom: “You can’t have a shower if it’s just trickling,” says Nunes, who is one of the leaders of a coalition of theoretical physicists supporting research at FRIB. Now, “FRIB is going to come in with a fire hose.”
Dripping with neutrons
That fire hose will also come in handy for pinpointing a crucial boundary known as the neutron drip line.

Try to stuff too many neutrons in a nucleus, and it will decay almost immediately by spitting out a neutron. Imagine a greedy chipmunk with its cheeks so full of nuts that when it tries to shove in one more, another nut pops right back out. The threshold at which nuclei decay in this way marks the ultimate limits for bound nuclei. On a chart of the known elements and their isotopes, this boundary traces out a line, the neutron drip line. So far, scientists know the location of this crucial demarcation up through, at most, the 10th element on the periodic table, neon.

“FRIB is going to be the only way to go heavier and far enough out to define that drip line,” says nuclear physicist Heather Crawford of Lawrence Berkeley National Laboratory in California. FRIB is expected to determine the neutron drip line up to the 30th element, zinc, and maybe even farther.
Near that drip line, where neutrons greatly outnumber protons, is where nuclei get especially strange. Lithium-11, with its capacious halo, sits right next to the drip line. Crawford focuses on magnesium isotopes that are close to the drip line. The most common stable magnesium isotope has 12 protons and 12 neutrons. Crawford’s main target, magnesium-40, has 12 protons and more than double that number of neutrons — 28 — in its nucleus.

“That’s right out at the limits of existence,” Crawford says. Out there, theories that predict the properties of nuclei are no longer reliable. Theoretical physicists can’t always be sure what size and shape a given nucleus in this realm might be, or even whether it qualifies as a bound nucleus. A given theory might also fall short when predicting how much energy is needed to bump the nucleus into its various energized states. The spacing of these energy levels acts as a kind of fingerprint of an atomic nucleus, one that’s highly sensitive to the details of the nucleus’ shape and other properties.

Sure enough, magnesium-40 behaves unexpectedly, Crawford and colleagues reported in 2019 in Physical Review Letters. While theories predicted its energy levels would match those of magnesium isotopes with slightly fewer neutrons, magnesium-40’s energy levels were significantly lower than its neighbors’.

In August, Crawford learned that she will be one of the first scientists to use FRIB. Two experiments she and colleagues proposed were selected for the first round of about 30 experiments to take place over FRIB’s first two years. She’ll take a closer look at magnesium-40, which, like lithium-11, has a Borromean nucleus. Crawford now aims to determine if her chosen isotope also has a haloed nucleus. That’s one possible explanation for magnesium-40’s oddness. Despite the fact that nuclei with halos have been known for decades, theories still can’t reliably predict which nuclei will be festooned with them. Understanding magnesium-40 could help scientists firm up their accounting of nuclei’s neutron adornments.
Elemental origins
Physicists want to be able to poke around, like mechanics under the hood, to understand the cosmic nuclear reactions that make the universe go. “Nuclear physics is like the engine of a sports car. It’s what happens in the engine that determines how well the car performs,” says nuclear physicist Ani Aprahamian of the University of Notre Dame in Indiana.

The cosmos powered by that engine can be a violent place for nuclei, punctuated with dramatic stellar explosions and extreme conditions, including matter crammed into ultratight quarters by crushing gravity. These environments beget wonders of nuclear physics unlike those normally seen on Earth. FRIB will let scientists get a glimpse at some of those processes.

For example, physicists think that certain neutron-rich environments are the cauldron where many of the universe’s chemical elements are cooked. This cosmic connection allowed nuclear physicist Jolie Cizewski to make good on a childhood dream.

When Cizewski was a little girl, she caught the astronomy bug, she says. “I decided I was going to become an astronomer so I could go into space.” It might seem that she took a left turn from her childhood obsession. She never made it to orbit and she didn’t become an astronomer.

But echoes of that childhood dream now anchor her research. Instead of peering at the stars with a telescope, she’ll soon be using FRIB to reveal secrets of the cosmos.

Cizewski, of Rutgers University in New Brunswick, N.J., is working to unveil details of the cosmic nuclear reactions responsible for the nuclei that surround us. “I’m trying to understand how the elements, in particular those heavier than iron, have been synthesized,” she says.

Many of the elements around us — and in us — formed within stars. As large stars age, they fuse progressively larger atomic nuclei together in their cores, creating elements farther along the periodic table — oxygen, carbon, neon and others. But the process halts at iron. The rest of the elements must be born another way.

A process called the rapid neutron capture process, or r-process, is responsible for many of those other elements found in nature. In the r-process, atomic nuclei quickly soak up neutrons and bulk up to large masses. The neutronfest is interspersed with radioactive decays that form new elements. The sighting of two neutron stars merging in 2017 revealed that such collisions are one place where the r-process occurs (SN: 11/11/17, p. 6). But scientists suspect it might happen in other cosmic locales as well (SN: 6/8/19, p. 10).

Cizewski and colleagues are studying an abbreviated form of the r-process that might thrive in supernovas, which may not have enough oomph for the full r-process. The team has zeroed in on germanium-80, which plays a pivotal role in the weak r-process. Physicists want to know how likely this nucleus is to capture another neutron to become germanium-81. At FRIB, Cizewski will slam a beam of germanium-80 into deuterium, which has one proton and one neutron in its nucleus. Knowing how often germanium-80 captures the neutron will help scientists nail down the neutron-slurping chain of the weak r-process, wherever it might crop up.
A Borromean bent
Like the interlinked Borromean rings, different facets of nuclear physics are closely entwined, from mysteries of the cosmos to the inner workings of nuclei. The exotic nuclei that FRIB cooks up could also allow physicists to tap into the very bedrock of physics by testing certain fundamental laws of nature. And there’s a practical side to the facility as well. Scientists could collect some of the isotopes FRIB produces for use in medical procedures, for example.

Physicists are ready for surprises. “Every time we build such a facility, new discoveries come and breakthroughs in science come,” Nazarewicz says. Like the 1980s discovery of lithium-11’s Borromean nucleus, scientists may find something totally unexpected.

‘Flashes of Creation’ recounts the Big Bang theory’s origin story

The Big Bang wasn’t always a sure bet. For several decades in the 20th century, researchers wrestled with interpreting cosmic origins, or if there even was a beginning at all. At the forefront of that debate stood physicists George Gamow and Fred Hoyle: One advocated for an expanding universe that sprouted from a hot, dense state; the other for a cosmos that is eternal and unchanging. Both pioneered contemporary cosmology, laid the groundwork for our understanding of where atoms come from and brought science to the masses.

In Flashes of Creation, physicist Paul Halpern recounts Gamow’s and Hoyle’s interwoven stories. The book bills itself as a “joint biography,” but that is a disservice. While Gamow and Hoyle are the central characters, the book is a meticulously researched history of the Big Bang as an idea: from theoretical predictions in the 1920s, to the discovery of its microwave afterglow in 1964, and beyond to the realization in the late 1990s that the expansion of the universe is accelerating.

Although the development of cosmology was the work of far more than just two scientists, Halpern would be hard-pressed to pick two better mascots. George Gamow was an aficionado of puns and pranks and had a keen sense of how to explain science with charm and whimsy (SN: 8/28/18). The fiercely stubborn Fred Hoyle had a darker, more cynical wit, with an artistic side that showed through in science fiction novels and even the libretto of an opera. Both wrote popular science books — Gamow’s Mr Tompkins series, which explores modern physics through the titular character’s dreams, are a milestone of the genre — and took to the airwaves to broadcast the latest scientific thinking into people’s homes.
“Gamow and Hoyle were adventurous loners who cared far more about cosmic mysteries than social conventions,” Halpern writes. “Each, in his own way, was a polymath, a rebel, and a master of science communication.”

While the Big Bang is now entrenched in the modern zeitgeist, it wasn’t always so. The idea can be traced to Georges Lemaître, a physicist and priest who proposed in 1927 that the universe is expanding. A few years later, he suggested that perhaps the cosmos began with all of its matter in a single point — the “primeval atom,” he called it. In the 1940s, Gamow latched on to the idea as way to explain how all the atomic elements came to be, forged in the “fireball” that would have filled the cosmos in its earliest moments. Hoyle balked at the notion of a moment of creation, convinced that the universe has always existed — and always will exist — in pretty much the same state we find it today. He even coined the term “Big Bang” as a put-down during a 1949 BBC radio broadcast. The elements, Hoyle argued, were forged in stars.

As far as the elements go, both were right. “One wrote the beginning of the story of element creation,” Halpern writes, “and the other wrote the ending.” We now know that hydrogen and helium nuclei emerged in overwhelming abundance during the first few minutes following the Big Bang. Stars took care of the rest.

Halpern treats Gamow and Hoyle with reverence and compassion. Re-created scenes provide insight into how both approached science and life. We learn how Gamow, ever the scientist, roped in physicist Niels Bohr to test ideas about why movie heroes always drew their gun faster than villains — a test that involved staging a mock attack with toy pistols. We sit in with Hoyle and colleagues while they discuss a horror film, Dead of Night, whose circular timeline inspired their ideas about an eternal universe.
And Halpern doesn’t shy away from darker moments, inviting readers to know these scientists as flawed human beings. Gamow’s devil-may-care attitude wore on his colleagues, and his excessive drinking took its toll. Hoyle, in his waning decades, embraced outlandish ideas, suggesting that epidemics come from space and that a dinosaur fossil had been tampered with to show an evolutionary link to birds. And he went to his grave in 2001 still railing against the Big Bang.

Capturing the history of the Big Bang theory is no easy task, but Halpern pulls it off. The biggest mark against the book, in fact, may be its scope. To pull in all the other characters and side plots that drove 20th century cosmology, Gamow and Hoyle sometimes get forgotten about for long stretches. A bit more editing could have sharpened the book’s focus.

But to anyone interested in how the idea of the Big Bang grew — or how any scientific paradigm changes — Flashes of Creation is a treat and a worthy tribute to two scientific mavericks.

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New ideas on what makes a planet habitable could reshape the search for life

When considering where to look for extraterrestrial life, astronomers have mostly stuck with what’s familiar. The best candidates for habitable planets are considered the ones most like Earth: small, rocky, with breathable atmospheres and a clement amount of warmth from their stars.

But as more planets outside the solar system have been discovered, astronomers have debated the usefulness of this definition (SN: 10/4/19). Some planets in the so-called habitable zone, where temperatures are right for liquid water, are probably not good for life at all. Others outside that designated area might be perfectly comfortable.

Now, two studies propose revising the concept of “habitable zone” to account for more of the planets that astronomers may encounter in the cosmos. One new definition brings more planets into the habitable fold; the other nudges some out.

“Both papers focus on questioning the classical idea of the habitable zone,” says astronomer Noah Tuchow of Penn State University. “We should extend the range of places that we look, so we don’t miss habitable planets.”
Some overlooked planets could be much bigger than Earth, and potentially receive no starlight at all. Astrophysicist Nikku Madhusudhan of the University of Cambridge and colleagues propose a new category of possibly habitable planet that could be found at almost any distance from any kind of star.

These hypothetical planets have a global liquid-water ocean nestled under a thick hydrogen-rich atmosphere (SN: 5/4/20). Madhusudhan calls them “Hycean” planets, for “hydrogen” and “ocean.” They could be up to 2.6 times the size of Earth and up to 10 times as massive, Madhusudhan and colleagues report August 25 in the Astrophysical Journal. That thick atmosphere could keep temperatures right for liquid water even with minimal input from a star, while the ocean could protect anything living from crushing atmospheric pressure.

“We want to expand beyond our fixated paradigm so far on Earthlike planets,” Madhusudhan says. “Everything we’ve learned about exoplanets so far is extremely diverse. Why restrict ourselves when it comes to life?”

In the search for alien life, Hycean planets would have several advantages over rocky planets in the habitable zone, the team says. Though it’s difficult to tell which worlds definitely have oceans and hydrogen atmospheres, there are many more known exoplanets in the mass and temperature ranges of Hycean planets than there are Earthlike planets. So the odds are good, Madhusudhan says.

And because they are generally larger and have more extended atmospheres than rocky planets, Hycean planets are easier to probe for biosignatures, molecular signs of life. Detectable biosignatures on Hycean planets could include rare molecules associated with life on Earth like dimethyl sulfide and carbonyl sulfide. These tend to be too low in concentration to detect in thin Earthlike atmospheres, but thicker Hycean atmospheres would show them more readily.

Best of all, existing or planned telescopes could detect those molecules within a few years, if they’re there. Madhusudhan already has plans to use NASA’s James Webb Space Telescope, due to launch later this year, to observe the water-rich planet K2 18b (SN: 9/11/19).

That planet’s habitability was debated when it was reported in 2019. Madhusudhan says 20 hours of observations with JWST should solve the debate.

“Best-case scenario, we’ll detect life on K2 18b,” he says, though “I’m not holding my breath over it.”

Astronomer Laura Kreidberg of the Max Planck Institute for Astronomy in Heidelberg, Germany, thinks it probably won’t be that easy. Planets in the Hycean size range tend to have cloudy or hazy atmospheres, making biosignatures more difficult to pick up.

It’s also not clear if Hycean planets actually exist in nature. “It is a really fun idea,” she says. “But is it just a fun idea, or does it match up with reality? I think we absolutely don’t know yet.”

Rather than inventing a new way to bring exoplanets into the habitable family, Tuchow and fellow Penn State astronomer Jason Wright are kicking some apparently habitable planets out. The pair realized that the region of clement temperatures around a star changes as the star evolves and changes brightness.

Some planets are born in the habitable zone and stay there their entire lives. But some, possibly most, are born outside their star’s habitable zone and enter it later, as the star ages. In the August Research Notes of the American Astronomical Society, Tuchow and Wright suggest calling those worlds “belatedly habitable planets.”

When astronomers point their telescopes at a given star, the scientists are seeing only a snapshot of the star’s habitable zone, the pair say. “If you just look at a planet in the habitable zone in the present day, you have no idea how long it’s been there,” Tuchow says. It’s an open question whether planets that enter the habitable zone later in life can ever become habitable, he explains. If the planet started out too close to the star, it could have lost all its water to a greenhouse effect, like Venus did. Moving Venus to the position of Earth won’t give it its water back.

On the other end, a planet that was born farther from its star could be entirely covered in glaciers, which reflect sunlight. They may never melt, even when their stars brighten. Worse, their water could go straight from frozen to evaporated, a process known as sublimation. That scenario would leave the planet no time with even a cozy wet puddle for life to get started in.

These planets are “still in the habitable zone,” Tuchow says. “But it adds questions about whether or not being in the habitable zone actually means habitable.”

How radio astronomy put new eyes on the cosmos

ne can only imagine what Grote Reber’s neighbors thought when, in 1937, the amateur radio enthusiast erected in his yard a nearly 10-meter-wide shallow bowl of sheet metal, perched atop an adjustable scaffold and topped by an open pyramid of gangly towers. Little could his neighbors have known that they were witnessing the birth of a new way of looking at the cosmos.

Reber was building the world’s first dedicated radio telescope. Unlike traditional telescopes, which use lenses or mirrors to focus visible light, this contraption used metal and circuitry to collect interstellar radio waves, low frequency ripples of electromagnetic radiation. With his homemade device, Reber made the first map of the sky as seen with radio-sensitive eyes and kicked off the field of radio astronomy.
“Radio astronomy is as fundamental to our understanding of the universe as … optical astronomy,” says Karen O’Neil, site director at Green Bank Observatory in West Virginia. “If we want to understand the universe, we really need to make sure we have as many different types of eyes on the universe as we possibly can.”

When astronomers talk about radio waves from space, they aren’t (necessarily) referring to alien broadcasts. More often, they are interested in low-energy light that can emerge when molecules change up their rotation, for example, or when electrons twirl within a magnetic field. Tuning in to interstellar radio waves for the first time was akin to Galileo pointing a modified spyglass at the stars centuries earlier — we could see things in the sky we’d never seen before.

Today, radio astronomy is a global enterprise. More than 100 radio telescopes — from spidery antennas hunkered low to the ground to supersized versions of Reber’s dish that span hundreds of meters — dot the globe. These eyes on the sky have been so game-changing that they’ve been at the center of no fewer than three Nobel Prizes.

Not bad for a field that got started by accident.

In the early 1930s, an engineer at Bell Telephone Laboratories named Karl Jansky was tracking down sources of radio waves that interfered with wireless communication. He stumbled upon a hiss coming from somewhere in the constellation Sagittarius, in the direction of the center of the galaxy.

“The basic discovery that there was radio radiation coming from interstellar space confounded theory,” says astronomer Jay Lockman, also of Green Bank. “There was no known way of getting that.”

Bell Labs moved Jansky on to other, more Earthly pursuits. But Reber, a fan of all things radio, read about Jansky’s discovery and wanted to know more. No one had ever built a radio telescope before, so Reber figured it out himself, basing his design on principles used to focus visible light in optical scopes. He improved upon Jansky’s antenna — a bunch of metal tubes held up by a pivoting wooden trestle — and fashioned a parabolic metal dish for focusing incoming radio waves to a point, where an amplifier boosted the feeble signal. The whole contraption sat atop a tilting wooden base that let him scan the sky by swinging the telescope up and down. The same basic design is used today for radio telescopes around the world.

For nearly a decade — thanks partly to the Great Depression and World War II — Reber was largely alone. The field didn’t flourish until after the war, with a crop of scientists brimming with new radio expertise from designing radar systems. Surprises have been coming ever since.
“The discovery of interstellar molecules, that’s a big one,” says Lisa Young, an astronomer at New Mexico Tech in Socorro. Radio telescopes are well suited to peering into the dense, cold clouds where molecules reside and sensing radiation emitted when they lose rotational energy. Today, the list of identified interstellar molecules includes many complex organics, including some thought to be precursors for life.

Radio telescopes also turned up objects previously unimagined. Quasars, the blazing cores of remote galaxies powered by behemoth black holes, first showed up in detailed radio maps from the late 1950s. Pulsars, the ultradense spinning cores of dead stars, made themselves known in 1967 when Jocelyn Bell Burnell noticed that the radio antenna array she helped build was picking up a steady beep … beep … beep from deep space every 1.3 seconds. (She was passed over when the 1974 Nobel Prize in physics honored this discovery — her adviser got the recognition. But an accolade came in 2018, when she was awarded a Special Breakthrough Prize in Fundamental Physics.)

Pulsars are “not only interesting for being a discovery in themselves,” Lockman says. They “are being used now to make tests of general relativity and detect gravitational waves.” That’s because anything that nudges a pulsar — say, a passing ripple in spacetime — alters when its ultraprecise radio beats arrive at Earth. In the early 1990s, such timing variations from one pulsar led to the first confirmed discovery of planets outside the solar system.

More recently, brief blasts of radio energy primarily from other galaxies have captured astronomers’ attention. Discovered in 2007, the causes of these “fast radio bursts” are still unknown. But they are already useful probes of the stuff between galaxies. The light from these eruptions encodes signatures of the atoms encountered while en route to Earth, allowing astronomers to track down lots of matter they thought should be out in the cosmos but hadn’t found yet. “That was the thing that allowed us to weigh the universe and understand where the missing matter is,” says Dan Werthimer, an astronomer at the University of California, Berkeley.
And it was a radio antenna that, in 1964, gave the biggest boost to the then-fledgling Big Bang theory. Arno Penzias and Robert Wilson, engineers at Bell Labs, were stymied by a persistent hiss in the house-sized, horn-like antenna they were repurposing for radio astronomy. The culprit was radiation that permeates all of space, left behind from a time when the universe was much hotter and denser than it is today. This “cosmic microwave background,” named for the relatively high frequencies at which it is strongest, is still the clearest window that astronomers have into the very early universe.

Radio telescopes have another superpower. Multiple radio dishes linked together across continents can act as one enormous observatory, with the ability to see details much finer than any of those dishes acting alone. Building a radio eye as wide as the planet — the Event Horizon Telescope — led to the first picture of a black hole.

“Not that anybody needed proof of the existence [of black holes],” Young says, “but there’s something so marvelous about actually being able to see it.”

The list of discoveries goes on: Galaxies from the early universe that are completely shrouded in dust and so emit no starlight still glow bright in radio images. Rings of gas and dust encircling young stars are providing details about planet formation. Intel on asteroids and planets in our solar system can be gleaned by bouncing radio waves off their surfaces.

And, of course, there’s the search for extraterrestrial intelligence, or SETI. “Radio is probably the most likely place where we will answer the question: ‘Are we alone?’” Werthimer says.
That sentiment goes back more than a century. In 1899, inventor Nikola Tesla picked up radio signals that he thought were coming from folks on another planet. And for 36 hours in August 1924, the United States ordered all radio transmitters silent for five minutes every hour to listen for transmissions from Mars as Earth lapped the Red Planet at a relatively close distance. The field got a more official kickoff in 1960 when astronomer Frank Drake pointed Green Bank’s original radio telescope at the stars Tau Ceti and Epsilon Eridani, just in case anyone there was broadcasting.

While SETI has had its ups and downs, “there’s kind of a renaissance,” Werthimer says. “There’s a lot of new, young people going into SETI … and there’s new money.” In 2015, entrepreneur Yuri Milner pledged $100 million over 10 years to the search for other residents of our universe.

Though the collapse of the giant Arecibo Observatory in 2020 — at 305 meters across, it was the largest single dish radio telescope for most of its lifetime — was tragic and unexpected, radio astronomers have new facilities in the works. The Square Kilometer Array, which will link up small radio dishes and antennas across Australia and South Africa when complete in the late 2020s, will probe the acceleration of the universe’s expansion, seek out signs of life and explore conditions from cosmic dawn. “We’ll see the signatures of the first structures in the universe forming the first galaxies and stars,” Werthimer says.
But if the history of radio astronomy is any guide, the most remarkable discoveries yet to come will be the things no one has thought to look for. So much about the field is marked by serendipity, Werthimer notes. Even radio astronomy as a field started serendipitously. “If you just build something to look at some place that nobody’s looked before,” he says, “you’ll make interesting discoveries.”

The fastest-spinning white dwarf ever seen rotates once every 25 seconds

The sun turns once a month and the Earth once a day, but a white dwarf star 2,000 light-years away spins every 25 seconds, beating the old champ by five seconds. That makes it the fastest-spinning star of any sort ever seen — unless you consider such exotic objects as neutron stars and black holes, some of which spin even faster, to be stars (SN: 3/13/07).

About as small as Earth but roughly as massive as the sun, a white dwarf is extremely dense. The star’s surface gravity is so great that if you dropped a pebble from a height of a few feet, it would smash into the surface at thousands of miles per hour. The typical white dwarf takes hours or days to spin.

The fast-spinning white dwarf, named LAMOST J0240+1952 and located in the constellation Aries, got in a whirl because of its ongoing affair with a red dwarf star that revolves around it. Just as falling water makes a waterwheel turn, so gas falling from the red companion star made the white dwarf twirl.

The discovery occurred the night of August 7, when astronomer Ingrid Pelisoli of the University of Warwick in Coventry, England, and her colleagues detected a periodic blip of light from the dim duo. The blip repeated every 24.93 seconds, revealing the white dwarf star’s record-breaking rotation period, the researchers report August 26 at arXiv.org.

The star’s only known rival is an even faster-spinning object in orbit with the blue star HD 49798. But that rapid rotator’s nature is unclear, with some recent studies saying it is likely a neutron star, not a white dwarf.

China’s lunar rock samples show lava flowed on the moon 2 billion years ago

Lava oozed across the moon’s surface just 2 billion years ago, bits of lunar rocks retrieved by China’s Chang’e-5 mission reveal.

A chemical analysis of the volcanic rocks confirms that the moon remained volcanically active far longer that its size would suggest possible, researchers report online October 7 in Science.

Chang’e-5 is the first mission to retrieve lunar rocks and return them to Earth in over 40 years (SN: 12/1/20). An international group of researchers found that the rocks formed 2 billion years ago, around when multicellular life first evolved on Earth. That makes them the youngest moon rocks ever collected, says study coauthor Carolyn Crow, a planetary scientist at the University of Colorado Boulder.

The moon formed roughly 4.5 billion years ago. Lunar rocks from the Apollo and Soviet missions of the late 1960s and 70s revealed that volcanism on the moon was commonplace for the first billion or so years of its existence, with flows lasting for millions, if not hundreds of millions, of years.
Given its size, scientists thought that the moon started cooling off around 3 billion years ago, eventually becoming the quiet, inactive neighbor it is today. Yet a dearth of craters in some regions left scientists scratching their heads. Parts of celestial bodies devoid of volcanism accumulate more and more craters over time, in part because there aren’t lava flows depositing new material that hardens into smooth stretches. The moon’s smoother spots seemed to suggest that volcanism had persisted past the moon’s early history.

“Young volcanism on a small body like the moon is challenging to explain, because usually small bodies cool fast,” says Juliane Gross, a planetary scientist at Rutgers University in Piscataway, N.J., not involved in the study.

Scientists had suggested that radioactive elements might offer an explanation for later volcanism. Radioactive decay generates a lot of heat, which is why nuclear reactors are kept in water. Enough radioactive materials in the moon’s mantle, the layer just below the visible crust, would have provided a heat source that could explain younger lava flows.

To test this theory, the Chang’e-5 lander gathered chunks of basalt — a type of rock that forms from volcanic activity — from a previously unexplored part of the moon thought to be younger than 3 billion years old. The team determined that the rocks formed from lava flows 2 billion years ago, but chemical analysis did not yield the concentration of radioactive elements one would expect if radioactive decay were to explain the volcanism.
This finding is compelling scientists to consider what other forces could have maintained volcanic activity on the moon.

One theory, says study coauthor Alexander Nemchin, a planetary scientist at the Beijing SHRIMP Center and Curtin University in Bentley, Australia, is that gravitational forces from the Earth could have liquefied the lunar interior, keeping lunar magma flowing for another billion or so years past when it should have stopped.

“The moon was a lot closer 2 billion years ago,” Nemchin explains. As the moon slowly inched away from the Earth — a slow escape still at work today — these forces would have become less and less powerful until volcanism eventually petered out.
Impacts from asteroids and comets also could have kept the moon’s volcanic juices flowing, but “at this point, any guess is a good guess,” says Jessica Barnes, a planetary scientist at the University of Arizona in Tucson not involved in the study.

“This is a good example of why we need to get to know our closest neighbor,” Barnes says. “A lot of people think we already know what’s going on with the moon, but it’s actually quite mysterious.”