Science

Nine hundred years ago, the Cahokia Mounds settlement just across the Mississippi River from present-day St. Louis bustled with roughly 50,000 people in the metropolitan area, making it one of the largest communities in the world. By 1400, however, the once-popular site was practically deserted, a mass departure that remains shrouded in mystery.

One popular theory is that the Cahokia residents abandoned the settlement after a massive crop failure brought on by a prolonged drought. But a new study published in the journal The Holocene by Natalie Mueller, assistant professor of archaeology at Washington University in St. Louis, and Caitlin Rankin, Ph.D. ’20, suggests the Cahokians likely had other reasons to leave town.

Rankin dug deep into the soil at the historic Cahokia site to collect isotopes of carbon, atoms left behind by the plants growing when the human population collapsed and drought was common across the Midwest.

All plants use one of two types of carbon, Carbon 12 and Carbon 13, for photosynthesis, but not all plants do photosynthesis the same way. Plants adapted to dry climates—including prairie grasses and maize, an important new crop during the Cahokia period—incorporate carbon into their bodies at rates that leave behind a tell-tale signature when the plants die and decay.

Most of the other plants that the Cahokians would have harvested for food—including squash, goosefoot and sumpweed—will leave a different signature, one they share with plants from wetlands and native forests.

Rankin’s samples showed that ratios of Carbon 12 and Carbon 13 stayed relatively consistent during that crucial period—a sign there was no radical shift in the types of plants growing in the area. “We saw no evidence that prairie grasses were taking over, which we would expect in a scenario where widespread crop failure was occurring,” Mueller said.

The Cahokians are known for their ingenuity, and Rankin said they may have had the engineering and irrigation skills to keep crops flourishing under difficult conditions. “It’s possible that they weren’t really feeling the impacts of the drought,” said Rankin, now an archaeologist with the Bureau of Land Management in Nevada.

Mueller added that the sophisticated society that blossomed at Cahokia almost certainly included a storage system for grains and other foods. Residents also enjoyed a varied and diverse diet—including fish, birds, deer, bear and forest fruits and nuts—that would have kept them nourished even if a few food sources disappeared.

To get a better grasp of the diets and agricultural practices of Indigenous people of the Midwest, Mueller hopes to build a database that collects paleo-botanical evidence from across the region.

“Gathering that information would help us see if people switched to different crops in response to climate change,” she said. She’s also planning to grow certain food crops in controlled conditions on campus to understand how they might have responded to ancient droughts and other challenges.

So, why did the Cahokians leave their land of plenty? Mueller suspects it was a gradual process. “I don’t envision a scene where thousands of people were suddenly streaming out of town,” she said. “People probably just spread out to be near kin or to find different opportunities.”

“They put a lot of effort into building these mounds, but there were probably external pressures that caused them to leave,” Rankin said. “The picture is likely complicated.”

How can you figure out which points lie on a certain curve? And how many possible curves do you count by a given number of points? These are the kinds of questions Pim Spelier of the Mathematical Institute studied during his Ph.D. research. Spelier received his doctorate with distinction on June 12.

Counting curves, what does that mean on an average day? “A lot of sitting and gazing,” Spelier replies. “When I’m asked what exactly I do, I can’t always answer that easily. Usually I give the example about the particle traveling through time.”

All possible curves

Imagine a particle moving through space and you follow the path the particle makes through time. That path is a curve, a geometric object. How many possible paths can the particle follow, if we assume certain properties? For example, a straight line can only pass through two points in one way. But how many paths are possible for the particle if we look at more difficult curves? And how do you study that?

By looking at all possible curves at the same time. For example, all possible directions from a given point form with each other a circle, and that is called a moduli space. And that circle is itself a geometric object.

The mathematical magic can happen because this set of all curves itself has geometrical properties, Spelier says, to which you can apply geometrical tricks. Next, you can make that far more complicated with even more complex curves and spaces. So not counting in three but, for example, in eleven dimensions.

Spelier tries to find patterns that always apply to the curves he studies. His approach? Breaking up complicated spaces into small, easy spaces. You can also break curves into partial curves. That way, the spaces in which you’re counting are easier. But the curves sometimes get complicated properties, because you have to be able to glue them back together.

Spelier says, “The goal is to find enough principles to determine the number of curves exactly.”

Seeking proof for points on curves

In addition to curves, Spelier also counted points on curves. He studied the question: how many solutions does a given mathematical equation have?

These are equations that are a bit more complicated than the a² + b² = c² of the Pythagorean theorem. That equation is about the lengths of the sides of a right triangle. If you replace the squares with higher powers, it is more difficult to investigate solutions. Spelier studied solutions in whole numbers, for example, 3² + 4² = 5².

Meanwhile, there is a method to find those solutions. Professor of Mathematics Bas Edixhoven, who died in 2022, and his Ph.D. student Guido Lido developed an alternative approach to the same problem. But to what extent the two methods match and differ was still unclear. During his Ph.D. research, Spelier developed an algorithm to investigate this.

The first person with an answer

Developing that algorithm is necessary to implement the method. If you want to do it by hand, you get pages and pages of equations. Edixhoven’s method uses algebraic geometry. Through clever geometric tricks, you can calculate exactly the whole number points of a given curve. Spelier proved that the Edixhoven-Lido method is better than the old one.

David Holmes, professor of Pure Mathematics and supervisor of Spelier, praises the proof provided. “When you’re the first person to answer a question that everyone in our community wants an answer to, that’s very impressive. Pim proves that these two methods for finding rational points are similar, an issue that really kept mathematicians busy.”

Doing math together

The best part of his Ph.D.? The meetings with his supervisor. After the first year, it was more collaboration than supervision, both for Spelier and Holmes. Spelier says, “Doing math together is still more fun than doing it alone.”

Spelier starts in September as a postdoc in Utrecht and is apparently not yet done with counting. After counting points and curves, he will soon start counting surfaces.

The first solar eclipse of 2024 is all set to darken the skies on April 8. This particular event will be a total solar eclipse, a rare occurrence on Earth. After this event, the next total solar eclipse in the same region will not be seen for two more decades. A total solar eclipse of similar impact is expected in 2044. This event will mainly be visible in North America, including Mexico, the US, and Canada. While a few more territories will observe it partially, the rest of the world cannot see it directly. Here’s everything you need to know about the latest solar eclipse, along with a list of all upcoming solar eclipses and more.

Total Solar Eclipse 2024: Date, Time, and Place

The total solar eclipse of 2024 will occur on April 8. The total darkening of the sky, also known as totality, will be visible across a 185-kilometre stretch between Mexico, the US, and Canada. It will start on Mexico’s Pacific coast at 11:07am PDT, and the eclipse will end on the Atlantic coast of Newfoundland, Canada, at 5:16pm NDT. As many as 18 different US States will also get to see it.

The total solar eclipse will not be visible from India. It will begin at 9:12 pm IST, a few hours after the Sun is set. Totality will start at 10:08pm IST, and the eclipse will end at 2:22am IST on April 9.

Total Solar Eclipse 2024: How to Watch it Live Online

While people in India and other countries, excluding North America, cannot physically witness the total solar eclipse, astronomy enthusiasts can still follow it online. There will be multiple live streams covering this rare celestial event. NASA will start its live stream on April 8 at 5:00pm GMT (10:30pm IST) and continue until 8:00pm GMT (1:30am IST). You can watch the stream here.

Skywatching website timeanddate.com will also live stream the total solar eclipse on its YouTube channel starting at 4:30pm GMT (10:00pm IST) on April 8. The stream will provide real-time updates and background information as well.

Finally, the University of Maine will send a high-altitude science balloon into the sky and live stream a view of the total solar eclipse from the stratosphere. It can be watched here on April 8, starting at noon GMT (5:30pm IST).

Total Solar Eclipse 2024: List of Countries to Watch the Celestial Event

The total solar eclipse of 2024 will only be visible in some parts of Mexico, the US, and Canada.

List of Upcoming Solar Eclipse

According to data from timeanddate.com, the following solar eclipses are expected to be observed from the Earth.

What is a Solar Eclipse?

A solar eclipse is an astronomical phenomenon where the Moon passes between the Earth and the Sun and blocks the Sun’s light either entirely or partially. These events are infrequent and occasional since the Moon needs to be in the same plane as the Sun and the Earth, which does not always happen. Even when an alignment does occur, it is more likely to be partial than full. This is the reason why total solar eclipses are so rare.

On average, the Earth can get between two to five solar eclipses in a year. However, most of these are partial eclipses and are not very noticeable. Total eclipses are dramatic and turn the sky dark, but they are only visible from a few locations. This is why the opportunity to experience an eclipse is often called a once-in-a-lifetime opportunity.

Different Types of Solar Eclipses

There are three types of solar eclipses. A solar eclipse can be defined as partial, total, or annular, depending on the Moon’s position. Here are the full details:

Partial solar eclipse: A partial solar eclipse occurs when the Moon partially covers the Sun, but some of the Sun’s light can still reach the Earth. When a partial solar eclipse occurs, a portion of the Sun appears to have vanished. It can be observed in a larger area.

Total solar eclipse: A total solar eclipse occurs when the Moon and the Sun are on the same plane, and the Moon is at such a distance from the Earth that it covers the Sun for a brief period. Unlike a partial solar eclipse, it is usually visible from a smaller strip of land.

Annular solar eclipse: Finally, during an annular solar eclipse, the Moon is placed far away from the Earth and is unable to cover the Sun entirely. At the peak of this solar eclipse, the Moon covers the central portion of the Sun, and only a ring of light can be seen from the Earth.

Things to Remember to View Upcoming Solar Eclipse Safely

While it is never recommended to look directly at the Sun since its intense brightness and harmful ultraviolet radiation can cause permanent damage to the unaided eye, this becomes even more important during a solar eclipse. Darkened skies can create a false impression that the Sun’s intensity is reduced and that it is safe to look at it; however, any escaping sunlight will cause the same amount of damage to the eye. This is why precautions must always be taken before viewing a solar eclipse event.

1. People should use safe solar viewing glasses when watching a solar eclipse directly.

2. Regular sunglasses, no matter how dark, are not safe to look at the Sun directly.

3. Binoculars, camera lenses, telescopes, or any other optical devices should not be used with solar viewing glasses, as concentrated solar rays can burn through the filter.

4. Proper solar filters should be added to optical devices before viewing the Sun through them.

5. If solar glasses are unavailable, people can opt for indirect viewing of the solar eclipse. NASA highlighted the pinhole projector method, where a small hole punched into an index card can project an image of the Sun on a surface through which the eclipse can be seen.

Frequently Asked Questions (FAQs) 

What is so special about the solar eclipse 2024?

The 2024 total solar eclipse is one of the rare celestial events that occur across the globe. It will be the most watched solar eclipse as it passes through various large cities. Moreover, it is also the last total solar eclipse across the United States for 20 years.  

How long will the 2024 eclipses last?

According to official NASA data, the total solar eclipse will last 4 minutes and 28 seconds. In most places, it will be visible for approximately 3.5 and 4 minutes. 

What is the timing of solar eclipse on 8 April 2024?

As per the Indian Standard Time (IST), the total solar eclipse will start at 9:12 pm, while the totality will begin at 10:08 pm. The eclipse will end on April 9, 2024, at 2:22 am. 

Is the April 8th solar eclipse visible in India?

Sadly, the total solar eclipse will only be visible in the United States and not in India. 
 

I’m about to lie to you. I’m going to tell you all the lofty reasons why I wrote my book Rosewater, like interrogating the usual setting of alien invasions in the Global North, and the loss of the colonial metaphor for alien invasions, and what’s the Black African perspective on these things, anyway?

These are only partially true and, to be honest, are post-hoc explanations of the journey my subconscious took me on.

In point of fact, I wrote Rosewater after I read about two conjoined twins who shared a brain and seemed able to read each other’s thoughts. I thought this would be a great conceit for telepathy and from there, a book about a telepath. It was in working out the biology of such a thing that issues of who and why came into it. How would such a person negotiate their social environment? What is a romantic relationship like if one person can read the mind of the other? What ethics apply? Personally, I thought knowing the inner thoughts of people around you would be an isolating ability, absolutely horrifying. Hence Kaaro, my unheroic protagonist. Hence Aminat, his love interest, and so much more.

In other words, I followed my intellectual curiosity. That curiosity sucked in a childhood spent reading about CIA psi experiments and MKULTRA/MKDELTA; The Andromeda Strain by Michael Crichton; an (at the time) obscure Argentine graphic novel called El Eternauta by Héctor Germán Oesterheld and Francisco Solano López; and at tent revivals.

Let’s linger here for a minute. Imagine a wide field – it might be grassy, but it’s more likely to be bare red earth due to persistent trampling. Now think of a vast tent that can house hundreds. Let’s go inside. There are very few seats, and everybody who can stand does. Up front, there’s a preacher, usually (but not exclusively) a man, armed with an encyclopaedic knowledge of Bible verses and eyes fevered with the Holy Ghost. When I was a kid in Nigeria, this kind of thing happened all the time. The most striking image was on the outside: piles of wheelchairs, walking sticks, gurneys and broken up plaster-of-Paris, all discarded by the newly healed who no longer needed them.

This imagery inspired the alien biodome in Rosewater, that and a similar dome in El Eternauta. I couldn’t read Spanish when I came across the book (still can’t), but there was a dome in the middle of town, and they clearly suffered from an alien invasion. This probably cemented the link between aliens and domes in my childhood mind. Oesterheld, like so many others with Leftist views, was disappeared by Argentina’s military government.

Inspiration aside, Rosewater subverts the expectations of invasion narratives and what the cost of survival for humanity might be, while at the same time being a story about people, not technology or fantastical set pieces.

The premise? Nigeria as ground zero in an alien invasion. Our main character, Kaaro, gets powers from the aliens, but people like him are dying. Why? How to stop this? The answer has consequences for humanity.

It’s a Trojan horse story where the wooden horse is universal healthcare and unlimited power supply; at the same time, it’s a story of alien invasion as a slow, unrecognised pandemic. I’m a doctor, and I can’t help thinking in pestilential modes.

I harkened back to the symbolism of empire in H. G. Wells, but I didn’t think aliens would come in ships or utilise tripods. Space travel is expensive. What would we have that would make it worth the travel for extraterrestrials?

And who are the aliens? What do they represent? These questions came later, in revision, and in the following two volumes, The Rosewater Insurrection and The Rosewater Redemption. Rosewater became more about neocolonialism. What has happened to us? Who pre-thinks our thoughts for us? What if there were Orwellian thought police?

I like to write science fiction that non-fans can read. I try to avoid neologisms and any science that can’t be extrapolated from today. I don’t enjoy fiction that needs a glossary.

Whatever the reasons for writing it, I had to set the story in a believable world. The kind of world that interested me involved the social reaction to localised unlimited resources like health and electricity. How would that change what we think of as society?

The book won and was nominated for prizes, notably the Arthur C. Clarke Award. Winning that was a kind of homecoming, since my childhood spent watching Arthur C. Clarke’s Mysterious World was part of what fired my interest in science fiction. The trilogy of books was nominated for the Hugo Award for Best Series. That was somewhat gratifying, because it meant someone other than my mother thought this story was affecting.

I hope you enjoy your visit to Rosewater. I hope it challenges what you think of as science fiction. I hope it delights and horrifies you.

Rosewater, published by Orbit Books, is available now. It is the latest pick for the New Scientist Book Club: sign up here to read along with our members

Nitrogen is an important and abundant element on Earth. In fact, nitrogen in the gas state is the most abundant gas in the atmosphere. This element is in our body as part of our DNA and in the center of hemoglobin. But nitrogen is also involved in our health.

Saturated nitrogen-containing heterocycles are among the most common molecular fragments in chemical compounds, particularly within medicinal chemistry. These motifs, which are frequently found in a wide range of top-selling pharmaceuticals, enhance biological activities when included in drug-like structures. However, synthesizing these cyclic amines presents significant challenges.

Researchers from the Institute of Chemical Research of Catalonia (ICIQ) have engineered a novel and facile metal-free intramolecular C(sp³)–N bond forming protocol that enables the efficient synthesis of biorelevant cyclic molecules, along with other nitrogen-containing heterocycles. This work, published in Nature Synthesis, introduces new tools for advancing synthetic organic chemistry.

About a century ago, Hofmann, Löffler and Freytag (HLF) described a mechanism to generate cyclic compounds without using metals. This transformation relies on radical mechanisms based on hydrogen atom transfer reactions. Over the past decades, the use of hypervalent iodine reagents (HIRs) has significantly increased the synthetic applicability and sustainability of these methods.

However, several daunting challenges remain. HLF methodology still exhibits a high selectivity towards five-membered ring formation. This is unfortunate, as one of the most frequent nitrogen cyclic compounds in approved drugs is piperidine, a six-membered ring. Moreover, this reactivity cannot be translated to the formation of lactones, another prevalent architecture in pharmaceuticals, due to undesired side reactions.

Old reagents, new tricks

In an effort to address these shortcomings, the research groups led by Prof. Monica H. Pérez-Temprano and Prof. Feliu Maseras took a novel mechanistic approach that shifts from the traditional HLF mechanism to a versatile new pathway. This innovative method bypasses the classical hydrogen atom transfer process and enhances the synthetic applications of HIRs in metal-free C(sp³)–N bond forming reactions.

The breakthrough presented in the work involves the use of hexafluoro-2-propanol (HFIP) as a solvent to unlock a single electron transfer mechanism between HIRs and the substrates. This process generates a radical cation that initiates the intramolecular C(sp³)–N bond forming reaction.

“HFIP is a fascinating yet intriguing solvent with unique physicochemical properties, that has become pivotal in C–H functionalization reactions. While its use in metal-free HIR-mediated transformations is well-documented, it was unprecedented that this solvent could provoke a distinct mechanistic paradigm that circumvents the traditional HAT processes,” explains Prof. Pérez-Temprano.

“Both experimental and computational studies support this mechanistic proposal, highlighting HFIP’s multifunctional role in facilitating the reaction. The experimental mechanisms were further clarified with Density Functional Theory (DFT) calculations, carried out by Jiale Xie herself. Jiale is the first author of this work and is carrying out her Ph.D. at ICIQ,” adds Prof. Feliu Maseras.

In a study published in Nature Astronomy, Profs. Shen Laiquan, Bai Haiyang, et al. from Prof. Wang Weihua’s group at the Institute of Physics of the Chinese Academy of Sciences have clarified the respective effects of irradiation and impacts on the formation of metallic iron nanoparticles (npFe⁰).

Based on precise observations of glass beads returned by the Chang’e-5 mission, they showed that the formation of small and large npFe⁰ with distinct optical effects is independently controlled by solar wind irradiation and micrometeorite impacts.

npFe⁰ are widely distributed on the moon, and their accumulation changes the optical spectrum of the lunar surface over time. How the surface color changes depends largely on the size of the npFe⁰: Smaller npFe⁰ redden the reflectance spectra, while larger npFe⁰ cause darkening.

The resultant color variations greatly complicate remote sensing studies, posing long-term puzzles to astronomers. Furthermore, the origin of npFe⁰ of different sizes was not well understood before this study.

npFe⁰ are known as products of space weathering, which includes the two main agents: micrometeorite impacts and solar wind irradiation. Yet the specific roles of these two agents in the formation of different-sized npFe⁰ have been unclear, hindering our understanding of color variations of the lunar surface or asteroids in complex space environments.

“We discovered that the glass beads in the Chang’e-5 lunar soil can preserve iron particles of different sizes, from about 1 nanometer to 1 micrometer,” said Prof. Bai.

“It is generally difficult to distinguish npFe⁰ of different origins observed together in single samples. Here we used the rotation feature of the impact glass beads to clearly distinguish npFe⁰ formed before and after the solidification of the host glass beads.”

In this study, the scientists found numerous discrete large npFe⁰, tens of nanometers in size, which tended to concentrate towards the extremities of the glass beads. This concentration effect can cause ultralarge npFe⁰ to protrude from the extremities.

Such a feature is exactly consistent with the migration phenomenon occurring in rotational glass-forming droplets triggered by hypervelocity impacts. In such scenarios, Fe0 with higher density than the matrix migrates to the extremities driven by centrifugal forces, indicating that these large npFe⁰ were formed in impact-derived melts before the glass beads solidified.

In contrast, they also identified abundant small npFe⁰, several nanometers in size, densely populating the surfaces of the glass beads. These small npFe⁰ exhibit distribution characteristics similar to irradiation-induced vesicle damage.

Along the depth direction of the glass beads, both small npFe⁰ and vesicles gradually decrease in size and abundance, corresponding to the decreasing amount of implanted solar wind ions with increasing depth.

Furthermore, when the size of the lunar grains is smaller than twice the penetration depth of the solar wind ions, small npFe⁰ can completely fill up the tiny grains. These results emphasize that solar wind irradiation is the primary driver of the observed small npFe⁰.

The study demonstrates that solar wind irradiation and micrometeorite impacts both play important but distinct roles in npFe⁰ formation. The independent growth of small and large npFe⁰ revealed in this research matches well with many remote sensing measurements, providing valuable insights for understanding and predicting the optical properties of airless bodies exposed to different space environments.

A research team proposed a new synthetic strategy of COFs based on a new topology that remotely separates donor (D) and acceptor (A) units in 3D lattice to produce the expected metastable photo-induced charge-separated states.

The researchers synthesized four 3D COFs with zyg topology for the first time by connecting unequal hexagonal monomers with a square building block. This structure type exhibits fused Olympic rings-shaped pores, forming two types of hexagonal channels with a maximum diameter of 3.5 nm, which provides a geometrical platform for stabilizing charge-separated states in the 3D lattice, as well as space for efficient guest transport.

Subsequently, the researchers obtained the photo-induced photochromic radical states in two zyg-type COFs containing photoactive electron donor moieties (triphenylamine and phenothiazine). The catalytic results combined with theoretical calculations revealed that the isolated radical states of these COFs performed better in the photosynthesis of H₂O₂ due to the enhancement of light-harvesting and carrier-transporting abilities as well as the reduction of activation energy of intermediates.

Remarkably, the radical state of the phenothiazine-based COF showed a H₂O₂ synthesis rate of 3324 μmol g^-1 h^-1, a significant increase in photocatalytic activity by 400% compared with the parent state, making it one of the best catalysts for the photocatalytic synthesis of H₂O₂.

This work will provide inspiration for the development of highly efficient 3D COF photocatalysts built on functional organic building blocks assembled in a topological structure that can facilitate light-induced charge separation.

The research is published in the journal National Science Review. The team includes Ya-Qian Lan and Yong Yan’s group at South China Normal University (SCNU), with the first author of the paper being Ms. Tian-Tian Ma, a Ph.D. candidate at SCNU, and the corresponding authors being Profs. Ya-Qian Lan and Yong Yan at SCNU.