Christoforos Kotsakis, a professor of geodesy at the Aristotle University of Thessaloniki in Greece, developed a new method for analyzing GNSS data to better capture the changes in the planet's surface. He found that the poles are rising and the equator's bulge has been shrinking, each by about 0.04 inch (1 millimeter) per year between 2011 to 2015. That's a small number, considering Earth's diameter at the equator is about 7,926 miles (12,756 kilometers). But that change is bigger than between 1997-2000, when Earth was becoming about 0.02 inch (0.5 mm) rounder per year. This means Earth's shape is rounding at 0.016 inch (0.4 mm) more per year with each decade that passes.
The shift is being driven by polar ice melt, which takes pressure off the Earth's crust and allows it to rise slowly, similar to how rising bread dough springs back after you press a finger into it, Kotsakis reported. Meanwhile, increased mass toward the equator puts pressure on the crust there, reducing its bulge. However, there's a catch: When considering the solid Earth and the ocean together, the planet is getting flatter by about 0.03 inches (0.8 mm) a year because the ocean is getting bulgier at the equator as water shifts away from the poles. This 'water weight' overwhelms the rounding happening in the rock below.
These shifts are also slowing Earth's rotation, other research has shown.
Researchers also track Earth's changing shape using measurements of its gravity field, which varies depending on the mass of particular regions. GNSS changes and gravity field measurements don't match up perfectly, Kotsakis found, which indicates that the planet's shape and gravity field aren't in perfect lockstep. However, the two methods can be used together to track the major effects of climate change, especially the melting of Greenland and Antarctica and the varying movements of ocean water.
'> Climate change is literally altering the shape of our planet "The Upper Colorado River Basin has historically been considered more resilient because it receives more precipitation, particularly snowfall in the Rocky Mountains," Oyedele told Live Science in an email. "I think the important takeaway is that we should not assume that the Upper Basin will remain relatively resilient simply because it has historically received more precipitation and snowmelt."
The Lower Basin comprises parts of Nevada, California and Arizona. Less rain and snowfall means the Lower Basin naturally has less groundwater recharge, or less replenishment from other water sources, than the Upper Basin. On top of that, the Lower Basin generally has higher evaporation rates and substantial water demands, given that roughly 30 million of the 40 million people that depend on the Colorado River for water live in the Lower Basin, Oyedele said.
In the new study, published Oct. 13 in the journal Water Resources Research, researchers used satellite and hydrological data to estimate groundwater depletion across the Colorado River Basin between 2004 and 2023. The data included measurements of surface water, soil moisture and snow-water storage, as well as observations from the Gravity Recovery and Climate Experiment mission and its successor, called the Follow-On.
The results showed that groundwater depletion has been a persistent problem in the Colorado River Basin over the past two decades, but losses accelerated in 2019. The three-year drought that began in 2020 is the principal cause of this, because it shrank the snowpack in the Rocky Mountains, increased evaporation and boosted water demand across the basin, Oyedele said.
During the drought between 2020 and 2022, the Upper Basin lost around 4.2 cubic miles (17.5 cubic kilometers) of groundwater, while the Lower Basin lost about 2.3 cubic miles (9.4 cubic km). In total, the Colorado River Basin lost 14 cubic miles (58.3 cubic km) of groundwater — equivalent to 25 million Olympic-size swimming pools' worth of water — during the study period, between 2004 and 2023.
It's unclear why the deficit is so much higher in the Upper Basin than in the Lower Basin, but the Upper Basin's proximity to and dependence on the mountains for aquifer recharge probably didn't help, Oyedele said. As snow melts, some of it replenishes groundwater, so a reduction in snowfall between 2020 and 2022 would have affected the Upper Basin particularly badly, she noted.
The Upper Basin also recorded more aquifer recharge during wet periods before the drought than the Lower Basin did, so it's possible that the pronounced decline during the drought was linked to a higher initial amount of groundwater in the Upper Basin, Oyedele said.
The Upper Basin includes parts of Colorado, Wyoming, Utah and New Mexico, while the Lower Basin comprises parts of Nevada, California and Arizona. (Image credit: U.S. Geological Survey)Next, the researchers used advanced statistical methods to explore the relationship between groundwater and surface water in the Colorado River Basin. Due to global warming and the overallocation of the Colorado River's water in a 1922 document, the river's flow is now 35% less than it was on average in the 20th century. Water scarcity in the basin has reached alarming levels, according to the study, and Lake Mead and Lake Powell, the two largest reservoirs in the U.S., dropped to record lows in August.
The team found that in the Upper Basin, groundwater levels evolve in the same direction as surface water, but with a slight delay. This suggests groundwater losses occur due to a lack of recharge and more aquifer pumping during periods of drought, when surface water levels drop. In the Lower Basin, however, this link is weaker and more complex. The results showed that groundwater losses sometimes preceded surface water declines during the study period, suggesting that groundwater depletion is not simply tied to less surface water trickling into the ground or to humans extracting groundwater when there's less surface water available. Instead, groundwater is consistently being overused, Oyedele said.
"This distinction is important because it suggests that groundwater depletion is not simply a direct response to surface-water shortages," she said. "Human water use, particularly sustained groundwater extraction, may also play a significant role."
Looking ahead, it's hard to tell if the Upper Basin will continue to lose more groundwater than the Lower Basin and what that would mean for the region, Oyedele said. What seems clear, however, is that the Upper Basin is more vulnerable to drought than experts had thought.
"Continued warming, changes in snowpack, prolonged drought, and increasing water demand could place additional pressure on groundwater resources across both basins," Oyedele said. However, future groundwater responses will depend on several factors, including precipitation, snowmelt, water use and management decisions, she added.
On the management side, Oyedele suggested tackling groundwater and surface water together rather than as two separate resources. Groundwater helps to sustain river flows, and rivers can recharge aquifers — so the two are interconnected. Groundwater often serves as a backup during drought, but it shouldn't be treated as an unlimited reserve, she said.
'> Surprising new pattern of groundwater loss may signal a turning point for the Colorado River Basin (JWST). The metals may offer new clues about how Earth got its share of heavy elements — but it could also make one of the greatest mysteries about our local black hole even harder to solve.
Scientists say the material spotted by JWST likely came from supernovas — stellar explosions that blasted the metal into the region around Sagittarius A (Sgr A*), the monster black hole in the middle of our galaxy.
The metals, detected as gas, appear to have the same composition as several nearby stars, which suggests both the stars and the gas originated at the same time. Researchers shared the observations in a paper published Oct. 19 in The Astronomical Journal, following up on work published in The Astrophysical Journal in May.
"We know there's a black hole at the centre of our galaxy pulling material into itself, but we see that it's eating a lot less material than other supermassive black holes, and more slowly," Nicole Ford, first author of the new paper and a doctoral student in astrophysics at McGill University in Montreal, said in a statement. "Part of understanding why this is happening means looking at the properties of the materials available for it to consume, including gas, dust and the stars orbiting around it."
JWST orbits at Lagrange point 2, which is about 1 million miles (1.5 million kilometers) from Earth in the opposite direction of the sun. The telescope identified the heat signatures of specific gas clouds billowing near the black hole, as well as the metal content within those clouds.
"These findings could advance understanding of how metals are distributed around supermassive black holes in more distant galaxies, as well as the processes that supplied Earth with many of these elements," McGill researchers said in the statement. The metals' presence "influences how quickly gases cool, which in turn influences how readily the gas can be drawn into a black hole," they added.
The previous study in The Astrophysical Journal showed that gas emissions near the black hole have been influenced by conditions in the local clouds. Unfortunately, this means the gas alone cannot serve as a proxy for how often the black hole has been active, the researchers said.
'> James Webb telescope discovers surprising trove of metals around the Milky Way's supermassive black hole
from the University of Oslo's Museum of Cultural History.
"Here we have a coin bearing the king's portrait and a cross, with another cross on the reverse," University of Oslo coin expert Svein Gullbekk said in the statement. "It is a Christianisation coin on a grand scale."
Olaf is credited with establishing Christianity in Norway — an early step toward its full conversion about a generation later.
"We can see how King Olaf used coinage to legitimise the new faith and to establish himself as a Christian king of European standing," Gullbekk said. "This is branding."
Haraldsson learned about Christianity when he joined Viking raids against England and France as a young man, and he was baptized in the French city of Rouen in about 1013, according to the statement.
He became Norway's king in 1015, and in about 1024 proclaimed that only Christianity would be legal, according to the University of Bergen. Much of Norway, however, remained faithful to the Norse gods during his rule, especially around the central Trøndelag region and in the eastern parts of the country.
But Olaf was made a Christian saint shortly after his death in 1030. He is now recognized as one of the first Christian kings of Norway and the first Norwegian king to issue coins in his own name.
"I could see that it read ONLAF R+ NORMANORV. … Could this really be a coin of Olaf Haraldsson that I was holding?" Skogsfjord said in the statement. "And it was! It was a very special moment."
The coin was struck between about 1024 and 1028, near the end of the Viking Age, and circulated for 20 to 25 years before someone deposited it in the hoard, the statement said.
Although the minting of the coin was a political and religious act, the coin also seems to have been used as currency; both sides bear numerous small cut marks, which was a common way of determining whether a coin was made completely of silver.
Gullbekk said Haraldsson himself had decided what the coins would look like and may have been present when they were minted.
"It is entirely possible that this very coin from Mørstad was once held in the king's own hand," he said in the statement.
'> Extremely rare Viking Age coin from the reign of 'Olaf the Holy' may have been 'held in the king's own hand'
The German physicist Werner Heisenberg wrote in 1947 that the reactor for the "Nazi bomb" project — which culminated in Germany's B8 nuclear reactor — was almost finished at the end of World War II.
Heisenberg, who led the reactor's development, claimed the reactor was "just insufficient" to create a self-sustaining fission reaction and that it lacked only a "relatively small amount of uranium" to work.
If it had worked, the B8 reactor would have confirmed that a fission chain reaction was possible, marking a key step toward the German development of an atomic bomb. It could have also spurred the development of specialized fission reactors used to create weapons-grade plutonium from uranium. Instead, the atomic bomb was developed first by the United States and was used to force the surrender of Japan in August 1945. (Germany had already surrendered in May 1945.)
The new study, published Sept. 29 in the journal PNAS Nexus, used historical documents and forensic investigations of two of the project's surviving uranium cubes to refute Heisenberg's claim. The new research indicates that the German B8 reactor had less than half the amount of "heavy water" and about half the amount of uranium it would have needed for a continuous chain reaction.
"My results argue that Heisenberg was off by roughly a factor of two," said first author Patrick Park, a doctoral student at Princeton University who co-wrote the study while at Columbia University.
Park said Heisenberg's mistake was understandable: His calculations were only approximate, and the project was relocated to a rock cellar in the town of Haigerloch, Germany, after Berlin was bombed.
My results argue that Heisenberg was off by roughly a factor of two.
Patrick Park, doctoral student at Princeton University
"People were dying or starving and so these reactor calculations were not his first priority," while many details of neutron physics were unknown at that time, Park told Live Science in an email. "Given these circumstances, I think he did the best he could."
Heavy water
To answer the question of how far the reactor for the Nazi bomb project got, the scientists began by tracing archival records of hundreds of uranium cubes that had been used by German scientists. The B8 reactor consisted of five concentric circles of uranium cubes suspended on chains within the heavy water tank. The German scientists planned to place a radium-beryllium neutron source into the reactor's core to kick-start the chain reaction with a flood of neutrons that would split the uranium nuclei and release more neutrons, furthering the chain reaction.
Heavy water is a form of water that contains the neutron-heavy hydrogen isotope deuterium. Like the mainly-graphite blocks and rods used in many reactors, it can be used to "moderate" or slow down fast neutrons created in a fission reaction so they trigger fission — and more neutrons — in nearby uranium atoms. The Germans also used small amounts of graphite in their reactor, but as a coating to reflect neutrons back into the chamber.
A cube of natural uranium from the German atomic bomb project. (Image credit: John T. Consoli, University of Maryland College Park, MD.)By combining the records of the cubes, heavy water and graphite used by the German scientists with measurements of the two surviving cubes, the study authors created a mathematical model of the reactor that agreed closely with historical measurements. This enabled them to establish that the heavy water reactor was far from achieving a stable reaction. The findings also helped them examine the suggestion that the Germans should have instead built a graphite-based reactor like the nuclear pile developed at the University of Chicago to build the American bomb.
But the study authors determined that a graphite-moderated reactor was unfeasible in wartime Germany because the local supply of coal available to create graphite contained high levels of neutron-absorbing boron, making it useless.
Instead, the heavy water used in the B8 reactor was produced at a single factory in Norway, which was occupied by Germany from April 1940 until May 1945. However, the reactor contained only about 370 gallons (1,400 liters) of heavy water, instead of the more than 780 gallons (roughly 3,000 liters) it would have needed, the researchers determined.
Heavy water makes up a tiny fraction of a percent of ordinary water, and extracting it by electrolysis in the Norwegian factory took extraordinary effort. The factory was producing as much heavy water as it could, but the B8 reactor would have needed more than twice the amount it produced during the entire war, the researchers wrote.
Another finding is that the B8 reactor had about half the amount of uranium it would have needed to sustain a fission chain reaction. The reactor contained a total of 664 cubes, each weighing about 5.11 pounds (2.32 kilograms), for a total of 3,390 pounds (1,540 kilograms) of uranium. Similar cubes were distributed among other experimental groups, giving a total inventory in wartime Germany of about 1,100 cubes of uranium.
But the researchers determined that the B8 reactor would have needed at least 1,200 cubes to work. Germany, therefore, was not about to develop a reactor for an atomic bomb in 1945. Contrary to Heisenberg's claims, the heavy-water reactor was not nearly ready, and a working graphite reactor was impossible.
"We conclude Germany could not have built heavy water nor graphite reactors during World War II," the researchers wrote.
Mark Walker, a historian at Union College in Schenectady, New York, who wasn't involved in the study, said the findings explain Germany's decision to develop a heavy-water reactor, since a graphite reactor was not feasible and they didn't know at the time how much heavy water would be needed.
Walker is the author of "Hitler's Atomic Bomb: History, Legend, and the Twin Legacies of Auschwitz and Hiroshima" (Cambridge University Press, 2024) and a noted expert on Germany's wartime nuclear efforts. He agreed that Germany could not have made a graphite reactor during World War II.
"This paper argues that if the Germans had done something they did not do, then this would have failed," he told Live Science in an email. "While this is counterfactual history, it is an interesting engineering analysis."
'> Uranium from World War II reveals how close the Nazis were to an atomic bomb