The first-ever discovery of an extraterrestrial radioactive isotope on Earth has scientists rethinking the origins of the elements on our planet.
The tiny traces of plutonium-244 were found in ocean crust alongside radioactive iron-60. The two isotopes are evidence of violent cosmic events in the vicinity of Earth millions of years ago.
Star explosions, or supernovae create many of the heavy elements in the periodic table, including those vital for human life, such as iron, potassium and iodine.
To form even heavier elements, such as gold, uranium and plutonium it was thought that a more violent event may be needed, such as two neutron stars merging.
However, a study led by Professor Anton Wallner from The Australian National University (ANU) suggests a more complex picture.
“The story is complicated – possibly this plutonium-244 was produced in supernova explosions or it could be left over from a much older, but even more spectacular event such as a neutron star detonation,” lead author of the study, Professor Wallner said.
Any plutonium-244 and iron-60 that existed when the Earth formed from interstellar gas and dust over four billion years ago has long since decayed, so current traces of them must have originated from recent cosmic events in space.
The dating of the sample confirms two or more supernova explosions occurred near Earth.
“Our data could be the first evidence that supernovae do indeed produce plutonium-244,” Professor Wallner said
“Or perhaps it was already in the interstellar medium before the supernova went off, and it was pushed across the solar system together with the supernova ejecta.”
Professor Wallner also holds joint positions at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and Technical University Dresden in Germany, and conducted this work with researchers from Australia, Israel, Japan, Switzerland and Germany.
The VEGA accelerator at Australian Nuclear Science and Technology Organisation, (ANSTO) in Sydney was used to identify the tiny traces of the plutonium-244.
Featured image: This false-color composite from NASA Spitzer Space Telescope and NASA Chandra X-ray Observatory shows the remnant of N132D. Credit: NASA/JPL-Caltech/Harvard-Smithsonian CfA
References: (1) A. Wallner et al. 60Fe and 244Pu deposited on Earth constrain the r-process yields of recent nearby supernovae, Science (2021). DOI: 10.1126/science.aax3972 (2) Daniel Clery. Trace seabed plutonium points to stellar forges of heavy elements, Science (2021). DOI: 10.1126/science.abj4596
A team of researchers from the University of Rhode Island’s Graduate School of Oceanography and their collaborators have revealed that the abundant microbes living in ancient sediment below the seafloor are sustained primarily by chemicals created by the natural irradiation of water molecules.
The team discovered that the creation of these chemicals is amplified significantly by minerals in marine sediment. In contrast to the conventional view that life in sediment is fueled by products of photosynthesis, an ecosystem fueled by irradiation of water begins just meters below the seafloor in much of the open ocean. This radiation-fueled world is one of Earth’s volumetrically largest ecosystems.
The research was published today in the journal Nature Communications.
Justine Sauvage, lead author of the study, measures dissolved oxygen content in sediment cores collected in the North Atlantic. Photo courtesy of Justine Sauvage
“This work provides an important new perspective on the availability of resources that subsurface microbial communities can use to sustain themselves. This is fundamental to understand life on Earth and to constrain the habitability of other planetary bodies, such as Mars,” said Justine Sauvage, the study’s lead author and a postdoctoral fellow at the University of Gothenburg who conducted the research as a doctoral student at URI.
The process driving the research team’s findings is radiolysis of water – the splitting of water molecules into hydrogen and oxidants as a result of being exposed to naturally occurring radiation. Steven D’Hondt, URI professor of oceanography and a co-author of the study, said the resulting molecules become the primary source of food and energy for the microbes living in the sediment.
“The marine sediment actually amplifies the production of these usable chemicals,” he said. “If you have the same amount of irradiation in pure water and in wet sediment, you get a lot more hydrogen from wet sediment. The sediment makes the production of hydrogen much more effective.”
Why the process is amplified in wet sediment is unclear, but D’Hondt speculates that minerals in the sediment may “behave like a semiconductor, making the process more efficient.”
The discoveries resulted from a series of laboratory experiments conducted in the Rhode Island Nuclear Science Center. Sauvage irradiated vials of wet sediment from various locations in the Pacific and Atlantic Oceans, collected by the Integrated Ocean Drilling Program and by U.S. research vessels. She compared the production of hydrogen to similarly irradiated vials of seawater and distilled water. The sediment amplified the results by as much as a factor of 30.
“This study is a unique combination of sophisticated laboratory experiments integrated into a global biological context,” said co-author Arthur Spivack, URI professor of oceanography.
The implications of the findings are significant.
“If you can support life in subsurface marine sediment and other subsurface environments from natural radioactive splitting of water, then maybe you can support life the same way in other worlds,” said D’Hondt. “Some of the same minerals are present on Mars, and as long as you have those wet catalytic minerals, you’re going to have this process. If you can catalyze production of radiolytic chemicals at high rates in the wet Martian subsurface, you could potentially sustain life at the same levels that it’s sustained in marine sediment.”
Sauvage added, “This is especially relevant given that the Perseverance Rover has just landed on Mars, with its mission to collect Martian rocks and to characterize its habitable environments.”
D’Hondt said the research team’s findings also have implications for the nuclear industry, including for how nuclear waste is stored and how nuclear accidents are managed. “If you store nuclear waste in sediment or rock, it may generate hydrogen and oxidants faster than in pure water. That natural catalysis may make those storage systems more corrosive than is generally realized,” he said.
The next steps for the research team will be to explore the effect of hydrogen production through radiolysis in other environments on Earth and beyond, including oceanic crust, continental crust and subsurface Mars. They also will seek to advance the understanding of how subsurface microbial communities live, interact and evolve when their primary energy source is derived from the natural radiolytic splitting of water.
This study was supported by the U.S. National Science Foundation and the U.S. National Aeronautics and Space Administration. The project is also affiliated with the Center for Dark Energy Biosphere Investigations.
Featured image: Marine sediment samples used in the irradiation experiments. Photo courtesy of Justine Sauvage
Rutgers-led study sheds light on subsurface melting of thick ice billions of years ago.
The most habitable region for life on Mars would have been up to several miles below its surface, likely due to subsurface melting of thick ice sheets fueled by geothermal heat, a Rutgers-led study concludes.
“Even if greenhouse gases like carbon dioxide and water vapor are pumped into the early Martian atmosphere in computer simulations, climate models still struggle to support a long-term warm and wet Mars,” said lead author Lujendra Ojha, an assistant professor in the Department of Earth and Planetary Sciences in the School of Arts and Sciences at Rutgers University-New Brunswick. “I and my co-authors propose that the faint young sun paradox may be reconciled, at least partly, if Mars had high geothermal heat in its past.”
Our sun is a massive nuclear fusion reactor that generates energy by fusing hydrogen into helium. Over time, the sun has gradually brightened and warmed the surface of planets in our solar system. About 4 billion years ago, the sun was much fainter so the climate of early Mars should have been freezing. However, the surface of Mars has many geological indicators, such as ancient riverbeds, and chemical indicators, such as water-related minerals, that suggest the red planet had abundant liquid water about 4.1 billion to 3.7 billion years ago (the Noachian era). This apparent contradiction between the geological record and climate models is the faint young sun paradox.
On rocky planets like Mars, Earth, Venus and Mercury, heat-producing elements like uranium, thorium and potassium generate heat via radioactive decay. In such a scenario, liquid water can be generated through melting at the bottom of thick ice sheets, even if the sun was fainter than now. On Earth, for example, geothermal heat forms subglacial lakes in areas of the West Antarctic ice sheet, Greenland and the Canadian Arctic. It’s likely that similar melting may help explain the presence of liquid water on cold, freezing Mars 4 billion years ago.
The scientists examined various Mars datasets to see if heating via geothermal heat would have been possible in the Noachian era. They showed that the conditions needed for subsurface melting would have been ubiquitous on ancient Mars. Even if Mars had a warm and wet climate 4 billion years ago, with the loss of the magnetic field, atmospheric thinning and subsequent drop in global temperatures over time, liquid water may have been stable only at great depths. Therefore, life, if it ever originated on Mars, may have followed liquid water to progressively greater depths.
“At such depths, life could have been sustained by hydrothermal (heating) activity and rock-water reactions,” Ojha said. “So, the subsurface may represent the longest-lived habitable environment on Mars.”
NASA’s Mars InSight spacecraft landed in 2018 and may allow scientists to better assess the role of geothermal heat in the habitability of Mars during the Noachian era, according to Ojha.
Scientists at Dartmouth College, Louisiana State University and the Planetary Science Institute contributed to the study.
References: Lujendra Ojha, Jacob Buffo, Suniti Karunatillake, Matthew Siegler, “Groundwater production from geothermal heating on early Mars and implication for early martian habitability”, Science Advances 02 Dec 2020: Vol. 6, no. 49, eabb1669 DOI: 10.1126/sciadv.abb1669 https://advances.sciencemag.org/content/6/49/eabb1669
Scientists at Osaka University create seaweed-shaped sodium titanate mats made of nanofibers that can remove cobalt ions from water, which may help provide a source of safe, recycled drinking water by removal of heavy metals and radionuclides.
A team of researchers at Osaka University has developed a nanopowder shaped like seaweed for a water filter to help remove toxic metal ions (Fig. 1). Made of layered sodium titanate, the randomly oriented nanofibers increase the efficacy of cobalt-II (Co2+) ion capture. This work might lead to cheaper and more effective solutions for filtering water that is currently unusable due to hazardous heavy metals or radioactive fallout.
As the global population continues to increase, so will the need for drinkable water. Sadly, many water sources have become contaminated with heavy metals, such as cobalt, from industrial waste or radioactive runoff. Sodium titanate has been widely used to filter out these toxic substances, but its efficiency is not enough. Sodium titanate is generally a two-dimensional layered material, but its crystal structure can vary based on the chemical composition and preparation method. To effectively capture radioactive and/or heavy metal ions, the morphological control of the sodium titanate is very important.
Now, researchers from the Institute of Scientific and Industrial Research at Osaka University have developed a new method to create highly efficient sodium titanate filters. “We used a template-free alkaline hydrothermal process to produce the mats,” first author Yoshifumi Kondo says. The researchers found that increasing the hydrothermal synthesis time caused the initially round crystals to become elongated and fibrous, and to form the seaweed-shaped mats consisting of the randomly oriented nanofibers (Fig. 2). This seaweed-like nanoscale morphology increased the surface area of the mats, which improved the removal efficiency of Co2+ during sorption tests.
“Due to the progress of global warming and serious environmental pollution, the need for safe ways to remove radioactive materials and heavy metals from water resources has become even more critical,” senior author Tomoyo Goto says. Compared with a commercially available material, the nanostructured sodium titanate mats showed improved performance for capturing Co2+ ions. The method is expected to be applied for other purification systems that remove heavy metals and radionuclides from wastewater (Fig. 3).
Developing safe and sustainable fuels for nuclear energy is an integral part of Los Alamos National Laboratory’s energy security mission. Uranium dioxide, a radioactive actinide oxide, is the most widely used nuclear fuel in today’s nuclear power plants. A new “combustion synthesis” process recently established for lanthanide metals — non-radioactive and positioned one row above actinides on the periodic table — could be a guide for the production of safe, sustainable nuclear fuels.
“Actinide nitride fuels are potentially a safer and more economical option in current power-generating systems,” said Bi Nguyen, Los Alamos National Laboratory Agnew postdoc and lead author of research recently published in the journal Inorganic Chemistry, which was selected as an American Chemical Society Editors’ Choice Featured Article.
“Nitride fuels are also well suited to future Generation IV nuclear power systems, which focus on safety, and feature a sustainable closed reactor fuel cycle. Actinide nitrides have superior thermal conductivity compared to the oxides and are significantly more energy dense,” said Nguyen. Nitrides are a class of chemical compounds that contain nitrogen, versus oxides, which contain oxygen.
Actinide nitride fuels would provide more safety and sustainability because of their energy density, offering up more energy from less material, as well as better thermal conductivity — allowing for lower temperature operations, giving them a larger margin to meltdown under abnormal conditions.
Actinide nitrides, however, are very challenging to make and the production of large amounts of high purity actinide nitrides continues to be a major impediment to their application. Both actinides and lanthanides are at the bottom of the periodic table and potential methods to make actinide materials are typically first tested with the lanthanides because they behave similarly, but are not radioactive.
Los Alamos National Laboratory and Naval Research Laboratory scientists discovered that LnBTA [lanthanide bis(tetrazolato)amine] compounds can be burned to produce high-purity lanthanide nitride foams in a unique technique called combustion synthesis. This method uses a laser pulse to initiate dehydrated LnBTA complexes, which then undergo a self-sustained combustion reaction in an inert atmosphere to yield nanostructured lanthanide nitride foams. This work was funded by the Laboratory Directed Research and Development (LDRD) program.
LnBTA compounds are easily prepared in bulk and their combustion is readily scalable. There is an ongoing collaboration between the Laboratory’s Weapons Modernization and Chemistry divisions to examine actinide analogues for combustion synthesis of actinide nitride fuels.
Earth-size planets can have varying amounts of radioactive elements, which generate internal heat that drives a planet’s geological activity and magnetism.
The amount of long-lived radioactive elements incorporated into a rocky planet as it forms may be a crucial factor in determining its future habitability, according to a new study by an interdisciplinary team of scientists at UC Santa Cruz.
That’s because internal heating from the radioactive decay of the heavy elements thorium and uranium drives plate tectonics and may be necessary for the planet to generate a magnetic field. Earth’s magnetic field protects the planet from solar winds and cosmic rays.
Convection in Earth’s molten metallic core creates an internal dynamo (the “geodynamo”) that generates the planet’s magnetic field. Earth’s supply of radioactive elements provides more than enough internal heating to generate a persistent geodynamo, according to Francis Nimmo, professor of Earth and planetary sciences at UC Santa Cruz and first author of a paper on the new findings, published November 10 in Astrophysical Journal Letters.
“What we realized was that different planets accumulate different amounts of these radioactive elements that ultimately power geological activity and the magnetic field,” Nimmo explained. “So we took a model of the Earth and dialed the amount of internal radiogenic heat production up and down to see what happens.”
What they found is that if the radiogenic heating is more than the Earth’s, the planet can’t permanently sustain a dynamo, as Earth has done. That happens because most of the thorium and uranium end up in the mantle, and too much heat in the mantle acts as an insulator, preventing the molten core from losing heat fast enough to generate the convective motions that produce the magnetic field.
With more radiogenic internal heating, the planet also has much more volcanic activity, which could produce frequent mass extinction events. On the other hand, too little radioactive heat results in no volcanism and a geologically “dead” planet.
“Just by changing this one variable, you sweep through these different scenarios, from geologically dead to Earth-like to extremely volcanic without a dynamo,” Nimmo said, adding that these findings warrant more detailed studies.
“Now that we see the important implications of varying the amount of radiogenic heating, the simplified model that we used should be checked by more detailed calculations,” he said.
A planetary dynamo has been tied to habitability in several ways, according to Natalie Batalha, a professor of astronomy and astrophysics whose Astrobiology Initiative at UC Santa Cruz sparked the interdisciplinary collaboration that led to this paper.
“It has long been speculated that internal heating drives plate tectonics, which creates carbon cycling and geological activity like volcanism, which produces an atmosphere,” Batalha explained. “And the ability to retain an atmosphere is related to the magnetic field, which is also driven by internal heating.”
Coauthor Joel Primack, a professor emeritus of physics, explained that stellar winds, which are fast-moving flows of material ejected from stars, can steadily erode a planet’s atmosphere if it has no magnetic field.
“The lack of a magnetic field is apparently part of the reason, along with its lower gravity, why Mars has a very thin atmosphere,” he said. “It used to have a thicker atmosphere, and for a while it had surface water. Without the protection of a magnetic field, much more radiation gets through and the surface of the planet also becomes less habitable.”
Primack noted that the heavy elements crucial to radiogenic heating are created during mergers of neutron stars, which are extremely rare events. The creation of these so-called r-process elements during neutron-star mergers has been a focus of research by coauthor Enrico Ramirez-Ruiz, professor of astronomy and astrophysics.
“We would expect considerable variability in the amounts of these elements incorporated into stars and planets, because it depends on how close the matter that formed them was to where these rare events occurred in the galaxy,” Primack said.
Astronomers can use spectroscopy to measure the abundance of different elements in stars, and the compositions of planets are expected to be similar to those of the stars they orbit. The rare earth element europium, which is readily observed in stellar spectra, is created by the same process that makes the two longest-lived radioactive elements, thorium and uranium, so europium can be used as a tracer to study the variability of those elements in our galaxy’s stars and planets.
Astronomers have obtained europium measurements for many stars in our galactic neighborhood. Nimmo was able use those measurements to establish a natural range of inputs to his models of radiogenic heating. The sun’s composition is in the middle of that range. According to Primack, many stars have half as much europium compared to magnesium as the sun, and many stars have up to two times more than the sun.
The importance and variability of radiogenic heating opens up many new questions for astrobiologists, Batalha said.
“It’s a complex story, because both extremes have implications for habitability. You need enough radiogenic heating to sustain plate tectonics but not so much that you shut down the magnetic dynamo,” she said. “Ultimately, we’re looking for the most likely abodes of life. The abundance of uranium and thorium appear to be key factors, possibly even another dimension for defining a Goldilocks planet.”
Using europium measurements of their stars to identify planetary systems with different amounts of radiogenic elements, astronomers can start looking for differences between the planets in those systems, Nimmo said, especially once the James Webb Space Telescope is deployed. “The James Webb Space Telescope will be a powerful tool for the characterization of exoplanet atmospheres,” he said.
An international team of scientists have unveiled the world’s first production of a purified beam of neutron-rich, radioactive tantalum ions. This development could now allow for lab-based experiments on exploding stars helping scientists to answer long-held questions such as “where does gold come from?”
In a paper published in Physical Review Letters, the University of Surrey together with its partners detail how they used a new isotope-separation facility, called KISS, which is developed and operated by the Wako Nuclear Science Centre (WNSC) in the High Energy Accelerator Research Organization (KEK), Japan, to make beams of heavy tantalum isotopes.
The chemical element of tantalum is extremely difficult to vaporise, so the team had to capture radioactive tantalum atoms in high-pressure argon gas, ionising the atoms with precisely tuned lasers. A single isotope of radioactive tantalum could then be selected for detailed investigation.
In the study, the team found that when produced in a metastable state, tantalum-187’s nucleus fleetingly rotated in an irregular manner. The team discovered that tantalum-187’s gamma-ray “fingerprint” was characteristic of a prolate (American football) shape but simultaneously with a hint of an oblate (pancake) shape.
The team believe their results hint at the possibility of tantalum’s more dramatic shape-change to a full oblate rotation which they aim to explore in detail in future experiments.
Philip Walker, Emeritus Professor of Physics at the University of Surrey, said: “Theory suggests that just two more neutrons could tip the shape of tantalum-187 from prolate to oblate, so tantalum-189 is an objective for future investigation. However, it now seems to be a real possibility to go further and reach uncharted tantalum-199, with 126 neutrons, to test the exploding-star mechanism.”
Yoshikazu Hirayama, Associate Professor of WNSC in KEK, said: “Our KISS is a unique facility which can provide unexplored heavy nuclei, such as tantalum-187, 189, and 199, for the studies of exotic nuclear structures. We have started to delve into the mechanism of the synthesis of elements in the universe through the nuclear studies at KISS.”
References: P. M. Walker, Y. Hirayama, G. J. Lane, H. Watanabe, G. D. Dracoulis, M. Ahmed, M. Brunet, T. Hashimoto, S. Ishizawa, F. G. Kondev, Yu. A. Litvinov, H. Miyatake, J. Y. Moon, M. Mukai, T. Niwase, J. H. Park, Zs. Podolyák, M. Rosenbusch, P. Schury, M. Wada, X. Y. Watanabe, W. Y. Liang, and F. R. Xu, “Properties of 187Ta Revealed through Isomeric Decay”, Phys. Rev. Lett. 125, 192505 – Published 6 November 2020. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.192505
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