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Radioisotope generators − inside the ‘nuclear batteries’ that power faraway spacecraft

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Radioisotope
Voyager 1, shown in this illustration, has operated for decades thanks to a radioisotope power system. NASA via AP
Benjamin Roulston, Clarkson University Powering spacecraft with solar energy may not seem like a challenge, given how intense the Sun’s light can feel on Earth. Spacecraft near the Earth use large solar panels to harness the Sun for the electricity needed to run their communications systems and science instruments. However, the farther into space you go, the weaker the Sun’s light becomes and the less useful it is for powering systems with solar panels. Even in the inner solar system, spacecraft such as lunar or Mars rovers need alternative power sources. As an astrophysicist and professor of physics, I teach a senior-level aerospace engineering course on the space environment. One of the key lessons I emphasize to my students is just how unforgiving space can be. In this extreme environment where spacecraft must withstand intense solar flares, radiation and temperature swings from hundreds of degrees below zero to hundreds of degrees above zero, engineers have developed innovative solutions to power some of the most remote and isolated space missions. So how do engineers power missions in the outer reaches of our solar system and beyond? The solution is technology developed in the 1960s based on scientific principles discovered two centuries ago: radioisotope thermoelectric generators, or RTGs. RTGs are essentially nuclear-powered batteries. But unlike the AAA batteries in your TV remote, RTGs can provide power for decades while hundreds of millions to billions of miles from Earth.

Nuclear power

Radioisotope thermoelectric generators do not rely on chemical reactions like the batteries in your phone. Instead, they rely on the radioactive decay of elements to produce heat and eventually electricity. While this concept sounds similar to that of a nuclear power plant, RTGs work on a different principle. Most RTGs are built using plutonium-238 as their source of energy, which is not usable for nuclear power plants since it does not sustain fission reactions. Instead, plutonium-238 is an unstable element that will undergo radioactive decay. Radioactive decay, or nuclear decay, happens when an unstable atomic nucleus spontaneously and randomly emits particles and energy to reach a more stable configuration. This process often causes the element to change into another element, since the nucleus can lose protons.
A graphic showing a larger atom losing a particle made of two protons and two neutrons and transforming into a smaller atom.
Plutonium-238 decays into uranium-234 and emits an alpha particle, made of two protons and two neutrons. NASA
When plutonium-238 decays, it emits alpha particles, which consist of two protons and two neutrons. When the plutonium-238, which starts with 94 protons, releases an alpha particle, it loses two protons and turns into uranium-234, which has 92 protons. These alpha particles interact with and transfer energy into the material surrounding the plutonium, which heats up that material. The radioactive decay of plutonium-238 releases enough energy that it can glow red from its own heat, and it is this powerful heat that is the energy source to power an RTG.
A circular metal container with a glowing cylinder inside.
The nuclear heat source for the Mars Curiosity rover is encased in a graphite shell. The fuel glows red hot because of the radioactive decay of plutonium-238. Idaho National Laboratory, CC BY

Heat as power

Radioisotope thermoelectric generators can turn heat into electricity using a principle called the Seebeck effect, discovered by German scientist Thomas Seebeck in 1821. As an added benefit, the heat from some types of RTGs can help keep electronics and the other components of a deep-space mission warm and working well. In its basic form, the Seebeck effect describes how two wires of different conducting materials joined in a loop produce a current in that loop when exposed to a temperature difference.
The Seeback effect is the principle behind RTGs.
Devices that use this principle are called thermoelectric couples, or thermocouples. These thermocouples allow RTGs to produce electricity from the difference in temperature created by the heat of plutonium-238 decay and the frigid cold of space.

Radioisotope thermoelectric generator design

In a basic radioisotope thermoelectric generator, you have a container of plutonium-238, stored in the form of plutonium-dioxide, often in a solid ceramic state that provides extra safety in the event of an accident. The plutonium material is surrounded by a protective layer of foil insulation to which a large array of thermocouples is attached. The whole assembly is inside a protective aluminum casing.
A piece of machinery, which looks like a metal cylinder with fan-like structures outside it.
An RTG has decaying material in its core, which generates heat that it converts to electricity. U.S. Department of Energy
The interior of the RTG and one side of the thermocouples is kept hot – close to 1,000 degrees Fahrenheit (538 degrees Celsius) – while the outside of the RTG and the other side of the thermocouples are exposed to space. This outside, space-facing layer can be as cold as a few hundred degrees Fahrenheit below zero. This strong temperature difference allows an RTG to turn the heat from radioactive decay into electricity. That electricity powers all kinds of spacecraft, from communications systems to science instruments to rovers on Mars, including five current NASA missions. But don’t get too excited about buying an RTG for your house. With the current technology, they can produce only a few hundred watts of power. That may be enough to power a standard laptop, but not enough to play video games with a powerful GPU. For deep-space missions, however, those couple hundred watts are more than enough. The real benefit of RTGs is their ability to provide predictable, consistent power. The radioactive decay of plutonium is constant – every second of every day for decades. Over the course of about 90 years, only half the plutonium in an RTG will have decayed away. An RTG requires no moving parts to generate electricity, which makes them much less likely to break down or stop working. Additionally, they have an excellent safety record, and they’re designed to survive their normal use and also be safe in the event of an accident.

RTGs in action

RTGs have been key to the success of many of NASA’s solar system and deep-space missions. The Mars Curiosity and Perseverance rovers and the New Horizons spacecraft that visited Pluto in 2015 have all used RTGs. New Horizons is traveling out of the solar system, where its RTGs will provide power where solar panels could not. However, no missions capture the power of RTGs quite like the Voyager missions. NASA launched the twin spacecraft Voyager 1 and Voyager 2 in 1977 to take a tour of the outer solar system and then journey beyond it.
A diagram of a Voyager probe, with its parts labeled and a cylinder broken into three parts coming off its side labeled 'RTGs'.
The RTGs on the Voyager probes have allowed the spacecraft to stay powered up while they collect data. NASA/JPL-Caltech
Each craft was equipped with three RTGs, providing a total of 470 watts of power at launch. It has been almost 50 years since the launch of the Voyager probes, and both are still active science missions, collecting and sending data back to Earth. Voyager 1 and Voyager 2 are about 15.5 billion miles and 13 billion miles (nearly 25 billion kilometers and 21 billion kilometers) from the Earth, respectively, making them the most distant human-made objects ever. Even at these extreme distances, their RTGs are still providing them consistent power. These spacecraft are a testament to the ingenuity of the engineers who first designed RTGs in the early 1960s. Benjamin Roulston, Assistant Professor of Physics, Clarkson University This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Artificial Intelligence

AI ‘reanimations’: Making facsimiles of the dead raises ethical quandaries

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AI
This screenshot of an AI-generated video depicts Christopher Pelkey, who was killed in 2021. Screenshot: Stacey Wales/YouTube
Nir Eisikovits, UMass Boston and Daniel J. Feldman, UMass Boston Christopher Pelkey was shot and killed in a road range incident in 2021. On May 8, 2025, at the sentencing hearing for his killer, an AI video reconstruction of Pelkey delivered a victim impact statement. The trial judge reported being deeply moved by this performance and issued the maximum sentence for manslaughter. As part of the ceremonies to mark Israel’s 77th year of independence on April 30, 2025, officials had planned to host a concert featuring four iconic Israeli singers. All four had died years earlier. The plan was to conjure them using AI-generated sound and video. The dead performers were supposed to sing alongside Yardena Arazi, a famous and still very much alive artist. In the end Arazi pulled out, citing the political atmosphere, and the event didn’t happen. In April, the BBC created a deep-fake version of the famous mystery writer Agatha Christie to teach a “maestro course on writing.” Fake Agatha would instruct aspiring murder mystery authors and “inspire” their “writing journey.” The use of artificial intelligence to “reanimate” the dead for a variety of purposes is quickly gaining traction. Over the past few years, we’ve been studying the moral implications of AI at the Center for Applied Ethics at the University of Massachusetts, Boston, and we find these AI reanimations to be morally problematic. Before we address the moral challenges the technology raises, it’s important to distinguish AI reanimations, or deepfakes, from so-called griefbots. Griefbots are chatbots trained on large swaths of data the dead leave behind – social media posts, texts, emails, videos. These chatbots mimic how the departed used to communicate and are meant to make life easier for surviving relations. The deepfakes we are discussing here have other aims; they are meant to promote legal, political and educational causes.
Chris Pelkey was shot and killed in 2021. This AI ‘reanimation’ of him was presented in court as a victim impact statement.

Moral quandaries

The first moral quandary the technology raises has to do with consent: Would the deceased have agreed to do what their likeness is doing? Would the dead Israeli singers have wanted to sing at an Independence ceremony organized by the nation’s current government? Would Pelkey, the road-rage victim, be comfortable with the script his family wrote for his avatar to recite? What would Christie think about her AI double teaching that class? The answers to these questions can only be deduced circumstantially – from examining the kinds of things the dead did and the views they expressed when alive. And one could ask if the answers even matter. If those in charge of the estates agree to the reanimations, isn’t the question settled? After all, such trustees are the legal representatives of the departed. But putting aside the question of consent, a more fundamental question remains. What do these reanimations do to the legacy and reputation of the dead? Doesn’t their reputation depend, to some extent, on the scarcity of appearance, on the fact that the dead can’t show up anymore? Dying can have a salutary effect on the reputation of prominent people; it was good for John F. Kennedy, and it was good for Israeli Prime Minister Yitzhak Rabin. The fifth-century B.C. Athenian leader Pericles understood this well. In his famous Funeral Oration, delivered at the end of the first year of the Peloponnesian War, he asserts that a noble death can elevate one’s reputation and wash away their petty misdeeds. That is because the dead are beyond reach and their mystique grows postmortem. “Even extreme virtue will scarcely win you a reputation equal to” that of the dead, he insists. Do AI reanimations devalue the currency of the dead by forcing them to keep popping up? Do they cheapen and destabilize their reputation by having them comment on events that happened long after their demise? In addition, these AI representations can be a powerful tool to influence audiences for political or legal purposes. Bringing back a popular dead singer to legitimize a political event and reanimating a dead victim to offer testimony are acts intended to sway an audience’s judgment. It’s one thing to channel a Churchill or a Roosevelt during a political speech by quoting them or even trying to sound like them. It’s another thing to have “them” speak alongside you. The potential of harnessing nostalgia is supercharged by this technology. Imagine, for example, what the Soviets, who literally worshipped Lenin’s dead body, would have done with a deep fake of their old icon.

Good intentions

You could argue that because these reanimations are uniquely engaging, they can be used for virtuous purposes. Consider a reanimated Martin Luther King Jr., speaking to our currently polarized and divided nation, urging moderation and unity. Wouldn’t that be grand? Or what about a reanimated Mordechai Anielewicz, the commander of the Warsaw Ghetto uprising, speaking at the trial of a Holocaust denier like David Irving? But do we know what MLK would have thought about our current political divisions? Do we know what Anielewicz would have thought about restrictions on pernicious speech? Does bravely campaigning for civil rights mean we should call upon the digital ghost of King to comment on the impact of populism? Does fearlessly fighting the Nazis mean we should dredge up the AI shadow of an old hero to comment on free speech in the digital age?
a man in a suit and tie stands in front of a microphone
No one can know with certainty what Martin Luther King Jr. would say about today’s society. AP Photo/Chick Harrity
Even if the political projects these AI avatars served were consistent with the deceased’s views, the problem of manipulation – of using the psychological power of deepfakes to appeal to emotions – remains. But what about enlisting AI Agatha Christie to teach a writing class? Deep fakes may indeed have salutary uses in educational settings. The likeness of Christie could make students more enthusiastic about writing. Fake Aristotle could improve the chances that students engage with his austere Nicomachean Ethics. AI Einstein could help those who want to study physics get their heads around general relativity. But producing these fakes comes with a great deal of responsibility. After all, given how engaging they can be, it’s possible that the interactions with these representations will be all that students pay attention to, rather than serving as a gateway to exploring the subject further.

Living on in the living

In a poem written in memory of W.B. Yeats, W.H. Auden tells us that, after the poet’s death, Yeats “became his admirers.” His memory was now “scattered among a hundred cities,” and his work subject to endless interpretation: “the words of a dead man are modified in the guts of the living.” The dead live on in the many ways we reinterpret their words and works. Auden did that to Yeats, and we’re doing it to Auden right here. That’s how people stay in touch with those who are gone. In the end, we believe that using technological prowess to concretely bring them back disrespects them and, perhaps more importantly, is an act of disrespect to ourselves – to our capacity to abstract, think and imagine. Nir Eisikovits, Professor of Philosophy and Director, Applied Ethics Center, UMass Boston and Daniel J. Feldman, Senior Research Fellow, Applied Ethics Center, UMass Boston This article is republished from The Conversation under a Creative Commons license. Read the original article.

STM Daily News is a vibrant news blog dedicated to sharing the brighter side of human experiences. Emphasizing positive, uplifting stories, the site focuses on delivering inspiring, informative, and well-researched content. With a commitment to accurate, fair, and responsible journalism, STM Daily News aims to foster a community of readers passionate about positive change and engaged in meaningful conversations. Join the movement and explore stories that celebrate the positive impacts shaping our world.

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Science

Coral reefs face an uncertain recovery from the 4th global mass bleaching event – can climate refuges help?

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Coral reefs
The Great Barrier Reef stretches for 1,429 miles just off Australia’s northeastern coast. Auscape/Universal Images Group via Getty Image
Noam Vogt-Vincent, University of Hawaii Tropical reefs might look like inanimate rock, but these colorful seascapes are built by tiny jellyfish-like animals called corals. While adult corals build solid structures that are firmly attached to the sea floor, baby corals are not confined to their reefs. They can drift with ocean currents over great distances to new locations that might give them a better chance of survival. The underwater cities that corals construct are home to about a quarter of all known marine species. They are incredibly important for humans, too, contributing at least a trillion dollars per year in ecosystem services, such as protecting coastlines from wave damage and supporting fisheries and tourism. Unfortunately, coral reefs are among the most vulnerable environments on the planet to climate change. Since 2023, exceptionally warm ocean water has been fueling the planet’s fourth mass coral bleaching event on record, causing widespread mortality in corals around the world. This kind of harm is projected to worsen considerably over the coming decades as ocean temperatures rise.
file 20250507 56 t2zqkd.jpg?ixlib=rb 4.1
A healthy coral reef in American Samoa, left, experiencing coral bleaching due to a severe marine heatwave, center, and eventually dying, right. The Ocean Agency and Ocean Image Bank., CC BY-NC
I am a marine scientist in Hawaii. My colleagues and I are trying to understand how coral reefs might change in the future, and whether new coral reefs might form at higher latitudes as the tropics become too warm and temperate regions become more hospitable. The results lead us to both good and bad news.

Corals can grow in new areas, but will they thrive?

Baby corals can drift freely with ocean currents, potentially traveling hundreds of miles before settling in new locations. That allows the distribution of corals to shift over time. Major ocean currents can carry baby corals to temperate seas. If new coral reefs form there as the waters warm, these areas might act as refuges for tropical corals, reducing the corals’ risk of extinction.
Coral reefs made up of many individual coral polyps.
A close-up of double star corals (Diploastrea heliopora) off Indonesia. Bernard DuPont/Flickr, CC BY-SA
Scientists know from the fossil record that coral reef expansions have occurred before. However, a big question remains: Can corals migrate fast enough to keep pace with climate change caused by humans? We developed a cutting-edge simulation to find the answer. Field and laboratory studies have measured how coral growth depends on temperature, acidity and light intensity. We combined this information with data on ocean currents to create a global simulation that represents how corals respond to a changing environment – including their ability to adapt through evolution and shift their ranges. Then, we used future climate projections to predict how coral reefs may respond to climate change. We found that it will take centuries for coral reefs to shift away from the tropics. This is far too slow for temperate seas to save tropical coral species – they are facing severe threats right now and in the coming decades.
How coral reefs form.

Underwater cities in motion?

Under countries’ current greenhouse gas emissions policies, our simulations suggest that coral reefs will decline globally by a further 70% this century as ocean temperatures continue to rise. As bad as that sounds, it’s actually slightly more optimistic than previous studies that predicted losses as high as 99%. Our simulations suggest that coral populations could expand in a few locations this century, primarily southern Australia, but these expansions may only amount to around 6,000 acres (2,400 hectares). While that might sound a lot, we expect to lose around 10 million acres (4 million hectares) of coral over the same period. In other words, we are unlikely to see significant new tropical-style coral reefs forming in temperate waters within our lifetimes, so most tropical corals will not find refuge in higher latitude seas. Even though the suitable water temperatures for corals are forecast to expand poleward by about 25 miles (40 kilometers) per decade, corals would face other challenges in new environments. Our research suggests that coral range expansion is mainly limited by slower coral growth at higher latitudes, not by dispersal. Away from the equator, light intensity falls and temperature becomes more variable, reducing growth, and therefore the rate of range expansion, for many coral species. It is likely that new coral reefs will eventually form beyond their current range, as history shows, but our results suggest this may take centuries.
Two fish hide among the spikes of coral.
Fish hide out in the safety of Kingman Reef, in the Pacific Ocean between the Hawaiian Islands and American Samoa. Coral reefs provide protection for many species, particularly young fish. USFWS, Pacific Islands
Some coral species are adapted to the more challenging environmental conditions at higher latitudes, and these corals are increasing in abundance, but they are much less diverse and structurally complex than their tropical counterparts. Scientists have used human-assisted migration to try to restore damaged coral reefs by transplanting live corals. However, coral restoration is controversial, as it is expensive and cannot be scaled up globally. Since coral range expansion appears to be limited by challenging environmental conditions at higher latitudes rather than by dispersal, human-assisted migration is also unlikely to help them expand more quickly. Importantly, these potential higher latitude refuges already have rich, distinct ecosystems. Establishing tropical corals within those ecosystems might disrupt existing species, so rapid expansions might not be a good thing in the first place.
file 20250507 56 e4ih71.jpg?ixlib=rb 4.1
A temperate reef near southern Australia, which could be threatened by expansions of tropical coral species. Stefan Andrews/Ocean Image Bank, CC BY-NC

No known alternative to cutting emissions

Despite enthusiasm for coral restoration, there is little evidence to suggest that methods like this can mitigate the global decline of coral reefs. As our study shows, migration would take centuries, while the most severe climate change harm for corals will occur within decades, making it unlikely that subtropical and temperate seas can act as coral refuges. What can help corals is reducing greenhouse gas emissions that are driving global warming. Our study suggests that reducing emissions at a faster pace, in accordance with the Paris climate agreement, could cut the coral loss by half compared with current policies. That could boost reef health for centuries to come. This means that there is still hope for these irreplaceable coral ecosystems, but time is running out.The Conversation Noam Vogt-Vincent, Postdoctoral Fellow in Marine Biology, University of Hawaii This article is republished from The Conversation under a Creative Commons license. Read the original article.

The science section of our news blog STM Daily News provides readers with captivating and up-to-date information on the latest scientific discoveries, breakthroughs, and innovations across various fields. We offer engaging and accessible content, ensuring that readers with different levels of scientific knowledge can stay informed. Whether it’s exploring advancements in medicine, astronomy, technology, or environmental sciences, our science section strives to shed light on the intriguing world of scientific exploration and its profound impact on our daily lives. From thought-provoking articles to informative interviews with experts in the field, STM Daily News Science offers a harmonious blend of factual reporting, analysis, and exploration, making it a go-to source for science enthusiasts and curious minds alike. https://stmdailynews.com/category/science/

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Arizona Monsoon 2025 Forecast: Above-Normal Rainfall Expected Across the State

The Climate Prediction Center’s 2025 outlook predicts above-normal rainfall for Arizona’s monsoon season, with higher temperatures expected statewide. Learn what this means for Phoenix and how to prepare.

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Arizona monsoon 2025

Arizona residents can anticipate a wetter-than-average monsoon season in 2025, according to the latest outlook from the Climate Prediction Center. The forecast indicates a 33% to 50% chance of above-normal precipitation across most of the state, with the highest probabilities in east-central Arizona.

What’s Driving the Forecast?

Several factors contribute to the optimistic precipitation outlook:

Soil Moisture Conditions: Unusually dry soil across the Southwest can enhance monsoon activity. Dry soils heat up more quickly, potentially strengthening the thermal low that draws moisture into the region. ENSO-Neutral Conditions: The Climate Prediction Center notes a 74% chance of ENSO-neutral conditions persisting through the Northern Hemisphere summer. Such conditions often lead to more typical monsoon patterns, without the suppressing effects associated with El Niño.

What to Expect in Phoenix

For Phoenix, the outlook suggests a 39% chance of above-normal precipitation, a 33% chance of near-normal precipitation, and a 28% chance of below-normal precipitation during the July-September monsoon period. While the probabilities don’t guarantee a wetter season, the highest likelihood leans toward increased rainfall.

Preparing for Monsoon Season

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With the potential for increased rainfall, it’s essential to prepare for the associated hazards:

Flash Flooding: Heavy downpours can lead to sudden flash floods, especially in urban areas and dry washes. Dust Storms (Haboobs): Strong winds ahead of thunderstorms can create massive dust storms, reducing visibility and air quality. Lightning and Downburst Winds: Severe thunderstorms can produce dangerous lightning and sudden, strong wind gusts.

Safety Tips

Stay Informed: Monitor weather forecasts and alerts from trusted sources like the National Weather Service. Avoid Flooded Areas: Never drive through flooded roadways; turn around, don’t drown. Secure Outdoor Items: High winds can turn unsecured objects into projectiles. Prepare an Emergency Kit: Include essentials like water, non-perishable food, flashlight, batteries, and first aid supplies.

For a detailed overview of the 2025 Arizona Monsoon Outlook, you can watch the following video:

2025 Arizona Monsoon Outlook

For more information and updates, visit 12News.

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Source: 12News

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