The first nuclear weapon test, code-named "Trinity," took place in the New Mexico desert at 5:30 a.m. on July 16, 1945. This test was a proof of concept for the secret nuclear science taking place at Los Alamos as a part of the Manhattan Project during World War II and would lead to the atomic bombs being dropped on Hiroshima and Nagasaki, Japan, just a few weeks later.

Since those detonations, the development of nuclear weapons has accelerated. Countries around the world have built their own nuclear stockpiles, including over 5,000 nuclear warheads held by the U.S.

Yet, even though the basic components of this technology are no longer secret, nuclear weapon development remains a scientific and engineering challenge. But why are nuclear weapons still so difficult to produce?

A big part of the difficulty comes from deriving the chemical elements used inside these weapons to create an explosion, Hans Kristensen, director of the Nuclear Information Project at the Federation of American Scientists, told Live Science in an email.

"That basic idea of a nuclear explosion is that nuclear [fissile] materials are stimulated to release their enormous energy," he said. "To produce fissile material of sufficient purity and sufficient quantity is a challenge [and] this production requires considerable industrial capacity."

Related: How many nuclear bombs have been used?

The enormous release of energy is called a nuclear fission reaction. When this reaction occurs, a chain reaction starts where the atoms are split apart to release energy. This is the same kind of reaction that makes nuclear energy possible.

Uranium and plutonium enrichment

The fissile material inside a nuclear bomb is primarily isotopes of uranium and plutonium, which are radioactive elements, Matthew Zerphy, a professor of practice in nuclear engineering at Penn State, told Live Science. Natural uranium consists of different isotopes, including a large amount of uranium-238 (U-238) and a smaller amount of uranium-235 (U-235), which is more readily fissionable. To access this more fissionable isotope, uranium ore is mined and then goes through several processes for "enrichment" in which the U-235 concentration is increased so that it can be used for nuclear weapons.

"One way to enrich uranium is to turn it into a gas and spin it very rapidly in centrifuges," Zerphy said. "Because of the difference in mass between U-235 and U-238, the isotopes are split, and you can separate out U-235."

For weapons-grade uranium, this separation continues up to concentrations of over 90% U-235, Zerphy said. The most challenging part of this process, which can take weeks to months, is the chemical transformation of the element itself, which requires intensive energy and specialized equipment. One chemical hazard during this process is the possible release of uranium hexafluoride (UF₆), a highly toxic substance that, if inhaled, can damage the kidneys, liver, lungs, brain, skin and eyes.

The process to produce weapons-grade plutonium is even trickier, he said, because this element does not occur naturally like uranium does. Instead, plutonium is a byproduct of nuclear reactors using uranium fuel, which means to produce plutonium, scientists need to handle radioactive, spent nuclear fuel and process the material through "intense" chemical processing. The processing of this material can also pose a safety risk if a critical mass is collected accidentally, Zerphy said, which is the smallest amount of fissile material needed to sustain a self-sustaining fission reaction.

"You'd be very careful to not have that happen while you're in the process of making these components to make sure that things aren't inadvertently brought together and entering some kind of criticality," he said, which could lead to an accidental explosion.

Related: Why did the atomic bomb dropped on Hiroshima leave shadows of people etched on sidewalks?

Although the scientific principles of bringing these components together is well understood, creating and controlling this reaction in a fraction of a second can still be difficult.

"The weapons are designed such that when they are detonated a 'supercritical' mass of fissile material is created very quickly … in a very small space," Zerphy said. "This causes an exponential increase in the number of fissions spreading throughout the material almost instantaneously."

This quick spread of atomic fission is a big part of what makes a nuclear reaction so destructive, he said.

In the case of thermonuclear weapons, which were developed after World War II and use a combination of both nuclear fission and fusion to create an even stronger explosion, a standard fission reaction then has to spark a secondary and stronger fusion reaction. This fusion reaction is the same kind of power found at the center of the sun.

Nuclear weapons testing

Once these weapons are created, scientists and engineers need to be sure the weapons will work as needed, should they ever be used. When nuclear weapons were first developed, scientists would test the weapons themselves at test sites (which devastated the environment of the "deserted" areas where they were tested, as well as people and animals that lived nearby). In contrast, modern weapon testing relies on computer models. This is part of the work done by the National Nuclear Security Administration (NNSA).

"NNSA … develop[s] tools for qualifying weapon components and certifying weapons, ensuring their survivability and effectiveness in various scenarios," an NNSA spokesperson told Live Science in an email. "This involves advanced simulations using supercomputing systems, materials science, and precision engineering to ensure weapons function as intended."

Ultimately, the complexity and challenges of building these weapons may explain why so few nuclear superpowers exist in the world today.

Editor's note: This article was updated at 12:54 p.m. ET on March 20 to note that nuclear weapons have nuclear reactions, not chemical ones, as was previously stated in the top image caption. It was updated again at 7:05 p.m. ET on March 31 to clarify how natural uranium is enriched to increase U-235 concentrations.

Periodic table of elements quiz: How many elements can you name in 10 minutes?

It's a classic science fiction scenario: An enormous asteroid is discovered hurtling toward Earth that is sure to trigger a cataclysmic extinction upon impact. Intrepid scientists have only a year to launch a preemptive strike against the space rock — to knock it off course or blow it to bits — with the fate of humankind at stake. Can they stop it?

This doomsday scenario is, in all likelihood, one humans alive today will never have to face. Astronomers have mapped the trajectories of more than 33,000 asteroids that make occasional close approaches to Earth, and none pose any risk of impact for at least the next 100 years. 

Still, scientists understand that disaster can descend with little warning; thousands of asteroids move hidden in the sun's glare, including many rocks large enough to obliterate entire cities, and the European Space Agency (ESA) warns that dozens of "planet killer" asteroids — those measuring wider than 0.6 mile (1 kilometer) and capable of triggering a global extinction event — still lurk undiscovered in our solar system. 

For this reason, space agencies take the doomsday scenario "very seriously," Brent Barbee, an aerospace engineer at NASA's Goddard Spaceflight Center and a professor of aerospace engineering at the University of Maryland, told Live Science. And after years of research — including the world's first mission to deflect an actual asteroid in space — the international community's efforts have yielded two viable ways of changing a potentially deadly asteroid's course: hitting it with a high-speed impactor, or pummeling it with nuclear explosives.

Related: NASA's most wanted: The 5 most dangerous asteroids in the solar system

The kinetic impactor method

Currently, the only proven way to deflect an asteroid is the kinetic impactor method — essentially, a very, very high-stakes game of cosmic pool.

"The kinetic impactor is a spacecraft that basically just rams into the asteroid at high speed and transfers its momentum to the asteroid, much like playing billiards," Barbee said. "But then the ejected material that comes off the asteroid from the impact point can provide additional momentum change for the asteroid and push it a little bit harder."

NASA tested the kinetic impactor method with the recent Double Asteroid Redirection Test (DART) — a $325 million mission that intentionally crashed a speeding spaceship into the 580-foot-wide (177 meters) asteroid Dimorphos in Sept. 2022. 

Dimorphos posed no threat to Earth but made a prime target due to its size and orbit around a larger companion asteroid, Didymos. Following the successful impact on Sept. 26, Dimorphos' orbit around Didymos slowed by a whopping 33 minutes — a result of both the impact and the massive plume of dust ejected from the asteroid's surface. The mission — humanity's first and so far only attempt to alter the course of an asteroid — was a smashing success. 

However, the kinetic impactor method has its drawbacks, Barbee said. Particularly, the bigger the target asteroid is, the more kinetic impactors are required to deflect it. 

For example, to deflect an asteroid measuring roughly 2,000 feet (610 m) wide — or about three times the size of Dimorphos — scientists would need to simultaneously launch between 39 and 85 Falcon Heavy rockets carrying kinetic impactors, Barbee said, citing the results of a mock asteroid deflection exercise conducted at the International Academy of Astronautics Planetary Defense Conference this year. To deflect an asteroid measuring 4,900 feet (1.5 km) wide — a true "planet killer" — we'd need to simultaneously launch anywhere from 565 to 1,266 kinetic impactors, depending on which part of Earth the asteroid was poised to strike. (A glancing blow takes less mass to deflect than a dead-center hit).

"Either way, those numbers are completely impractical," Barbee said. 

The nuclear option

The current "best option" for deflecting a large asteroid is to launch a nuke at it, Barbee said.

"A single appropriately sized nuclear explosive device was, in our analysis, found to be capable of deflecting even the 1.5 kilometer size asteroid," he added.

Logistically, the process would begin like a routine interplanetary mission, with a nuclear weapon mounted securely atop a standard launch vehicle, then delivered to the asteroid on a small spacecraft. From there, the weapon could be detonated near the asteroid during a high-speed flyby — or, ideally, the nuke-carrying spacecraft could rendezvous with the target asteroid, orbiting it for months or even years to find the perfect angle of approach, much like NASA's OSIRIS-REx spacecraft did with asteroid Bennu from Dec. 2018 to Oct. 2020. The ideal spot for a nuclear detonation would be within a few hundred feet of the asteroid, Barbee said.

Then, the explosion — a blast that would look nothing like any nuclear bomb ever detonated on Earth.

"Space, of course, is a vacuum… so you don't get a big pressure wave, or any of the thermal effects of a terrestrial detonation," Barbee said. "You get a whole lot of radiation all at once."

This torrent of radiation would penetrate and vaporize a thin outer layer of the asteroid's surface. Then, like a kinetic impactor on steroids, the vaporized material would shoot off the asteroid, giving the rock a powerful shove away from the explosion. If positioned correctly, the explosion would knock the planet-killer off its collision course with Earth. 

This method could be equally effective at disrupting smaller "city killer" asteroids, too — those measuring at least 165 feet (50 m) in diameter, which is generally considered the minimum size for an asteroid to reach Earth's surface, Barbee said. While a kinetic impact against such a rock runs the risk of fragmenting it, forming chunks of unknown sizes moving in unpredictable ways, a well-placed nuke could simply "blow the asteroid to smithereens," solving the problem at once, Barbee added. 

However, for now the "nuke it" method exists only in simulations based on data from terrestrial explosions. Many factors, including the size and composition of the asteroid, and the timeframe and trajectory of its approach to Earth, would ultimately impact such a mission's success.

Timing is everything

The biggest challenge with both methods is timing. In their Planetary Defense Conference exercises, astronomers were given 15 years' warning before the hypothetical asteroid's impact with Earth. This gave them ample time to plan, launch and rendezvous a spacecraft with the asteroid.

If a real planet-killer was discovered just a year or two before impact, things would get dicey.

"The typical interplanetary mission development timeline is about five years," Barbee said. "The way things stand right now, getting something off the ground in a year would be very difficult. I don't want to say outright that it would be impossible, but it would certainly be a big challenge."

That's why the best planetary defense is detecting asteroids early — charting them, monitoring them, and developing a contingency plan of attack. Many ground-based observatories are already on the case, with several space-based missions — including NASA's NEO Surveyor and ESA's NEOMIR satellites — in the works to join them. Hopefully, together, these eyes on the skies will keep scientists well informed about any killers lurking in the cosmic fog.

"Asteroid impacts are one of the few natural disasters that we actually have the means to both foresee and prevent," Barbee said. "And so we're taking advantage of that fact and trying to become as prepared as possible."

To prevent the outbreak of World War III, which could involve the use of nuclear weapons, the world's superpowers have developed a system of diplomacy and deterrence. Despite this, since 1945 several crises have brought the U.S. and the Soviet Union (now the Russian Federation) close to a third devastating conflict. 

In the autumn of 1962 the Cuban Missile Crisis brought the governments of the United States and the Soviet Union close to the point of a nuclear conflict. Since then both the U.S. and the U.S.S.R., then Russia, have maintained direct, continual communication channels in order to avoid an accidental launch of nuclear weapons and triggering the global catastrophe of World War III, according to the Nuclear Threat Initiative.

The threat of World War III

World War II ended soon after nuclear bombs were dropped on Hiroshima brought about the first possibility of nuclear annihilation in human history. The proliferation of nuclear weapons then gave rise to the potential for an exchange of atomic bombs and later intercontinental ballistic missiles (ICBM), according to the U.S. National Park Service capable of wreaking destruction on a massive scale.  

The use of the atomic bombs against the Japanese cities of Hiroshima and Nagasaki that ended World War II in the Pacific in 1945 demonstrated the awesome destructive capability of such weapons.

However, the development of nuclear weapons was not to remain exclusively with the United States. The Soviet Union conducted its first nuclear test on August 29, 1949, according to the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), a non–profit set up by the U.N. to monitor and enforce the 1996 treaty banning nuclear testing. 

It wasn't long before the Soviets deployed their own arsenal of nuclear weapons, creating the possibility of a global conflict with the use of potentially devastating consequences for the world.  

Safeguards against World War III

The U.S. and Soviet Union came to the brink of nuclear war during the Cuban Missile Crisis, in 1962, according to the Office of the Historian. One of the big challenges facing the leaders of both nations was the slow and unreliable channels of communication between the two leaders, President John F. Kennedy and Chairman Nikita Khrushchev, according to a paper in the Journal of Global Security Studies. 

The potentially devastating outcome of this crisis caused the two nations to create and maintain safeguards to prevent miscommunication and the unintentional or inadvertent outbreak of World War III.  

One of these safeguards is a communications hotline between the two nations' capitals, which was instituted in August 1963. This hotline was intended to provide "direct communication between the White House and the Kremlin," Roger Hermiston, author of "Two Minutes to Midnight: 1953 – The Year of Living Dangerously" (Biteback Publishing, 2021) told Live Science in an email. 

Over the years additional safeguards were put in place, including the 1971 Agreement on Measures to reduce the Risk of Outbreak of Nuclear War and the 1972 Agreement on the Prevention of Incidents at Sea. 

The Moscow–Washington hotline

As early as 1954, the Soviet government suggested the implementation of safeguards against an accidental nuclear exchange, and nearly a decade later, on June 20, 1963, the Soviet and U.S. governments signed the Memorandum of Understanding Between the United States of America and the Union of Soviet Socialist Republics Regarding the Establishment of a Direct Communications Link, according to the U.S. Department of State.

The first hotline between Moscow and Washington D.C. utilized teletype equipment that was manufactured both in the U.S. and the Soviet Union and then exchanged. The circuitry routed from Washington, D.C., through London, Copenhagen, Stockholm, Helsinki, and on to Moscow, while a backup radio line linked the destination points through Tangier, in northwestern Morocco.

In the 1980s, the hotline was upgraded with fax equipment, and a secure computer email link was implemented in 2008.

According to Hermiston, the hotline is a complement to a number of "broad safeguards including reducing the amount of nuclear weapons in circulation, and developing treaties like the Intermediate–Range Nuclear Forces (I.N.F.) Treaty in 1987, the Strategic Arms Reduction Treaty (S.T.A.R.T.) in 1991 and the Strategic Offensive Reduction Treaty (S.O.R.T.) in 2002.  

"Interestingly, on Jan. 3, 2022, the five big nuclear powers — U.S., China, Russia, France and the U.K. — signed a joint statement committing themselves to Preventing Nuclear War and Avoiding Arms Races," Hermiston wrote.

1953: The pivotal year

According to Hermiston, a nuclear arms race between the world's superpowers began in 1953, and prompted safeguards to be put in place.  By the early 1950s, the development of nuclear weapons with far greater destructive capacity than the first bombs were in various stages of research and deployment, particularly the hydrogen bomb. 

"1953 was the year in which the world moved a dangerous step forward from the atomic bomb to the new terrifying super bomb — a thermonuclear explosive based on hydrogen fusion, up to a thousand times more destructive than the bombs that destroyed Hiroshima and Nagasaki," Hermiston wrote.  

"The Americans had produced their prototype H–Bomb — codenamed Ivy Mike — in November 1952. Next the Russians successfully tested their own, codenamed Joe–4, in August 1953.  As a result, the Doomsday Clock, that measurement of how close the world is to Armageddon, was moved to two minutes to midnight, the closest it had been in seven years of Cold War."

The augmentation of the U.S. and Soviet nuclear stockpiles magnified the importance of direct communication between the superpowers, according to Hermiston. "As the Soviets grew their stockpile under [Premier Leonid] Brezhnev. parity between the two great powers came in the mid–70s.  The phrase "Mutually Assured Destruction" (M.A.D.) was first coined and declared by U.S. Secretary of State Robert McNamara in the early 1960s."

Simply put, MAD asserted that a nuclear strike by one power would invoke a retaliatory strike by the other, leading to the devastation of both, and in turn, a global nuclear holocaust.

"By 1962, the year of the Cuban Missile Crisis, U.S. possessed 25,540 nukes, the Soviets had 3,356 and the U.K. had 211," Hermiston wrote.   

According to Hermiston, the nuclear weapons stockpiles among the world powers by the end of 1953 were as follows:

• U.S.A.: 1,169 
• Soviet Union: 120 
• U.K.: 1

Brushes with fate

Since its inception, the Moscow–Washington hotline has been utilized on several occasions, providing that vital link between the Kremlin, the White House and the Pentagon. 

The hotline, sometimes referred to as "MOLINK" according to the New York Times archive, was reportedly activated during the Six Day War of 1967, the Indo–Pakistani War of 1971, the Yom Kippur War of 1973, the Turkish invasion of Cyprus in 1974, the Soviet invasion of Afghanistan in 1979, recent Russian military intervention in Syria, and perhaps on other occasions.

Recent reports indicate that the military establishments of the United States and Russia have opened a direct, tactical hotline to mitigate the possibility of an accidental military encounter during the current Russian operations in Ukraine, according to the U.S. Department of State.  A senior U.S. official told NBC News in early March 2022, "The Department of Defense recently established a de–confliction line with the Russian Ministry of Defense on March 1 for the purposes of preventing miscalculation, military incidents, and escalation."

Such a safeguard is warranted given the proximity of Russian forces operating in Ukraine to the frontiers of Poland, Romania, Hungary and other NATO countries.

Hermiston sees the currently unstable situation through the lens of history. "In 1953, the most worrying moments came after the death of [Soviet Premier Josef] Stalin, with the Korean War still raging," he assessed.  

"There was optimism that we might enter a new era of 'détente' with the Soviets, but the problem was no one really knew what his successors in the Kremlin were thinking.  Two weeks after Stalin's funeral, the shooting down of a British Lincoln bomber by a Soviet MiG fighter – killing all six crew – was a dangerous flashpoint.  

Today, MAD is entrenched and acknowledged, so Putin's disturbing rhetoric will remain just that — rhetoric. By attacking the West with nuclear weapons, he would invite the destruction of his own country."

Can World War III be prevented?  Reason and logic, perhaps, will prevail, while existing safeguards may be expected to serve their purpose.

Additional resources

To learn more about how close we are to World War III, listen to this discussion from Boston University. Additionally, to explore the history of nuclear weapons, visit the website of the International Campaign to Abolish Nuclear Weapons.

Bibliography

• "The Biden–Putin Summit: What is “Strategic Stability” and Why Is It Important to U.S.–Russia Relations?". The Nuclear Threat Initiative (2021). 
• "Series: Intercontinental Ballistic Missiles". The National Park Service.
• "29 August 1949 – First Soviet nuclear test". Comprehensive Nuclear Test Ban Treaty Organization
• "The Cuban Missile Crisis, October 1962". The Office of the Historian. 
• "Trusting Through the Moscow–Washington Hotline: A Role Theoretical Explanation of the Hotline's Contribution to Crisis Stability". Journal of Global Security Studies (2020).
•  "Two Minutes to Midnight: 1953 – The Year of Living Dangerously" (Biteback Publishing, 2021).
• "1971 Agreement on Measures to reduce the Risk of Outbreak of Nuclear War". U.S. Department of State.
• "1972 Agreement on the Prevention of Incidents at Sea". U.S. Department of State. 
• "Memorandum of Understanding Between The United States of America and The Union of Soviet Socialist Republics Regarding the Establishment of a Direct Communications Link". U.S. Department of State. 
• "One crisis alone justified the hot line". The New York Times (1973). 

Scientists have developed a new method to identify and trace the origins of hundreds of uranium cubes that went missing from the Nazi atomic weapons program.

More than 600 "Heisenberg cubes"  — vital components of the Nazis' plans to build both a nuclear reactor and an atomic bomb and named after Werner Heisenberg, one of the German physicists who created them  — were seized from a secret underground laboratory at the end of World War II and brought to the United States. Over 1,200 uranium cubes were believed to be created across Nazi Germany. But today, researchers only know the locations of roughly a dozen. 

The new technique, tested on a cube that mysteriously found its way to the researchers at the Pacific Northwest National Laboratory (PNNL) in Washington state, was presented Tuesday (Aug. 24) at a meeting of the American Chemical Society and could help track down illegally trafficked nuclear material.

Related: The 22 weirdest military weapons

Alongside their own cube, the researchers have access to a few others held by research collaborators. They hope their new technique will be able to not only confirm the cubes' provenance in Nazi Germany, but also tie them to the specific labs where they were first created.

"We don't know for a fact that the cubes are from the German program, so first we want to establish that," Jon Schwantes, a senior scientist at the PNNL, said in a statement. "Then, we want to compare the different cubes to see if we can classify them according to the particular research group that created them."

When Adolf Hitler first came to power, German nuclear experiments were at the cutting edge of research. In 1938, German radiochemists Otto Hahn and Fritz Strasserman were the first to split the atom to release enormous amounts of energy. During World War II, German scientists competed to find a way to transform cubes of uranium into plutonium — a key ingredient in early nuclear bombs — using prototype reactors. 

German scientists hung the cubes, just 2 inches (5 centimeters) wide on each side, on cables and submerged them in "heavy" water, in which hydrogen is replaced by a heavier isotope called deuterium. The German scientists hoped their reactors would trigger a self-sustaining chain reaction, but their designs failed.

Two prominent physicists led these experiments: Kurt Diebner, who ran experiments at Gottow, and Werner Heisenberg, who conducted them first in Berlin and later in a secret lab below a medieval church in Haigerloch to better hide from Allied troops. Heisenberg, a Nobel Prize-winning physicist who was once called a "white Jew" by a rival physicist, Johannes Stark, for his open admiration of Albert Einstein's work on relativity and quantum mechanics, nonetheless worked to build an atomic bomb for Nazi Germany.

After discovering Heisenberg's lab in 1945, U.S. and British forces retrieved 664 of the cubes that were buried in a nearby field and shipped them to the U.S. Some may have been used in the American nuclear weapons effort, while others found their way into the hands of collectors.

The chaotic collapse of the Nazi nuclear program likely means that many of the cubes could still be out there. Hundreds of the cubes from Diebner's laboratory disappeared. Reports abound of physicists who acquired cubes handing them out as souvenirs, and the Smithsonian Institution in Washington D.C. even has a cube that was discovered in a drawer in New Jersey. Another cube, retrieved from a German creek, was said to have been tossed in by Heisenberg himself during his desperate flight from advancing Allied forces.

The PNNL researchers suspect they have a Heisenberg cube, but they aren't sure. To test the cube's origins, the team is relying on radiochronometry, a technique geologists use to date samples of ancient rocks and minerals based on the presence of naturally occurring radioactive isotopes. The technique could reveal the age of the cube and, potentially, where the original uranium was mined. This technique might not just be useful in finding the origins of the Heisenberg cubes, but in tracing the provenance of other smuggled nuclear materials.

Because different Nazi laboratories applied different chemical outer coatings to their cubes to limit oxidation, a second technique the team is developing could also trace the cubes to the scientists who created them. The researchers have already discovered that their cube, believed to be from Heisenberg's lab, actually has the styrene-based coating from Diebner's lab. This finding means the cube could be one of those that Diebner reportedly sent to Heisenberg, who was trying to gather more fuel for his new reactor, Schwantes said.

Despite being essential applications in developing tracing techniques for nuclear material today, the cubes are an unsettling reminder of how close we came to an altogether different history.

"I'm glad the Nazi program wasn't as advanced as they wanted it to be by the end of the war," said Brittany Robertson, a doctoral student at PNNL. "Because otherwise, the world would be a very different place."

Originally published on Live Science.

In October 1961, the Soviet Union dropped the most powerful nuclear bomb in history over a remote island north of the Arctic Circle.

Though the bomb detonated nearly 2.5 miles (4 kilometers) above ground, the resulting shockwave stripped the island as bare and flat as a skating rink. Onlookers saw the flash more than 600 miles (965 km) away, and felt its incredible heat within 160 miles (250 km) of Ground Zero. The bomb's gargantuan mushroom cloud climbed to just below the edge of space.

This was RDS-220 — also known as the Tsar Bomba. Nearly 60 years after the bomb's record-shattering detonation, no single explosive device has come close to matching its destructive power. Last week, Rosatom State Atomic Energy Corporation (Russia's state atomic agency) released 40 minutes of previously classified footage, showing the bomb's journey from manufactor to mushroom cloud. Now, you can watch it all on YouTube. (The countdown to detonation begins at 22:20).

Related: Doomsdays: Top 9 real ways the world could end

Soviet Premier Nikita Khrushchev personally commissioned the construction of the Tsar Bomba in July 1961, Popular Mechanics reported. While Krushchev wanted a 100-megaton nuclear weapon, engineers ultimately presented him with a 50-megaton version — equivalent to 50 million tons (45 million metric tons) of TNT detonated at once. Even with half of the premier's requested payload, the bomb was unfathomably powerful. The bomb was thousands of times stronger than the nukes detonated by the United States over Hiroshima and Nagasaki during World War II, and dwarfed the detonation of Castle Bravo — the most powerful nuclear weapon ever tested by the United States — which yielded just 15 megatons (13 million metric tons).

As the new footage shows, the Tsar Bomba was enormous, weighing 27 tons (24 metric tons) and measuring about as long as a double-decker bus. An aerial bomber carried the massive weapon high over the Novaya Zemlya islands in the Russian Arctic, then dropped it via parachute before clearing the area. The explosion was so powerful that it actually knocked the aircraft out of the sky, causing the plane to plummet 3,000 feet (900 m) before the pilot could right it, according to Popular Mechanics.

Thankfully, no human casualties have been attributed to the Tsar Bomba detonation, and no bomb matching its power was ever tested again. In 1963, the United States, the Union of Soviet Socialist Republics (USSR) and the United Kingdom signed the Limited Nuclear Test Ban Treaty, which prohibited airborne nuclear weapons tests.

Since then, atomic tests have carried on underground as nations continue to stockpile nuclear weapons, occasionally changing the geography of the Earth around them. One 2018 nuclear test conducted in North Korea caused an entire mountain to collapse over the test facility — a reminder, perhaps, that the world hardly needs another Tsar Bomba in order to wreak devastating nuclear damage.

Originally published on Live Science.

A vast cloud of nuclear radiation that spreadover continental Europe in 2017 has been traced to an unacknowledged nuclear accident in southern Russia, according to an international team of scientists.

The experts say the cloud of radiation detected over Europe in late September 2017 could only have been caused by a nuclear fuel-reprocessing accident at the Mayak Production Association, a nuclear facility in the Chelyabinsk region of the Ural Mountains in Russia, sometime between noon on Sept. 26 and noon on Sept. 27.

Russia confirmed that a cloud of nuclear radiation was detected over the Urals at the time, but the country never acknowledged any responsibility for a radiation leak, nor has it ever admitted that a nuclear accident took place at Mayak in 2017. [Top 10 Greatest Explosions Ever]

The lead author of the new research, nuclear chemist Georg Steinhauser of Leibniz University in Hanover, Germany, said that more than 1,300 atmospheric measurements from around the world showed that between 250 and 400 terabecquerels of radioactive ruthenium-106 had been released during that time.

Ruthenium-106 is a radioactive isotope of ruthenium, meaning that it has a different number of neutrons in its nucleus than the naturally occurring element has. The isotope can be produced as a byproduct during nuclear fission of uranium-235 atoms.

Although the resulting cloud of nuclear radiation was diluted enough that it caused no harm to people beneath it, the total radioactivity was between 30 and 100 times the level of radiation released after the Fukushima accident in Japan in 2011, Steinhauser told Live Science.

The research was published today (July 29) in the journal Proceedings of the National Academy of Sciences.

Ruthenium release

The cloud of radiation in September 2017 was detected in central and eastern Europe, Asia, the Arabian Peninsula and even the Caribbean.

Only radioactive ruthenium-106 — a byproduct of nuclear fission, with a half-life of 374 days — was detected in the cloud — Steinhauser said.

During the reprocessing of nuclear fuel — when radioactive plutonium and uranium are separated from spent nuclear fuel from nuclear power reactors — ruthenium-106 is typically separated out and placed into long-term storage with other radioactive waste byproducts, he said.

That meant that any massive release of ruthenium could only come from an accident during nuclear fuel reprocessing; and the Mayak facility was one of only a few places in the world that carries out that sort of reprocessing, he said.

Advanced meteorological studies made as part of this new research showed that the radiation cloud could only have come from the Mayak facility in Russia. "They have done a very thorough analysis and they have pinned down Mayak — there is no doubt about it," he said.

The accident came a little more than 60 years since a nuclear accident at Mayak in 1957 caused one of the largest releases of radiation in the region's history, second only to the 1986 explosion and fire at the Chernobyl nuclear power plant, which is now in the Ukraine. [Chernobyl Nuclear Disaster 25 Years Later (Infographic)]

In the 1957 accident, known as the Kyshtym disaster after a nearby town, a tank of liquid nuclear waste at the Mayak facility exploded, spreading radioactive particles over the site and causing a radioactive plume of smoke that stretched for hundreds of miles.

Nuclear accident

The study showed that the 2017 accident at Mayak was unlikely to have been caused by a relatively simple release of radioactive gas, Steinhauser said. Rather, a fire, or even an explosion, might have exposed workers at the plant to harmful levels of radiation, he added.

Russia has not acknowledged that any accident occurred at the Mayak facility, maybe because plutonium is made there for thermonuclear weapons. However, Russia had established a commission to investigate the radioactive cloud, Steinhauser said.

The Russian commission ruled that there was not enough evidence to determine if a nuclear accident was responsible for the cloud. But Steinhauser and his team hope it may look again at this decision in the light of the new research.

"They came to the conclusion that they need more data," he said. "And so we feel like, okay, now you can have all of our data — but we would like to see yours as well."

Any information from Russia about an accident at the Mayak facility would help scientists refine their research, instead of having to rely only on measurements of radioactivity from around the world, Steinhauser said.

The international team of scientists involved are keenly interested in learning more about its causes. "When everybody else is concerned, we are almost cheering for joy, because we have something to measure," he said. "But it is our responsibility to learn from this accident. This is not about blaming Russia, but it is about learning our lessons," he said.

• Images: Chernobyl, Frozen in Time
• 15 Secretive Places You Can Now See on Google Earth (And 3 You Can't)
• Lessons From 10 of the Worst Engineering Disasters in US History

Originally published on Live Science.

The U.S. Air Force's E-4B, otherwise known as the "doomsday plane" may be able to withstand the force of a nuclear detonation.

This mostly windowless Boeing 747 was designed during the Cold War, and it indeed looks like a blast from the past, according to CNBC's Amanda Macias who recently got an inside look at the plane.

The craft is equipped with older analog flight instruments, rather than modern digital technology. The analog equipment is less likely to be fried by the electromagnetic pulse released after a nuclear blast, they reported. It also has shielding to protect its crew from nuclear and thermal effects during a nuclear war. [7 Technologies That Transformed Warfare]

With its giant fuel tanks and ability to refuel in the air from other aircraft, the doomsday plane can stay airborne for several days. It holds 67 satellite dishes and antennas, meaning its crew can communicate with anyone, anywhere in the world, even sending messages to the Navy's ballistic missile submarines, according to DefenseNews.

That being said, most of its capabilities are classified, according to CNBC. The Air Force has four of these E-4B aircraft, each standing at nearly 6 stories tall. Sporting 18 bunks, six bathrooms, a galley and a briefing room among other rooms, each can fly 112 crew members.

Currently, one is being used by Acting Defense Secretary Patrick Shanahan to travel to various parts of the world. On Tuesday morning (May 28), he boarded the craft in Maryland en route to Asia for a weeklong trip.

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Originally published on Live Science.

"I think that it could be an H-bomb test at an unprecedented level, perhaps over the Pacific," North Korea's Foreign Minister Ri Yong Ho told reporters this week during a gathering of the United Nations General Assembly in New York City, according to CBS News. Ri added that, "it is up to our leader."

Hydrogen bombs, or thermonuclear bombs, are more powerful than atomic or "fission" bombs. The difference between thermonuclear bombs and fission bombs begins at the atomic level. [The 10 Greatest Explosions Ever]

Fission bombs, like those used to devastate the Japanese cities of Nagasaki and Hiroshima during World War II, work by splitting the nucleus of an atom. When the neutrons, or neutral particles, of the atom's nucleus split, some hit the nuclei of nearby atoms, splitting them, too. The result is a very explosive chain reaction. The bombs dropped on Hiroshima and Nagasaki exploded with the yield of 15 kilotons and 20 kilotons of TNT, respectively, according to the Union of Concerned Scientists. 

In contrast, the first test of a thermonuclear weapon, or hydrogen bomb, in the United States in November 1952 yielded an explosion on the order of 10,000 kilotons of TNT. Thermonuclear bombs start with the same fission reaction that powers atomic bombs — but the majority of the uranium or plutonium in atomic bombs actually goes unused. In a thermonuclear bomb, an additional step means that more of the bomb's explosive power becomes available.

First, an igniting explosion compresses a sphere of plutonium-239, the material that will then undergo fission. Inside this pit of plutonium-239 is a chamber of hydrogen gas. The high temperatures and pressures created by the plutonium-239 fission cause the hydrogen atoms to fuse. This fusion process releases neutrons, which feed back into the plutonium-239, splitting more atoms and boosting the fission chain reaction.

Governments around the world use global monitoring systems to detect nuclear tests as part of the effort to enforce the 1996 Comprehensive Test Ban Treaty (CTBT). There are 183 signatories to this treaty, but it is not in force because key nations, including the United States, did not ratify it. Since 1996, Pakistan, India and North Korea have carried out nuclear tests. Nevertheless, the treaty put in place a system of seismic monitoring that can differentiate a nuclear explosion from an earthquake. The CTBT International Monitoring System also includes stations that detect the infrasound — sound whose frequency is too low for human ears to detect — from explosions. Eighty radionuclide monitoring stations around the globe measure atmospheric fallout, which can prove that an explosion detected by other monitoring systems was, in fact, nuclear.

Original article on Live Science.

For the second week in a row, the United States Air Force has tested an unarmed intercontinental ballistic missile (ICBM).

The Minuteman III ICBM was launched from a silo at California's Vandenberg Air Force Base this morning (May 3) at 3:02 a.m. EDT (0702 GMT; 12:02 a.m. local California time), military officials said.

The Air Force also conducted a test of an unarmed Minuteman III from Vandenberg just after midnight local time last Wednesday (April 26).

The two tests have come amid relatively high tensions with North Korea, an unpredictable, nuclear-armed nation that has repeatedly stated a desire to destroy the United States and its allies, including South Korea and Japan."The purpose of the ICBM test launch program is to validate and verify the effectiveness, readiness and accuracy of the weapon system, according to Air Force Global Strike Command," Air Force officials wrote Saturday (April 29) in a statement announcing the test launch.

Pyongyang has been conducting missile tests of its own recently, in violation of United Nations resolutions. The country performed one such test on April 16 and another on April 29. Both of these launches apparently involved medium-range missiles; North Korea is working to develop an ICBM, but most experts think the nation has not mastered the technology yet. (North Korea is a secretive nation whose leaders tightly control the flow of information into and out of the country, so it's tough to get quality information about its weapons program.)

The Minuteman program began in the 1950s, and the first missile, the Minuteman I, was deployed in the early 1960s. The Air Force currently has about 450 Minuteman III ICBMs, which are spread among bases in Wyoming, Montana and North Dakota, according to the fact sheet.Though the missiles involved in the recent Minuteman III tests were unarmed, the three-stage missile can carry nuclear warheads. The Minuteman III has a maximum range of more than 6,000 miles (9,650 kilometers), according to an Air Force fact sheet.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

A man diving off the coast of British Columbia, Canada, may have stumbled upon a nuclear weapon that the United States lost decades ago.

Now, the Royal Canadian Navy is scoping out the strange object to see if it is indeed a Mark IV bomb that was jettisoned by an American pilot in 1950 just before his plane crashed.

The man, Sean Smyrichinsky, was using an underwater scooter to hunt for sea cucumbers near Pitt Island, when he came upon a weird bagel-shaped object. After straying from his boat, he came upon a bizarre object that looked a bit like a half-cut bagel the size of a king-sized bed, he told CBC. [Flying Saucers to Mind Control: 7 Declassified Military & CIA Secrets]

"I came out from the dive and I came up and I started telling my crew, 'My god, I found a UFO. I found the strangest thing I'd ever seen!' Smyrichinsky told CBC. "It resembled, like, a bagel cut in half, and then around the bagel these bowls molded into it."

Long lost nuke

When he came to shore, he started asking around. He soon came upon the strange tale of the Convair 36-B, a bomber that took off from Elison Air Base in Alaska in 1950 and was flying near British Columbia when its engines caught fire. The plane was testing how well it could carry a Mark IV "Fat Man," an 11,000 pound (4,900 kilogram) atomic bomb similar to those dropped in Hiroshima and Nagasaki, according to news.com.au.

The official story was that crew parachuted to safety and the plane itself sank in the Pacific Ocean.

However, a few years later, people stumbled across the plane wreck in the remote B.C. mountains, three hours inland from where it was supposed to have crashed, according to " Lost Nuke: The Last Flight of Bomber 075," by Dirk Septer (Heritage House Publishing 2016).

"After years of silence, the United States finally admitted to losing its very first nuclear bomb; the incident was its first Broken Arrow, the code name for accidents involving nuclear weapons," Septer wrote in "Lost Nuke."

One mystery remained, though: Did the bomb detonate in the ocean or blow up over the mountains?

Not so deadly

After Smyrichinsky heard the story, he Googled the bomb and found an image that looked strikingly like the object he found.

Though finding a nuclear weapon sitting neglected in the ocean is scary, even if the strange object is the actual lost bomb, it likely contains no radioactive material. The original Mark IV bomb was a dummy capsule, Major Steve Neta of the Canadian Armed Forces, told CBC.

Finding a weapon under the waves is surprisingly common. The ocean is littered with nearly 5 million tonnes of chemical weapons lost between 1919 and 1980, according to Hakai Magazine.

Original article on Live Science.

A well-placed nuclear explosion could actually save humanity from a big asteroid hurtling toward Earth, just like in the movies, a new study suggests.

Scientists at Los Alamos National Laboratory, a United States Department of Energy facility in New Mexico, used a supercomputer to model nukes' anti-asteroid effectiveness. They attacked a 1,650-foot-long (500-meter) space rock with a 1-megaton nuclear weapon — about 50 times more powerful than the U.S. blast inflicted on Nagasaki, Japan, to help end World War II.

The results were encouraging.

"Ultimately this 1-megaton blast will disrupt all of the rocks in the rockpile of this asteroid, and if this were an Earth-crossing asteroid, would fully mitigate the hazard represented by the initial asteroid itself," Los Alamos scientist Bob Weaver said in a recent video released by the lab. [Video: Nuclear bomb takes out asteroid]

In the 3-D modeling study, run on 32,000 processors of the Cielo supercomputer, the blast went off at the asteroid's surface. So the nuke likely wouldn't have to be deposited deep into a threatening space rock, a dangerous job Bruce Willis and his astronaut crew tackled in the 1998 film "Armageddon."

Weaver stressed that nuclear bombs would likely be deployed only as a last resort, if an impact loomed just months away. And other researchers caution that a nuclear blast might have negative side effects, such as sending a hail of many small space rocks toward Earth instead of a single big one.

If humanity had more notice of an impending impact, there are several other asteroid defense strategies we might be able to employ, scientists have said.

For example, we could send a robotic probe out to rendezvous and ride along with the potentially dangerous asteroid. The spacecraft's modest gravity would exert a tug on the space rock as the two cruise through space together. Over months or years, this "gravity tractor" method would pull the asteroid into a different, more benign orbit.

We have the know-how to pull off such a mission. Multiple probes have met up with rocks in deep space, including NASA's Dawn spacecraft, which is currently orbiting the huge asteroid Vesta. And in 2005, Japan's Hayabusa probe plucked some pieces off the asteroid Itokawa, sending them back to Earth for analysis.

Humanity could also simply slam the rendezvous craft into the asteroid, relying on brute force rather than a gentle gravitational tug to push it off course. This impactor approach would not be as precise as the gravity tractor technique, researchers say, but it could still do the job under certain circumstances.

We've demonstrated the ability to accomplish this more aggressive mission as well. In 2005, for example, NASA sent an impactor barreling into the comet Tempel 1 to determine the icy object's composition.

Discussions about asteroid deflection aren't just academic exercises. Huge impacts are a part of our planet's history; one wiped out the dinosaurs 65 million years ago, and it's just a matter of time before another big space rock lines Earth up in its sights, astronomers say. 

This story was provided by SPACE.com, a sister site to LiveScience. You can follow SPACE.com senior writer Mike Wall on Twitter: @michaeldwall. Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

The world’s first atomic bomb test might have exposed unaware civilians in New Mexico to thousands of times the recommended level of public radiation exposure, according to reconstructed data in a new study.

The research, led by the Centers for Disease Control and Prevention (CDC), found that ingestion of radioactive materials—primarily from irradiated rainwater and goat’s milk—might have been a substantial contributor to public radiation exposure that was largely not accounted for.

The findings come on the 62nd anniversary of the world’s first atomic explosion and were presented at the recent annual meeting of the Health Physics Society.

‘Trinity’

The world’s first nuclear weapons test took place on July 16, 1945 in the desolate White Sands deserts of New Mexico. In a cryptic reference to a John Donne poem that he knew and loved, J. Robert Oppenheimer, lead physicist of the Manhattan Project and scientific director of the test, dubbed the location “Trinity.”

At 5:29:45 a.m. local time, a plutonium-based atomic bomb was detonated atop a 100-foot steel tower erected at Trinity specifically for the test. Scientists hoped that exploding the bomb at an elevated height would reduce the amount of radioactive dust raised by the explosion. They also needed to simulate the air-drop method of deployment that was eventually used by the real bombs.

The Trinity bomb was an exact replica of “Fat Man,” the second and last nuclear weapon ever used in war. Fat Man was detonated over Nagasaki, Japan less than a month after the Trinity test.

Exploding with an energy equal to about 20 kilotons of TNT, the blast carved a crater in the Earth more than 1,000 feet wide and 10 feet deep. Radioactive fallout from the blast was detected as far away as Indiana.

Heat from the explosion was so intense that sand grains fused to form a reflective layer of radioactive, green glass, called “Trinitite,” on the desert floor.

Dangerous radiation

Because of its importance in the war, the Trinity test was conducted in secret. Little was known about the dangers of radiation exposure in the 1940s, so local residents were not warned or evacuated in advance of—or even following—the test. As a result, people in surrounding areas were exposed to radiation by breathing contaminated air, eating contaminated foods, and drinking affected water and milk. Some ranches were located within 15 miles of ground zero, and commercial crops were grown nearby.

In the hours after the blast, five monitoring teams traveled along local roads recording radiation levels. The highest radiation levels from Trinity were measured in a swath 12 miles long and one mile wide that started near an area 16 miles northeast of ground zero. Around nearby ranches, exposure rates around 15 Roentgen per hour were measured just three hours after detonation.

Currently, the Nuclear Regulatory Commission states that members of the public should not receive more than 2 millirem (about 0.002 Roentgen) of radiation in any one hour from external radiation sources in any public area. The exposure rates following the Trinity test were more than 10,000 times this recommended dose level.

T.E. Widner, the director of the new CDC study, said he thinks evacuations would have certainly been arranged if scientists and physicians had known about the long-term effects of radiation exposure, even if the publicity threatened the mission.

Trinity is now open twice a year to the public, on the first Saturdays of April and October for six hours each time. According to the public affairs office at White Sands, a one-hour visit to ground zero will result in a whole body exposure of one-half to one millirem. To put this in perspective, a U.S. adult receives 360 millirems on average every year from natural and medical sources.

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