What would actually happen if a nuclear weapon were detonated in space?

This isn't just the stuff of science fiction — it's a scenario that researchers have studied closely, and the implications are deeply unsettling. From disrupting satellite a nuclear detonation in space would have immediate, global consequences — even without a single casualty on the ground.

In today’s episode, we’re exploring how our growing dependence on space-based infrastructure — for communications, surveillance, and national security — is changing the conventional calculus around nuclear deterrence.

How are major nuclear powers, including Russia, responding to this shifting landscape? Are we on the verge of a space-based nuclear arms race? And what can be done now to preserve space as a peaceful domain?

My guest is Bill Hennigan, author of the At the Brink series, which We recorded this conversation live at the Carnegie International Nuclear Policy Conference — and it’s a fascinating look into how the nuclear order may be evolving in ways that are still underappreciated.

I've been hanging around the United Nations these past few days attending events related to consultations on lethal autonomous weapons systems—so-called killer robots. These are AI-powered weapons systems that can select and strike targets without human control. This is not the stuff of science fiction. These weapons exist today, and they are becoming more powerful—and, frankly, more accessible. They can be relatively inexpensive and deployed by both states and non-state actors, including terrorist groups.

As of now, there are no meaningful international regulations governing the use or development of these lethal autonomous weapons systems. There is a clear gap in our global governance of these technologies.

Here at the United Nations, delegates have been discussing ways to close that gap—potentially through a new legally binding international treaty to regulate or even ban some of these systems.

My guest today, Anna Hehir, is at the forefront of this effort. She is the Head of Military AI at the Future of Life Institute. In our conversation, Anna explains exactly what these weapons entail, where and how they are being used today, and what the future may look like if they continue to be developed without rules or oversight. We then discuss the process of getting a potential treaty on lethal autonomous weapons systems—and why, even if key players do not join such a treaty, it could still make a meaningful difference.

Eliana Johns hunts for nuclear weapons. She’s a senior research associate at the Federation of American Scientists, where her team uses open-source intelligence — or OSINT — to uncover secrets about countries’ nuclear capabilities and intentions. In fact, much of what we know today about China’s nuclear arsenal comes from her colleagues’ work, which used commercial satellite imagery to reveal that China is undertaking a massive nuclear buildup — at a pace far exceeding publicly available estimates from U.S. intelligence agencies.

In our conversation, Johns explains where OSINT has worked best and why greater transparency around nuclear weapons is essential for a more stable and peaceful world.

We recorded this live at the Carnegie International Nuclear Policy Conference.

The race to succeed António Guterres is unofficially underway. His term as UN Secretary-General ends in December 2026, but the backroom jockeying has already begun. In this episode, Mark and Anjali are joined by Richard Gowan of the International Crisis Group to break down the early contenders, how shifting geopolitics could shake up the selection process, and the daunting mess the next Secretary-General is likely to inherit. But first, they react to Trump’s eyebrow-raising pick for UN Ambassador: recently fired National Security Advisor Mike Waltz.

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The legendary international relations scholar Joseph Nye passed away on May 7th at the age of 88. He’s best known, of course, for developing and advancing the idea of “soft power”—the ability to influence others and shape outcomes through attraction, persuasion, and cultural or ideological appeal rather than coercion or force. But over his singularly illustrious career, he authored hundreds of scholarly articles and dozens of books on international relations.

To honor is legacy and memory, I wanted to share our conversation from way back in 2014.

We began our conversation talking about Russia’s (then recent) annexation of Crimea and occupation Ukraine, and what it suggests about long held ideas in international relations theory. We then pivot to his personal story, including his childhood in New Jersey and how his entry into the world of international relations was as an Africanist—he wrote an award-winning thesis as a Rhodes Scholar on decolonization in East Africa. Of course, we also discussed at length how he came up with the idea of “soft power,” which, as he explains, stemmed from an “a-ha!” moment while sitting in his kitchen.

In just the first four months of the Trump administration, several pillars of American foreign policy have been upended — USAID dismantled, most foreign aid frozen, and the rules-based international trade system thrown into disarray. Could nuclear policy be next?

To find out, I spoke with Alexandra Bell, President and CEO of the Bulletin of the Atomic Scientists and a former senior State Department official on nuclear issues. She breaks down the key decisions facing the administration — and the risks tied to some of the options on the table, particularly around missile defense. We also unpack the state of nuclear diplomacy with Russia and China, and why forcing trilateral arms control talks is likely a dead end.

This conversation is a clear-eyed look at the current state of play in Trump’s nuclear policy — and where it may be headed next.

We recorded this live at the Carnegie International Nuclear Policy Conference. More conversations are coming soon. To catch them live, subscribe below or get the Substack app.

The Comprehensive Test Ban Treaty, better known as the CTBT, expressly prohibits its signatories from testing nuclear weapons. It was opened for signature in 1996 and is now one of the most widely adopted treaties in the world.

Since the Comprehensive Nuclear-Test-Ban Treaty was opened for signature in 1996, there have been ten nuclear tests conducted worldwide. These include two tests by India and two by Pakistan in 1998, and six tests by North Korea between 2006 and 2017 .​ This limited number of tests since 1996 stands in stark contrast to the more than 2,000 nuclear tests conducted in the preceding five decades, highlighting the CTBT's significant role in establishing a global norm against nuclear testing

My guest today, Robert Floyd, is the Executive Secretary of the Comprehensive Test-Ban Treaty Organization, which—as the name suggests—is the international body responsible for monitoring and facilitating the implementation of this treaty. It does so, in part, through a sophisticated global monitoring system capable of detecting a nuclear test anywhere in the world. I sat down with Robert Floyd on the sidelines of the Carnegie International Nuclear Policy Conference in Washington, DC, earlier this month, where he explained why the CTBT has been so successful in constraining nuclear testing—and what challenges the treaty now faces amid a rapidly shifting geopolitical landscape.

This episode is produced in partnership with Lex International Fund, a philanthropic fund dedicated to strengthening international law to solve global challenges. It is part of a series that demonstrates the impact of Treaties on state behavior that we are calling "when treaties work"

Ankit Panda’s new book delivers a stark message: we’ve entered a new nuclear age. This one is shaped by rising U.S.–Russia tensions, China’s emergence as a major nuclear power, and a wave of tech breakthroughs — including AI — that are transforming the nuclear landscape. The result? A world where nuclear security is more complicated, and more dangerous, than ever.

In The New Nuclear Age: At the Precipice of Armageddon, Panda breaks down the key trends driving this shift. In our conversation, he explains why this moment is so perilous — and how we might avoid stumbling into a new nuclear war.

We recorded this live at the Carnegie International Nuclear Policy Conference. More conversations are coming soon.