Lead Time on the Pad

The Sky Over Chelyabinsk

Mara: February 15th, 2013. It's morning in Chelyabinsk, Russia, and people are commuting or already at work. A rock comes in out of the sky and explodes above them, releasing about half a megaton of energy. Windows shatter. A zinc factory roof collapses. Right under its path, the shock wave knocks people off their feet. Reports count more than a thousand people hurt. Nobody had seen it coming.

Eli: The listener who wrote in asked it plainly: if an asteroid were heading for Earth, do we actually have a plan? Today's angle is the lead-time paradox separating deep-space deflection from terrestrial evacuation.

Mara: Since that morning, agencies have written alarm rules, crashed a spacecraft into an asteroid on purpose, and sat through a real scare. Underneath all of it sits a blunter matter: when a rock is coming, does someone launch something at it, or does someone tell a city to leave?

Eli: And Chelyabinsk was the small one. The Tunguska blast over Siberia flattened more than two thousand square kilometres of forest. That was back in 1908.

Mara: And the air only protects so far. Most meteors break up on the way down. But NASA's inspector general notes that objects bigger than about ten metres can survive the descent and cause destruction around where they hit. Chelyabinsk's was twice that. What happens when one is spotted in time is a matter of rules, and Eli brought the rulebook.

The Thresholds of Alarm

Eli: The rulebook runs through the United Nations. A UN resolution recommended the International Asteroid Warning Network, IAWN, and it works alongside a group called SMPAG. Three orbit centres, one at NASA, one at ESA and one called NEODyS, cross-check every risky calculation. If an object bigger than ten metres shows better than a one percent chance of hitting, IAWN issues a warning.

Mara: Chelyabinsk's rock was twice that size. It'd have cleared the bar, had anyone spotted it.

Eli: That one percent matters. SMPAG's trigger to start planning a space mission uses it too. The rock has to be bigger than fifty metres. And the impact has to fall within the next fifty years. Keep that one percent in mind, because a real asteroid would test it.

Mara: Years before those lines were written, one small rock got the full treatment. October 6th, 2008. An astronomer at the Mount Lemmon telescope in Arizona spots an asteroid two to three metres across, on approach to Earth. It's the first time anything has been seen in space before hitting the planet. NASA alerts government agencies and puts out a public notice. Early the next morning, over northern Sudan, it breaks apart about 37 kilometres up. A flight crew over Chad sees the sky suddenly flash.

Eli: Only hours, for a rock a tenth Chelyabinsk's width.

Mara: Hours were enough. A NASA trajectory scientist at JPL put it simply: "We had accurately predicted when and where TC3 would enter over the Sudan." The sky side worked. Who gets told, and who has to act, is a separate chain.

The Kinetic Punch

Eli: That chain went formal in the US in 2016, when NASA set up its Planetary Defense Coordination Office to lead on finding, tracking and warning about dangerous asteroids and comets. Its trigger echoes SMPAG's. If any hazardous object shows a one percent or greater chance of hitting within fifty years, the office drafts the notices NASA sends to the Executive Office of the President and Congress. TC3's hours of warning would now travel a written route.

Mara: And at the far end of that route sits an emergency manager, not an astronomer.

Eli: FEMA, specifically. Once NASA flags an impact threat to the US, FEMA alerts federal, state and local authorities and owns the ground response, evacuations and recovery included, with a 2021 interagency report recommending the National Security Advisor coordinate the overall US response.

Mara: So the alarm has somewhere to go. Whether anything could answer it in space was the open part. September 26th, 2022. At the Johns Hopkins Applied Physics Laboratory, a team watches its spacecraft, DART, close on Dimorphos, an asteroid NASA puts at about 170 metres wide. DART is moving seven times faster than an assault-rifle bullet. Boulders rush into view. The mission systems engineer calls out: "It's amazing, guys! Oh my goodness, look at that! Unbelievable!" DART's body hits right between two big boulders, its solar panels striking both.

Eli: On a rock that threatened nobody. The program scientist, Tom Statler, said so: "We're doing this test when we don't need to, on an asteroid that isn't a danger, just in case we ever DO need to and we discover an asteroid that IS a danger."

Mara: It worked. Dimorphos orbits a bigger asteroid, and that orbit came out about thirty-three minutes shorter. The surprise was what did the pushing. Rock and debris blasted off the surface, and the recoil from that escaping material multiplied DART's push somewhere between two and five times.

Eli: More of the shoving than the spacecraft?

Mara: Set that beside Chelyabinsk, a rock eight times narrower that arrived unannounced and hurt so many. In 2022 a spacecraft moved something far bigger, on purpose. Kinetic deflection works; that much is now on the record. Whether a proven method means a spacecraft ready to fly is the part still open.

The Standby Illusion

Eli: It doesn't. DART's thirty-three minutes proved the physics, helped along by what's called the momentum enhancement factor, the extra kick from debris thrown outward off the rock. But in April 2026, Scientific American reported there is "no fully operational mitigation strategy for addressing a potentially hazardous asteroid." The field, it said, "largely exists in the realm of scientific study."

Mara: So nothing's sitting on a pad, waiting to launch.

Eli: Nothing. And building one is slow. A 2018 planning document for the space agencies estimates two to three years just to design and launch a scouting mission. Then it still has to travel there. A US interagency working group said in 2021 that a reconnaissance mission likely needs more than three years of warning. And a deflection spacecraft takes at least three years to build and prepare, before it ever flies.

Mara: Which brings Chelyabinsk back. That was an airburst: the rock never reached the ground. It blew apart in the air, and the blast wave did the damage.

Eli: Not a hole in the ground?

Mara: And a pressure wave is something people can be moved away from.

Eli: That's the official fallback. The same 2018 document says that with only weeks or months of warning, warning messages and civil defense are likely the only actions taken. Civil defense here means the emergency response on the ground: moving people out from under the blast. A 2010 National Research Council report found no deflection method ready on short notice. And the US has no dedicated federal operational plan for hazards from space, so FEMA would work from its all-hazards checklists, with evacuations starting when a state asks.

Mara: Then a real case tested the alarm. Late January 2025. Asteroid 2024 YR4's chance of hitting Earth in 2032 climbs past one percent. That's the line from earlier, and it trips. IAWN, the astronomers who check orbits and raise the alarm, sends out its warnings. SMPAG, the space agencies that would plan any mission, starts discussing. The odds keep climbing, to a reported peak of about three percent. Kelly Fast later described "an interesting process in January as more observations were taken to help try to narrow down in 2032 where exactly it was going to go."

Eli: SMPAG's conclusion on January 31st: "too early to take immediate action."

Mara: By February 20th, fresh observations had pulled the odds down to 0.28 percent. Days later, IAWN's final notice said YR4 posed no significant potential for a future impact with Earth. One official who, before retiring, worked on the US notification process put the deeper issue plainly: "the decision to actually do something is not entirely a science decision in my opinion. It's a political decision."

Eli: So the alarm went off on time, Mara. Behind it stood a group saying it was too early, a political decision nobody ended up having to make, and, had the odds held, a spacecraft still years from being built.

The Warning Clock

Mara: With years of notice, the first tool anyone reaches for is the kinetic impactor. The space agencies' planning assessment rates its technology readiness high, and it's the only method ever tested on an asteroid. That's the reading held by Tom Statler and NASA's planetary defense officer, Lindley Johnson: a proven, scalable tool, given enough warning. Before DART launched, Johnson told CBS News why blowing a rock up is no answer, since the material keeps coming: "it's just buckshot instead of a rifle ball."

Eli: Mara, the other reading starts where warning runs short or the rock runs big. NASA's 2023 strategy says a nuclear explosive device may then be the only thing with enough force. That's nuclear disruption: a nuclear blast used on the rock, delivering far more force than a spacecraft collision can. Kelly Fast, who described the YR4 search, holds that reading, and so does Melanie Bochmann: kinetic deflection alone falls short for big, rubble-pile – loose heaps of rock held together by gravity – or short-warning cases.

Mara: That reading just gained evidence. At CERN, Bochmann's group, OuSoCo, which she co-leads with Karl-Georg Schlesinger, hit an iron-nickel meteorite with beam pulses. They watched it soften, flex, then re-strengthen, ending about two and a half times stronger, without breaking. Bochmann's conclusion: "at least for metal-rich asteroid material – a larger device than previously thought can be used without catastrophically breaking the asteroid." Rockier material is their next test.

Eli: Law is the hurdle: existing treaties restrict nuclear weapons and nuclear explosions in space.

Mara: And the clock is the other hurdle. No known asteroid poses a significant threat for at least a hundred years. Apophis, the famous one, passes safely on April 13th, 2029. It'll come within about 31,600 kilometres, inside the belt where geosynchronous satellites orbit, matching Earth's rotation to stay over one spot. But the catalogue has gaps. An estimated 25,000 near-Earth asteroids are at least 140 metres across, big enough for regional devastation. As of 2023, NASA counted only about 42 percent of them found.

Eli: So most of the big ones are still unfound.

Mara: That's NEO Surveyor's job. It's an infrared space telescope NASA is targeting for launch in 2027 or 2028. NASA says that within about a decade, it should find more than 90 percent of objects that size. The stakes, in NASA's own words: "Currently, an asteroid impact is the only natural disaster we might be able to prevent."

Eli: Prevention runs on lead time, though. Put the pieces together and warning time decides it: decades of notice means a spacecraft sent to move the rock.

Mara: So the answer to the listener is yes, there is a plan: networks that sound the alarm at set odds, and a deflection method proven on Dimorphos. But without years of warning, the plan that actually works is evacuation. Chelyabinsk's rock came out of the daytime sky, where night-time telescopes weren't looking, and at twenty metres it sits far below Surveyor's target size. For a rock like that, the plan is still to spot it, warn, and get people clear.

Eli: Three signals to watch. Whether ESA's Hera spacecraft shows DART left a distinct crater, or reshaped the rubble inside Dimorphos. Whether any space agency puts an interceptor, or ready-built hardware, on permanent standby. And whether the UN writes rules allowing a nuclear device against an asteroid in an emergency.

Mara: A topic to look into is airburst.

Eli: Follow science with Angle through other episodes as planetary defense protocols develop.

Mara: And that's the story. I'm Mara.

Eli: And I'm Eli. Thanks for listening, and until next time.