Planetary Defense: How NASA Proved It Could Move an Asteroid — and the Real Plan If One Is Headed Straight for Earth

In September 2022, a spacecraft roughly the size of a golf cart slammed into an asteroid at 22,000 km/h. On purpose. The asteroid moved. Scientists had hoped to shift its orbit by at least 73 seconds. The actual result: 33 minutes.

That test — buried under political news cycles, barely trending — may be the most important experiment humanity has ever run. Because the question it answered wasn't just scientific.

Can we actually stop one?

Yes. If we have enough time. And right now, that "if" is the part nobody's talking about.

Did the DART mission actually work?

Yes. Unambiguously. NASA's DART spacecraft (Double Asteroid Redirection Test) launched in November 2021 and reached the Didymos asteroid system 10 months later. Its target was Dimorphos — a 160-metre moonlet orbiting a larger rock called Didymos. Think of it as shooting a golf cart to redirect a stadium being orbited by a grain of sand.

Dimorphos was deliberately chosen because it poses zero threat to Earth. It was a test track. A controlled experiment to answer the most consequential physics question our species has ever asked: if we aim something at an asteroid, does it actually move?

It moved. Spectacularly. When DART hit, it didn't just push Dimorphos with its own mass — the impact blasted thousands of tonnes of rock and dust into space. That ejecta cloud acted like a rocket exhaust, amplifying the deflection far beyond what the spacecraft alone could achieve. The 73-second goal became a 33-minute shift. The model worked better than expected.

To be fair: Dimorphos is small. It's not a 1-kilometre civilization-ender. And its composition — loosely packed rubble — may have made it more receptive to deflection than a solid iron asteroid. Scientists are already running models to understand how well DART's approach scales up. The answer isn't fully in yet.

What is a potentially hazardous asteroid?

NASA classifies any space rock that passes within 0.05 AU of Earth — about 7.5 million kilometres — and measures more than 140 metres across as a Potentially Hazardous Asteroid (PHA). At 140 metres, a direct hit would devastate a region the size of a large country. At 300 metres, it rewrites a continent. At 1 kilometre, it's a global event.

Right now, over 2,300 PHAs are tracked in the catalogue. None show a confirmed Earth-impact trajectory. But the word "confirmed" is carrying enormous weight there — because the catalogue is incomplete.

Scientists estimate roughly 25,000 asteroids exist in the 140-metre-plus range. As of the latest surveys, only about 40% have been found. The rest are dark, rocky, and absorb radar rather than reflecting it. They are essentially invisible until they are close. And "close" in asteroid terms can still mean incoming.

How much warning would we actually have?

This is the part that keeps planetary defense scientists awake at night. The answer depends entirely on one thing: when we spot it.

In February 2013, a 20-metre rock entered the atmosphere over Chelyabinsk, Russia. Warning time: zero. It approached from the direction of the Sun — the one blind spot every ground-based survey shares. It released 30 times the energy of the Hiroshima bomb. Blew out windows in six cities. Injured more than 1,500 people. And it was only 20 metres.

Chelyabinsk was tiny on the cosmic scale. A 140-metre object hits with roughly 1,000 times that energy. A 500-metre rock would erase a metropolitan area and everything within 100 kilometres. A 1-kilometre impactor causes global darkening, crop failure, mass starvation. The 66-million-year-old crater in Yucatán came from something 10 kilometres across.

We've catalogued almost all the 1 km+ objects. The gaps are in the middle — the ones that could end a city or a small country — which is exactly where the survey work is still catching up.

What's the actual plan if we find one headed for Earth?

NASA, ESA, and the UN coordinate through two bodies: IAWN (the International Asteroid Warning Network) and SMPAG (the Space Mission Planning Advisory Group). The response playbook changes entirely based on how much lead time exists.

How are we going to find the ones we've missed?

NASA's answer is the NEO Surveyor — an infrared space telescope designed specifically to find the dark asteroids that ground-based surveys miss. Unlike visible-light surveys, it detects heat signatures, which means it can identify a black, radar-absorbing rock that would be completely invisible to Catalina or Pan-STARRS from the ground.

Operating from space also removes the fundamental flaw in current ground-based coverage: the Sun-blind zone. NEO Surveyor is designed to survey from an interior solar orbit, able to look inward toward the Sun-facing sky that ground telescopes simply cannot access. It's the fix for the exact gap that let Chelyabinsk through undetected.

Projections suggest it could cut the remaining undetected 140-metre population by more than half — in years rather than the decades it would take using ground-based surveys alone. Finding them earlier is the whole ballgame.

What's the closest hazardous asteroid right now?

Today — September 11, 2026 — an Apollo-class asteroid designated 2026 OH3 is making a close pass at 12.3 lunar distances, roughly 4.7 million kilometres from Earth. It's travelling at 20.2 km/s. That's fast enough to cross the distance from Earth to the Moon in under six hours.

It was discovered just two months ago, on July 16, 2026. Its H-magnitude (21.4) points to a diameter somewhere between 200 and 400 metres — comparable in scale to the Empire State Building lying on its side. It's formally classified as HAZARDOUS based on its orbital characteristics. This pass is safe. But its orbital period brings it back.

2026 OH3 is a clean illustration of why the detection timeline matters. Two months of lead time — the gap between its discovery and today's closest approach — would be nearly useless in a real threat scenario. No kinetic impactor could be built and launched in 60 days. No gravity tractor could be positioned. Evacuation planning would be the only card left to play.

You can watch 2026 OH3 and every other tracked near-Earth object in real time using the SkyLens live tracker — it pulls directly from the same JPL and CelesTrak feeds that planetary defense scientists monitor. There are currently 16,022 objects tracked in the catalogue above us right now. Most are benign. The goal of the entire planetary defense apparatus is to find the one that isn't — early enough to do something about it.

DART showed we have the tool. NEO Surveyor is designed to give us the time. The gap in between — the asteroids already out there, undiscovered, on orbits we haven't calculated yet — is the part that still keeps the scientists watching.

For more on how we track what's overhead, read our orbital mechanics explainer or browse related stories on the SkyLens blog.