A decade after the Chelyabinsk airburst underscored our vulnerability to space rocks, planetary defense has matured into a coordinated, global enterprise. Astronomers now scan the skies nightly to find and track near‑Earth objects, agencies practice response plans, and engineers test ways to nudge hazardous asteroids off course. The goal is pragmatic: detect threats early, characterize them quickly, and have credible options to mitigate impact risk. While the odds of a devastating strike remain low in any given year, the consequences are high enough that governments and scientists treat asteroid impacts and related cosmic hazards as a long‑term public safety challenge.
The first line of defense is finding potential impactors. Survey telescopes such as Pan‑STARRS, the Catalina Sky Survey, ATLAS, ZTF, and NASA’s NEOWISE scan the sky and feed discoveries to the Minor Planet Center for verification and orbit calculation. NASA’s Sentry II and the Scout system assess impact probabilities as new data arrive, while ESA’s NEO Coordination Centre maintains independent risk lists. The United States established the Planetary Defense Coordination Office in 2016 to organize detection, characterization, and emergency response with domestic and international partners.
The long‑standing U.S. mandate to find 90% of near‑Earth objects larger than 140 meters is still a work in progress, driving investments in new sensors. Testing deflection is no longer hypothetical. In 2022, NASA’s DART spacecraft struck the asteroid moonlet Dimorphos, shortening its orbital period around Didymos by about 33 minutes and confirming kinetic impact as a viable deflection technique.
The collision’s ejecta plume amplified the momentum transfer, a key factor for future mission designs. The Italian LICIACube flyby and a global network of telescopes documented the aftermath in detail. ESA’s Hera mission is set to perform a close‑up survey of the Didymos–Dimorphos system later this decade to precisely measure DART’s effects and refine models. Better discovery tools are on the way.
NASA’s NEO Surveyor, an infrared space telescope planned for late‑decade launch, is designed to find hard‑to‑spot asteroids that are dark or orbit near the Sun from Earth’s perspective. The Vera C. Rubin Observatory’s wide, rapid sky coverage is expected to accelerate discoveries once full survey operations begin in the mid‑2020s. Planetary radar from NASA’s Goldstone antenna, often paired bistatically with the Green Bank Telescope, provides high‑resolution sizes, shapes, and spin rates after Arecibo’s collapse reduced global radar capability.
Europe is building its Flyeye (NEOSTEL) telescope to broaden independent search capacity and speed up follow‑up. Preparation extends beyond hardware. The International Asteroid Warning Network and the Space Mission Planning Advisory Group, working under UN auspices, coordinate alerts, data standards, and mission concepts across agencies. NASA and FEMA run regular tabletop exercises to rehearse evacuation, communications, and disaster response for realistic impact scenarios, and similar drills occur at the biennial Planetary Defense Conference.
Long‑period comets remain a special challenge because they can appear with shorter warnings, prompting efforts to improve all‑sky coverage and rapid characterization. Meanwhile, agencies also track solar storms with missions like NASA’s Parker Solar Probe and ESA’s Solar Orbiter, and plan dedicated space‑weather sentinels such as ESA’s Vigil, recognizing that “cosmic threats” include the Sun’s ability to disrupt power grids and satellites. Looking ahead, the 2029 close pass of asteroid Apophis offers a rare rehearsal to test observation campaigns and operational coordination on a benign but scientifically rich target.
