If the asteroid that wiped out the dinosaurs strikes today, the results would be devastating. It would produce an explosion billions of times more powerful than all the nuclear weapons on Earth combined. A monstrous crater, perhaps hundreds of kilometres wide would be formed, releasing a huge amount of energy into the atmosphere. The initial impact would also cause widespread destruction, with tsunamis, earthquakes, and wildfires sweeping across the globe. This would cause a global climate change, with temperatures dropping and the atmosphere becoming filled with dust and smoke. The prolonged darkness, similar to a nuclear winter, would inhibit photosynthesis thereby triggering the collapse of food chains. Our bright, green world would turn dark and grim, and many animals and plants might not survive, just like the dinosaurs. So NASA is actively working on developing a planetary defence system to protect us from asteroid impacts.