Earth’s atmosphere is thin compared with the planet, but at asteroid speeds it behaves less like a gentle breeze and more like a wall. Pressure and heat build rapidly, cracks spread, and a rocky body can break apart in a powerful midair burst.
NASA says an airburst would be a likely outcome for an object in YR4’s size range if one entered the atmosphere. Tunguska is the classic example: the object exploded miles above Siberia in 1908, leaving no obvious crater but flattening an enormous sweep of forest.
That history explains why YR4’s size and close approach commanded attention when an Earth impact still appeared among its possible paths. The current orbit forecast points to a flyby, but the physics remains fascinating: a rock this size sits in the range where the atmosphere—not the ground—would likely stage the main event.