Scientists map seven-stage process of how meteorites survive Earth's atmosphere

Everyone has watched a bright line streak across the night sky and called it something—a shooting star, a meteor, an asteroid. Most of us don't think much beyond the moment it vanishes. But that brief flash, lasting only seconds, is the culmination of a violent and precisely ordered sequence of events that scientists have only recently begun to map in detail.

A team from the SETI Institute and NASA Ames Research Center has now documented exactly what happens to a space rock—the technical term is bolide—as it tears through Earth's atmosphere on its way to the ground. The work, published in Meteoritics & Planetary Science, identifies seven distinct phases that every meteorite undergoes during entry and descent. The researchers analyzed video and image data from 75 meteorite falls, measuring entry angles, rotation rates, and how much mass each object shed along the way. What they discovered overturned a long-held assumption: space rocks don't simply evaporate from the intense heat and light of atmospheric friction. Instead, melting and fragmentation are what actually control how much material a rock loses as it falls.

The seven phases begin the moment a bolide enters the atmosphere and continue through to ground impact. The rock brightens, then brightens further as a fireball forms. It maintains that brightness while its surface begins to melt. The front edge starts to break apart, followed by the rear. Finally, melting and fragmentation continue until the glow fades, the melting stops, and wind carries away the crusted pieces. The altitude at which each phase occurs varies depending on the rock's composition and angle of entry—a critical detail for understanding what happens when a bolide explodes mid-air rather than reaching the ground intact.

Dr. Peter Jenniskens, the lead researcher and a meteor astronomer at both institutions, explained the significance plainly: "We used to think that solid rocks would evaporate from the enormous heat and brilliant light generated in the air collision. We found instead that first melting and then fragmentation controls how a rock loses mass." This distinction matters enormously for planetary defense—the field concerned with predicting and preparing for impacts from space objects.

The motivation for the study came from a specific, recent tragedy. On February 15, 2013, a 20-meter asteroid entered Earth's atmosphere above Chelyabinsk, Russia, traveling at 19 kilometers per second. It exploded at an altitude of roughly 30 kilometers, releasing energy equivalent to about 30 times the Hiroshima bomb. The blast shattered windows across more than 7,200 buildings in six cities. Approximately 1,500 people were injured, most from flying glass. Understanding the mechanics of how that rock broke apart—and how similar rocks might behave in the future—could help scientists predict the damage an incoming bolide might cause before it arrives.

The Chelyabinsk event was not unprecedented. More than a century earlier, on June 30, 1908, a much larger bolide exploded over Tunguska, Russia. That object was 50 to 100 meters across and detonated at an altitude of 5 to 10 kilometers, releasing roughly 1,000 times the energy of the Hiroshima bomb. The blast flattened approximately 80 million trees across an area exceeding 2,150 square kilometers. Both events demonstrate the stakes involved in understanding how space rocks behave as they enter the atmosphere.

The terminology matters too, though it often gets tangled in casual speech. A meteoroid is any space rock smaller than one meter. An asteroid is larger than one meter. A meteor is the visible streak of light produced when either object burns through the atmosphere. A meteorite is what survives the journey and lands on the ground. The distinction is not merely semantic—it reflects different stages of the same object's journey, and understanding each stage is what allows scientists to predict outcomes and prepare defenses.