When a space rock enters Earth’s atmosphere, it can transform from a cold, solid object into a glowing fireball before pieces of it finally reach the ground as meteorites. For decades, scientists have often described this process as a rock simply “burning up” or evaporating because of extreme atmospheric heating.
A new study suggests the reality is much more complicated.
Researchers examined 75 meteorite falls recorded through photographs and videos and identified seven distinct stages in the journey from space rock to meteorite. Their findings, published in Meteoritics & Planetary Science, show that melting and fragmentation—not simply evaporation—are the main processes controlling how these rocks lose mass, slow down and eventually reach Earth’s surface.
“We used to think that solid rocks would evaporate from the enormous heat and brilliant light generated in collisions with air,” said lead author Dr. Peter Jenniskens, a meteor astronomer at the SETI Institute and NASA Ames Research Center. “We found instead that first melting and then fragmentation control how a rock loses mass.”
From Meteor to Fireball
The journey begins high above Earth, where the atmosphere is still extremely thin.
Phase 1: The First Glow
As a space rock races into the atmosphere, it collides with air molecules at tremendous speed. These collisions create a powerful shock wave in front of the object and heat both the surrounding gas and the rock.
The heated material begins to glow, producing what we commonly call a meteor or shooting star.
At this stage, the object may still be relatively intact, but its interaction with the atmosphere has already begun changing it.
Phase 2: Getting Brighter
As the rock moves deeper into the atmosphere, the air becomes denser. More frequent collisions produce greater heating, making the meteor brighter.
Some meteors also reveal another interesting feature: rotation.
Researchers observed regular changes in brightness that indicate some rocks are spinning rapidly. The fastest-spinning objects in the study completed a rotation in just 0.5 to 5 seconds.
These brightness variations provide scientists with clues about the shape, rotation and physical condition of the incoming rock.
Phase 3: Melting Creates a Fireball
Eventually, the meteor becomes extremely bright and develops into a fireball.
This is where one of the study’s most important discoveries appears.
Rather than simply evaporating because of the heat, the rock begins to melt. The enormous airflow then strips molten material from its surface. The melted droplets are carried away and gradually evaporate.
This melting process can remove a significant amount of the object's mass.
Eric Stern, formerly of NASA Ames and now chief scientist at Hyperspace Technologies Inc., explained that laboratory experiments cannot reproduce the enormous radiation and extreme conditions experienced by naturally entering rocks at these speeds.
The behavior observed in real atmospheric entries suggests that melting and erosion play a much larger role than previously assumed.
Phase 4: Reaching a Melting Balance
At roughly 60 kilometers above Earth’s surface, the fireball enters the fourth stage.
Here, the rock reaches what researchers describe as a melting equilibrium. Its brightness may remain relatively constant or increase at a steady rate.
By this point, melting can have removed as much as 40% of the original mass of the space rock.
But the biggest change is still ahead.
Breaking Apart Under Pressure
Phase 5: Fragmentation Begins
As the object plunges deeper into the atmosphere, the air becomes much denser. Increasing atmospheric pressure begins to push the rock apart.
The fireball may suddenly flare several times as pieces break away.
Surprisingly, the researchers discovered that fragmentation can begin when the air pressure is only about one-fifth of the strength measured in meteorites found on Earth.
Why do these rocks break so easily?
The researchers believe their history in space may provide the answer. Before reaching Earth, many meteoroids experience collisions with other objects. These impacts can create cracks and weaken their internal structure.
As a result, an apparently solid rock may already contain hidden damage before it enters the atmosphere.
Once fragmentation begins, the remaining material can shrink and slow down much more rapidly.
Stu Pilorz of the SETI Institute said the researchers were able to connect this slowdown caused by fragmentation with earlier mathematical descriptions of atmospheric ablation.
A Natural “Vacuum” Behind the Rock
The researchers also discovered an interesting effect involving the back of the main rock.
If the rear portion remains intact, the fast-moving object creates a low-pressure region behind it. This acts somewhat like a vacuum, helping pull smaller fragments into its wake.
As a result, many of these fragments can travel together and land within a relatively narrow area.
This helps explain why meteorites from the same event can sometimes be found concentrated in what scientists call a strewn field.
Phase 6: The Final Breakup
Eventually, the back of the main space rock also breaks apart.
This marks the sixth stage and produces one final bright flare. The fragmentation can send smaller pieces flying outward at higher relative speeds.
Interestingly, these final flashes are often red rather than the bright green color seen earlier.
By this stage, the rock has already slowed considerably, changing the way its fragments interact with the atmosphere.
Researchers also found that meteorites weighing more than about 20 grams tended to spread over a wider area in some meteorite falls. Many appeared to originate from areas close to the original rock’s surface, particularly its backside.
Phase 7: The Final Fall
The seventh and final stage occurs when the remaining fragments continue melting and fragmenting until they slow enough to stop glowing.
The intense heating ends, leaving the surviving pieces with a thin, dark fusion crust on their surfaces.
These are now meteorites.
However, their journey is not quite finished. Once they stop glowing, atmospheric winds can push the darkened fragments away from their original trajectory before they finally land.
In other words, a meteorite found on Earth is not simply a piece of rock that survived a fiery fall. It is the end product of a complex sequence involving heating, melting, fragmentation, slowing and atmospheric winds.
What Meteorites Reveal About Dangerous Asteroids
The study could also help scientists understand much larger objects entering Earth’s atmosphere.
The 75 meteorite falls examined by the researchers included several different types of meteorites. By comparing how these materials behaved at different altitudes, scientists could determine when various stages of atmospheric entry occurred.
These findings may also provide valuable information about larger asteroids, including objects ranging from the size of a car to several tens of meters across.
According to Jenniskens, asteroids up to tens of meters in diameter can also behave like solid rocks because they generally rotate faster than much larger rubble-pile asteroids.
A real-world example occurred in 2013, when an approximately 20-meter-wide asteroid exploded over Chelyabinsk, Russia. The researchers say that object passed through the same basic sequence of atmospheric processes.
Understanding these seven stages could therefore help scientists better predict how incoming asteroids lose mass, fragment and slow down—and, importantly, where their surviving pieces might land.
The next time a shooting star flashes across the night sky, it is worth remembering that the brief streak of light represents only one moment in a much longer story. From its first collision with the atmosphere to its final fall as a meteorite, a space rock undergoes a remarkable transformation—one controlled not simply by “burning,” but by the powerful combination of melting, fragmentation and atmospheric pressure.
Reference: Peter Jenniskens et al, Bolide Light Curve Systematics from 75 Recovered Meteorites, Meteoritics & Planetary Science (2026). DOI: 10.1111/maps.70203
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