Peter Jenniskens of the SETI Institute and NASA Ames Research Center has mapped seven stages that a falling space rock passes through, from first glow in the upper atmosphere to the last flicker of light before landing. The study draws on video and photographs of 75 documented meteorite falls. Its central result is that melting and then violent fragmentation, rather than simple evaporation, decide how much of a rock survives to reach the ground.
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Jenniskens led the paper with Stuart Pilorz of the SETI Institute, Darrel Robertson of NASA Ames and Eric Stern, formerly of NASA Ames and now chief scientist at Hyperspace Technologies. The team tracked each fireball’s light curve and recorded the altitude at which each type of rock entered each stage.
The seven stages from first glow to landing
The ScienceDaily report and the SETI Institute release number the stages one to seven without formal names; the labels below summarise what each describes.
- Stage 1, high-altitude glow: air becomes dense enough to form a shock wave ahead of the rock, and collisions heat it until it glows as a meteor.
- Stage 2, brightening meteor: the meteor brightens in thicker air, and some rocks spin fast enough to produce regular brightness changes.
- Stage 3, fireball with melting: melting becomes the main way mass is lost, as fast airflow strips molten droplets.
- Stage 4, melting equilibrium: at roughly 60 kilometres altitude brightness stays steady or rises gradually, and melting alone can remove up to 40% of the mass.
- Stage 5, breakup begins: rising air pressure fractures the rock, which flares repeatedly and slows sharply.
- Stage 6, rear breakup: the back of the rock fragments in a last bright flare, usually red because the meteor has slowed, and pieces are ejected at higher relative speeds.
- Stage 7, final glow and landing: melting and fragmentation continue until the pieces stop glowing, leaving a thin fusion crust, and wind can push them off course before they land.
Two transitions in the sequence carry the main result. Between stages three and four melting settles into a steady balance that can strip up to 40% of the original mass, and between stages four and five rising pressure shifts the loss from melting to breakup. The sequence matters to anyone modelling entry because it shows rocks do not simply shrink smoothly on the way down; they lose mass in a series of distinct regimes, each with its own altitude range that depends on the type of rock.
Melting and fragmentation, not evaporation, remove the mass
Jenniskens said the data point to melting first and then fragmentation as the controls on how a rock loses mass, a different picture from the older idea that atmospheric entry mostly evaporates material. Fragmentation can begin at about one-fifth the strength of recovered meteorites, possibly because of heating and cracks from earlier impacts, according to the paper in Meteoritics & Planetary Science, titled “Bolide light curve systematics from 75 recovered meteorites.”
Spin rates and scatter also come out of the light curves. The fastest-rotating rocks turned in 0.5 to 5 seconds, and meteorites over about 20 grams tended to scatter more widely. Robertson noted that small meteorites fall in a narrow strip on the ground, which matters to anyone searching a strewn field for the pieces. The red colour of the final flashes is itself a clue, since it reflects a meteor that has already slowed, and the thin fusion crust that coats surviving pieces forms only after melting stops. Reading those features from video lets the team place each recovered rock at a stage and altitude without having seen the rock fall in person, which is what makes 75 recoveries a usable data set.
Chelyabinsk and the limits of the laboratory
Jenniskens said the 20-metre asteroid behind the 2013 Chelyabinsk airburst in Russia went through the same phases. A Sandia-led consortium poster puts that body at about 1,200 tonnes entering at roughly 19 kilometres per second, with peak brightness near 29 kilometres altitude. A 2013 research report, which gave an impact speed of about 19 kilometres per second and a breakup most efficient around 30 kilometres altitude with light brighter than the sun to observers 100 kilometres away, and which credited Jenniskens as co-lead author of the Science report with Olga Popova leading the field study, estimated that 4,000 to 6,000 kilograms of meteorites reached the ground, including a fragment of roughly 650 kilograms pulled from Lake Chebarkul.
Laboratory tests have limits here. The SETI summary notes that an arcjet experiment at NASA Ames cannot fully reproduce the radiation of a natural entry at these speeds, which is why fireball video remains the main evidence. The count to watch is 75: each of the seven stages is read from those documented falls, and the next set of recovered meteorites with video will show whether the stage altitudes hold for other rock types.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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