Meteorites
Space rocks that survive the fall to a planet's surface.
Overview
A meteoroid that survives its passage through the atmosphere and reaches the ground is a meteorite. They are free samples of asteroids — and occasionally of the Moon and Mars — delivered without a spacecraft, and they include the oldest solid material available for laboratory study.
- Meteoroid, meteor and meteorite are three different things: the object, the light, and the survivor.
- The oldest meteorite inclusions date the Solar System to about 4.567 billion years.
- A few meteorites are confirmed to come from Mars and the Moon, identified by composition and trapped gases.
- Antarctica yields disproportionately many finds because dark stones are conspicuous on ice.
The words, and what each one names
- A meteoroid is the solid object while it is still in space — smaller than an asteroid, with no sharp boundary between the terms.
- A meteor is the luminous phenomenon as the object heats and ablates in the atmosphere. The light comes mainly from ionised air along the path, not from the object burning.
- A meteorite is what reaches the ground. Most meteoroids do not produce one; they ablate entirely at high altitude.
- A fireball is an exceptionally bright meteor. A bolide is one that fragments explosively.
Classification
Meteorites fall into three broad groups. Stony meteorites are the most common; within them, chondrites contain chondrules — small spherical grains that formed as free-floating molten droplets in the early solar nebula and were never subsequently melted. Chondrites therefore preserve primordial material, and carbonaceous chondrites additionally contain water-bearing minerals and organic compounds.
Achondrites lack chondrules and come from bodies that were heated enough to differentiate. Iron meteorites are iron–nickel alloy, understood as fragments of the cores of such bodies, and their large crystalline Widmanstätten patterns record cooling over millions of years — an internal structure that can only form deep inside a substantial parent body. Stony-iron meteorites contain both.
Dating the Solar System
Calcium–aluminium-rich inclusions in primitive chondrites are the oldest dated solids formed in the Solar System, with radiometric ages around 4.567 billion years. That measurement is the basis for the Solar System's accepted age, and it comes from meteorites rather than from any planetary sample — Earth's own oldest rocks are considerably younger because the planet has continuously reprocessed its crust.
This is a good example of a value that Asteria Star records with its measurement basis attached. It is a radiometric determination on specific inclusions, with a stated uncertainty, not a round figure.
Meteorites from the Moon and Mars
A small number of meteorites originate from the Moon and from Mars, launched by large impacts and eventually intercepted by Earth. Lunar origin is confirmed by direct comparison with Apollo samples. Martian origin is established chiefly by trapped gas whose composition matches the Martian atmosphere as measured by the Viking landers — a distinctive isotopic signature that is very hard to reproduce any other way.
ALH 84001, a Martian meteorite recovered in Antarctica, became widely known after a 1996 paper proposed that features within it might be biological. That interpretation did not survive scrutiny — non-biological explanations account for the observed features — and it remains a useful case study in how extraordinary claims are tested.
Where they are found
Meteorites fall roughly uniformly across Earth, but recovery is heavily biased. Antarctic blue-ice fields concentrate them: dark stones are unmistakable against ice, ice flow accumulates them in predictable areas, and the cold dry conditions limit weathering. Hot deserts are productive for similar reasons of visibility and preservation.
'Falls' — meteorites recovered after an observed fireball — are scientifically more valuable than 'finds', because they are fresher and their atmospheric trajectory can sometimes be reconstructed to determine the original orbit, linking a laboratory sample to a specific region of the Solar System.
Continue in the data
Catalogues, hubs, and reference pages that hold the underlying records for this topic.
Frequently asked
- What is the difference between a meteor and a meteorite?
- A meteor is the streak of light produced as an object enters the atmosphere — mostly emission from ionised air along its path. A meteorite is the solid object if any part of it survives to reach the ground. Most meteors leave no meteorite at all, ablating completely at high altitude.
- How do we know some meteorites came from Mars?
- Chiefly from trapped gas. Certain meteorites contain gas whose elemental and isotopic composition matches the Martian atmosphere as measured directly by the Viking landers — a distinctive fingerprint that is very difficult to produce any other way. Their mineralogy and oxygen isotope ratios corroborate it.
- How old are meteorites?
- The oldest components — calcium–aluminium-rich inclusions in primitive chondrites — give radiometric ages of about 4.567 billion years, and this is the basis for the accepted age of the Solar System. They are older than any rock available on Earth, because Earth's crust has been continuously reprocessed by geological activity.
- Why are so many meteorites found in Antarctica?
- Because recovery conditions are exceptional, not because more fall there. Dark stones are highly visible on ice, glacial flow concentrates them in predictable stranding zones, and the cold dry environment limits chemical weathering so specimens survive in good condition for long periods.