Topic

#Asteroid geology

How meteorites are traced back to a small number of asteroids and the collisions that broke them apart.

Most meteorites are pieces of asteroids, and many can be traced to a surprisingly small number of parent bodies. When asteroids collide, they shatter into families of fragments travelling on similar orbits. Over millions of years, the gentle push of sunlight and the pull of Jupiter steer some of those fragments onto paths that cross Earth's.

The L chondrites are a striking example. Many of them were heavily shocked in a single break-up about 470 million years ago, and fossil meteorites from that time are found in ancient limestone in Sweden, showing that Earth was struck far more often for a while afterwards.

By comparing meteorites in the laboratory with the colours of sunlight reflected from asteroids, scientists match groups of meteorites to their likely sources, such as the HED meteorites to the giant asteroid Vesta.

Part of Meteorites across the sciences.

Lessons (15)

Achondrites: rocks from melted worldsAchondrites are stony meteorites without chondrules. They come from worlds that melted, and many of them look surprisingly like volcanic roc
Asteroids: the parent bodiesMeteorites are samples of asteroids, and asteroids are leftovers from the building of the planets.
Early Solar System chronologyMeteorites let us build a timeline of the first few million years of the Solar System with a precision that seems almost impossible. Here is
Fireball networks: from sky to orbitWhen a fireball is filmed from several places at once, scientists can find where its meteorites landed and trace where they came from in spa
Iron meteorite groupsStructure tells you what an iron meteorite looks like when etched, but chemistry tells you which parent body it came from. Here you will lea
Iron meteorites: cores, cooling and dynamosIron meteorites preserve quantitative records of how asteroid cores crystallised and cooled, and even whether they generated magnetic fields
The journey through the atmosphereEvery meteorite survived one of the most violent journeys in nature. Here we follow a meteoroid from the edge of space to the ground, step b
Delivery: from asteroid families to EarthWhich asteroids are our meteorites actually coming from? Dynamics, spectroscopy and exposure ages are converging on answers.
Ordinary chondrites: H, L and LLRoughly four in every five meteorites seen to fall are ordinary chondrites. They are divided into three groups, H, L and LL, and learning to
Oxygen isotopes: the fingerprint of originOxygen makes up nearly half of most rocks by mass, and its three stable isotopes carry a signature that distinguishes parent bodies.
Petrologic types: from wet to hotThe number after a chondrite's group letter, as in H5 or CM2, is its petrologic type. It tells you what happened to the rock inside its
Primitive achondrites and ureilitesBetween chondrites and fully melted achondrites lie rocks caught in the act of melting. They reveal how differentiation begins.
The classification frameworkMeteorite classification is a hierarchy built on petrology, bulk chemistry and isotopes.
The NC–CC isotopic dichotomyNucleosynthetic isotope anomalies split meteorites into two great families that formed in separate regions of the disc.
Where do meteorites come from?Meteorites are visitors from far away. Most come from a ring of rocks called the asteroid belt, and a few come from the Moon and Mars.

Courses (9)

Atmospheric entry and fragmentationA meteoroid is decelerated, heated and often shattered by the air. Simple models of drag and ram pressure explain where it breaks up and how
Mass spectrometry and oxygen isotopesMass spectrometers measure isotope ratios to within about ten parts per million. Oxygen's three isotopes then sort meteorites into famil
Shock, craters and deflecting an asteroidHypervelocity impacts generate shock pressures that transform minerals. This final lesson connects shock metamorphism, crater evidence and t
Spectroscopy: matching meteorites to asteroidsSunlight reflected from an asteroid carries the absorption fingerprints of its minerals.
The journey from the asteroid beltMost meteorites begin as fragments of asteroids between Mars and Jupiter. This lesson follows the long, slow route that brings a few of them
Forces and orbitsAsteroids, planets and meteoroids all move under gravity. This lesson applies Newton's laws and circular motion to orbits, and explains
Isotopes as fingerprintsAtoms of the same element can have different numbers of neutrons. The ratios of these isotopes in a meteorite act like a fingerprint for the
Our Solar System and where space rocks liveThe Sun, eight planets, their moons and millions of smaller bodies make up our Solar System.
The small bodies of the Solar SystemBetween and beyond the planets are millions of asteroids and comets. This lesson sets out where they are, how far away they are and how a pi

Books (1)

Meteorite Classification: The Professional's GuideA working reference for classifiers, curators and postgraduate researchers. It sets out current practice for every meteorite type: the fifte

Famous meteorites (6)

BarwellOn Christmas Eve 1965 a shower of stones fell on a Leicestershire village, the largest meteorite fall recorded in Britain.
ImilacA pallasite scattered across the Atacama Desert, whose weathered pieces look like metal sponges.
JuvinasA single basaltic stone that fell in southern France in 1821 and helped show that some asteroids once had volcanoes.
KaidunA small stone that fell on a military base in Yemen in 1980 and turned out to be a jigsaw of many different worlds.
KapoetaA howardite that fell in South Sudan in 1942 – a piece of the battered surface of the asteroid Vesta.
Tagish LakeA fragile carbon-rich meteorite that fell onto a frozen Canadian lake in 2000 and was collected without being touched by bare hands.

Meteorite types (21)

AcapulcoitesFine-grained rocks that only just began to melt. Named after Acapulco in Mexico, which fell in 1976, acapulcoites are fine-grained rocks of
AubritesPale, almost iron-free rocks made of enstatite, from an extremely oxygen-poor world.
CI chondritesThe chemically most primitive rocks known: their make-up matches the Sun's. CI chondrites, named after Ivuna in Tanzania, match the comp
CV chondritesLarge chondrules and big white inclusions, the oldest solids in the Solar System. Allende is the classic.
EL chondritesLow-iron enstatite chondrites. EL chondrites have less metal than EH chondrites and contain alabandite, a manganese sulphide, instead of nin
Enstatite chondritesChondrites formed with almost no oxygen to spare, full of rare minerals unknown on Earth's surface.
IID ironsFine to medium octahedrites rich in gallium and germanium. IID irons are fine to medium octahedrites with about 10–11% nickel and high galli
IIE ironsIrons full of silicate fragments, possibly from asteroid Hebe. IIE irons are octahedrites of varying coarseness that often contain silicate
IIF ironsA small group of magmatic irons. IIF is a small magmatic group of irons with distinctive trace-element patterns. Only a handful are known.
IIIE ironsCoarse octahedrites, separated from IIIAB by their chemistry. IIIE irons are coarse octahedrites with about 8–9% nickel.
IIIF ironsA small group with very low gallium and germanium. IIIF irons are medium to coarse octahedrites with about 7–8% nickel and very low gallium
Iron meteoritesAlmost pure iron-nickel metal, mostly from the cores of asteroids that melted and were later shattered.
K chondrites (Kakangari grouplet)A tiny grouplet with a mix of features found in no other chondrite group. K chondrites are named after Kakangari in India, which fell in 189
L chondritesLow-iron ordinary chondrites: the single most common group of meteorites. L chondrites have less metal than H chondrites, typically 4% to 10
Main-group pallasitesNine in ten pallasites: magnesium-rich olivine in metal related to the IIIAB irons.
PallasitesGem-like olivine crystals set in iron-nickel metal. Pallasites contain large olive-green crystals of olivine embedded in iron-nickel metal.
Primitive achondritesRocks that began to melt but were never fully processed: halfway between chondrites and igneous rocks.
Pyroxene and ungrouped pallasitesPallasites that fit neither main group nor Eagle Station, among them the pyroxene-bearing pair Vermillion and Yamato 8451.
R chondrites (rumurutiites)Highly oxidised chondrites with almost no metal. R chondrites are named after Rumuruti in Kenya, the only one seen to fall (1934).
Ungrouped achondritesMelted rocks that match no known group: each may be the only sample of its own world. Some achondrites fit none of the named groups.
WinonaitesPrimitive achondrites related to the silicate inclusions in IAB irons. Named after the Winona meteorite, found buried in a Sinagua ruin in A

Space missions (1)

MBR ExplorerThe United Arab Emirates' planned tour of the asteroid belt, ending with a landing.

Glossary (12)

Questions and answers (20)

Did asteroids ever have magnetic fields?Yes, some did. Studies of meteorites suggest that several early asteroids had molten metal cores that produced magnetic fields, like a small
How do scientists tell which parent body a meteorite came from?Mainly by oxygen isotopes, which act like a fingerprint, together with chemistry, mineralogy and other isotope systems that group meteorites
How do we know a meteorite came from Mars?Gas trapped in glass inside some Martian meteorites matches the unusual atmosphere measured on Mars by the Viking landers in 1976.
How do we know which asteroid a meteorite came from?Usually we only know the likely type or region of asteroid, by matching how meteorites and asteroids reflect light, reconstructing fireball
How hot did the insides of asteroids get?It varied. Some asteroids stayed cool enough for ice to melt but not rock, while others reached 1,000 °C or more and melted completely into
How is shock in a meteorite measured?Scientists examine minerals under a polarising microscope, looking for features such as fractures, mosaic patterns, glass and high-pressure
How many different parent bodies do meteorites come from?Probably more than a hundred. Meteorite groups and ungrouped meteorites suggest dozens of iron meteorite parent bodies alone, plus many more
What does a meteorite's weathering grade mean?A weathering grade, from W0 to W6, describes how much a meteorite has rusted and changed since landing on Earth, from fresh to almost comple
What is a brachinite?A brachinite is a rare olivine-rich achondrite, thought to be the residue left after an early asteroid partly melted and lost its basaltic m
What is a CV chondrite?A CV chondrite is a carbonaceous chondrite with large chondrules and abundant CAIs, such as Allende, the source of many key discoveries abou
What is a ureilite?A ureilite is an unusual achondrite made of olivine and pyroxene with carbon, including graphite and tiny diamonds, from a parent body shatt
What is an R chondrite?An R chondrite, or Rumuruti chondrite, is a rare, highly oxidised chondrite with abundant iron-rich olivine and almost no metal.
What is aqueous alteration in meteorites?Aqueous alteration is the change of minerals by liquid water inside asteroids, which turned olivine, pyroxene and metal into clays, carbonat
What is the asteroid belt like?The asteroid belt is a huge, mostly empty region between Mars and Jupiter where millions of rocky bodies orbit the Sun, usually very far apa
What is the asteroid belt?The asteroid belt is a broad region between the orbits of Mars and Jupiter where most known asteroids orbit the Sun.
What is the Gibeon meteorite?Gibeon is a large iron meteorite shower in Namibia, scattered over a huge strewn field in prehistoric times, famous for its delicate Widmans
What was the Tagish Lake meteorite?Tagish Lake is a fragile, carbon-rich meteorite that fell on a frozen lake in Canada on 18 January 2000 and was collected frozen, preserving
Where do meteorites come from?Most meteorites are fragments of asteroids, chipped off in collisions in the asteroid belt between Mars and Jupiter.
Why are most meteorites chondrites?Most meteorites are chondrites because unmelted, chondritic asteroids are abundant in the parts of the asteroid belt that feed material to E
Why do iron meteorites come from so many parent bodies?Iron meteorites come from the cores of many small planetesimals that melted early; their strength lets them survive while the rocky outer la

Meteor showers (2)

The Southern Delta Aquariids meteor showerSouthern Delta Aquariids meteor shower: peak around 30–31 July, active about 12 July to 23 August.
The Tau Herculids meteor showerTau Herculids meteor shower: peak around 30–31 May, mainly in outburst years, active late May to early June.

Impact events (1)

The Ordovician meteorite rainWhen an asteroid broke apart and Earth was showered with meteorites for millions of years.

Asteroids (1)

CeresCeres was the first object found in the gap between Mars and Jupiter. Giuseppe Piazzi spotted it from Palermo on the first night of 1801, an

Comets (1)

Comet Schwassmann–Wachmann 3A comet caught falling to pieces, which gave the Tau Herculid shower its first real display in 2022.

Micrometeorites (1)

Fossil micrometeorites and the air of the ancient EarthMicrometeorites trapped in ancient rocks are tiny probes of the past. Iron spherules 2.7 billion years old have been used to test what the u

People (1)

Daniel KirkwoodThe astronomer who discovered in 1866 the gaps in the asteroid belt made by Jupiter's gravity, now called the Kirkwood gaps.