Meteorites and Cosmic Dust

Fragments of asteroids, the Moon, and Mars that fall to Earth, plus the fine interplanetary dust, all serving as hand samples of the Solar System.

Definition

Meteorites are fragments of asteroids and other bodies that survive passage through the atmosphere to reach a planet's surface, and cosmic dust is the population of microscopic interplanetary particles that pervade the Solar System.

Scope

This topic covers meteorites and interplanetary dust as the physical samples that link planetary science to laboratory analysis. It treats the classification of meteorites into chondrites, achondrites, stony-irons, and irons; their primitive components such as chondrules, calcium-aluminum-rich inclusions, and presolar grains; their use in dating the Solar System and tracing nebular and parent-body processes; and the collection and study of micrometeorites, cosmic spherules, and interplanetary dust particles.

Core questions

• How are meteorites classified, and what parent bodies do they come from?
• What do chondrules and refractory inclusions reveal about the early solar nebula?
• How are meteorites used to date the formation of the Solar System?
• What can interplanetary dust and presolar grains tell us about materials predating the Sun?

Key theories

Chondrites as primitive nebular samples

Chondritic meteorites are little-altered aggregates of early Solar System materials, including chondrules and refractory inclusions, that record conditions in the solar nebula before planet formation.

Refractory inclusions as the oldest solids

Calcium-aluminum-rich inclusions are the oldest dated Solar System solids, and their radiometric ages set the zero point for the timeline of planet formation.

Mechanisms

Collisions liberate fragments from asteroids and, occasionally, from the Moon and Mars; these survive atmospheric entry to land as meteorites whose mineralogy and isotopes record nebular and parent-body history. Radiometric dating of refractory inclusions and chondrules pins the Solar System's age, while presolar grains preserve material from earlier stars.

Clinical relevance

Meteorites provide the ground-truth chemistry and chronology of the Solar System, anchoring its absolute age, the timeline of planet formation, and the inventory of organic and volatile materials delivered to the early Earth.

History

The extraterrestrial origin of meteorites was established in the early 19th century. Radiometric dating in the 20th century, notably Patterson's measurement of the Solar System's age from meteorites, and later high-precision lead-isotope ages of refractory inclusions, built a detailed chronology. Antarctic and desert meteorite collection and the discovery of lunar and Martian meteorites greatly expanded the available samples.

Debates

Origin of chondrules

How chondrules, the millimetre-sized melt droplets in chondrites, were heated and rapidly cooled in the solar nebula remains an unresolved problem in meteoritics.

Key figures

• Harry McSween
• Yuri Amelin
• Alexander Krot
• Gerald Wasserburg

Seminal works

• mcsween1999
• amelin2002

Frequently asked questions

How old is the Solar System?

Radiometric dating of the oldest solids in meteorites gives an age of about 4.57 billion years, which defines the start of the Solar System.

Can meteorites come from the Moon or Mars?

Yes, large impacts can blast rock off the Moon and Mars into space, and some of these fragments eventually land on Earth as identifiable lunar and Martian meteorites.