What the Oldest Meteorites Say about the Early Solar System (preview)

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Microscopic analyses of chondrites, the oldest rocks in the solar system, are filling in details of what our neighborhood in space was like shortly before the planets formed

By Alan E. Rubin

HIDDEN GEMS: The ?jewels? in this polarized light micrograph of a slice from a chondrite are chondrules, tiny beads of silicate minerals. Despite this chondrite's beauty, it belongs to the class known as ordinary. Image: J. M. DEROCHETTE

In Brief

• Chondritic meteorites are made of the stuff that formed the planets, moons, asteroids and comets. Each chondrite group has its own distinctive textural and compositional characteristics.
• From these properties, the author and other scientists have inferred roughly the locations where the chondrite groups formed and the relative amount of dust present in those regions.
• The dust distribution resembles that seen in protoplanetary disks of dust and gas swirling around several stars known as T Tauri stars?in particular, young, one- to two-million-year-old versions about as massive as our sun. This resemblance suggests that T Tauri systems are good analogues of the sun and its own disk during the early stages of solar system history.

I pity Astronomers. They can see the objects of their affection?stars, galaxies, quasars?only remotely: as images on computer screens or as light waves projected from unsympathetic spectrographs. Yet many of us who study planets and asteroids can caress pieces of our beloved celestial bodies and induce them to reveal their innermost secrets. When I was an undergraduate astronomy major, I spent many a cold night looking through telescopes at star clusters and nebulae, and I can testify that holding a fragment of an asteroid is more emotionally rewarding; it offers a tangible connection with what might otherwise seem distant and abstract.

The asteroidal fragments that fascinate me most are the chondrites. These meteorites, which constitute more than 80 percent of those observed to fall from space, derive their name from the chondrules virtually all of them contain?tiny beads of melted material, often smaller than a rice grain, that formed before asteroids took shape early in the solar system's history. When we examine thin slices from chondrites under a microscope, they become beautiful to behold, not unlike some of the paintings by Wassily Kandinsky and other abstract artists.

This article was originally published with the title Secrets of Primitive Meteorites.

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