WHAT DOES A METEORITE LOOK LIKE?

METEORITES ON EARTH LOOK VERY DIFFERENT FROM THEY WAY THEY DID DRIFTING THROUGH SPACE.

During a meteorite's 10- to 15-second trip through the atmosphere, air friction heats its surface to a red-hot 1,800 degrees Celsius. This friction can melt the meteorite, and can carry away up to 90 percent of the original mass, leaving interesting surface features. Once a meteorite lands, weathering begins to change and destroy its surface.

WRAPPED IN BLACK GLASS

Rocks floating through the vacuum of space are chilled to well below freezing. When a meteorite passes through Earth's atmosphere, its inside stays cold even as its surface melts away. Before it hits the ground, the molten surface solidifies into a thin glassy coating, called fusion crust. Crystals of magnetite—an iron-oxide mineral—color the fusion crust black. The broken surface of Modoc shows contrast between its lighter-colored interior and its dark fusion crust.

METEORITE DRIPPINGS

Some meteorites, such as Stannern, have tiny bumpy lines—called flow lines—running down their sides, like wax drippings on a candle. Flow lines form on meteorites that hold a fairly stable orientation as they pass through the atmosphere. Air pressure melts the surface and pushes the droplets backward. As the rock cools, the last flowing drips freeze into flow lines.

NOSE TO THE GROUND

Meteorites with a well-formed nose cone shape, like Miller, are very rare. They develop when the meteorite stays in a constant orientation as it passes through the atmosphere. The side facing Earth melts and erodes into an aerodynamic cone shape.

FINGERPRINTS OF THE ATMOSPHERE

The little fingerprintlike indentations seen on the surfaces of many meteorites, such as Glorieta Mountain, show how the rock melted as it passed through the atmosphere. These impressions, called regmaglypts, were scooped out by the superheated air swirling around the tumbling meteorite.

Early spacecraft, like capsules from the Gemini and Mercury missions, had heat shields that were designed to partly melt away from the intense heat of reentering Earth's atmosphere. The melting bits of shield carried away the heat, keeping the inside of the capsule cool. This same process keeps the inside of a meteorite cool as it passes through the atmosphere.

EXPOSED TO THE ELEMENTS

Some meteorites, such as Dalgety Downs, sit outside for thousands of years before they're discovered. Rain, wind, heating and cooling can cause weathering of the surface-rust and cracks that eventually break a meteorite to pieces. Weathering begins as soon as moisture in the air contacts the meteorite's surface. Even slight weathering begins to destroy clues to the rock's original composition.

The 14-ton Willamette meteorite, found in an Oregon forest in 1902, has a nearly perfect nose cone shape. Arriving at this museum in 1906, Willamette is now displayed in the Rose Center for Earth and Space. Over hundreds of years, rainwater mixed with sulfur deposits in the meteorite to form acid, which burned round cavities into its surface.

THIS IS NOT A METEORITE

Many hunks of ordinary rock or metal look like meteorites. One example is leftover material from an industrial furnace, called slag. Slag often contains gas bubbles, while meteorites do not. Other common "meteowrongs" include iron-rich rocks formed on Earth, fallen pieces of manmade satellites and lava rocks polished in streams.