SCIENCE

A gem-studded meteorite that fell in Sudan offers clues about the protoplanets that likely existed in our solar system’s violent past. (National Geographic)

What are meteorites? Use our resource to learn more.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• Ten years ago, amateur and professional astronomers tracked a meteoroid headed to Earth. Then, they tracked it as it blazed across the sky. Finally, they tracked to the desert of Northern Sudan. (Read the full story here.) What they found was the Almahata Sitta meteorite. How did the space rock go from meteoroid to meteorite? Use our resource for some help.
  • Meteoroid, meteor, and meteorite are different names for the same rock at different points on its collision course with Earth.
    • Meteoroids are lumps of rock and metal that orbit the sun. Meteoroids, especially the tiny particles called micrometeroids, are extremely common throughout the solar system. They orbit the sun among the rocky inner planets, as well as the gas giants that make up the outer planets. Meteoroids are even found on the very edge of the solar system, in regions called the Kuiper belt and the Oort cloud.
    • Meteors are “shooting stars”—streaks of light in the sky caused by a meteoroid crashing through Earth’s atmosphere. When a meteoroid enters the Earth’s upper atmosphere, it heats up due to friction from the air. The heat causes gases around the meteoroid to glow brightly, and a meteor appears. The Almahata Sitta meteor burned as a bolide, one of the brightest and most massive types of meteor. (Superbolides, the most massive type of meteor, can burn 30 times brighter than the sun and explode in the atmosphere with the energy of 500 tons of TNT. Read about a remarkable superbolide here.)
    • Meteorites are the final stage in the journey of a space rock. Meteorites are the bits of space rock that fall to Earth. Dust-sized particles called micrometeorites make up 99% of the approximately 50 tons of space debris that falls on the Earth’s surface every day. Some meteorites, however, are as large as boulders.
      • The Almahata Sitta meteorite is actually a collection of about 600 fragments of the meteor, which, like most bolides, exploded before it hit the ground. (The name “Almahata Sitta” simply means “Station Six” in Arabic. Station Six is a train station in Northern Sudan near where the first meteorite fragments were found.)

• The Almahata Sitta meteorite is a type of meteorite called a ureilite. How do urelities differ from other meteorites?
  • “Unlike other meteorites, which can be traced to parent bodies such as asteroids, Mars or the moon by comparing the ratios of different varieties of elements, these rocks have no known source. They seem to have been formed inside bodies that no longer exist. And they always contain tiny flecks of diamond.”
  • Ureilites are a type of achondrite meteorite. Achondrites are the rarest type of meteorites, making up about 3% of all known space rocks. Most achondrites (not ureilites) are formed from impacts on the Moon, Mars, or the brittle outer layer of asteroids.

• How do diamonds in the Almahata Sitta meteorite seem to support the theory that the rock formed in the interior of a long-lost planet?
  • The diamonds in the Almahata Sitta meteorite contain inclusions—tiny mineral deposits trapped inside the incredibly strong, hard structure of the diamond itself. (On Earth, inclusions are often considered impurities, flaws, or imperfections, although they lend blue diamonds their striking color. Learn more about that here!)
  • Both the impurities (crystals of chromite, phosphate, and iron-nickel-sulfide) and the diamond itself “could only have formed under incredible pressure — the equivalent of diving 600 kilometers into Earth’s interior or attempting to hold up 100,000 tons with your bare hands.” These pressures only exist in the interior of Moon- to Mars-sized planetary bodies.

• So, what happened to this long-lost planet?
  • Technically, it wasn’t quite a planet. The likely origin of the Almahata Sitta meteorite was a protoplanet or planetary embryo. Protoplanets are “balls of gas, dust, and rock about the size of Mercury or Mars [that] once swirled around our young sun.”
    • Protoplanets are similar to dwarf planets such as Ceres or Pluto, with more radioactive elements present. Through continual impacts with other protoplanets, radioactive decay, and gravitational pressure, heavier elements sink to the center of protoplanets in a process called planetary differentiation. According to the new research, diamonds in the Almahata Sitta meteorite formed in the mantle of a differentiated protoplanet.
  • While astronomers can’t say for sure what happened to the protoplanet parent of the Almahata Sitta meterorite, “many researchers believe that the early inner solar system was crowded with large protoplanets that yanked and tugged at each other’s orbits until they finally crashed, coalesced or disintegrated. By the end of that era, about 100 million years after the birth of the solar system, only the four current terrestrial planets remained.”

TEACHERS TOOLKIT

Nat Geo: Diamonds From Outer Space Formed Inside a Long-Lost Planet

Washington Post: These diamonds from space formed inside a long-lost planet, scientists say

Nat Geo: What is a meteorite?

(extra credit!) Nature Communications: A large planetary body inferred from diamond inclusions in a ureilite meteorite