SCIENCE

A 4.565-billion-year-old space rock hints at the way Earth and other rocky planets took shape. (Phys.org)

What is a meteorite? Use our introductory reference to learn more.

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

Discussion Ideas

• NWA 11119 is the oldest igneous meteorite yet dated. What does NWA stand for?
  • Northwest Africa. The space rock was discovered in a sand dune in the west African nation of Mauritania in 2016. Thousands of meteorites are classified as “NWA,” as the Sahara Desert is one of the richest repositories of meteorites on Earth. (The Antarctic Desert is another.)
    • Although the meteorite was discovered in 2016, no one knows when it actually fell to Earth—the rock could have been in the sand for weeks or for centuries.

 

• NWA 11119 is the oldest igneous meteorite yet dated. What is an igneous meteorite?
  • Igneous rocks are formed by the cooling of magma or lava. Meteorites are space rocks that fall to Earth’s surface. So, igneous meteorites formed from some type of volcanism on an extraterrestrial body, such as a planet, moon, or asteroid.
    • In fact, NWA 11119 was formed during “one of the very first volcanic events to take place in the solar system.” (!)
    • NWA 11119 is a type of igneous meteorite known as an achondrite. Achondrites are a type of stony meteorite containing no hardened droplets (chondrules). Achondrites are the rarest type of meteorites, making up just 3%-8% of all known space rocks.
      • NWA 11119 is further described as a ureilite, an even rarer type of achondrite. Ureilites are achondrites with unknown origins—not our Moon, or Mars, or an identified asteroid.
        • The diamond-studded Almahata Sitta meteorite is another well-known ureilite—and a possible sister rock of NWA 11119. Learn more about the Almahata Sitta here.

 

• NWA 11119 is older than our solar system’s rocky inner planets and moons. So where did it form?
  • NWA 11119 may be a remnant of volcanic activity on a long-gone planetesimal or protoplanet. Protoplanets are similar to dwarf planets such as Ceres or Pluto, with more radioactive elements present.
    • Nat Geo describes protoplanets as “balls of gas, dust, and rock about the size of Mercury or Mars [that] once swirled around our young sun … [M]any 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.”
  • NWA 11119 may also be a remnant of an asteroid. Asteroids are the debris of protoplanets, “the remains from the formation of the solar system formation some 4.6 billion years ago.” Today, asteroids orbit the sun in a thick “Asteroid Belt” between Mars and Jupiter.

 

• Scientists have tentatively linked the formation of NWA 11119 to a specific process associated with planetary formation. What is this process?
  • planetary differentiation. Planetary differentiation describes the process by which heavy elements sink to the center of protoplanets through 1) continual impacts and collisions with other protoplanets and asteroids, 2) radioactive decay, and 3) gravitational pressure. These heavier elements evolve into a planetary core and mantle, while lighter elements evolve into a planetary crust.
    • The new research indicates NWA 11119 was formed in the crust of a differentiated protoplanet. (That’s the big takeaway here.)

 

• How is NWA 11119 different from most meteorites? Take a look at the beautiful Almahata Sitta to spot some contrasts.
  • The most obvious difference is its color. The Almahata Sitta meteorite is what a “typical” meteorite looks like—black, shiny, dense. NWA 11119 is lighter-colored, porous, and flecked with clear and green crystals.
  • As its appearance indicates, the mineralogy of NWA 11119 is “is very, very different from anything that we’ve worked on before,” says one scientist. NWA 11119 includes a huge proportion of silica, while most meteorites are composed mostly of basalt.
    • “It has the highest abundance of silica and the most ancient age (4.565 billion years old) of any known igneous meteorite. Meteorites like this were the precursors to planet formation and represent a critical step in the evolution of rocky bodies in our solar system.”

 

• Take another look at the Almahata Sitta. Why do some scientists think that NWA 11119 may be a sister-rock to the Almahata Sitta?
  • Key chemistry (oxygen isotopes) in both space rocks are identical, although their mineralogy is very different, “suggesting that they all are from the same parent body – perhaps a large, geologically complex body that formed in the early solar system.”
    • The Almahata Sitta may have formed in the mantle of such a protoplanet, while NWA 11119 may have formed in the crust.

 

• How does the mineralogy of NWA 11119 help us understand the early solar system?
  • “This research is key to how the building blocks of planets formed early in the solar system,” says one scientist. “When we look out of the solar system today, we see fully formed bodies, planets, asteroids, comets and so forth. Then, our curiosity always pushes us to, to ask the question—How did they form? How did the Earth form? This is basically a missing part of the puzzle that we’ve now found that tells us these igneous processes act like little blast furnaces that are melting rock and processing all of the solar system solids. Ultimately, this is how planets are forged.”

 

TEACHERS TOOLKIT

Phys.org: Researchers uncover remnants of early solar system

The Meteoritical Society: NWA 11119

Nat Geo: What is a meteorite?

Nat Geo: Diamonds from Space Hint at a Long-Lost Planet

(extra credit!) Nature Communications: Silica-rich volcanism in the early solar system dated at 4.565 Ga