Oldest known meteorite gives scientists insight into planet formation

Object originated beyond Earth somewhere in the early solar system.
By Laurel Kornfeld | Aug 07, 2018
A meteorite dated to be the oldest known is giving scientists new insights into the formation process of the solar system and its rocky planets.

Found in a sand dune in Mauritania, the 4.6-billion-year-old meteorite, designated NWA 11119, is a lighter color than most, is studded with green crystals, and shows signs of having undergone a hardening process via cooling.

University of New Mexico (UNM) graduate student Poorna Srinivasan studied the meteorite using an electron microscope and a computed tomography scan to determine the rock's composition.

"The mineralogy of this rock is very, very different from anything that we've worked on before. I examined the mineralogy to understand all of the phases that comprise the meteorite. One of the main things we saw first were the large silica crystals of tridymite, which is similar to the mineral quartz. When we conducted further image analyses to quantify the tridymite, we found that the amount present was a staggering 30 percent of the total meteorite--this amount is unheard of in meteorites and is only found at these levels in certain volcanic rocks from the Earth," Srinivasan emphasized.

Chemical and isotopic analyses confirmed the meteorite originated somewhere in the solar system beyond Earth, but scientists cannot link it to an asteroid or other object observed telescopically.

However, its composition is sufficiently similar to those of two other meteorites, leading researchers to believe all three originated from the same parent object, possibly a planetestimal in the early solar system.

A collision between the original object and another planetestimal or asteroid could have cause the parent object to break apart. Several of the fragments could have fallen into Earth's atmosphere and landed as meteorites.

"The age of this meteorite is the oldest igneous meteorite ever recorded," said Carl Agee, director of UNM's Institute of Meteoritics. "Not only is this just an extremely unusual rock type; it's telling us that not all asteroids look the same. Some of them look like the crust of the Earth because they're so light colored and full of SiO2 (silicon dioxide). These not only exist, but it occurred during one of the very first volcanic events to take place in the solar system."

Silica-rich meteorites like HWA 11119 were precursors of planet formation and hold the key to understanding how rocky planets formed, noted Daniel Dunlap of Arizona State University's (ASU) School of Earth and Space Exploration.

"This is basically a missing piece 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."

Findings of the study have been published in the journal Nature Communications.


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