When a meteor flashes across the night sky, it’s more than a beautiful streak of light.
It’s a delivery from deep space—an ancient piece of rock that has traveled for billions of years to reach Earth.
These meteorites are like time capsules, preserving clues about how the solar system formed long before Earth existed.
Scientists study them to understand the earliest steps that led to planets, including the one we live on today.
Lawrence Livermore National Laboratory (LLNL) researcher Thomas Kruijer has been exploring how meteorites can unlock the story of our solar system’s beginning.
In a recent review paper for Space Science Reviews, which will later appear in a textbook, he explains how these tiny rocks help scientists piece together events from more than 4.5 billion years ago.
The ultimate mystery is how planets capable of supporting life—like Earth—came to be. Kruijer says that while we still don’t have a complete answer, meteorites provide some of the strongest clues.
To understand why meteorites matter, it helps to go back to the very start. Before the planets existed, the sun was surrounded by a swirling disk of gas and dust called the protoplanetary disk.
This material came from a massive molecular cloud that collapsed under its own gravity. The disk was extremely hot at first, but it cooled over time. As it cooled, dust grains began sticking together.
These clumps grew larger and larger until they became small rocky bodies called planetesimals. These were the building blocks of planets, ranging from about one to one hundred miles across.
Planetesimals are crucial because planets like Earth were made by merging many of them together.
But since we can’t go back in time to observe the process, scientists rely on meteorites—fragments of ancient planetesimals that survived until today. Many of them come from the asteroid belt, a region filled with leftover material from the early solar system.
When scientists examine meteorites in the lab, they can measure their chemical makeup and determine how old they are.
Some meteorites contain tiny inclusions and spheres called calcium-aluminum–rich inclusions and chondrules. These formed very early, making them some of the oldest solid materials in the solar system. Their ages offer a timeline for when the first planetesimals began to form.
Not all meteorites are the same. Some come from planetesimals that never melted—they stayed cool enough to preserve their original mixture of minerals. These are known as undifferentiated meteorites, and they act like untouched archives from the solar system’s early days.
Others come from bodies that heated up and melted. In these differentiated meteorites, heavy metals like iron sank to the center, forming cores, while lighter material rose to the surface.
Studying iron meteorites, for example, gives scientists clues about what the deep interiors of planetary bodies look like. This is especially valuable because we can’t sample Earth’s core directly.
LLNL plays a major role in studying meteorites. The lab specializes in analyzing extremely tiny samples with high precision.
This includes measuring isotopes, identifying chemical signatures, and determining exact ages. When NASA’s OSIRIS-REx spacecraft returned samples from asteroid Bennu—the first U.S. mission to bring asteroid material back to Earth—LLNL scientists were among the first to analyze the precious grains.
The team is now preparing for the next major wave of space samples. As NASA’s Artemis missions plan to return astronauts to the moon and bring back new lunar material, LLNL researchers are upgrading their techniques by practicing on Apollo-era moon rocks. Their goal is to strengthen the lab’s ability to study lunar samples for decades to come.
These scientific tools have uses beyond space research. LLNL’s expertise in analyzing tiny mineral samples also supports nuclear forensics, a field that investigates the origins and history of nuclear materials.
Kruijer hopes that insights from meteorites will eventually feed into advanced computer models of how the protoplanetary disk behaved. He also believes review papers like his are important because they gather complex scientific information into one clear, expert-written source—something that even the best AI summaries can’t fully replace.
Meteorites may be small, but they hold some of the oldest secrets in the universe. By unlocking their messages, scientists get closer to understanding how Earth formed—and what makes a planet capable of supporting life.
