a Meteorite tells a tale of ancient events

Did you know that a meteorite can tell us about ancient titanic explosions and collisions that occurred long before the Sun existed? It’s true—and, according to scientists at the Facility for Rare Isotope Beams at Michigan State University, studies of these meteorites can give important clues to that long-ago time in galaxy history.

Meteorite: a Space Rock from the Past

Every day, material falls from the sky and lands on the surface of Earth. It can be as small as a speck of dust or a boulder-sized (or, rarely, a larger) object. When a space rocks lands on the surface of our planet, we call them “meteorites.” They come from asteroids and even from other planets. There’s a whole class called “Mars meteorites” that actually DO come from Mars. They started their trips to Earth when something plowed into the surface of Mars and craters. Some of the rocks blasted out to space and made their way to our planet. Others come from asteroids that collided, sending showers of debris hurtling through space.

Each asteroid carries minerals and crystals, for example. Scientists can study them to understand interesting things about conditions when the asteroids formed. Since they formed early in the history of the solar system, we can get fascinating clues before and during the birth of the Sun and planets. And, some asteroids also contain elements that could only form in cataclysmic events that predated the solar system.

A Little Cosmic Chemistry

Space rocks, the planets, even our own bodies, contain elements that were made in stellar explosions. We contain a lot of hydrogen, too. But, that all came from the Big Bang. But, the elements such as silver or iron or carbon come from the bellies of stars. These are called the “heavy” elements. They form in a process called “nucleosynthesis.” It occurs inside the stars when atoms of elements are slammed together to form new ones.

In our Sun, the process is currently taking hydrogen atoms and making helium. In the future, helium will become the dominant fuel in the solar core. However, in the far future, after the Sun has become a white dwarf, conditions in its core will cause it to produce carbon. For more massive stars, the process goes further, all the way to the creation of iron in the core.

But, as scientists now know, not all the elements are created inside stars exclusively. There’s a special process that makes some of the heavier elements. These are such elements as iodine, gold, platinum, uranium, plutonium, and curium. It’s called the “rapid neutron capture process,” or “r-process” and it occurs in extremely catastrophic events. These would be the explosions of the largest stars, the violent collisions of neutron stars, or a mashup between a neutron star and a black hole. These events are fairly rare in the universe, but when they do happen, the r-process takes place. Resulting neutrons gather in nucleus of atoms of certain elements and then converted into protons. The r-process builds up heavier nuclei as more neutrons are captured. (Keep in mind that in the periodic table the number of protons in an element’s nucleus defines its atomic number and “weight”).

Radioactivity Tells a Tale

It turns out that some of the nuclei produced by the r-process are radioactive. That means they spontaneously emit energy and subatomic particles. This process can take millions of years for the “parent” substance to decay to create stable nuclei. So, what kind of radioactive nuclei get created?

Iodine-129 and curium-247 are two good examples. They came from some event shortly before the Sun formed. Eventually, they became part of materials that coalesced to form space rocks, and eventually planetesimals that existed in the solar nebula. Some collided to create planets and moons. Others remained in interplanetary space over the next billions of years. Eventually, those space rocks fell to Earth as meteorites.

All this time, inside these meteorites, the radioactive decay generated an excess of stable nuclei. Scientists in laboratories can measure those nuclei to figure out the exact amounts of iodine-129 and curium-247 that were present before the solar system formed.

The existence of certain elements in meteorites tells us that something happened just before the Sun and planets were born. But what? That’s more of a challenge. It’s somewhat like trying to remember what your parents were like before you were born. You can’t. You can only look at pictures of them, but that’s not a first-hand experience.

Meteorite Clues Inform Models

At the moment, scientists don’t know exactly what happened to produce the elements in the meteorites. They just know that to get those elements the event was massive and energetic. But, was it a collision of neutron stars? Did a massive star die somewhere in the region near where our solar system formed? Did a black hole and a neutron star get too close together and merge? All those are possibilities for the creation of the elements that eventually ended up in meteorites.

I find it pretty cool that scientists can now “diagnose” a long-ago event from the existence of isotopes in meteorites. It’s all good knowledge that can be used in simulations of star death and massive collisions. In turn, their work will give us more insight into those kinds of events and their effects on nearby regions of space.

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