Meteorites: Magnetic messengers from space
Since the dawn of history, humans have been fascinated by what lies beyond our own planet. This natural human curiosity has spawned books, movies, missions and research that all seek to explore the mysteries of outer space.
One tool for piecing together this puzzle is the study of meteorites, the interplanetary messengers that bring missives from other worlds and help us understand the origin and makeup of our solar system.
Meteorites are pieces of space rock that wander into Earth’s orbit and fall to the surface. They come from various places in our solar system, including asteroids, the moon and even planets, like Mars.
The Center for Meteorite Studies (CMS) at Arizona State University is dedicated to studying these space rocks and applying the knowledge gained to several areas of study. Encompassing over 30,000 individual meteorite specimens, CMS is the world’s largest university-based meteorite collection.
Meenakshi Wadhwa, director of the center and a professor in the School of Earth and Space Exploration, says that the rewards of studying these extraterrestrial rocks are endless.
“The interesting thing about meteorites is that they look like any other ordinary rock, but when you look at them in detail, their chemistry and their mineral compositions will tell you something about how they formed and the kind of environment that they formed in,” says Wadhwa. “We can learn something fundamental about the geology of the planets they formed on, which is why people are drawn in by these rocks.”
The work being done at the center includes examination of meteorites blasted off the surface of Mars, which can provide a history of the planet, as well as the status of its water and atmosphere. Most meteorites, however, originate from asteroids, which formed before the planets were formed. The study of such meteorites and their molecules also provides a timescale of some of the earliest events that occurred in our solar system.
The hunt for these specimens on Earth can require a great deal of patience. But occasionally, we get to witness the falling of this extraterrestrial rubble to our planet’s surface.
On April 22, 2012, a meteorite classified as a carbonaceous chondrite, or a meteorite that is rich with carbon compounds, entered Earth’s atmosphere and dispersed over Sutter’s Mill in Coloma, California.
While studying fragments of the Sutter’s Mill meteorite last year, ASU researchers led by Sandra Pizzarello, a professor emeritus in the Department of Chemistry and Biochemistry, made a significant discovery.
In addition to containing some of the oldest material in the solar system, pieces of the Sutter’s Mill meteorite contained organic molecules not previously found in any other meteorites. These molecules were released in experiments that mimicked conditions on ancient Earth.
In a paper published in the Proceedings of the National Academy of Sciences, the scientists wrote that the organic compounds released from the Sutter’s Mill meteorite were likely formed when the parent asteroid experienced extreme heat. Such compounds “could equally have been produced on the early Earth by carbonaceous meteorites upon encountering analogous conditions and environments,” they noted.
These findings are extremely important in the study of molecular evolution and even the development of life. They suggest a greater availability of organic molecules from outer space than previously thought possible.
“Meteorites are the recipient of carbons which could have spurred all life on Earth,” says Pizzarello. “To study meteorites, to get a full inventory of what the meteorites could have brought to the Earth, is very important in the context of understanding the origins of life.”
Sutter’s Mill is an example of a fallen meteorite. Typically, meteorites are classified as either falls or finds. Falls are seen entering the Earth’s atmosphere in the form of a fireball, and finds are, as the name implies, found.
Finding meteorites on Earth without witnessing the fall can prove difficult. According to Pizzarello, finds are most easily identified in Antarctic regions, where they stand out against the white snow. However, many can resemble everyday rocks, and it is therefore helpful to recognize the differences.
Meteorites from Mars and the moon have a different chemical and mineral composition than rocks found on Earth. It is therefore extremely beneficial for scientists and researchers to collect these recently fallen samples, lest they become contaminated after spending too much time among the elements on Earth’s surface.
Elizabeth Dybal is an ASU sophomore majoring in geology who assists in research for the Center for Meteorite Studies. On the subject of identifying meteorites, she mentions a tongue-in-cheek term to classify everyday rocks mistaken for their space-based siblings.
“We call them ‘meteor-wrongs,’” says Dybal. “Sometimes these can be slag or igneous rock.”
If the suspected meteorite is marked by tiny holes on the surface, giving it a spongy appearance, it is probably volcanic or terrestrial rock. Conversely, meteorites will contain a significant amount of extraterrestrial iron and nickel, so a common test to identify them is to use a magnet. If a magnet does not adhere to the specimen, it is not a meteorite. However, many Earth rocks can also attract magnets, so this test is simply a first step.
Researchers can also analyze these rocks by their age, as many meteorites are the same age as the solar system, or about 4.5 billion years old. This helps identify meteorites because, due to erosion and reformation, no Earth rocks are this old.
Dybal studies the chemical and mineral composition of meteorites, which provides another way of distinguishing them from Earth rocks, as well as a wealth of other information.
She takes fragments of meteorites and separates minerals from these fragments using a sifter. The minerals are grouped together and then analyzed for isotopes of specific elements using a mass spectrometer.
“The data gained from this will tell us when the meteorite was first created and/or first crystalline by using half-life dating,” says Dybal. “This can help determine where or what environment the meteorite came from.”
Dybal believes the hands-on experience she is getting will benefit her in the future.
“Since working at the center in the lab is really hands-on, it’s a great experience for what I'll be doing in grad school and afterwards,” she says. “It’s given me more insight into how my classes will apply and prep me for the future.”
The benefits of working with such a renowned collection and the contributions of student researchers are what make the center so successful, according to Wadhwa. Public interest in these extraterrestrial bodies has remained constant and likely always will.
“People are fascinated by space,” says Wadhwa. “People love to answer fundamental questions about our very origins. How did life begin? Those are the kinds of questions that people studying meteorites are trying to answer, and it’s something that resonates with the kid in all of us.”
The School of Earth and Space Exploration, the Department of Chemistry and Biochemistry, and the School of Geographical Sciences and Urban Planning are academic units of the College of Liberal Arts and Sciences.
Written by Lorraine Longhi, Office of Knowledge Enterprise Development