'Fireball' meteorite that fell to Earth in 2018 reveals its secrets
Posted October 27, 2020 1:52 p.m. EDT
CNN — A 12-million-year-old meteorite that fell to Earth in January 2018 is covered in more than 2,600 organic compounds, according to new research. Meteorites such as this one likely acted as messengers early in Earth's history, delivering the building blocks of life, the researchers said.
A fireball meteor was seen streaking across the sky over the Midwest and Ontario on the evening of January 16, 2018. Weather data helped scientists quickly track where the pieces of the meteor fell to Earth so they could collect them before the samples from space were contaminated too much by Earth.
"Weather radar is meant to detect hail and rain," said lead study author Philipp Heck, curator at the Field Museum in Chicago and associate professor at the University of Chicago, in a statement. "These pieces of meteorite fell into that size range, and so weather radar helped show the position and velocity of the meteorite. That meant that we were able to find it very quickly."
Elements on Earth, including liquid water, can change the chemical makeup of a meteorite before it's even collected.
But the Hamburg meteorite -- collected less than two days after it fell to Earth -- is a prime example of a largely unaltered meteorite.
Meteorite hunter Robert Ward found the first piece of the meteorite sitting on the frozen surface of Strawberry Lake, which is near Hamburg, Michigan. Ward and private collector Terry Boudreaux donated the meteorite to the Field Museum so it could be studied.
"This meteorite is special because it fell onto a frozen lake and was recovered quickly. It was very pristine. We could see the minerals weren't much altered and later found that it contained a rich inventory of extraterrestrial organic compounds," Heck said. "These kinds of organic compounds were likely delivered to the early Earth by meteorites and might have contributed to the ingredients of life."
The study published in the journal Meteoritics & Planetary Science on Tuesday.
"When the meteorite arrived at the Field, I spent the entire weekend analyzing it, because I was so excited to find out what kind of meteorite it was and what was in it," said Jennika Greer, study coauthor and a doctoral student at the Field and the University of Chicago, in a statement.
"With every meteorite that falls, there's a chance that there's something completely new and totally unexpected."
Here's what they learned.
Souvenir from space
The Hamburg meteorite is largely pristine because it was collected so quickly after falling to Earth. This means the meteorite didn't sit still long enough to become weathered, for its metals to begin rusting, for water to seep in through cracks and contaminate it or for its minerals (like olivine) to be altered.
This quick recovery of the meteorite makes it "remarkable," Heck told CNN in an email. And the buzz around the meteorite led it to be well studied and analyzed by researchers at 24 different institutions.
Scientists believe the Hamburg meteorite was ejected from its parent asteroid about 12 million years ago, traveling through space until it landed on Earth. An analysis of the meteorite revealed that the rock had been exposed to cosmic rays while zipping through space for 12 million years.
The meteorite came from an asteroid that formed 4.5 billion years ago, only about 20 million years after the formation of our solar system, Heck said.
The 2,600 different organic compounds that cover the Hamburg meteorite were formed in its parent asteroid.
It's what is known as an H4 chondrite, a type of meteorite that isn't known to be rich in organics.
"This meteorite shows a high diversity of organics, in that if somebody was interested in studying organics, this is not normally the type of meteorite that they would ask to look at," Greer said. "But because there was so much excitement surrounding it, everybody wanted to apply their own technique to it, so we have an unusually comprehensive set of data for a single meteorite."
Typically, carbonaceous chondrites are a thousand times richer in organics than H4 chondrites, Heck said. Near-Earth asteroid Bennu, which was recently sampled by NASA's OSIRIS-REx mission, is rich in carbon.
"The fact that this ordinary chondrite meteorite was rich in organics provides support of the hypothesis that meteorites played an important role in delivering organic compounds to early Earth," Heck said. "Meteorites fell to our planet throughout Earth's history also before life formed and possibly delivered some of the building blocks for life onto Earth."
The organic matter in the meteorite was originally once heated to up to 1,200 degrees Fahrenheit while it was still part of its parent asteroid. This actually reduced the diversity of the organic compounds in the meteorite from millions to a couple thousand. But Heck was still stunned by how many organic compounds were still in the meteorite despite the heat-induced changes it experienced.
The researchers found hydrocarbons, as well as compounds containing sulfur and nitrogen.
"Much more work needs to be done to better understand the individual chemical pathways of the different compounds and the different processes that the organic matter went through," Heck said.
The Hamburg meteorite can be compared with other samples collected in the future -- including the pristine samples being returned from asteroids by the Japan Aerospace Exploration Agency's Hayabusa2 mission and NASA's OSIRIS-REx mission. The first sample from the asteroid Ryugu will be delivered to Earth by Hayabusa2 in December, while the sample from Bennu will return in 2023.
"But we also keep looking out for new meteorite falls," Heck said. "Every meteorite that falls to Earth is worth studying, as it may provide a unique perspective onto the solar system and may shed new light on its history and our origins."