Obtaining samples from asteroids is so scientifically valuable two science agencies have sent spacecraft to bring us rocks and dust. Yet just as one is getting ready to stow its precious cargo, we have learned one sample came to us instead, collected two years ago before terrestrial conditions had a chance to alter it.
Hundreds of meteorites are collected every year, providing us with insight into the composition of asteroids. A few have value far above the rest, and a paper in Meteoritics & Planetary Science adds the Hamburg meteorite as one of these.
Most exceptional meteorites are defined by their origins, for example pieces blasted off Mars in major impacts. The Hamburg meteorite's distinctive feature is how untouched it is. Organic compounds form the building blocks for life, and one popular hypothesis holds their arrival on Earth from meteorites was essential for providing the spark here. Although we have long known certain meteorites contain these compounds, we usually only find them after they have been on Earth long enough to be transformed.
"Scientists who study meteorites and space sometimes get asked, do you ever see signs of life? And I always answer, yes, every meteorite is full of life, but terrestrial, Earth life," Dr Philipp Heck of the Field Museum said in a statement. "As soon as the thing lands, it gets covered with microbes and life from Earth. We have meteorites with lichens growing on them.”
On January 16, 2018, a bright fireball was reported by 674 people from Georgia to Canada. The incoming pieces of space rock were of similar size to hail, allowing their path to be tracked with weather radar. This provided an excellent indication of where the landing sites were of the bits that survived atmospheric entry. Two days later, six were retrieved and another 13 pieces, weighing 1 kilogram (2.2 pounds) combined, were collected over the next two weeks.
Even that might not have been quick enough to preserve them under other conditions, but several pieces, including the first, landed on the frozen Strawberry Lake, near Hamburg, Michigan, leaving no opportunity for water to penetrate. The finder, Robert Ward, donated the first piece to the Field Museum, where Heck and graduate student Jennika Greer studied it.
The Hamburg meteorite was revealed as an H4 chondrite class – not the rarest sort, but accounting for only 4 percent of known meteorites.
"We could see the minerals weren't much altered and later found that it contained a rich inventory of extraterrestrial organic compounds," Heck said. Rich indeed, 2,600 different organic compounds have been identified within it.
“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," Greer added. The enthusiasm generated by Hamburg's swift recovery meant this has been one of the best-studied meteorites of all time, and the exchange of information between teams using different approaches has enriched everyone's understanding.
The meteorite is thought to have come from a 40 to 60-centimeter-wide (16 to 25-inch) piece blasted off a larger asteroid 12 million years ago, after forming 4.5 billion years before.
The paper does not discuss whether the discovery sheds light on the possibility of meteorites helping to launch life on Earth, but Heck told The Guardian it added weight to the idea.