Carbon-rich meteorites that crash to Earth carry a wealth of information from far-flung regions of outer space. Now, it seems that some extraterrestrial baggage survives the long journey intact. A new study shows that carbon molecules known as fullerenes can originate outside the solar system and ride in on meteors.
The researchers also isolated fullerenes from a clay sediment layer deposited during an asteroid impact 65 million years ago. Some scientists believe that this collision, marking the so-called Cretaceous-Tertiary (KT) boundary, led to the demise of the dinosaurs (SN: 3/1/97, p. S20: https://www.sciencenews.org/sn_arc97/75th/rm_essay.htm). The sediment fullerenes also contain noble gases with unusual isotope ratios.
This research lends support to the idea that organic molecules from space could have played a role in starting the chemical processes necessary for the origin of life (SN: 1/9/99, p. 24: https://www.sciencenews.org/sn_arc99/1_9_99/Bob1.htm). “It confirms the possibility of organic compounds surviving the trauma of a large [meteor] impact,” says Jeffrey L. Bada of the University of California, San Diego.
In 1996, Becker’s group discovered fullerenes in rocks from the Sudbury Impact Crater in Ontario. This crater was made by an asteroid that hit Earth 1.85 billion years ago. These fullerene molecules contained helium with isotope ratios that are “truly out of this world, almost out of the solar system,” says Bada.
The 1996 work “came under thorough examination and scrutiny,” says Becker, because the fullerenes in the crater may have arrived intact from elsewhere in the universe or formed on Earth, perhaps during the asteroid’s fiery impact.
Last year, Becker and her colleagues for the first time found fullerenes within a meteorite.
More recently, the researchers ground up several grams of samples from two meteorites and the KT boundary sediment. They extracted fullerenes and heated them under vacuum to make “the gas [inside] pop out,” says Becker.
The ratio of two helium isotopes, helium-3 and helium-4, was higher in these fullerenes than in air. Most dramatic, in the Allende meteorite fullerenes, the ratio was several thousand times greater than in the atmosphere.
The high ratio confirms the fullerenes’ extraterrestrial origins. “If you get the unusual helium ratios, there’s no other way to explain it,” says Bada.
“The helium got trapped at the time when the fullerenes formed and remained there for billions of years,” Becker explains. “These trapped gases can tell us about the early history of the universe.”
The researchers extracted mostly carbon-60 and carbon-70, but the meteorites also contain an abundance of larger fullerenes, Becker notes. More difficult to extract, they may contain most of the trapped gases.
The results “strongly suggest that the fullerenes are extraterrestrial,” says Dieter Heymann, emeritus professor at Rice University in Houston, who recently heard Becker lecture. However, it’s unclear when they formed, he adds.
