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ArrowMass Spectrometry: How to Weigh an Atom

By Kristen Coyne

In early 2006, like a stork with a special delivery, a space capsule from NASA’s storied Stardust mission drifted down to the Utah desert beneath a white and orange parachute. While there were no swaddled babies on board, the capsule did contain a precious payload related to birth – not human, but cosmic. Cushioned in a special gel was a smattering of comet dust originating from the outer limits of the solar system.

Magnet Academy

The Stardust treasure trove contained the first extraterrestrial material imported to the planet since the Apollo astronauts hauled back moon rocks decades earlier. Though weighing a fraction of an ounce, the comet dust promised to unlock even more tantalizing secrets than those lunar artifacts: The particles came from much farther away in the solar system, and dated from a time before the moon – or even the planets – existed.

During the $212-million Stardust project, the spacecraft traveled more than 3 billion miles over seven years, rendezvous-ing with the comet Wild 2 during the second of three orbits around the sun. The end of the mission marked the beginning of another adventure: Examining the comet particles with powerful scientific instruments called mass spectrometers, which are able to identify what isotopes the stuff is made of.

Comet Wild 2

Isotopes are atoms of the same element that have different atomic weights, due to varying numbers of neutrons (the neutrally-charged particles found in an atom's nucleus). Depending on the isotopes that make up a particular sample, researchers glean clues about its origin and how it was formed.

PHYSICS FACTOID: All elements have stable isotopes; some have more, some less. Hydrogen, for example, has only two, while xenon has nine.

Research on Stardust comet dust is underway in labs worldwide, including within the Geochemistry Program at the Magnet Lab. Though less sexy than a rocket ship blasting through space at 48,000 miles per hour, this phase of the project is just as significant and compelling. It takes place, however, on an entirely different scale, featuring numbers not only mind-bogglingly large, but mind-bogglingly small. The particles scientists will be studying are measured in microns (µm) – even fractions of microns. A human hair, with a width of about 100 microns, is vast compared to most of the comet particles researchers will be slicing, dicing and scrutinizing.

Micron Scale

But good things come in small packages, and these tiny particles may hold answers to some of our weightiest questions. How did comets form? Did material from outside our solar system contribute to their makeup? Exactly what building blocks were used to create our solar system? Did comets make life on Earth possible by transporting critical elements to the planet? Could they do the same for other planets?

Dr. Munir Humayun, an associate professor in geochemistry at Florida State University working at the MagLab, is among the elite group of scientists granted access to the Stardust booty. He even designed a special type of mass spectrometer to measure the particles and reveal data that could shine a light on how they and the solar system were formed.

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