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Highlighted Team Member: Timothy McCoy
Smithsonian Meteorite Expert Helps MESSENGER Team Understand Mercury’s Surface


McCoy (left), on a 2010 field trip examining volcanoes in New Mexico as analogs for planetary volcanism.

MESSENGER Participating Scientist Timothy McCoy had always been interested in space, and as a child he dreamed of becoming an astronomer. But ultimately, he said, he found physics to be “too theoretical to be very interesting at the highest levels.”

A geology class at Eastern Illinois University got him interested in rocks. “I loved the idea of being able to hold a rock in your hand and learn its story; that was very satisfying,” he explained. “Knowing that we had rocks from outer space, I took up geology as my major in the middle of my junior year of college.”

He went on to earn an M.S. from the University of New Mexico and a Ph.D. from the University of Hawaii, and received post-doctoral training at the NASA Johnson Space Center before landing at the Smithsonian's National Museum of Natural History, where he’s worked for 18 years, most recently serving as chair of the Department of Mineral Sciences and Curator-in-Charge of the nation’s meteorite collection.

He became involved with the MESSENGER mission in 2007 through its Participating Scientist program. “I had been following MESSENGER since its early development and had an interest in Mercury from a group of meteorites that I worked on years ago,” he said.

He brings to the team extensive experience in using meteorites as a tool to understand the origin and evolution of their parent bodies. “I’ve spent a couple of decades working on meteorites that formed under highly-reduced conditions (under which there is little free oxygen in the rocks), and I help interpret the chemistry, mineralogy, and structure of Mercury in the context of what I know about these conditions.”

He also makes specific predictions about how scientists might expect elements to behave and how they might test those predictions in subsequent observations.

McCoy joined the team in time to be a part of the observations collected during MESSENGER’s historic first flyby of Mercury in January 2008. But things really picked up once the probe entered orbit about Mercury in March 2011, he said.

“For someone primarily interested in geochemistry, nearly all of the really interesting geochemical observations have happened since we’ve been in orbit and had the chance to gather data from the Gamma-Ray Spectrometer, X-Ray Spectrometer, and Neutron Spectrometer,” he said. “We’ve also greatly refined what we know and now understand – that most of our previous models for the formation of Mercury were wrong – and we’ve subsequently been able to explore a whole new set of models.”

One of these discoveries stemmed from experiments McCoy conducted 15 years ago during which he and a team of scientists melted highly-reduced meteorites and produced melts rich in volatiles, with low iron and high magnesium. “We wrote an entire paper about how these experiments might apply to Mercury, but I’m not sure we believed it even when we published the paper,” he said. “As it turns out, those experiments are not a bad match for the surface of Mercury, and we have been reanalyzing those 15-year-old samples to see if we can explain other chemical features we see on Mercury.”

Over the past seven years, there have been many memorable moments from the mission, but he said the one that stands out is when scientists realized that Mercury is enriched in volatile elements such as sodium, potassium, and sulfur.

“We had to throw out most of the existing models and develop new ideas for the formation of Mercury,” he said. “It isn’t often you work on a mission that redefines the history of a planet, but MESSENGER is doing just that, and it is probably one of the few things I’ll do in my career that my grandchildren will actually learn about in school.”

Another defining moment (“in terms of the really geeky stuff,” he said) was realizing that scientists could do targeted observations for geochemistry.

“There is a very small (a few hundred kilometers across) spot on Mercury that formed by explosive volcanism,” he explained. “If we could measure the composition of that deposit, we could learn a great deal about how the volcanism occurred. We realized that if we turned the spacecraft as we passed over the spot, the Sun just might produce a solar flare that would excite X-rays and let us measure the composition.”

As far as he knows, he said, this had never been attempted for geochemical information, although it is commonly done for imaging. “The team put in a lot of hard work, and it actually worked.”

When he’s not studying rocks, McCoy said he spends a lot of time with his family: his wife, Darlene, and two sons, age 12 and 14. He’s involved in the Boy Scouts, he takes a walk every day with Darlene and the family dog, and they grow white corn in northern Virginia.

McCoy is also an active member of the Miami Tribe of Oklahoma, and he combines his passion for geology with his intense exploration of his cultural heritage.

Science and indigenous cultures share many commonalities, he said. “Both are ways of interpreting our world based on direct observations, either over a short period of time to test a specific hypothesis for science, or extended over many generations and passed on through stories for indigenous cultures,” he said. “The overlap is particularly strong for planetary science, where observations are interpreted in the context of place.”


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